Basic Service Training Materials
Student Study Guide
Basic Electric
This material is proprietary to Komatsu America Corp. and is not to be reproduced,
used, or disclosed except in accordance with written authorization from Komatsu.
It is our policy to improve our products whenever it is possible and practical to do so.
We reserve the right to make changes or add improvements at any time without
incurring any obligation to install such changes on products sold previously.
Due to this continuous program of research and development, periodic revisions may be
made to this publication. It is recommended that customers contact Komatsu America
Corp. Training Department for information on the latest revision.
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Foreword
Purpose of This Manual
The purpose of this manual is to train the reader on basic topics before attending factory
service schools. Completion of the Basic Service Training Materials is the first step
necessary for becoming a skilled technician. After completion of the Basic Subjects, the
next step is attendance in a factory troubleshooting course followed by other courses as
necessary. Learning the basics contained in this manual allows the Komatsu America
Corp. Training Department to design factory schools which are cost efficient and which
emphasize “need to know” tasks and topics while avoiding non-essential information
and activities.
How to Use This Manual
This manual can be used as a handout to support local in-house training or as a self
study reference that can be used by new employees, shop trainees, experienced
technicians new to our product line, and as a refresher for trained technicians.
Start with Chapter 1 and study the chapters in sequence. At the end of each chapter is
an assessment. When you feel that you thoroughly understand the key points of each
chapter, you are ready to take the assessment. There are two methods for completing
each chapter assessment:
1.
Instructor-Led Course
If you are taking this Basic Subject course as an instructor-led course, your
instructor will provide a copy of each chapter assessment and an Answer Sheet.
Answer the questions by circling the most correct answer on the assessment itself,
then fill in the Answer Sheet according to your answers you marked on the
assessment. When you have completed all the assessments turn them into your
instructor along with your Answer Sheet. The instructor is provided with an answer
key and will grade your assessment and will input your scores into the Komatsu
Learning Management System.
The instructor will also return your graded
assessment to you indicating missed questions. You must receive a combined
80% score or better for all chapter assessments to successfully complete this
course.
Note: Do no mail your assessments or Answer Sheet to Komatsu.
2.
Self Study Course
If you are taking this Basic Subject course as a self study course, you will need to
either print or make a copy of each chapter assessment and answer each question
by circling the most correct answer. When you are satisfied with your answers, you
can:
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a.
Turn the assessments into your instructor along with your Answer Sheet. The
instructor is provided with an answer key and will grade your assessment and
will input your scores into the Komatsu Learning Management System. Or,
b.
Log-in to the Komatsu Learning Management System (LMS), using your
extranet username and password. Go to the LMS site, enroll in this Basic
Subject course, after your enrollment has been approved, you can launch the
course, then click on the Assessment link and answer each question. Your
grade will be scored and tracked automatically. Note: Online questions are
in random order. You will receive a Score Sheet summary at the end of each
chapter assessment which will indicate which questions were missed, if any.
You must receive a combined 80% score or better for all chapter
assessments to successfully complete this course.
Should you change employers, you should inform us so we can move your Komatsu
America Corp. training records to the new dealer and location.
If your score is less than 80%, you are not ready to attend factory schools. When you
have studied the problem areas, retake the assessment and follow the instructions as
before.
Manuals in the Basic Service Training Series
Komatsu America Training Department has prepared a complete series of “Basic
Service Training Manuals.” The titles of these manuals are:
•
•
•
Basic Engine
Basic Electric
Basic Hydraulic
•
•
Basic Power Train
Basic Undercarriage
In-House Training Materials
An instructor guidebook has been prepared for each topic in the Basic Service Training
Series. Each instructor guidebook is comprised of the following component parts:
1.
2.
3.
4.
5.
6.
7.
Introduction with course description, objectives and preparation for training.
Instructional guide with a sequence of instruction chart and lesson plans.
Lesson outline for each lesson.
A list of support media.
Slide masters and PowerPoint program.
Assessments.
Answer key for assessments.
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Table of Contents
Chapter
1
2
3
4
5
Topic
Fundamentals of Electricity
Electric Symbols
Starting System
Charging System
Air Preheat Circuits
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1-1
2-1
3-1
4-1
5-1
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Chapter 1
Fundamentals of Electricity
INTRODUCTION
It would be hard to imagine a world without electricity. From the time we awake in the morning
until shutting off the lights at night, our lives have been made easier and more comfortable
through the use of electricity. Recently, some of the most revolutionary advances in the
development of construction equipment have involved the addition of new electronic monitor
and control systems. Therefore, it is important for the service technician to possess a
complete understanding of electricity and how it works.
In this chapter of the Basic Electric Systems course the following topics will be studied:
•
•
•
•
•
•
•
•
•
•
•
Composition of Matter
Electricity
Conductors, Insulators, and Semiconductors
Current, Voltage and Resistance
Types of Circuits
Ohm's Law
Electric Power
Magnetism
Electromagnetism
Electromagnetic Induction
Capacitors
COMPOSITION OF MATTER
All matter is composed of small particles called
atoms. An atom consists of a nucleus
(comprised of protons and neutrons) around
which electrons revolve in fixed orbits.
The protons in the nucleus of an atom have a
positive (+) charge, and the electrons, which
revolve around it, have a negative (-) charge.
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Figure 1.1 – An Atom
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Normally, the positive charge of the nucleus is
equal to the negative charge of all electrons,
which are in orbit around it. Also electrons in
orbit farthermost from the nucleus receive less
attractive force then those electrons in orbit
nearer the nucleus.
Therefore, when the
Figure 1.2 – Difference between an insulator and
electrons in the outermost orbit receive a strong a conductor.
external force (or attraction), they can be pulled
out of their orbit and float among the atoms as
(free electrons). The difference between metals, such as silver and copper; which conduct
electricity easily, and insulators such as glass or wood, which conduct very little electricity,
depends upon the number of free electrons in outermost orbit.
Elements whose atoms have less than four electrons in their outer rings are generally good
conductors of electricity.
On the other hand, elements with more than four electrons in their outer rings are poor
conductors and are called insulators.
The fewer electrons in the outer ring of conductors are more easily dislodged from their orbits.
When something occurs which disturbs the normal neutrality of an atom, then the free
electrons (in the outer most ring) will flow from one atom to another.
ELECTRICITY
Electricity is the flow of electrons from atom to
atom in a conductor.
The word electricity comes from the ancient
Greek work for amber - elektron. The early
Greeks observed that when amber (a fossilized
resin) was rubbed with a cloth, it would attract
bits of material such as dried leaves. Later,
scientist showed that this property of attraction
occurred in other materials such as rubber and
glass but did not occur with materials such as
copper or iron. The materials, which had this
property of attraction when rubbed with a cloth,
were described as being charged with an
electric force. At the same time it was noticed
that some of these charged materials were
attracted by a attracted by a charged piece of
glass and that others were repelled.
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Figure 1.3 – A comb run through your hair will
become charged and attract bits of paper.
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Benjamin Franklin is credited as the first to call
these two kinds of charges (or electricity)
positive and negative. We now know that
what was actually being observed was an
excess or deficiency in the materials of
electrons.
Figure 1.4 – Like charges repel and unlike
charges attract.
In the illustration shown in Figure 1.5, it can be
seen that before the blanket was rubbed on the
ebonite rod, the protons (+) and electrons (·)
were equal, so the normally "positively" charged
ebonite rod is unchanged. However, after
rubbing the rod with the blanket, some of the
free electrons from the blanket was rubbed off
and transferred to the ebonite. Now there is an
excess of negative electrons in the rod so it has
changed from a "positive" charge to a
"negative" charge.
Figure 1.6 – Positive and negative charge.
Figure 1.5 – Electricity by friction.
When two metallic bodies, such as A and B
shown in Figure 1.7, are respectively charged
with a positive and a negative charge and a wire
C is connected between them, then the free
electrons in B will be attracted to the positive
charges in A and move through wire C, to cause
the flow of an electrical current.
Figure 1.7 – Electron current flow.
At this time the direction of current flow is in the
opposite direction to the movement of electrons
as is illustrated in Figure 1.7
Figure 1.8 – Electric current (the movement of
free electrons
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CONDUCTORS, INSULATORS AND SEMI-CONDUCTORS
Conductors - It has been found that the number of electrons in the outer ring of an atom
determines the force with which they are held in orbit by the protons in the nucleus. If the
number of electrons in the outer rings numbers less than four, the force is rather weak.
Conductors are those elements, which have less than four electrons in their outer most ring.
This allows the easy passage of electrons from one atom to another anytime something
disturbs the normal neutrality of the atom.
Insulators - Elements, which have more than four electrons in their outer ring, are held in their
orbits by very strong forces. These types of elements do not pass electrons easily and are
called, insulators.
Semiconductors - Semiconductors have exactly four electrons in the outer ring of their atoms.
They are neither good conductors or good insulators. Most semiconductors are made of
silicon.
The diodes and transistors found in an electrical circuit are semiconductors.
Figure 1.9 – Atomic structure of silicon and
germanium.
Silicon, germanium and other materials used to
made semiconductors are rarely used alone
because they have few free electrons, making it
difficult to pass large currents through them.
Shown in Figure 1.9 is a representation of the
molecular structure of a silicon and a
germanium atom. Notice that both have four
electrons in their outer rings. These four
electrons are called, valence electrons. A
valence electron is an electron in the outer or
next to outer ring of an atom, which can
participate in forming a chemical bond with
other atoms.
In a pure crystal of silicon or germanium, the
atoms are arranged in such a way that the four
valence electrons are shared by adjacent
atoms. This is known as covalent bonding.
Figure 1.10 – Covalent bonding of a silicon
crystal.
In this condition, there are no free electrons
available, just as with an insulator. However,
unlike an insulator, the covalent bonds are not
strong, and a certain number of valence
electrons will become available as free
electrons.
Next, atoms of different elements are added to the pure silicon or germanium crystal to
improve its conductivity. This process is referred to as doping. Semiconductors, which have
been doped, are sometimes called, impurity semiconductors. Impurity semiconductors are
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classified as either N-type or P-type, depending upon the type of impurity (other element) that
has been added.
In Figure 1.11, pure silicon has been doped with
phosphorus. Because phosphorus has five
valence electrons, only four of these will
combine with the silicon atoms, leaving one
unattached.
As this electron cannot be
attached to any atom it can move freely
throughout the crystal, and thus becomes a free
electron. Because one free electron is available
for every atom of phosphorus, it follows that the
more atoms of phosphorus there are, the
greater is the number of free electrons.
Therefore, through doping, the amount of
current allowed to flow can be controlled. The
most common elements used to make N-type
semiconductors are phosphorus (P), arsenic
(As) and Antimony (Sb).
Figure 1.11 – N-type semiconductor crystal.
The P-type of semiconductor is commonly doped with Aluminum (AL), Gallium (Ga) or Indium
(In). Doping with these elements creates a different molecular structure.
When aluminum (Al) is doped to pure silicon, as shown in Figure 1.12, there will be a
deficiency of one electron in the covalent bond where an aluminum atom enters the crystal
lattice. This is because aluminum has three valence electrons. Because a balance is
maintained between positive and negative charges in the covalent bond, it would appear that
there are no electrical charges in the bond. However, when an electron jumps out of the
lattice, this balance is upset, and the resulting hole can be considered to gain an equivalent
positive charge.
This hole is called a positive hole, meaning a
hole with a positive charge. A positive hole acts
in the same way as a free electron to increase
the conductivity of a semiconductor. This is
because the bonds between the atoms of a
semiconductor such as silicon are weak, and
the valence electrons are continually searching
for places in which they can move. Thus, when
a hole forms and produces a minute voltage, a
Figure 1.12 – P-type semiconductor crystal.
valence electron will avail itself of the
opportunity by breaking its bond and moving
into the positive hole, (Figure 1.12). When an electron moves to a positive hole, another
positive hole will be formed at the place vacated by that electron. As a result, another electron
will move into the newly formed positive hole, and so on. In this way, the presence of one
positive hole will result in the movement of one electron after another, making for higher
conductivity in the semiconductor.
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Figure 1.13 – Analysis of current flowing in P-type semi-conductor.
Current is actually produced by movement of electrons. However, it is possible to consider it
as being due to the movement of the positive holes, (Figure 1.13).
Lets pause now and reflect upon what we have learned so far about conductors, insulators and
semiconductors.
•
Electricity is the flow of electrons from
atom to atom in a conductor.
•
Conductors are materials which permit
the free movement of many electrons.
•
Insulators are materials that do not permit
the free movement of many electrons.
•
Semiconductors are materials, which can
be made to function as an insulator or
conductor depending upon the direction of
current flow.
Figure 1.14 – Conductor.
Figure 1.15 – Insulator.
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The use of semiconductors is increasing each year. They have made the vacuum tube, which
often required replacement, obsolete. The reason for this is obvious when reading the
following list of advantages that semiconductors have over vacuum tubes.
Advantages:
1. Small and light
2. Low operating voltage
3. Instantaneous operation because heat is not
generated by its construction
4. Low power consumption and high efficiency
5. Long life
Figure 1.16 – Semi-conductor.
6. High reliability
7. Low noise
Most of the semiconductors used on construction equipment are either diodes or transistors.
Diodes - The word diode basically means a 2-electrode vacuum tube. A semiconductor diode
consists of P- and N-type semiconductors joined together, (Figure 1.17).
The junction between the two semiconductors is known as a PN junction, (Figure 1.17). In the
diagrammatic symbol of a PN junction, the anode (positively charged electrode) is marked A
and the cathode (negatively charged electrode) is marked K.
A diode acts like a one way check valve for
electricity. It is the PN junction, which gives it
this ability because the semiconductor
properties change at the junction face.
Figure 1.17 – Diode.
A P-type semiconductor contains many positive
holes, while a N-type semiconductor has many
electrons. A PN junction behaves like a wall,
and therefore by simply joining P- and N-type
semiconductors it will be impossible for the
positive holes and electrons to cross the
junction and unite with each other.
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Figure 1.18 – Diode with no voltage applied.
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However, when voltage is applied, the electrons
in the N-type semiconductor will be attracted in
the direction of the positive voltage, and the
positive holes in the P-type semiconductor will
be attracted by the negative voltage, hence
electrons and positive holes will simultaneously
cross the junction, resulting in a flow of current,
(Figure 1.19).
Figure 1.19 – Diode with forward voltage applied.
If a reverse voltage is applied, the positive holes
in the P-type semiconductor will be drawn to the
left, while the electrons in the N-type
semiconductor will be drawn to the right. As a
result, the holes and electrons will not cross the
junction and no current will flow (Figure 1.20).
Therefore, whether or not current flows through
a diode depends upon the direction of the
Figure 1.20 – Diode with reverse current applied.
applied voltage across the PN junction. This
action is called rectification. A voltage, which
is applied in the direction, which results in the flow of current across the junction, is called a
forward voltage, while a voltage in the direction, which prevents the flow of current, is called a
reverse voltage.
Following is a drawing showing the typical construction of the types of diodes we have been
discussing.
The core element of the diode is a very fine P-N
junction. The P-type semiconductor is made of
pure silicone (as high as 99.99% pure) and a
very small quantity of phosphorus or arsenic.
The N-type semiconductor is also made of pure
silicone (again as high as 99.99%) but a very
small amount of aluminum or gallium is added.
The effect of these added impurities is as
follows.
Figure 1.21 – Construction of a diode.
When the P-type end is positive and the N-type
end is negative, the P-N junction permits current to flow instantly in the normal direction. The
junction produces a constant 0.5 to 1 volt drop regardless of the current flowing through the
junction. This type diode consumes power directly proportional to the amount of current
passing through it. All of this consumed power is changed into heat, consequently, if more
current passes than the diode was designed to handle, to much heat is generated and in
extreme cases the diode will be burned away.
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When the P-type end is negative and the N-type end is positive, the P-N junction will not allow
any appreciable flow of current. If any voltage exceeding the value specified for the diode is
applied, the junction will be destroyed and its current obstruction function will be lost. The
resulting current flow will burn up the diode.
Other diodes - Several different effects can be achieved with a diode depending upon the
type and amount of other elements doped with the semiconductor material.
One specially designed type of diode is a zener diode. This type of diode is very heavily
doped during its manufacture to ensure a large amount of current carrying electrons and holes.
This allows the zener diode to conduct current in the reverse direction without damage if the
proper circuit design is used. The unique operating characteristic of the zener diode is that it
will not conduct current in the reverse direction below a certain predetermined voltage. For
example, a zener diode could be made so that it doesn't pass current until 28 volts is achieved,
then suddenly it begins to conduct reverse current. This type of diode is used in control
circuits.
Another type of diode is the photovoltaic
diode. This diode is made so that when light
strikes the surface of its PN junction, a voltage
is generated, which results in the flow of
current.
This occurs because the light removes the
barrier at the junction surface, allowing the
positive holes in the P-type semiconductor to
migrate to the N-type semiconductor, and the
electrons in the N-type semiconductor to move
to the P-type connector.
Figure 1.22 – Photovoltaic effect.
Yet another type of diode is made to create a
tunnel effect.
With a tunnel effect diode, as forward voltage
is gradually increased, the resulting current will
also increase. However, when the voltage
reaches a certain point, the current will Figure 1.23 – Tunnel effect.
suddenly fall off. When the voltage is further
increased, the current will start to rise once again, (Figure 1.23).
A light emitting diode is constructed in such a way that a red, green or yellow light is emitted
when voltage is applied to it.
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Figure 1.25 – Voltage not applied to PNP
transistor.
Figure 1.24 – Transistor construction.
Transistors - A transistor is a semiconductor device that is used to control current flow. It is
making the old toggle type switch obsolete.
A transistor is a device consisting of a PN junction that is combined with another P- or N-type
semiconductor. Therefore, there are two types classified as either PNP or NPN transistors,
depending upon the order in which the P-type and N-type semiconductors are combined with
each.
Because of the difference in the way the PNP and NPN transistors are combined, the
directions of both the applied voltage and the resulting currents are opposite each other.
Figure 1.24 shows how they differ in construction and direction of current flow.
Because a transistor consists of two PN junctions, in the absence of an externally applied
voltage the holes and electrons in the P- and Ntype regions will be unable to cross junctions,
and there will be no current flow.
Also, if voltage is applied between the base and
collector of the transistor so that the base is
positive in respect to the collector, the basecollector PN junction will be reverse biased,
causing electrons in the base and holes in the
collector to be drawn to their respective
electrodes. In this condition, virtually no current
can flow. (Figure 1.26)
Figure 1.26 – Reverse voltage applied between
base and collector of PNP transistor.
If we leave the base to collector voltage unchanged, and also apply voltage between the
emitter and the base of the transistor so that the emitter is positive with respect to the base,
the emitter-base PN junction will be forward biased, causing the holes in the emitter to move
towards the base, (Figure 1.27). Because the base is made much thinner than the emitter, the
number of electrons in the base is much smaller than the number of holes in the emitter.
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Consequently, only a very small number of the holes that enter the base region from the
emitter combine with the electrons in the base. Most of the remaining holes proceed through
the base to the base-collector PN junction. Upon reaching the junction, the holes are attracted
by the negative potential of the collector, and pass through the junction into the collector.
When the holes enter the collector region, they are further attracted by the collector potential,
and then pass right out of the collector region. The current resulting from the migration of
holes through the collector is called the collector current. That current which is produced by
the movement of holes from the emitter to the base is called the emitter current. And the
current produced by some of the holes from the emitter combining with the electrons from the
base is called the base current.
CURRENT, VOLTAGE AND RESISTANCE
Because the numbers of electrons in the base of
a PNP transistor are so few, the flow of current
can be considered in the terms of the movement
of the holes, that is, from emitter to collector.
Figure 1.27 – PNP transistor with forward voltage
applied between the emitter and base. Also,
reverse voltage between base and collector.
In the case of a NPN transistor, the various
voltages are applied in the reverse direction to
those of a PNP transistor.
Figure 1.28 – In a NPN transistor the voltages
and currents are opposite those of a PNP
transistor.
If the flow of current in the NPN transistor is
thought of in terms of the migration of electrons,
the direction of current flow will be in the
reverse direction of a PNP transistor. However,
in all other respects both types are identical.
Current - As was pointed out earlier, current is the flow of electrons. You have already
learned that actually it is the electrons in the outer rings of the atoms of conductor type
materials, which can move. The heat of normal room temperature is usually sufficient to
liberate the outer electrons in a good conductor. This means that there are a large number of
electrons that are free in these types of materials and very little energy is required to cause
them to move freely from one atom to the next. This type of movement has no value to us
because it is random movement of electrons. This random movement of electrons from atom
to atom is normally equal in all directions. Therefore, electrons are not lost or gained by any
particular part of the conductor material at this time.
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When we want current to flow, we make one
end of our conductor (usually a copper wire)
positive and the other end of the wire negative
so that all the free electrons will be attracted to
the positive end of the wire and repelled from
the negative end. (Figure 1.29)
This movement of free electrons in the same
direction along the wire is called current flow.
This flow is measured in amperes.
One ampere [A] is an electric current of 6.28
billion billion electrons passing a certain point in
the conductor in one second.
Figure 1.29 – Current flow.
One thousandth of an ampere is called a
milliampere [mA].
Figure 1.30 – One ampere [A] of current.
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Voltage - Voltage is the force, which causes the
current to flow in a conductor.
Voltage can be generated by a storage battery
using chemicals, or by a generator using
mechanical means. Voltage is a potential
force that can exist even when there is no
current flow in a circuit, (Figure 1.31). For
example, a storage battery may have a Figure 1.31 – Electric potential (volts).
potential of 12 volts between its positive (+) and
negative (-) terminals even though no current-consuming electrical devices are connected.
Therefore, voltage can exist without current, but current cannot exist without the force or push
of voltage.
Voltage is available between two points when a positive charge exists at one point and a
negative charge exists at the other.
The greater the charges at each point, the greater the voltage.
Figure 1.32 – Voltage.
You can consider a battery or generator to be
an electron pump. For example, when a wire is
connected from the positive to the negative side
of a battery or electric generator, a closed wire
loop is formed and a constant electric current
will circulate through the wire.
The motive force that causes the electric
current to continuously flow is called an
electromotive force. Voltage is the unit for
measuring electromotive force.
Man uses voltage and current in controlled
amounts. But in nature, voltage and current
can get out of control. For example, a bolt of
lightning during an electrical storm may contain
over a million volts before it strikes the ground.
Resistance - All elements, even conductors,
offer some resistance to the flow of current.
Two things cause this.
First, each atom
resisting the removal of an electron due to
attraction to its core. And secondly, when free
electrons travel through a metal they bounce or
collide with countless other electrons and atoms
which retards their travel speed, (Figure 1.34).
Figure 1.33 – Electromotive force.
Figure 1.34 – Collisions of countless electrons –
resistance.
The collisions create resistance and cause heat in the conductor.
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The basic unit of resistance is the ohm. One ohm is the resistance that will allow one ampere
of current to flow when the potential is one volt. This is an expression of Ohm's Law, which we
will study more closely later on. The symbol Ω represents resistance. Therefore, 8 Ω means
eight ohms of resistance.
In our machines we use wire to conduct the electron flow to and from the electric devices. The
wire must be of the proper size for the amount of current passing through it. For example, if
we direct a lot of electrons through a very small diameter wire, the wire will start to heat up
(due to all the collisions of electrons) and could burn off the insulation or melt the wires.
Therefore, it is important to know that the amount of resistance in a wire depends upon:
1. the length of the wire
2. the cross-sectional area of the wire
3. the temperature of the wire.
Figure 1.35 – The specific resistance of a wire
depends upon its dimensions.
If the length of a wire is doubled, the resistance between the wire ends will be doubled. So,
the longer the wire, the greater the resistance.
Also, if the cross-sectional area of a wire is
reduced by half, the resistance for any given
length is doubled. Smaller diameter wires have
more resistance than large diameter wires.
Figure 1.36 – A smaller diameter wire has more
resistance.
And as temperature increases, either because
of changes in ambient temperature or due to the
countless collisions of electrons during current
flow, the resistance also rises. So, the hotter
the wire, the greater the resistance.
Most manufacturers use the smallest wire for the application to reduce costs. When an
electrical appliance is added to a circuit without considering the wire size, it may draw more
amps than anticipated and the volts will drop. Excessive heat will develop in the wire due to its
normal resistance. If the wire gets too hot, it may melt or the insulation will be damaged. This
is why the selection of the correct wire size is so important.
TYPES OF CIRCUITS
There are three types of electrical circuits found in construction equipment. These types are
series circuits, parallel circuits, and series-parallel circuits.
Series circuits - Series circuits link their components together one after the other. In a series
circuit, the total resistance is the sum of all resistors in the circuit.
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The drawing in Figure 1.37 shows a series
circuit such as one you might find representing
a string of Christmas tree lamps. There are four
light bulbs (resistors) shown in the circuit and if
each had 4 ohms resistance, there would be a
total of 16 ohms resistance in the circuit.
Figure 1.37 – Series circuit.
Also, if four 1.5 volt flashlight batteries (A, B, C
and D) are connected in series, the voltage of
each is added to the others in series, so the
total circuit voltage becomes 6 volts, (Figure
1.38).
By connecting more batteries in the series,
higher voltages can be obtained. However, it
must be kept in mind that the current available
will depend upon the current discharging ability
of the smallest or weakest battery of the entire
battery bank. Because of this fact, batteries of
the same capacity are connected in typical
series circuits.
Figure 1.38 – Flashlight batteries in series
connection.
Figure 1.39 – Two 12 volt batteries in series.
Often you will find that the construction
equipment manufacturer has set up the
electrical circuit with two 12 volt batteries
connected together in series, (Figure 1.39).
Two 12 volt batteries have been put together to
form a 24 volt system. The battery symbols
shown are typical of those found in most
Komatsu publications. Notice that ampere hour
rating is also indicated. The capacity of a
battery is specified as the product of the current
drawn and the time elapsed to discharge the
battery (current x discharge period) and is
denoted in amphere-hours, abbreviated (Ah).
Therefore, a battery with a capacity of 120 Ah is
capable of supplying a current of 12 ampheres
continuously for 10 hours.
Remember the following key points about series circuits:
1. The current through each resistor is the same.
2. The voltage drop across each resistor will be different if the resistances are different.
3. The sum of the voltage drops equals the source voltage.
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Parallel circuits - In a parallel circuit, the
voltage drop across each resistor is equal to the
potential of the current source since there is a
separate path for current to flow through each
resistor, (Figure 1.40).
The parallel circuit has several advantages over
a series circuit.
If one of the electrical
components in a series circuit burns out, it will Figure 1.40 – Parallel circuit.
affect all the components in the series. In other
words, when the series wire is broken, none of the electrical devices in the same series will
work. On the other hand, if one electrical component in a parallel circuit is burned out, it is the
only one affected because current flows through the other electrical devices by way of
separate routes. Also, because of the separate routes, the total resistance in a series circuit is
minimized, permitting us to operate more electrical actuators with the same power source.
Assuming that the light bulbs (resistors) shown in Figure 1.40 have a resistance value of four
(4) ohms each, the total resistance in this parallel circuit will only be four (4) ohms because
there is a separate path for current to flow through each resistor.
Now examine the flashlight batteries connected
in parallel in Figure 1.41. When batteries are
connected in this way, the circuit voltage does
not increase, but the available current
(amperes) rises. Because amps are drawn
equally from all batteries in the parallel circuit,
the number of electrical devices, or amount of
resistance, which use current can be increased
while employing the same force (volts).
Figure 1.41 – Flashlight batteries in a parallel
connection.
Remember the following key points about parallel circuits:
1. The voltage across each resistor is the same.
2. The current through each resistor will be different if the resistance values are different.
3. The sum of the separate currents equals the total current in the circuit.
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Series-Parallel - The total current in a series-parallel circuit is equal to the total voltage divided
by the total resistance. Current flow in the
circuit will divide to flow through all parallel
paths, and come together again to flow through
series parts of the circuit. It will divide to flow
through a branch circuit, and then repeat this
division if the branch circuits itself subdivides
into secondary branches.
Figure 1.42 – Series parallel circuit.
As in parallel circuits, the current through any
branch resistance is inversely proportional to
the resistance of the branch. In other words, the greater current flows through the least
resistance. However, all of the branch currents always add up to equal the total circuit current.
The total circuit current is the same at each end of a series-parallel circuit, and is equal to the
current flow through the voltage source.
Some very large machines have batteries
connected in a series-parallel configuration as
shown in Figure 1.44. Two sets of two 12 volt,
200 ampere hour rated batteries are first
connected in series. This results in a combined
voltage of 24 volts, which is the voltage
requirement of the machine.
The series
connection didn't have any affect on the
available amps but, more than 200 Ah is
needed. By joining the two series batteries
(parallel connection) we now have 400 Ah with
a force of 24 volts.
Figure 1.43 – How current flows in a seriesparallel circuit.
Figure 1.44 – Series-parallel connected batteries.
OHM'S LAW
By now you should be realizing that there is a definite relationship between current, voltage
and resistance. This relationship was studied years ago by a German mathematician, George
Simon Ohm. He made a mathematical analysis and wrote a description of this relationship,
which is now known as Ohm's Law. This law says that the current flowing in a circuit is
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directly proportional to the voltage (applied electromotive force) and inversely proportional
to the resistance.
Referring to Figure 1.45, current I flowing
through two points a and b in a conductor is
proportional with the voltage, and is inversely
proportional with the resistance between the
two points.
What this means is that when the resistance is
constant, if a low voltage is applied a small
current is the result. Also, if a higher voltage is
Figure 1.45 – Ohm’s Law
applied, a large current is the result.
In
addition, when the electromotive force (volts) is
constant, and if the resistance is low, a large current can pass through the resistor. When the
resistance is higher, a smaller current passes through the resistor.
Due to George Ohm's studies, we now have a mathematical equation, which is a basic tool for
all who work with electrical circuits.
E
I= —
R
In the equation above, current is represented by the letter "I", voltage by the letter "E", and
resistance by the letter "R".
The value of this equation is that when two factors are known, the remaining unknown factor
can be calculated. With the help of simple algebra, the equation can also be
written as:
E= IxR
or as
E
R= —
I
Which of the three ways (formulas) of expressing Ohm's Law you might choose to employ
depends on two things:
1. What facts you know to start off with about the circuit.
2. What facts you need to know about it.
There is an easy way to remember which way or formula to use. Look at the triangle in Figure
1.46.
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Now consider a circuit in which you know the
values of any two of the three factors -voltage,
current, and resistance - and want to find out
the third. The rule for working the memory aid
to give you the correct formula is to put your
finger over the letter in the triangle whose value
you want to know. The formula for calculating
that value is given by the two remaining letters.
Figure 1.46 – Ohm’s Law memory aid.
For example, when you know the values of
current and resistance in a circuit, but don't
have a voltmeter, put your finger over the "E"
and you can see that you are left with the
formula you need - I x R.
Figure 1.47 – Finding the voltage.
Figure 1.48 – Finding the resistance.
When you know the values of current and voltage, but you have no ohmmeter to measure the
resistance, put your finger over the letter R. You are left with the formula
E
—
I
Substitute the known values for E and I, then divide to find R.
If the voltage and resistance of a circuit is
known to you; but your ammeter is broken, you
could use the memory aid as shown in Figure
1.49 to find the current value. Put your finger
over the I and read the formula:
E
—
R
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Figure 1.49 – Finding the current.
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There are two rules you must follow when your using the Ohm's Law formula or you will come
up with the wrong answers. First, you must express all values in the correct units of
measurement. That is:
●
Current is always expressed in amperes.
●
Voltage is always expressed in volts.
●
Resistance is always expressed in ohms.
The second rule is to sketch out a rough diagram of the circuit you are considering. This will
provide a visual aid to write down values and help you troubleshoot the circuit.
For example, suppose you have an unknown resistor connected across a battery. You
measure the voltage across the resistor and find it to be 12 volts. You also measure the
current flowing as 3 amperes. You want to know the resistance of the resistor; but you have
do not have an ohmmeter.
First draw the circuit diagram, and fill it in with
the information you already have. Now use the
Ohms Law memory aid to find the correct
formula to use to find resistance. In other
words, cover the R and you can see that the
formula is:
E
R = —
I
Figure 1.50 – Using a diagram and finding
resistance.
Now substitute into this equation the known values and you will get:
R=
E
— = 4
I
which is the value of the resistor in ohms.
ELECTRIC POWER
As you know, whenever a force of any kind causes motion, work is being done. When a
mechanical force, for instance, is used to lift a weight, work is being done.
You have also learned that a difference in potential between any two points in an electric
circuit gives rise to a voltage, which when the two points are connected together, causes
electrons to move and current to flow. Here is an obvious case of a force causing motion, and
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thus of causing work to be done. Whenever a voltage causes electrons to move, therefore,
work is done by moving them.
The rate at which the work of moving electrons from point to point is called electric power. It
is represented by the symbol P, and the unit of electric power is the watt, represented by the
symbol W. One watt (W) represents the rate of power involved in supplying a current of one
amp (I) flow when one volt (E) is applied over a period of one second.
Power formula - Electrical energy can be converted to heat, light, acoustical or mechanical
energy. The rate of energy conversion is really what the engineer means by the work power.
The rate at which work is done in moving electrons through a resistor obviously depends on
how many electrons there are to be moved. In other words, the power consumed in a resistor
is determined by the voltage measured across it, multiplied by the current flowing through it.
The formula is:
POWER = VOLTAGE X CURRENT
Another way to show the power formula is:
WATTS = VOLTS X AMPERES
The formula P = E x I or simply P = EI is therefore used as the actual equation type formula.
Horsepower - The term horsepower is used to express a unit of mechanical power. When
converted to electric power:
1 HP = 746 (W) (Foot Pound HP)
1 PS = 735 (W) (Metric horsepower)
Amount of electric power - As discussed before, power is the amount of electric work
performed over a unit of time (one second). The amount of electric power is defined as the
total electric energy either generated or dissipated during a certain time period.
THE AMOUNT OF ELECTRIC POWER = ELECTRIC POWER X TIME
The unit of electric power is watt/per second (abbreviated "Ws") or joule (abbreviated "J").
However, when measuring large quantities of power, the unit (Wh) or watt-hour is used.
Joule heat - British physicist James Prescott Joule discovered that the electric power
consumed in a resistance is completely changed into heat. This phenomenon is now referred
to as Joule's Law. The relationship between a watt and a joule is shown in the following
formula.
1 (Ws) = 1 (J)
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MAGNETISM
Over a thousand years ago it was observed that a lodestone (fragments of iron ore found in
nature) would attract pieces of iron. It was also discovered that a long piece of iron ore, or
iron bar, suspended in air would align itself so that one end would always point toward the
North Pole of the earth. This end of the iron bar became known as the north pole (N pole) and
the other end the south pole (S pole). Such a piece of iron ore was called a bar magnet. This
principle became the basis for the compass, which has been used as a navigational aid ever
since.
The force, which attracts pieces of steel and
steel filings, is called magnetism.
Further investigations revealed that an
attractive force was exerted upon bits of iron or
iron filings even though they were some
distance away from the bar magnet. It became
apparent that a force existed in the space
immediately around the magnet. This space is
called the field of force or magnetic field. Figure 1.51 – Lodestone.
This magnetic field can be described as
imaginary lines, which flow out of the north pole and enter the south pole.
Figure 1.52 shows the lines of magnetic force emitting from the north pole and disappearing at
the south pole. Notice that the density of these lines are greater near the bar magnet. This
signifies that the strength of the magnetic field gets weaker with distance.
Figure 1.52 – Magnetic lines of force.
Figure 1.53 – Magnetic lines of force come out of
the N pole and enter the S pole.
We have said that the lines of force always leave the N pole and enter the S pole of a magnet.
Figure 1.53 shows that when a small compass needle, which is a small bar magnet, is located
in the magnetic field of a strong bar magnet, the compass needle will align itself so it is parallel
with the lines of force. This alignment takes place because the magnetic lines must enter the
S pole and exit the N pole of the compass needle.
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In Figure 1.54 we see that unlike poles of two
magnets are attracted to each other. Also
shown are two magnets with their South poles
facing each other. A force of repulsion is seen to
exist between these two magnets.
These
examples show a fundamental law of
magnetism.
Figure 1.54 – Attraction and repulsion of a
magnet’s poles.
Unlike poles attract each other and like poles
repel each other.
Exactly what magnetism is, and how it exerts a
field of force, can best be explained by either
one of two theories.
The first theory states that a magnet is made up
of a very large number of small magnetized
particles. When a bar of iron is not magnetized,
the small magnetic particles are arranged in a
random manner as shown in the upper half of
Figure 1.55. But when the bar of iron becomes
a magnet, the magnetic particles are aligned so
that their individual effects add together to form
a strong magnet.
Figure 1.55 – First theory of magnetism
(particles are aligned).
Figure 1.56 – Attraction of a piece of steel.
The second theory about magnetism concerns
the electron. The electron has a circle of force
around it, and when the electron orbits are
aligned in a bar of iron so that the circles of
force add together, the bar of iron is
magnetized.
While iron is one of the better known magnetic
materials, remember that some materials are
non-magnetic since they never exhibit any of the
properties of magnetism. Some of the nonmagnetic substances are wood, glass and
copper.
The reason that a piece of soft steel is attracted is because it is easier for the lines to pass
through the steel than through space. As shown in Figure 1.56, the lines become
concentrated in the steel to magnetize the piece.
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ELECTROMAGNETISM
In 1820 the relation between electricity and
magnetism was discovered. Before this time it
was believed that magnetism existed only in the
lodestone or iron ore found in nature and there
was no relationship at all between electricity
and magnetism.
An experiment with a compass and a wire
carrying current revealed the connection
between electricity and magnetism. When the
compass was held over the wire, the needle
turned so it was crosswise of the wire.
Figure 1.57 – Electric current creates its own
magnetic field.
Since the only thing known that would attract a compass needle was magnetism, it was
obvious that the current in the wire created a magnetic field around the wire.
The nature of the magnetic field around the wire is revealed when the current-carrying wire is
run through a piece of cardboard, and iron filings are sprinkled on the cardboard. The iron
filings align themselves to show a clear, distinct pattern of concentric circles around the wire.
The concentration, or density, of the concentric circles is seen to be very heavy near the wire,
and to decrease in density with the distance from the wire. Although the iron filings on the
cardboard show only the pattern or circles in one plane, it should be recognized that the
concentric circles extend the entire length of the current-carrying wire.
There is a positive relationship between the current flowing through the wire in Figure 1.58 and
the magnetic field lines around it. This relationship is called, "The law of the right hand screw".
Figure 1.59 – Relationship between the current
and magnetic field lines.
Figure 1.58 – Concentric fields of force around a
current-carrying wire.
If the direction of the current is the same as that for the advancing of a right hand screw, the
direction of the lines of force is parallel to, and in the same direction as the threads of the right
hand screw, (Figure 1.59).
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When a length of wire is wound into a coil, the
magnetic lines of force caused by a current
through the coil will all be aligned in the same
direction so that the coil may be considered as
equivalent to a bar magnet, and the end where
the lines of force appear is designated the north
pole, while the other end where the lines
disappear is the south pole.
The size of the magnetic field will be
proportional to the amount of current multiplied
times the number of revolutions or turns in the
coil of wire.
Figure 1.60 – Magnetic field induced by electric
current through a coil of wire.
When an iron core is placed in a coil as shown
in Figure 1.61, the strength of the coil magnet
will be increased substantially. This is because
the magnetic flux is induced in the iron, and iron
has the property of becoming magnetized with a
force several thousands of times greater than
air.
The strength of a magnetic field is represented
by the density of the magnetic lines of force.
Therefore, the strength of the magnetic poles
will depend on the flux density at the poles.
Figure 1.61 – Electromagnet.
The lines of magnetic force or flux in air are
assumed to flow from the north pole to the south
pole. Inside the magnet the flux flows from the
south pole to the north pole to form a ring of flux,
(Figure 1.62). This path of magnetic flux is
called a magnetic circuit. These flux lines will
exist regardless of any material being placed in
the flux stream.
Figure 1.62 – Magnetic circuit.
ELECTROMAGNETIC INDUCTION
In 1831 it was discovered that when a conductor
was moved across a magnetic field, a voltage or
electromotive force (e.m.f.) would be induced
in the conductor. This phenomenon is now
called electromagnetic induction.
The principle of electromagnetic induction is
illustrated in Figure 1.63. The depiction shows
that when a straight wire conductor is moved
across the magnetic field of a horseshoe
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Figure 1.63 – Electromagnetic induction.
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magnet, a small voltage will be seen on a
voltmeter. It should be noted that if the wire is
moved parallel with the lines of magnetic force,
no voltage is induced. The conductor must
cut across the lines of force in order to
induce a voltage.
We have learned earlier in this chapter that
voltage has polarity, that is, positive and
negative. We also stated that current flows from
the positive terminal of a voltage source through
the external circuit and then back to the negative
terminal of the voltage source.
Figure 1.64 – Fleming’s right-hand rule.
Sir John Ambrose Fleming, a British electrical
engineer who died in 1945 is credited with giving
us the now famous Right Hand Rule.
Fleming used his right hand to show the direction that induced current would flow when the
thumb is pointed in the direction of motion, and index finger is pointed in the direction of the
magnetic field.
Figure 1.65 – The right-hand rule in use.
Therefore, when a single wire conductor cuts the
magnetic lines of force, the direction of the
induced current (e.m.f.) would be from the top of
the paper surface through it to the underside,
(Figure 1.65). This is determined by holding the
fingers of the right hand, (Figure 1.64), and
placing the thumb in the direction of conductor
movement, and pointing the index finger in the
direction of the magnetic field (north to south).
So, when a conductor cuts the magnetic fields of force, an electric current is generated. The
direction of current flow is dependent upon the direction of conductor movement.
Figure 1.66 shows that changing the direction of conductor motion through a magnetic field
reverses the direction of current flow.
So far, we have been using examples, which show a conductor cutting the magnetic field of a
stationary magnet. If we were to hold the conductor stationary and then moved the magnet in
such a way that the magnetic fields would be cut, a voltage would again be generated.
Therefore, it can be concluded that a voltage will be induced in a conductor cutting across a
magnetic field whenever there is a relative motion between the two. Either the conductor or
the magnetic field can move.
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There are three factors, which can be used to
control the magnitude of the induced voltage.
These factors are:
1. The strength of the magnetic field. If the
magnetic field is made stronger, such as
using a larger magnet, more lines of force will
be cut by the conductor in any given interval
of time and the induced voltage will be
higher.
2. The speed at which the lines of force are
cutting across the conductor. If the speed
increases at which the lines of force are
being cut, more lines of force will be cut in
any given interval of time and the voltage will
be higher.
Figure 1.66 – The relationship between
3. The number of conductors that are cutting conductor motion and the direction of current
across the lines of force. If the straight wire flow.
conductor is wound into a coil, which is then
moved across the field, all the loops of wire are in series and the voltage induced in all the
loops will add together to give a higher voltage.
To summarize, the stronger the field, the greater
the speed; and the larger the number of
conductors, the higher will be the induced
voltage.
Figure 1.67 – Voltage can be increased by field
strength, speed and number of conductors.
There are three general ways in which a voltage
can be induced by the principle of electromagnetic induction.
These three ways are
Generated Voltage, Self-Induction and Mutual
Induction.
Generated Voltage - A generator is a device, which converts rotational energy into electrical
power. There are two basic types.
1. Alternating current generators (called alternators).
2. Direct current generators (called generators, DC generators or dynamos).
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In the alternator shown in Figure 1.68, two poles
of a permanent magnet rotor turn inside a coil.
The electromagnet is created by completing a
circuit between an electric storage battery, and
windings around an iron core. The connection
between the rotating iron core and stationary
wires to and from the battery is made possible
by use of brushes and slip rings. As the
magnetic poles rotate, the fields of magnetic
force are cut through many times, thereby
inducing current into the conductor (stator coil)
where it is intensified because of the numerous
coil windings. This electricity (voltage) is shown
being directed to a light bulb.
Figure 1.68 – Basic alternator construction.
Actually, as the magnet poles rotate, the
magnetic fields of force through the coil will
gradually change, (Figure 1.69). Each time a
pole crosses the stator core, the direction of
induced e.m.f. reverses.
When this relationship between the stationary
stator coil and rotating magnetic rotor is plotted
for a complete cycle the dotted curve and full
curve are obtained as shown in Figure 1.70.
Figure 1.69 – Direction of rotor rotation and
induced e.m.f.
The full line in Figure 1.70 represents the
induced electromotive force (e.m.f.) and the
dotted line the change of magnetic lines of force
passing through the coil. At position (a) of the
magnet, the lines passing through the coil will be
at maximum since the lines through the stator
are equally split through the top and bottom half.
When the rotor is rotated clockwise 90°, i.e.
position (b), no flux will be passing through the
stator coil and this is the point where the
magnetic fields of force are cut.
Figure 1.70 – Change in magnetic flux (fields of
force) through the coil and induced e.m.f.
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If the flux change is great in a short period of time the e.m.f. will be large. When the rotor is
turned at a constant speed, the e.m.f. will be maximum at 90° and 270° where the change in
flux will be the greatest at 180° and 360° where there is the least change.
Also, notice that the induced e.m.f. takes on a different polarity at every 180° of rotation. This
is called an alternating e.m.f. and the resultant current is called an alternating current.
Direct current generators - Direct current
alternators differ from alternators in construction.
The armature and coil assembly rotates inside
the stationary magnetic field.
The armature's shaft has a commutator
composed of two insulated half cylinders to
which the ends of the armature's coil are
connected.
Two brushes contact the
commutator.
When the armature turns clockwise, the current
flow through it will be switched in direction at
every 180° of rotation.
Figure 1.71 – DC generator construction.
However, Figure 1.71 shows that brush A
contacts segment a of the commutator, and
brush B contacts segment b. As a result, current
starts flowing from brush A. When the armature
rotates 180° as shown in Figure 1.72,
commutator segment b now contacts brush A,
and segment a contacts brush B. Therefore,
current will still flow from brush A.
Figure 1.72 – DC generator direction of current
Although an alternating current is induced in the flow.
armature of a DC generator, the commutator
and brush act as a switching device to supply current flowing in one direction.
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The current from a DC generator varies with
time as shown in Figure 1.73. Actual generators
have many windings and commutator segments
and the windings are overlapped so that the
pulsating current for two coils is smoothed out
as illustrated in Figure 1.74.
Figure 1.73 – Theory of the electric generator.
Figure 1.74 – Current from a DC generator.
Self Induction - When a battery and switch is
connected in series with a coil, and the switch is
closed to permit current to flow through the coil,
lines of magnetic force will suddenly appear
through the axis of the coil. As a result, an
electromotive force will be induced in the coil
and will act to oppose the current flow in the coil,
(Figure 1.75).
When the switch is opened, and the current is Figure 1.75 – Effect of self-induction.
suddenly disrupted, the magnetic field will
suddenly collapse to cause a counter e.m.f. to be induced in the coil to prevent the current
flow from being disrupted. This phenomenon is called, self-induction and the effect are
greater as the number of turns in the coil is increased and if the coil has an iron core, as the
core is made larger.
Figure 1.76 shows an iron cored coil with many windings that has a lamp rated at 100 volts
connected in parallel. Also, there is a 6 volt battery connected in series and the circuit is
controlled with a switch.
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In the example shown in Figure 1.76, when the
switch is turned "ON" (contacts closed) to
connect the 6 volt battery to the coil, the lamp
will not light because only 6 volts is supplied to
it. But, when the switch is then turned "OFF"
(contacts open), the battery will be disconnected
and the lamp will light up momentarily. Also, the
lamp will light up more intensely if the switch is
disconnected more rapidly. This is because the
number of windings on the iron core was
sufficient to increase the induced voltage to 100
or more volts when the switch was opened. The
bulb went out as soon as this counter e.m.f. was
dissipated.
Figure 1.76 – Example of self-induction – Bulb
lights up momentarily when switch is
disconnected.
Mutual Induction - Figure 1.77 shows an
example of mutual induction. Notice that the
circuit with coil P (primary) has a battery and a
switch connected in series with it. Also notice
that coil S (secondary) has more windings and
realize that in practice, coil S would be wound
over coil P. When the current through coil P is
shut off and on, an electromotive force is
induced in coil S.
Figure 1.77 – Mutual induction.
This happens because the magnetic field
created by the current flow through coil P changes as a result of the on-and-off switching. This
in turn causes an e.m.f. to build up in coil S. This principle is used to make a transformer.
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Transformers are a major class of coils having
two or more windings usually wrapped around a
common core made of laminated iron sheets.
Figure 1.78 is a drawing of a simple transformer.
Figure 1.78 - Transformer
If the current flowing through the primary coil is
fluctuating, then a current will be induced into
the secondary winding. A steady (DC) current
will not be transferred from one coil to the other.
Transformers have the ability to transform voltage and current to higher or lower levels. They
do not, of course, create power for nothing. Therefore, if a transformer boosts the voltage of a
signal, it reduces its current. And if it cuts the voltage of a signal, it raises its current. In other
words, the power flowing from a transformer
cannot exceed the incoming power!
Figure 1.79 shows how a transformer works. If
the transformer is connected to a DC power
source as shown in (a) at the left, the electric
lamp will light up only when the switch is turned
on and off. However, if the same transformer
were connected to an AC power source, the
electric lamp would stay on as long as the switch
is "ON" (contacts closed). This is because
alternating current changes in magnitude and
direction periodically with a constant frequency
so that the magnetic field induced by the
primary coil changes continuously. This in turn
causes an alternating e.m.f. to be induced in the
secondary coil which in this case is maintained
as long as the switch is "ON".
Figure 1.79 – How a transformer works.
The electric spark ignition system used in
automotive gasoline engines is illustrated in
Figure 1.80. The direct current from the 12 volt
battery is switched on-and-off by the contact Figure 1.80 – Electric spark ignition system.
points in the distributor. The direct current is
converted to a kind of alternating current, which is supplied to the primary winding of the
ignition coil.
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Figure 1.81 – Voltage increases from 12 to 200
volts at primary coil, then from 200 to 20,000
volts at secondary coil.
Figure 1.82 – 1:1 ratio = isolation transformer.
When the high point of the distributor lobes open the contact points, an e.m.f. of about 200 volts is
induced in the primary coil, so the magnetic field in the core induces a voltage of 10,000 to 20,000 volts
in the secondary windings. This high voltage is necessary to bridge the air gap at the electrode end of
the spark plug and start the burning of fuel in the combustion chamber, (Figure 1.81).
The ratio of primary to secondary turns determines a transformer's voltage ratio. This is
referred to as the turn’s ratio. The turn’s ratio is used to show the following examples of three
common types of transformers.
When the number of turns is identical for the primary and secondary windings, the ratio would
be 1:1. The primary voltage and current are transferred unaltered to the secondary circuit.
These types of transformers are called, isolation transformers.
Figure 1.83 – Step-up transformer.
Figure 1.84 – Step-down transformer.
The next type of transformer is called a, step-up transformer.
In a step-up transformer, the voltage is increased by the turn’s ratio. Therefore, a 1:5 turns
ratio will boost 5 volts at the primary circuit into 25 volts at the secondary circuit.
The voltage is reduced by the turn’s ratio in a step-down transformer. Thus a 5:1 turns ratio
will drop 25 volts at the primary circuit to five (5) volts at the secondary circuit.
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CAPACITORS
When two metal plates are arranged facing each
other and then connected to a battery, a
negative charge will appear on the metal plate
connected to the negative terminal of the battery
and a positive charge will appear on the plate
connected to the positive terminal. Lines of
electric force will exist between the plates,
causing them to be attracted to each other.
Figure 1.85 – Principle of a capacitor.
The positive and negative charges will
consequently remain on the respective plates. Such a device is used to store electricity and is
known as a static capacitor (commonly abbreviated to capacitor).
There are many types of capacitors but they all store electrons. The simplest capacitor is two
conductors separated by an insulating material called the dielectric. The dielectric can be
paper, plastic film, mica, glass, ceramic, air or a vacuum. The plates can be aluminum discs,
aluminum foil or a thin film of metal applied to opposite sides of a solid dielectric. The
conductor-dielectric-conductor sandwich can be rolled into a cylinder or left flat.
Capacitors are often the "KEY" ingredient of many electronic circuits. Besides storing
electrons for use at a later time, capacitors are also used to smooth the pulsating voltage from
the power supply, filtering it into a steady direct current (DC), which increases the life of
electronic devices. Also, a capacitor can be used to eliminate power spikes in digital logic
circuits, which can use lots of current when they switch from off to on and vice versa.
To see how capacitors work, look at the following drawings, which show the charging, and
discharging of a capacitor.
As shown in Figure 1.86, when a battery, switch
and ammeter are connected to the capacitor,
and the switch is closed, the pointer of the
ammeter will move at first, but will quickly return
to the rest position again. The reason for this is
that current initially flows in order to supply a
charge to the capacitor. However, it ceases to
flow when the magnitude of the charge reaches
the capacity of the capacitor. This process of
supplying an electric charge to the capacitor is
called, charging.
Once the capacitor is charged, it will retain its Figure 1.86 – Capacitor charging.
charge indefinitely even, if the switch is opened.
Thus, the voltage across the ends of the capacitor will be maintained at roughly the same
voltage as that of the battery.
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Warning! Capacitors can store a charge for a considerable time after the power switch
to them has been turned off. This charge
can be DANGEROUS! A large electrolytic
charged to only 5 to 10 volts can melt the tip of a
screwdriver placed across its terminals. High
voltage capacitors like those used in a television
set and photo flash units can store a lethal
charge!
Never touch the leads of a capacitor. At the
very least the jolt can throw you across a room!
Figure 1.87 – Never touch the leads of a
capacitor.
Figure 1.88 – Capacitor discharge.
1 - Farad
= 1F
1 - microfarad = 1 µF =
1 - picofarad
= 1 pF =
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As shown in Figure 1.88, when a low resistance
is connected across the capacitor terminals, a
current will flow through the resistor causing it to
heat up. In this way, the electric charge stored
in the capacitor will be expended in the form of
heat generated in the resistor, and the voltage
stored across the capacitor terminals will
gradually fall to zero. This process of losing the
charge stored in a capacitor is called
discharging.
The maximum charge of a capacitor is referred
to as its capacitance. The unit for measuring
capacitance is a farad. A 1-farad capacitor
connected to a 1-volt supply will store
6,280,000,000,000,000,000 electrons!
Most
capacitors have much smaller values. Small
capacitors are specified in picofarads (trillionths
of a farad) and larger capacitors are designated
in microfarad (millionths of a farad). Summing
up:
0.000 001 F
0.000 000 000 001 F
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Chapter 1 - Assessment
Fundamentals of Electricity
Instructions:
There is only one correct answer to each question. If there appears to be
more than one answer, select the most correct answer.
If an in-house instructor is administering this test, turn your answers in to the
instructor when you are finished. Your instructor will input your scores into
the Komatsu Learning Management System.
If you are taking the Basic Electric course as self-study, mark your answers
in the appropriate space on the answer sheet provided in the back of the
booklet. When you have completed all of the assessments for the entire
book, either:
a.
Turn the assessments into your instructor along with your Answer Sheet.
The instructor is provided with an answer key and will grade your
assessment and also input your scores into the Komatsu Learning
Management System. Or,
b.
Log-in to the Komatsu Learning Management System (LMS), using your
extranet username and password. Go to the LMS site, enroll in this
Basic Subject course, after your enrollment has been approved, you can
launch the course, then click on the Assessment link and answer each
question. Your grade will be scored and tracked automatically. Note:
The online assessment questions are in random order.
1. What is electricity?
a. The flow of electrons from atom to atom in a conductor.
b. The flow of protons from atom to atom in a conductor.
c. The flow of neutrons from atom to atom in a conductor.
d. The flow of volts within a conductor.
2. Which of the following best describes semiconductor type elements?
a. Elements that have less than four electrons in their outer most ring.
b. Elements that neutrons in their outer most ring.
c. Elements that have exactly four electrons in their outer most ring.
d. Elements that have more than four electrons in their outer most ring.
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Chapter 1 Assessment
3. What is an ampere?
a. A measurement of potential electrical force.
b. A measurement of current.
c. A measurement of protons within a circuit.
d. A measurement of resistance to the flow of electricity.
4. Many Komatsu and Dresser products use diodes in their electronic systems. How
are these electric components used?
a. They are one-way electrical check valves.
b. They are used for rectification.
c. They are used to conduct current in the reverse direction.
d. Depending upon the application and type of diodes, any of the above tasks could be
accomplished using diodes.
5. The force of current is measured in which of the following units?
a. Amperes.
b. Volts.
c. Ohms, returned to the neutral position.
d. Microfarads.
6. What is resistance in an electrical system?
a. A potential force.
b. The tendency of each atom to resist the removal of an electron due to attraction toward
the core.
c. Collisions of countless electrons and atoms as the electrons move through the
conductor.
d. A combination of “b” and “c” above.
7. Which of the following best describes Ohm’s Law?
a. Ohm’s Law can be expressed in each of the three ways shown in “b”, “c”, and “d” below.
b. I = E
Amperes = Volts
R
Ohms
c. E = IR
Volts
= Amperes X Ohms
d. R = E
Amperes = Volts
I
Amperes
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Chapter 1 Assessment
8. The “Right Hand Rule” is used by electricians throughout the world to determine the
direction of current flow. Who is credited with giving us this rule?
a. James Prescott Joule.
b. George Simon Ohm.
c. John Ambrose Fleming.
d. Elmer R. Farad.
9. Which of the following is not a factor, which can be used to control the magnitude of
induced voltage?
a. Decrease or increase the strength of the magnetic field.
b. Changing the direction of conductor movement as it cuts the magnetic fields of force.
c. Increasing or decreasing the number of conductors that are cutting across the lines of
force.
d. Changing the speed at which the lines of force are cutting across the conductor.
10. Which of the following types of transformers would have more windings (turns) on
its secondary winding then its primary winding?
a. Analogous transformer.
b. Isolation transformer.
c. Step-up transformer.
d. Step-down transformer.
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Chapter 2
Electric Symbols
INTRODUCTION
From the beginning man has used marks, figures and objects to represent words or sounds. The
ancient Egyptians used hieroglyphics in this way, and Chinese written characters express
thought or meaning.
Today we have a universal means for communicating how electrical power is controlled and
transmitted in a circuit. Electrical engineers from all nationalities can understand these pictorial
and graphic symbols. These signs show the interconnection of components and component
functioning.
Knowing the meaning of the electrical symbols, which represent the components used on
construction equipment, will enable technicians to read the electrical schematics provided by
manufacturers. Because electrical schematics are like "road maps" that show how the current in
a circuit will flow, this new ability will help them locate the source of electrical problems when they
occur.
In this chapter you will study the common electric symbols used in Komatsu and Dresser
publications. These signs will be presented in the following order:
•
•
•
•
•
•
Common Symbols
Light Circuit Symbols
Gauge, Instrument & Monitor Panel Symbols
Starting Circuit Symbols
Charging Circuit Symbols
Engine Preheat Circuit Symbols
COMMON SYMBOLS
Electrical wiring diagrams can be drawn utilizing
pictorial or graphic symbols. Figure 2.1 shows
the pictorial and graphic symbol for a headlight.
Either pictorial or graphic symbols may be found
in Komatsu and Dresser publications. Pictorial
symbols are very useful for showing the
interconnection of components. However, they Figure 2.1 – Pictorial and graphic symbol for a
are difficult to standardize from a functional basis. headlight.
Graphic symbols are simple to draw and
emphasize the function and methods of operation of components.
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Wiring - Wiring is used to connect one electrical
component to another within a circuit.
The lines of an electrical wiring diagram show the
circuit wiring and how current will flow from one
component to the next. Since these lines will
overlay on the drawing it is necessary to be able
to understand if the wires are joined or not.
Figure 2.2 – Unconnected wires.
As can be seen in the Figure 2.2, lines that
simply cross, or lines, which open at an
intersection of two wires and a line that jumps
over an intersecting line, are not joined.
On the other hand, connected wires or wires that
are spliced together will be shown with a dot at
the point of intersection as shown in the right and
middle drawing of Figure 2.3. Sometimes,
several lines will curve into one as is illustrated
on the left in Figure 2.3. This represents several
single wires coming together to form a single
wiring harness. This type will have identical
identification numbers at both ends of the
harness.
Figure 2.3 – Connected wires.
Most of the lines on an electrical schematic will
symbolize wiring from one electrical component
to another. These lines will be of normal
blackness. But sometimes the lines of one
circuit will be drawn bolder to show where
current is flowing at the moment or to show the
power circuit compared to all others on the
diagram.
Figure 2.4 – Normal and Power circuit lines.
Some lines shown in Komatsu books are not
representing wires. Long lines with short dashes,
which surround two or more symbols, show that
the items contained therein are mounted to the
same assembly.
Figure 2.5 – Long lines with short dashes
surround items mounted to the same assembly.
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Some schematics show twisted wires as is
portrayed in Figure 2.6.
Figure 2. 6 – Twisted wires.
Twisted wires are shown in a schematic when
the twisting has a purpose. Twisting the wires
going to and returning from an electric actuator is
an inexpensive way to stabilize changes of
current flow. Stabilizing the current flow adds to
the longevity of the electrical device.
Wires used to ground a circuit will have one of
the symbols shown in Figure 2.7.
Wire numbers - Because Komatsu
Corp. was formally two entirely
companies, there are two totally
meanings for the numbers, which label
wiring diagrams.
America
different
different
wires on
Figure 2.7 – Symbols for ground wire.
On Dresser, Galion and Haulpak schematics, the
wire number is used for identification. An
example is shown in Figure 2.8. Wire number 39
joins the two headlights. However, the wiring
numbers on Komatsu electrical schematics has
a different meaning.
Figure 2.8 – Sometimes the number is the wire
number from one end connector to the other end
connector.
The numbers shown on the wires in a Komatsu
electrical schematic represent the size of the
wire. Actually, these numbers depict the cross
sectional diameter in millimeters of the wire.
This dimension does not include the thickness of
the wires insulation. The forward of every
Komatsu Shop Manual contains a chart which
shows the wire designation number and its
meaning. This is helpful to mechanics because
the charts also identifies the safe current flow
allowable for each size wire. When a wire has
been burned, he can correctly size the
replacement wire from local sources by referring
to the chart and the schematic.
The letters following the numbers on Komatsu
wiring schematics represent the color of the wire.
For example, in Figure 2.9, W = white, B = black, G = green and GR = green wire with red stripe.
A standard wiring color code chart is also in the forward of Komatsu Shop Manuals.
Figure 2.9 – Komatsu wire numbers.
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Notice also that the connector in Figure 2.9 is labeled "CN-E2". The connector label in the
schematic matches the tag on the connector as it sits in the machine. The (S12) identifies the
style of connector and number of pins it is designed to accept. The electrical section of Komatsu
Shop Manuals contains charts, which shows the style of connectors used on the machine,
(Figure 2.10).
The pin side of electrical connectors is called the male connector and the socket side is referred
to as the female connector.
Figure 2.10 – Example of Komatsu connector
identification.
Figure 2.11 – Komatsu multiple pole connector.
Switches - There are many kinds of switches. Only the most common and basic types will be
discussed here. Special purpose switches, such as the starter switch, will be shown under the
appropriate sub-category.
Single pole - single throw switch is perhaps
the simplest of all switches. It is OFF when the
switch is open. It is ON when the contacts are
touching (switch closed). It is important to Figure 2.12 – Single pole – single throw switch.
realize that depending upon the switch's purpose,
it may be set up in a circuit in either a normally
ON or normally OFF position.
Double pole - double throw switches can
have several poles and sets of contact points.
Shown in Figure 2.13 is a double pole - double
throw switch. It is shown in the OFF or OPEN
position.
Figure 2.13 – Double pole – double throw switch.
Pull switches (single stage) are found on older
model machines to activate electrical appliances
such as the headlights.
Figure 2.14 – Pull switch – (single stage).
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Pull switches (double stage) have been used
to turn on the headlights and panel light in one
stage and the taillights in the second stage.
Figure 2.15 – Pull switch (double stage).
A manually operated push button switch
usually operates the horn button. As can be
seen in Figure 2.16, there are several types of
button switches. They can be set into the circuit
in either a normally OFF or normally ON position.
Pressure switches can be found depicted in
three ways.
Sensor switches of temperature, pressure,
level and position are depicted in Figure 2.18.
Figure 2.18 – Sensor switches.
Figure 2.16 – Button switches
The Haulpak Division uses the following sign for
a temperature-operated switch, (Figure 2.19).
Figure 2.19 – Haulpak temperature switch.
Figure 2.17 – Pressure switches.
An electromagnetic contact can be symbolized
in either the open or closed position. They may
be shown using either a pictorial or graphic
method, (Figure 2.20).
Figure 2.20 – Contact points.
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Magnetic switches can be symbolized in
several different ways depending upon which
product line publication you may be using. The
starter solenoid is a typical form of magnetic
switch. Shown in figure 2.21 are the most
common symbols used to depict a starter
solenoid.
Circuit breakers are also shown in three
dissimilar ways, (Figure 2.22).
Input devices - Input devices are those
components from which the circuit current will
Figure 2.21 – Magnetic switch symbols.
originate when the circuit is completed. The
most common input devices on construction
equipment are batteries, generators or alternators.
Batteries - Several symbols can be found
depicting batteries. Shown in Figure 2.23 is the
symbol for a one-cell battery.
Figure 2.22 – Circuit breaker symbols.
Figure 2.23 – One cell battery.
Figure 2.24 – Shortened battery symbol.
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Technically, one short line and long line is used
for each cell of a storage battery.
The
international standard for a storage battery cell is
2.2 volts.
Consequently, a 12-volt battery
symbol consists of six short and six long parallel
lines. However, because usually there are
several batteries on a machine and many short
and long lines would take up a lot of space in the
schematic drawing. As a result it is customary to
shorten the battery symbol as shown in Figure
2.24.
So that the reader will know the capacity of the
battery, shortened battery symbols often show
the voltage and ampere-hour rating as seen in
Figure 2.25.
Figure 2.25 – Battery capacity markings.
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Many Komatsu America International products
use a 24-volt electrical system. To attain this
voltage either two 12-volt batteries are
connected in series as shown in Figure 2.26 or
four 12-volt batteries are connected in
series-parallel as depicted in Figure 2.27.
Figure 2.26 – Two 12 volt batteries connected in
series.
The last way that you will find batteries
represented is pictorially. This method is typical
in Dresser publications. The last way that you
will find batteries represented is pictorially.
Figure 2.28 shows four batteries connected in
series.
Generators produce DC current. In the old days
Komatsu called DC generators, "Dynamo's".
Following are the symbols used to represent a
generator.
Figure 2.27 – Four 12-volt batteries connected in
series-parallel.
In Figure 2.29 you see two different ways that a
generator can be symbolized. The difference is
due to the way that the field coil, armature and
Figure 2.28 – Pictorial drawing of four batteries
connected in series.
brushes are depicted.
Many schematic
drawings will show a generator with one of the
simpler marks shown in Figure 2.30. The symbol
at the left could represent either a DC generator
or an alternator. The straight line under the G in
the symbol on the right specifies that this is a DC
generator.
Figure 2.29 – Two ways to symbolize a generator.
Alternators produce alternating current. A
rectifier is used with an alternator to change its
alternating current into direct current in most
Komatsu America International machinery.
Figure 2.31 shows one of the simplest symbols
for an alternator. The wave line under the G
indicates alternating current.
Figure 2.30 – Simple generator symbols.
Figure 2.31 – Simple alternator symbol.
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Figure 2.32 shows a more complex set of symbols. In combination they represent an alternator,
which has an external regulator.
The V and A in the pictorial portion of Figure 2.32 indicates that the rated voltage and amperage
rating is provided in this location.
An alternator with a built in regulator is symbolized in Figure 2.33.
Figure 2.32 – Pictorial and detailed graphic
symbols for an alternator without regulator.
Figure 2.33 – Alternator with built in regulator.
Output devices - Output devices are also known as actuators. They take the electrical current
and put it to work. Typical output devices are lamps, solenoids and motors.
Lamps are used in the following six circuits:
1. Head lamp (including head lamp, tail lamp, panel lamp, work lamp, clearance lamp and
license plate lamp) circuit.
2. Turn signal circuit.
3. Back-up lamp circuit.
4. Stop lamp circuit.
5. Parking lamp circuit.
6. Electric luminescence (EL) circuit.
The simplest indication of a lamp is a circle.
There are several variations of the symbol for a
lamp. Shown in Figure 2.34 are three ways to
show a single filament bulb.
When a bulb has two filaments, various
bright-ness is available by changing the
combination of the filaments actuated.
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Figure 2.34 – Single filament lamp bulb symbols.
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The wiring schematics found in Dresser product manuals usually do not show the lamp graphic
symbols shown in Figures 2.34 and 2.35. Instead, Dresser publications normally use pictorial
illustrations such as the one shown in Figure 2.36.
Figure 2.36 – Dresser pictorial lamp drawing.
Figure 2.35 – Double filament bulb symbols.
The Haulpak division normally uses the symbol
found in Figure 2.37 to indicate a lamp.
Haulpak schematics usually have a label such as
"R.H. Back-up Lt." or "Eng. Serv. Lt." above the
symbol so that the reader can see the purpose
of the lamp.
Solenoids are an electro-magnet with a metal
core, which is free to move when the circuit is
completed. The simplest symbol is as shown in
Figure 2.38.
Figure 2.37 – Haulpak lamp symbol.
Figure 2.38 – A solenoid is a coil with moveable
metal core.
Komatsu publications show solenoids as boxes
or rectangles with an X drawn from corner to
corner, (Figure 2.39).
The Haulpak division uses the symbol shown in
Figure 2.40.
Figure 2.39 – Common Komatsu solenoid symbol.
Solenoids are used in many applications. If it is
the desire of the schematic drafter to show the
function of the solenoid, a detail drawing such as
the two shown in Figure 2.41 might be used.
Motors - An electric motor is an actuator, which
converts electrical energy into mechanical
(rotary) force.
Figure 2.40 – Common Haulpak solenoid symbol.
Figure 2.41 – A fuel shut-off valve and some
relays are types of solenoids.
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Figure 2.42 – Motor symbols.
Figure 2.42 shows three ways to symbolize a
motor. A circle with a M inside is a common sign
for a motor. A wave under the M indicates that
the motor is an AC motor. If there is a line under
the motor, this means that the motor is a DC
motor.
The most common motor found in construction
equipment is the starting or cranking motor. In
Figure 2.43 are symbols for starting motors.
Again notice that Dresser books use pictorial
drawings rather than true electrical symbols to
illustrate motors.
Figure 2.43 – Komatsu starting motor symbols.
Notice that the Haulpak symbol for a cranking
motor does not put the M inside their circle but
they do label the symbol so that the reader
knows what it is, (Figure 2.45). Haulpak, like
many manufacturers does not use the same
motor symbol for every case. Shown in Figure
2.46 are two more examples of motor symbols
found on Haulpak schematics.
Figure 2.44 – Dresser cranking motor drawing.
Figure 2.46 – Haulpak wheel motor symbol.
Figure 2.47 – Haulpak grid blower motor symbol.
Figure 2.45 – Haulpak cranking motor symbol.
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Glow plugs and ribbon heaters - Glow plugs
and/or ribbon heaters are used to preheat the
intake air of a engine to aid starting in cold
weather.
Figure 2.48 – A single glow plug symbol.
Figure 2.49 – Glow plugs connected in series.
Figure 2.50 – Glow plugs connected in parallel.
Ribbon heaters are shown as resistors. Shown in Figure 2.51 is a simple ribbon heater with two
heating elements. The symbol used to illustrate this type of heater is shown at the right.
There are more complex ribbon heaters. Shown in Figure 2.52 is a ribbon heater used in the
Komatsu 110 series engine. It has six elements wired in a series parallel circuit.
Figure 2.51 – Two-element ribbon heater &
symbol.
Figure 2.52 – Six element ribbon heater
connected in a series parallel circuit.
Horns and Buzzers - Electrical horns contain a coil (electromagnet) that is energized when
electricity flows to them.
This magnet pulls a movable plate and at the same time opens a set of contact points. When the
contact points open, the coil is demagnetized, so the movable plate returns to its original position
by spring tension. At the same time the contact points are closed and the process is repeated.
In this way the movable plate continually strikes a diaphragm to cause the horn sound, (Figure
2.53).
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Figure 2.54 – Dresser horn symbol.
Figure 2.55 – Detailed electric schematic of a
Komatsu buzzer.
Figure 2.53 – Komatsu horn & two types of horn
symbols.
Figure 2.56 – Komatsu simple buzzer symbol.
Shown in Figure 2.54 is the pictorial illustration used for showing a horn in Dresser schematics.
The Haulpak Division uses air type horns. Therefore, you will not find a horn symbol on their
electric schematics.
Electrical warning buzzers are more complicated in design. They consist of a series of
transistors, capacitors and resistors, which create various surge current to the buzzer coil.
These repeated surges create the sound.
Fortunately, the detailed buzzer schematic is used only when explaining how the buzzer works.
The simple symbol shown in Figure 2.56 is the one normally found on Komatsu schematics.
Other devices - There are many other common electrical symbols that can be used alone or in
combination with others to illustrate how an electrical device works. Shown in the following
figures are some that appear frequently in Komatsu America International Company
publications.
Fuses are designed to protect a circuit from excessive current flow. They melt in two, thus
breaking the circuit if this occurs. There are two symbols for a fuse.
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Figure 2.57 – Two fuse symbols.
The fuse symbol shown on the left in Figure 2.57
is the most common. The symbol on the right is
only used to indicate an enveloped (cylinder)
type fuse.
Capacitors are components which store and
discharge electricity. They consist of two metal
plates facing each other via an insulator.
Capacitors were formerly called "condensers".
Figure 2.58 – Fixed and variable capacitor
symbols.
Capacitors can be built with fixed or variable
capacity, so there is a symbol for both types.
Coils are a wound spiral of two or more turns of
insulated wire, used to introduce inductance into
a circuit.
Figure 2.59 – Coil symbols.
Figure 2.60 – Fixed resistor symbols.
Figure 2.61 – Variable resistor symbols.
Resistors - The resistance in a circuit has a
limiting effect on the current that flows through it.
If there were no resistance, a limitless current
would flow instantaneously.
Resistors are
important electrical components made from
materials with various stable resistance values.
They are used to control the flow of current and
voltage into each portion of a circuit. Resistors
can be fixed or variable types.
Circuit breakers are an automatic switch that
stops the flow of electric current in a sudden
overload or otherwise abnormally stressed
electric circuit.
Figure 2.62 – Symbol for circuit breaker.
LIGHT CIRCUIT SYMBOLS
There are two basic types of light circuits found
on Komatsu machines. The older style, shown in
figure 2.63 uses manual pull or toggle type
switches.
Figure 2.63 – Old style head light circuit.
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Current flow for the lighting circuit shown in Figure 2.63 would be from the battery → fuse → light
switch → lamps → chassis ground.
Because we have already presented the electric symbols that make up this circuit, they will not
be repeated here.
The newer systems differ from the old by the
method of actuation. The manual pull and toggle
switches have contact points, which are subject
to arcing when being turned on or off. The newer
light systems use transistors in the monitor panel
as the on-off switch. Transistors do not have
contact points. Instead, when you push the
Figure 2.64 – PNP transistor symbol.
appropriate spot on the monitor panel you are
energizing the base of a transistor allowing current to flow through it from the light relay terminal
2 to ground. Due to the transistor's unique design, current can be controlled without arcing and
because of this it has a much longer life expectancy then contact type switches.
By looking at the light circuit diagram in Figure
2.65, you can see that the current flows from the
power source → the coil of the lamp relay →
transistor in the monitor panel → chassis ground.
Now that the lamp relay coil is actuated, the coil
becomes an electromagnet, which closes the
contacts 3 and 5. Then current flows from the
24-volt power source → fuse → relay terminal 3
→ relay terminal 5 → connectors M6 & M8 →
R.H. head lamp and → connectors M6, M10 &
M9 → Boom head lamp.
Figure 2.65 – Coil of lamp relay energized by
pressing panel transistor switch.
GAUGE AND INSTRUMENT SYMBOLS
Gauges and instruments inform the operator of
the condition of the machine. Older and less
complicated equipment uses standard direct
sensing devices.
However, newer, more
complex equipment uses electronic devices.
Both types, along with their electric symbols will
be shown in this section.
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Figure 2.66 – Lamps “ON”.
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Bourdon tube type pressure gauge - Because
of its simple structure, the bourdon tube gauge
has, in the past, been widely used as pressure
gauges.
You can see by the structure of the bourdon
tube gauge in Figure 2.67 that it is not electrical.
Newer style instrument panels use electrical
sensors to detect pressure or rather the absence
of pressure.
Figure 2.67 – Bourdon tube pressure gauge.
In Figure 2.68 observe that the oil pressure
switch symbol shows that the contacts are held
closed by a spring. This means that when the
key switch is turned ON and the engine is OFF,
the circuit to the low oil pressure warning light is
complete so the light is illuminated. However, if
the engine is running, and the oil pressure rises
above the strength of the spring, the circuit will
be broken and the light would go off.
Figure 2.68 – Oil pressure sensor and symbol.
Monitor panel - The newest electronic vehicles
no longer use individual gauges for each check
item. They use an electronic monitor with liquid
crystal type displays. This type has several
advantages over the older instruments. First,
electronic devices are miniaturized, allowing
more items to be monitored in the same space,
which held only five or six items. Second,
electronic monitors with liquid crystal displays
have higher durability. Finally, these monitors
contain micro chips which can be set up to
provide additional warning to the operator by
ringing a buzzer and causing warning lights to
flash. Sometimes electronic monitors can flash
troubleshooting signals, which help the service
technician to locate electronic problems.
Figure 2.69 – Electronic monitor panel.
The portion of the electronic monitor panel,
which "lights up" when there is no engine oil
pressure is shown in Figure 2.70.
If the engine oil pressure indicator is normal, it
goes ON when the key switch is turned on and
goes OFF while the engine is running. If there is
an abnormality, this light flashes and a buzzer
sounds.
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Figure 2.70 – Engine oil pressure indicator.
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Fuel gauge circuit - Machines using older
individual style gauges use a circuit similar to
that shown in Figure 2.71.
This system
effectively converts the fuel level of the tank into
an electrical value, which can be indicated on the
fuel gauge.
Figure 2.71 – Fuel gauge circuit.
The flow of current in the above circuit would be:
Battery → fuse → load balancer → fuel gauge
→ fuel tank sensor → chassis ground.
The load balancer contains resistors, which allow the use of a 12 volt fuel gauge in a 24 volt
system. The tank unit consists of a float linked to a variable resistor by an arm. In this way, as
the float movement changes, the resistance also changes proportionally.
Fuel level sensor - Newer fuel level sensors
work the same way as the old type. The key
components are still a float and variable resistor.
Figure 2.72 – Fuel level sensor.
The signal from the fuel level sensor goes to a micro-chip in the monitor panel. The micro-chip
has seven terminals, each wired to pass current at a different degree of resistance. Each
micro-chip terminal is connected to one of the seven bars on the liquid crystal fuel level indicator.
On the fuel level gage shown in Figure 2.73, all
bars below the appropriate level light up.
Oil level sensor - The typical oil level sensor
has a float that goes down if oil is lost or
consumed. The symbols used to show such a
device are in Figure 2.74.
Figure 2.73 – Fuel level gauge.
Figure 2.74 – Komatsu oil level sensor symbol.
If the float drops to a level where the above
circuit is broken, then the oil level indicator of the
monitor panel shown in Figure 2.75 will flash to
warn of the abnormality.
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Figure 2.75 – Oil level indicator.
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The Haulpak Division uses different symbols to
represent their fluid level sensors or switches.
These symbols are shown in Figure 2.76.
Temperature sensors - There are two types of
temperature sensors used today. The circuit
switch type, which is used with caution lamps,
and the resistance type. In Komatsu designed
machines, resistance type sensors are wired to
a micro-chip in the monitor panel.
Figure 2.76 – Haulpak level switch symbols.
When the temperature goes above or below the
set temperature of the switch type temperature
sensor, the switch is turned off. Then a monitor
panel display, such as the one shown in Figure
2.78, lights up or a warning lamp comes on. On
some machines the light flashes and an alarm
buzzer sounds.
The signal of the resistor type temperature
sensor found on Komatsu designed machines is
wired to a micro-chip with seven terminals. Each
terminal will pass current at a different resistance.
Changes in temperature change the resistance
of the sensor, so only the appropriate bar of the Figure 2.77 – Temperature sensor symbols.
liquid crystal display is illuminated.
Normally, engine water temperature and torque
converter oil temperature sensors are resistance
types. Shown in Figure 2.79 are the symbols
and monitor panel indications used with this type
sensor.
Figure 2.78 – High oil temperature indication.
Figure 2. 79 – Engine water and torque converter
temperature indications.
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Temperature gauge - Older design machines
use electrical type temperature gauges.
Figure 2.80 – Electric temperature gauge symbol.
The temperature sensor used in combination
with the old style gauge has a symbol as shown
in Figure 2.81.
STARTING CIRCUIT SYMBOLS
Figure 2.81 – Old style temperature sensor
symbol.
The components of a starting circuit are the
batteries, the master switch or battery relay
(depending on product line), the starting key
switch, the safety relay (if equipped) and the
starting solenoid and motor.
Because the
symbols for batteries have already been shown,
they will not be repeated here.
Master switch - A master switch is a manually
actuated battery disconnect switch.
It is
normally found on Dresser labeled products.
Figure 2.82 – Dresser pictorial master switch
symbol.
Battery relay - Battery relays are electrical
battery disconnect switches. They are used on
all Komatsu products and some Dresser and
Haulpak products.
By studying the symbols that make up the
structure of a battery relay you can see that it
consists of a coil, two sets of contacts and three
diodes. When current flows to the coil, the
contacts close to complete the machines
electrical circuit to ground.
Starter switch - The starter or key switch is
used to turn on the machine's electrical system,
start or stop the engine and is sometimes used
to actuate the cold weather starting aid.
Figure 2.83 – Combination of electric symbols
that represent a battery relay.
Figure 2.84 – Starter switch symbol.
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This switch has four positions as shown in Figure
2.85.
From the OFF position, rotate the key
counter-clockwise to the heat position if
preheating of the intake air is desired. This is a
spring loaded position so if your hand is removed,
the switch will return to the OFF position.
Turning the key clockwise from the OFF position
Figure 2.85 – Starting switch positions.
places the switch in the ON position and the
machine electric system is actuated. This is accomplished by sending current to the coil of the
battery relay to close its points and complete the circuit to ground. Finally, to crank the engine
for starting, turn the key clockwise from the ON position. This is also a spring loaded position so
that after the engine starts and your hand is removed, the switch will automatically return to the
ON position. The following chart is found at the bottom of all Komatsu electric schematics to
show the mechanic which switch terminals are hot in each position.
Safety relay - The safety relay is an electrical
device placed between the cranking (C) wire of
the starting switch and the C terminal of the
starting motor solenoid. Its purpose is to prevent
the engine from being cranked after it is running.
This protects the starter drive pinion and
flywheel gear from damage.
Figure 2.87 – Combination of symbols, which
represent a safety relay.
Figure 2.86 – Starting switch connection table.
Figure 2.88 – Current flow during cranking.
The symbols shown in Figure 2.87 represent the semi-conductor type safety relay, which has
been installed on Komatsu products for nearly twenty years. It consists of a coil, contacts, two
transistors, three diodes, one zener diode, three resistors and two capacitors. During cranking,
current flows through the switch as shown in Figure 2.88.
When the engine is running, the alternator begins producing electricity and some of it is directed
from the alternator R terminal to the R terminal of the safety relay to actuate its safety function.
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Current from the alternator passes through the
zener diode to actuate the base of the left hand
transistor. When this happens, main current
from the starter switch passes through the upper
resistor rather then the coil because it has less
resistance.
Since current no longer flows
through the coil, the contacts open and current
from the battery (B terminal) can not pass to the
starter solenoid (C terminal).
Frequently, a less detailed symbol is used for a
safety relay as shown in Figure 2.90.
Figure 2.89 – Current flow through the safety
relay when the engine is running.
Figure 2.90 – Simplest symbol for safety relay.
Starter solenoid and motor - The starting
motor is used to start the engine. Shown in
Figure 2.91 are the combination of symbols used
to show the details of its functioning.
Figure 2.91 – Symbols of a starter.
Notice that the symbols representing a starter
motor are placed in two boxes of dashed lines.
The bottom box contains the symbols for the
starter solenoid. Notice the current must pass
through it before reaching the motor, which is
symbolized in the top box.
This detailed
schematic is used to show current flow through
the solenoid and motor. Normally this detailed
schematic is not found on the machines electric
schematic diagram. Instead, one of the symbols
shown in Figure 2.92 is used.
Figure 2.92 – Simple starter & solenoid symbols.
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CHARGING CIRCUIT SYMBOLS
Typically the charging circuit consists of the batteries, an ammeter or charge lamp, the alternator
and regulator. Because they have already been presented, the battery symbols will not be
discussed here.
Ammeter - The ammeter is provided for
checking the current flow in the charging circuit.
The negative terminal of the ammeter is
connected to the B terminal of the alternator or
regulator and is also connected to the light
circuits. The positive terminal is connected to
the Acc terminal of the starting switch.
Figure 2.93 – Typical charging system.
During battery charging, the pointer of the
ammeter deflects to the (+) side on the right of Figure 2.94 – Ammeter symbol.
the dial, indicating that the current is flowing out
of the alternator. On the other hand, when current flows from the battery to the lamps, the
ammeter pointer deflects to the left (-) side on the dial.
Charge lamp - A charge monitor lamp is provided when an ammeter is not. These warning
lights advise the operator if there is a malfunction of the alternator. When the starting switch is
turned ON, it will light up, but it should go out when the engine speed rises. If the lamp lights up
during operation, something is wrong with the charging circuit.
Figure 2.95 – Two styles of charge lamps.
Two different symbols have been used on
charge lamps as can be seen in Figure 2.95.
Both come ON or FLASH if there is a charging
system problem. Older systems have lights that
come ON, and newer systems have lamps on
the monitor panel that FLASH while a buzzer
sounds.
Alternator with built in regulator - All current production machines are supplied with regulators
with built-in voltage regulators. Therefore, the symbols for an alternator and regulator are
combined.
Figure 2.96 – Alternator with regulator symbols.
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By studying the detailed schematic (left) of
Figure 2.96, you can see the star or "Y"
connection, the diode bridge and the excitor coil
of the alternator. The right side of the detail
schematic shows a lone diode, a zener diode,
two transistors, four resistors and two capacitors,
which make up the regulator unit. Also shown
(on the right) is the simplest type of symbol.
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Notice that this design of alternator has three terminals.
Some of the first machines to be fitted with an alternator and those with a DC generator had
external regulators.
Notice that alternators and DC generators with external type voltage regulators have four
terminals.
Figure 2.98 – Symbol for external regulator.
Figure 2.97 – Detailed and simple symbols for old
style alternator with external regulator.
ENGINE PRE-HEAT CIRCUIT SYMBOLS
There are five types of engine cold weather starting aids found on Komatsu products. These
are:
1.
2.
3.
4.
5.
Ether injection
Preheater
Glow plug
Ribbon heater
Automatic priming system (APS)
All but the ether injection type contain electric
components. In this section you will see the
electric symbols used to illustrate preheat
circuits.
Figure 2.99 – Typical preheat circuit.
As you can see, three components (batteries, battery relay and starter switch) of the preheat
circuit are also components of other electrical systems. Because these three have already been
discussed, only new symbols will be shown here.
Heater indicator - Some systems have a heater
signal or glow plug indicator wired in series with
the circuit. It is literally a small electric heater
installed on the instrument panel in front of the
Figure 2.100 – Symbol for heater indicator.
operator's seat. When the preheat system is
being used, current flows through this indicator
and it will be heated to a RED-HOT state simultaneously with the glow plugs.
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Resistor - Resistors are found in many electric
circuits. The resistors in engine preheat systems
have a special purpose.
Consider the circumstances under which an
operator would need to use the preheat circuit. Figure 2.101 – Resistor symbol.
In cold weather (0°C or 32°F) the operator has
two factors working against him when it comes to starting the engine. First, when ambient
temperature drops, the capacity of the battery will also drop. Secondly, glow plugs are simply
coils of wire with great resistance to current flow, consequently, they are draining the batteries
of potential cranking power all the time that they are being used. For these reasons design
engineers usually install the smallest voltage (or amperage draw) glow plug that will heat the
required volume of air in the shortest period of time. The resistors lower the system voltage from
24 volts to the voltage requirement of the glow plugs (usually 12 or 18 volts).
Circuit breaker - The circuit breaker prevents
the preheater or glow plugs from overheating
due to excessive current flow and protects the
circuit against damage due to a short circuit.
Figure 2.102 – Circuit breaker symbol.
Preheater/glow plug - The symbol for a
preheater and a glow plug is the same. Also, the
construction and appearance is identical. But a
purest will say that they are different. Actually,
the difference is in installation location and
number used per installation. Glow plugs are
installed at a rate of one per cylinder. Fewer
preheaters (one or two per intake manifold) are
used.
Figure 2.103 – Preheater or glow plug symbol.
Early model engines had glow plugs connected in series such as the circuit shown in Figure
2.104.
However, when glow plugs are connected in a series circuit they and other system components
share the same ground. Consequently, if one glow plug or component fails (open circuit), the
entire system is defective. For this reason newer glow plug systems are wired in a parallel
fashion as shown in Figure 2.105.
Figure 2.104 – Series glow plug circuit.
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Figure 2.105 – Parallel glow plug circuit.
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Ribbon heaters - Many of the newest design small diesel engines use ribbon heaters. It is
installed either before or after the intake manifold. There are single or multiply element ribbon
heaters.
Figure 2.106 – Ribbon heater and symbol.
Notice that the ribbon heater in Figure 2.106
appears to contain one coil. However, closer
inspection of the drawing and symbol shows that
it actually contains two coils connected in series.
Figure 2.107 – Series parallel ribbon heater with
symbol.
Some ribbon heaters, such as the one used in the Komatsu 110 series engine (Figure 2.107),
contain several coils connected in a series parallel manner.
Notice that with the above wiring arrangement of six coils, if one coil were to burn out, three coils
would continue to function.
Automatic priming system (APS) - When a
glow plug or ribbon heater system is used it is
possible for the operator to operate the preheat
system too long before cranking the engine. In
fact, power from the batteries may be used up so
there is insufficient current to crank the starting
motor. This is most likely in engines such as the
Komatsu 155 and 170 series, which have large,
bore diameters. Also, glow plugs are usually not
very effective for preheating large bore engines
so another method of preheating has been
developed. The APS method uses glow plugs to Figure 2.108 – Outline of APS system.
heat the intake air before cranking plus a small
fire is built in the intake manifold while the engine is cranking and warming up. The small intake
manifold fire heats the additional volume of intake air. This system has proven reliable because
of the following reasons.
1. The operator cannot use the system unless the engine is cold (engine water temperature
below 20°C or 68°F),
2. The glow plug preheat time has been fixed with a bi-metal timer.
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3. Fuel cannot be injected into the intake manifold unless the engine is running.
4. Preheat fuel nozzle opening is electrically controlled (10 times/second) to obtain optimum
atomization and burning of fuel.
5. Automatic system shut down when engine is warmed up (water temperature above 20°C or
69°F).
The automatic priming system (APS) is by far the
most complex of the preheat systems, but by
studying Figure 2.109, you can see that it is
made up mostly from simple electric devices we
have already discussed. This system contains
two switches, one lamp, four relays, one bi-metal
timer, batteries, battery relay, two fuses, a water
temperature sensor, an alternator, motor, two
resistors, two glow plugs, two fuel nozzles, and
an APS controller.
Figure 2.109 – APS circuit.
Panel switch - The panel switch is actually a
transistor type switch.
Even so, Komatsu
schematics show it as a simple push type switch
to help mechanics understand the function.
Figure 2.110 – Panel switch and symbol.
APS pilot lamp - When the preheat (APS) panel
switch is pressed, and if the engine coolant is
cold enough, the APS pilot lamp on the monitor
panel will light up. This indicates that the circuit
to the glow plugs is functioning. In about 15 to 20
seconds this lamp should go out, which is the
signal for the operator to start the engine.
Figure 2.111 – Engine preheater monitor lamp and
its schematic symbol.
Relays - Again look at Figure 2.109. The APS
contains four relays, the safety relay, the preheat
relay, the heater relay and the preheat back-up
relay. Each relay allows current to pass through
it under different specific conditions. Relays are
electric magnetic switches. Current cannot pass
through them unless the circuit through their coil
is completed. For example, in Figure 2.110 the
Figure 2.112 – Relay symbol.
safety relay is shown but the wires to and from its
coil are not. This is because the safety relay is
not really a part of the APS. It is activated when the start switch is turned ON. The safety relay
is shown in the APS circuit diagram because current must pass through it to enter the system.
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A more detailed explanation of each relay's function is given in Chapter 5.
Bi-metal timer - The bi-metal timer symbol looks like a relay, but it is constructed differently.
The top set of points are connected to two pieces of metal. These pieces of metal are either of
different types, different thicknesses, or both and are laminated together. When the bi-metal
strip is heated, one of the metals expands more then the other, causing the contact points to
either contact or pull apart (both types are available).
Figure 2.113 – Bi-metal timer symbol with
normally closed points.
Figure 2.114 – Bi-metal timer symbol with the
bi-metal heated and contacts open.
With the bi-metal timer shown in Figure 2.113, if the preheat switch was moved to the AUTO
position, current would flow through the contacts for a while. Notice that when current goes
through the contacts, it would also go through the coil and the bi-metal strip would begin to heat
up.
In the APS circuit, the bi-metal is connected to the APS pilot lamp so that when the APS is first
turned ON, the light lights up, but when the bi-metal is heated, the contacts open cutting the
current flow to the lamp. This advises the operator that the intake air has been heated
sufficiently to start the engine.
The symbol for a bi-metal timer sometimes uses
a coil rather than a resistor as the heating
element. Such is the case in the APS electric
schematic shown in Figures 2.109 and 2.115.
Figure 2.115 – Alternate bi-metal timer symbol.
Water temperature sensor - By looking at the APS schematic, you can see that current must
flow through the preheat relay before it reaches the APS controller or glow plugs. Also, current
cannot pass through it unless the coil/magnet is actuated. The APS water temperature sensor
completes the preheat relay's coil/magnetic circuit when the engine coolant is cold enough.
In Figure 2.116, the symbol is drawn as if the
engine coolant temperature were below 20°C or
68°F.
Figure 2.116 – APS water temperature sensor
symbol (contacts closed).
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APS controller - The contents of the APS
controller is a trade secret, therefore, its detailed
schematic diagram is not available. A simple
drawing which shows its terminal connections is
used instead.
The APS controller is an electrical pulse
generator. If or when it receives two input signals,
(one from the battery/glow plug route and one
from either the starting switch C terminal or the
alternator R terminal), then it intermittently opens
the solenoids of the fuel nozzles.
Figure 2.117 – APS controller symbol.
Fuel motor - Older design APS fuel nozzles get
their fuel from the feed pump circuit of the
mechanical injection pump assembly. Therefore,
the fuel available at the APS nozzles is not fully
pressurized until engine cranking has occurred
for several seconds. To shorten engine starting
time, an electric motor has been installed in the Figure 2.118 – Fuel supply motor symbol.
newest version. This electric motor begins
pumping as soon as the APS panel switch has been activated. Therefore, the fuel at the nozzles
is under pressure before cranking occurs and quicker starting is achieved.
Fuel nozzle - The APS fuel nozzle is a fuel
delivery device, which squirts atomized fuel into
the intake manifold. It consists of a small fuel
nozzle and electric solenoid. When the solenoid
is energized, fuel under pressure passes
Figure 2.119 – APS fuel nozzle symbol.
through its nozzle. As mentioned earlier, the
APS controller allows this to happen ten times per second.
Glow plugs - Glow plugs were discussed earlier
and they are used in the same manner in the
automatic priming system except that they have
one additional function. They are purposely
Figure 2.120 – APS glow plug symbol.
located to intercept the atomized fuel stream as
it leaves the fuel nozzles. Because they were
one of the first APS components to be activated, they are RED HOT by the time the engine is
cranked, so they provide the heat to ignite the fuel.
Notice that the glow plug symbol shown in the APS circuit diagram is different than the symbol
shown in Figure 2.103. Either symbol could be used.
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SEMICONDUCTOR SYMBOLS
In nearly every circuit today, one can find semiconductors. Most of the semiconductors found
on construction equipment are either diodes or transistors. Following are shown the symbols
you will see most often in Komatsu America International Company products.
Figure 2.121 - Diodes
Diodes - In our earlier discussions of diodes,
you were only shown the basic diode symbol
(top symbol in Figure 2.121). A common diode
is used as an electrical one way check valve.
Newly shown above are the symbols for a
luminous diode, constant voltage diode, and
photo diode. The red and green light emitting
diodes (LED’s) used in some diagnostic
systems are luminous type diodes. A more
common name for a constant voltage diode is
“zener diode”. A zener diode allows current to
flow in the reverse direction at a predetermined
voltage. These types are often used in
semiconductor voltage regulators. The bottom
diode symbol shows a photo diode. These
types are light sensitive.
Transistors - Transistors are also made
from semiconductor materials. They act
like switches to turn current flow on or off.
As one can see in Figure 2.121, there
are several different types of transistors.
Shown are the most frequently used
transistor symbols.
Figure 2.122 – Transistors.
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Chapter 2 - Assessment
Electric Symbols
Instructions:
There is only one correct answer to each question. If there appears to be more
than one answer, select the most correct answer.
If an in-house instructor is administering this test, turn your answers in to the
instructor when you are finished. Your instructor will input your scores into the
Komatsu Learning Management System.
If you are taking the Basic Electric course as self-study, mark your answers in
the appropriate space on the answer sheet provided in the back of the booklet.
When you have completed all of the assessments for the entire book, either:
a.
Turn the assessments into your instructor along with your Answer Sheet.
The instructor is provided with an answer key and will grade your
assessment and also input your scores into the Komatsu Learning
Management System. Or,
b.
Log-in to the Komatsu Learning Management System (LMS), using your
extranet username and password. Go to the LMS site, enroll in this Basic
Subject course, after your enrollment has been approved, you can launch
the course, then click on the Assessment link and answer each question.
Your grade will be scored and tracked automatically. Note: The online
assessment questions are in random order.
1. Study the symbol at the right. Which of the
following best describe the type item it
represents?
a. A normally open push type switch.
b. A normally closed push type switch.
c. A normally closed pull type switch.
d. A normally open pull type switch.
2. Study the symbol at the right. Which symbol
represents a pressure switch?
a. A
b. B
c. C
d. All are pressure switches.
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Chapter 2 Assessment
3. Which of the symbols at the right is not used to
illustrate a circuit breaker?
a. A
b. B
c. C
d. D
4. Which of the following does the detail at the
right represent?
a. Starter solenoid.
b. Battery relay.
c. Bi-metal timer.
d. Starter solenoid and motor.
5. Study the Komatsu wire connector symbol at the
right. What does the numbers shown above the
wire to pin number 7 represent?
a. The application identification.
b. The number of electrons (in thousands) the wire
is designed to carry.
c. The cross sectional diameter of the wire
excluding insulation.
d. The cross sectional diameter of the wire including
insulation.
6. Which symbol shown at the right represents a
bi-metal timer?
a. A
b. B
c. C
d. Both b. and c.
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Chapter 2 Assessment
7. Which symbol shown at the right is not a diode?
a. A
b. B
c. C
d. D
8. Which symbol shown at the right represents a
solenoid?
a. A
b. B
c. C
d. All of them.
9. Study the electrical symbols at the right. This
combination of symbols represents which of the
following components?
a. An alternator.
b. An alternator with regulator.
c. A starter with solenoid.
d. A battery relay.
10. Which symbol shown at the right represents a
transistor?
a. A
b. B
c. C
d. All of them.
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Chapter 2 Assessment
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Chapter 3
Starting System
INTRODUCTION
One of the most important electrical functions on construction machinery is to be able to rotate
the engine crankshaft with sufficient force and speed to ensure combustion for starting. The
combination of components that provide this vital function is referred to as the starting system.
It is necessary for the field service technicians to have a thorough understanding of starting
systems so that they can rapidly find the source of starting problems.
In this chapter you will examine a typical starting circuit and learn the construction and
functioning of its components. The contents of this chapter will be presented in the following
order:
•
•
•
•
Starting Circuit Diagram
Component Construction
- Battery
- Master switch
- Battery relay
- Key switch
- Start button
- Neutral start switch
- Starting motor
- Diode
- Fusible link
Maintenance
Troubleshooting
STARTING CIRCUIT DIAGRAM
Figure 3-1 shows a graphic illustration of a
typical starting system. You can see the normal
component lay-out by studying this diagram.
In order to understand this system more
thoroughly, additional starting system diagrams
follow which show the current flow in various
stages.
Figure 3.1 – Starting circuit diagram.
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Figure 3.2 shows the
current flow when the
starting (key) switch is
turned to the ON
position. This action
completes the circuit
to the coil of the
battery relay closing
the contact points Band E. The machine
electrical system is
now activated and
current is available at
the "B" terminal of the
starting motor and
safety relay.
Figure 3.3 shows the
current flow when the
Figure 3.2 – Current flow with starting switch ON.
engine
is
being
cranked
over
for
starting. This flow is
initiated by turning the
starting (key) switch to
the right past the ON
position to the spring
loaded
START
position (C terminal).
When held in this
position, current from
the battery flows from
the switch terminal "B"
to "C", then from the
switch contact "C"
through wiring to the
safety
relay
"S"
terminal. The safety
relay is constructed so
that
current
will
normally pass from
the safety relay "S"
terminal to its "C"
Figure 3.3 – Starting circuit current flow “while cranking”.
terminal. Current then
goes from the safety
relay "C" terminal on the starter magnetic (solenoid) switch. This current starts the initial gradual
rotation of the motor.
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Immediately after the initial starting of the motor,
a pinion gear (Figure 3.4) starts engaging a ring
gear on the engine flywheel so that the motor
can drive the engine.
Figure 3.4 – Pinion gear engaging the flywheel
mounted ring gear.
When this engagement is completed, the
magnetic switch also closes the large contacts
"B" and "M" of the starter solenoid to allow
greater intensity of current flow to the motor,
thereby allowing the motor to rotate at full speed
and maximum force.
If the "key" of the starting switch were held in the
START or "cranking" position after the engine is
started, there is the possibility of damage to the
flywheel ring gear, starter drive pinion gear or
starter motor. This could also happen if the key
switch were accidently turned to the START
position after the engine has been started.
Figure 3.5 – Starter motor.
To prevent this type of damage, many Komatsu
machines have a safety relay installed between
the key switch and the starter solenoid.
Figure 3.6 shows that after
the engine is started and the
alternator begins generating
electricity, current flows
from the alternator "R"
terminal to the safety relay
"R" terminal where it is used
to cut the flow of current
between the key switch and
the starter solenoid "C"
terminals.
Figure 3.6 – Safety relay function.
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COMPONENT CONSTRUCTION
The major components of any starting system are the battery, a battery relay or master switch,
a starting switch, a magnetic switch (sometimes referred to as a starter solenoid) and the starting
motor. Following is a description of these components and their function within the system. In
addition, some starting systems contain a safety relay, fusible link and a diode. Therefore,
explanations of the functioning of these components is also provided.
Battery - A battery is like a checking account at the bank. When pocket money is needed, you
can withdraw the amount needed. But you will soon run out of money in the account if no
deposits are made. Therefore, it is necessary to make deposits from time to time to ensure the
availability of funds when you need them.
The same is true of a battery. Electricity in the battery is used when starting the engine or when
using other electrical devices. But the battery will run down if it is used without recharging.
Using the electric charge deposited in the battery
is called, battery discharging. Filling the
battery with charge is called, battery charging.
A battery is a container partitioned into several
cells. Typically each cell is rated at 2.1 volts.
Therefore, there are three cells in a 6 volt battery
and six cells in a 12 volt battery. Each cell Figure 3.7 – A battery is often made up of identical
consists of positive and negative plates inserted cells connected together.
alternately. All positive plates within a cell are connected with one another and the same is true
of the negative plates. The greater the number of plates used, the more electric charge can be
deposited.
The plates are coated with special materials referred to as the active substances. The active
substance of the positive plates is lead peroxide which is coated on the grid of lead alloy where
the positive electricity develops. The negative plates have spongy lead coated on the grid where
the negative electricity develops. Both the positive and negative plates can produce electricity
only when they are immersed in a diluted sulfuric acid solution called electrolyte. If both types
of plates were to come into contact with each other, current flows and there would be a loss of
stored electricity. To prevent this from happening, separator sheets are placed between all
plates. Finally, all the positive plates of one cell are connected to all other positive plates in the
other cells of the battery where their combined energy is concentrated at the positive battery
terminal. All negative plates of all cells are linked to the smaller negative battery terminal.
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Nearly all batteries used in construction
equipment today are solid type batteries (Figure
3.8). This type battery has a case and cover
made of plastic which are heat melted together
during assembly. If one of its cells become
defective, the entire battery must be replaced.
Older compound type batteries had replaceable
cells but are rarely used today because of their
higher cost.
Figure 3.8 – Solid type battery.
When batteries are being charged, electricity is
sent to the battery by the alternator. This causes
a reaction between the diluted sulfuric acid
solution and the battery plates. This process
generates bubbles and heat within the cells so a
vent cap is provided.
Figure 3.9 shows the construction of a battery
vent cap. Each cell of a battery has one of these
vent caps. It has two purposes. One purpose is
to prevent dust and dirt from entering the cell.
The second purpose is to provide a passage
through which gas produced during charging of
the battery can escape. This venting device is
designed in such a way that the sulfuric acid in
the acid mist will not escape. This is important
as the sulfuric acid is needed to get the
appropriate chemical reaction between the
positive and negative plates of the battery during
charging.
How does electricity occur in a battery? When
the positive and negative terminals are Figure 3.9 – Battery vent cap.
connected to lamps and the motor, the lead
peroxide of the positive plates and the lead of the negative plates are turned into lead sulfate by
the sulfuric acid in the electrolyte, thereby generating electrical power for application of the lights
and motor. During current discharging, the plates undergo such a chemical change when the
circuit is complete. However, if the circuit is broken as when the control switch is turned off, this
chemical reaction stops.
Since the plates undergo a chemical change by absorbing sulfuric acid in the electrolyte, the
sulfuric acid in the electrolyte decreases as the chemical change of the plates advances. This in
turn increases the water content, thus reducing the specific gravity of the electrolyte. If the
specific gravity of the electrolyte is measured at this time, it is possible to know just how much
battery discharging has occurred.
As stated above, battery discharging causes the plates to undergo a change. Because of this,
too much discharging can cause the plates to bend or cause the peeling off of the active
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substances. Both of these defects will lead to premature failure of the battery or shorter life.
Therefore, it is important to recharge the batteries when the specific gravity drops below 1.20.
Battery capacity - If a uniform current is
continuously discharged from a fully charged
battery, the voltage of the battery gradually goes
down as shown in Figure 3.10.
Figure 3.10 – Final terminal voltage.
If the discharge time exceeds a certain period,
the voltage diminishes rapidly and the battery
suffers. Therefore, it is necessary to stop
discharging before the battery is damaged. The
voltage at this point is called final terminal
voltage.
The capacity of a battery is expressed in terms of an ampere-hour (Ah) rating. This rating
indicates the intensity of continuous current (amperage draw) the battery can provide over a
period of 20 discharge hours. After 20 continuous discharge hours the battery will have reached
its final terminal voltage. Figure 3.10 shows that the final terminal voltage of a single battery cell
when measured at 20 hour continuous discharge rate would be 1.75 volts. Therefore, if a 12 volt
battery had the same rating, its final terminal voltage would be 10.5 volts.
Therefore, a fully charged 12 volt battery with a
200 Ah rating can last 20 hours of continuous
use without causing a voltage drop below 10.5
volts when a constant 10A current load (three
40W bulbs) is applied as the load. Of course, if
the discharge load is greater, the length of
possible continuous use is decreased.
It is important to realize that the Ah ratings are
based on the electrolyte temperature being 25°C
(77°F). Therefore, if the temperature of the Figure 3.11 – Effect of electrolyte temperature on
electrolyte is different, the capacity can also vary. battery capacity.
As you can see in Figure 3.11, battery capacity decreases as the temperature of the electricity
falls. In other words, as the temperature drops, the period of time before the output voltage goes
down to final discharge voltage will be shortened. In fact, the chart shows that the capacity at
-20°C (-4°F) is about half of what it is at 25°C (77°F).
Therefore, in the winter it may be difficult to start your engine due to diminished battery capacity.
Also, cold weather causes the engine oil to thicken and this creates additional resistance to
engine rotation. For these reasons, make certain that the charging system is working and start
the engine with a fully charged battery. Absolutely avoid using a battery which is discharged
more than 25% in winter.
Electrolyte - As previously mentioned, electrolyte is the diluted sulfuric acid solution in which the
battery positive and negative plates are submerged.
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Battery voltage can recover to almost the original voltage if discharging is discontinued for some
time. But this does not mean that the lost or consumed power can be recovered when the
voltage rejuvenates. In fact, it is impossible to gauge the strength of a battery based on its
voltage readings.
However, we do know that the specific gravity of the battery decreases as it discharges.
Figure 3.12 – Specific gravity compared to
discharge ratio.
Figure 3.12 shows that the specific gravity of a
fully charged battery is 1.260. It also shows that
this same battery is 50% discharged if its specific
gravity reading is 1.160. At least this is true if the
electrolyte temperature is 20°C (68°F). But
specific gravity changes if the electrolyte
temperature is more or less than 20°C. The
specific gravity as electrolyte increases in
proportion to a drop in temperature at a rate of
0.0007 per every 1°C. The important point here
is that electrolyte is easier to freeze when the
specific gravity drops as a result of discharging.
By studying the chart in Figure 3.13 one can see
that there is no fear of the electrolyte freezing if it
is maintained at the proper specific gravity of
1.260 by charging. If specific gravity falls to
1.150 (approximately 50% of discharge rate) the
electrolyte will freeze at -15°C (5°F).
Figure 3.13 – Freezing point of electrolyte at
differing specific gravity readings.
Self-discharge or spontaneous discharge Even when a battery is not being used it looses
some of its charge. Batteries not in use should
be charged at least once a month in the summer
and twice per month in the winter.
Self-discharge can be reduced to a minimum by following the following procedures:
1. Store batteries which are not in use in a cool, dry place as self-discharge is accelerated in
high temperatures.
2. Remove batteries from vehicles not in operation and store in a cool place.
3. Recharge storage batteries once a month.
4. Keep the tops of batteries clean and dry. If a battery is dusty and moistened by electrolyte
or water, very slight current will flow and self-discharge will occur. Clean batteries with a
solution of baking soda and water.
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5.
Handle batteries with care. First, because spilled battery acid can burn your skin and
damage clothing. (Flush immediately with water and call a doctor if burning occurs.)
Secondly, because if a battery is damaged and particles of active substance comes off the
plates, the particles may make a connection between the positive and negative plates which
will result in rapid self-discharging of the battery.
6. Use only distilled water to replenish electrolyte level that has diminished due to evaporation.
Tap water contains minerals, which will settle at the bottom of the battery and cause it to
self-discharge.
7. Take care when working around batteries. Dropping a wrench or screwdriver across a
batteries terminals can cause serious damage. Also the resulting sparks could set off an
explosion, particularly during recharging as the fumes from a battery are combustible.
8. When disconnecting a battery, remove the negative ground strap first, then the positive lead.
Reverse this procedure when connecting a battery. This will prevent electrical shorting.
9. Make certain that you have connected a battery properly before attempting to start the
engine. This can be confirmed by observing the ammeter while turning the key switch on.
If the ammeter pointer moves from the center to the "-" (or "D") side when the light switch is
turned on, this indicates that the terminals are properly connected.
10. Do not crank the engine for longer than 30 seconds. Rest the battery at least 30 seconds
before cranking again. Cranking the engine for longer then 30 seconds can damage the
starter motor and decreases the charge of the battery. Look for causes of hard starting
before continuing.
Battery Relay/Master switch - There are two
types of switches found on Komatsu products,
which are used to remove voltage from circuit
wires when not in use. Their use eliminates the
possibility of short circuit or getting shocked
when
repairing
or
replacing
electrical
components. They are the master switch and
battery relay.
Master switch - A master switch or master
disconnect switch (Figure 3.14) is a manually
operated battery disconnect device.
Figure 3.14 – Master switch.
This simple devise is usually located between the
battery and chassis ground. It must be turned on
to get electrical power to the key switch and
monitor panel. Master switches are found on
Dresser, Galion and Haulpak product lines.
Figure 3.15 – Electric symbol for master switch.
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Battery relay - Komatsu designed products use
a battery relay. There are two types, the older
three terminal type and the current four terminal
type. Both types are electromagnetic switches
controlled from the starting key switch.
Figure 3.16 – Three terminal type battery relay.
Notice how the three terminals "E", "b-" and "BR"
are connected in Figure 3.17. When the starting
switch is turned ON, electric current flows
through the electromagnet within the relay
switch. This control circuit is formed between
the battery, starting switch (ON position) and the
battery relay electromagnet.
When the key switch is turned on, there is a
connection between its "B" and "BR" terminals
so current passes through it to the "BR" terminal
of the battery relay. The current will pass
through the coil to the "b-" terminal which is
connected to the negative terminal of the battery.
Figure 3.17 – Three terminal battery relay and its
circuit diagram.
Figure 3.18 – Circuit diagram of three terminal
Figure 3.18 shows that when the battery relay
control circuit is complete, the coil becomes an
electromagnet which draws the plunger in and
the main contact "C" is closed. The negative
terminal is now grounded through the "E"
terminal of the battery relay and the machine
electrical system is completely energized.
The current battery relay has four terminals. It
works the same as the three terminal type but
has added features which contribute to longer
life. Study Figure 19 and notice that the fourth
terminal is labeled "A". Early models used the
"A" label because the wire coming to this
terminal came from the alternator (via the safety
relay).
Today battery relays have their fourth terminal
labeled "R" because the current coming to the
battery relay at this terminal actually originates in
the built-in regulator portion of the alternator.
Figure 3.19 – Four terminal type battery relay
wiring.
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Shown in Figure 3.20 is an electrical schematic
we will use to show the battery relay function.
When the main (key) switch is ON, current flows
through battery relay "BR" terminal to field coil
"C", closing contact "P". Now the negative side
of the battery is connected to ground and the
machine electrical system is actuated.
If the main (key) switch is turned off while the
engine is running, the main contacts between -b
and E will remain closed and the battery will
continue to be charged from the "R" terminal,
(see Figure 3.22). Also during the time that the
engine is being shut down, but it is still turning
over due to flywheel inertia, current flows from
the alternator "N" or "R" terminal to coil "C" via
battery relay "A" (or "R") terminal. This prevents
voltage surges from damaging the electrical
components.
Battery relay connections - The battery relay
may be connected at either the negative or
positive side of the batteries. Which way
depends upon the need to use electrical
components when the engine is off.
Figure 3.20 – Battery relay internal circuit when
the main (key) switch is OFF.
Figure 3.21 – Battery relay internal circuit when
main (key) switch is ON.
Figure 3.22 – Current flow through battery relay
when engine turns over while main switch is OFF.
When it is anticipated that there will be no use of
the machines electrical system when the engine
is off, the battery relay is connected on the
negative side of the battery as shown in Figure
3.23. When configured this way, none of the
machines electrical components can be
energized until the battery relay contact points
have been closed.
Figure 3.23 – Battery relay on negative side of
battery.
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If some electrical components such as a
roadside hazard light or electric clock will be
needed when the engine is not running, the
battery relay is connected as shown in Figure
3.24. Notice that current for an independent
circuit could be gotten from terminal "B" without
activating the battery relay. So with this type of
set up, some electrical circuits could be used
without energizing all others.
Figure 3.24 – Battery relay connected on the
positive side of the battery.
Large machines have a large amperage draw.
The wires within a battery relay are not large
enough to carry the current in such a case. The
manufacturer could make a larger relay with
bigger wires or simply use two battery relays
connected in a series parallel circuit to share the
load.
Key Switch - There are three types of key
switches. One has two positions and the others
have four positions.
Figure 3.25 – Double battery relay set up.
Figure 3.26 – Two position type key switch.
Figure 3.27 – Dresser four position key switch.
The two position key starting switch will illuminate the instrument panel warning lights when
turned ON. If any of the lights do not come on, replace the bulbs. Turn the switch to the OFF
position to disconnect the electrical circuit to the instrument panel, and to shut down the engine.
This type switch is found primarily in the Dresser and Galion product lines. A separate starter
button is used when cranking the engine for starting.
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The functions of the Dresser four position key switch are as follows:
A This is the ACC (accessories) position and is used for added electrical accessories, which
may be required to be on without the engine running.
B This is the OFF position. Turn the switch to this position when turning off the engine or to
disconnect the electrical circuit to the instrument panel.
C This is the ON or RUN position. The instrument panel warning lights will be illuminated when
the switch is in this position.
D This is the START position. The cranking motor will engage and the instrument panel
warning lights will illuminate. Release the switch the instant the engine starts; the switch will
automatically return to the RUN position.
The Komatsu four position starting key switch is labeled - ON, OFF, HEAT and START. If the
key is turned to the ON position, it will remain there after being released. If the key is turned to
either the START or HEAT position, it will automatically spring back to ON or OFF (respectively)
after being released.
Figure 3.29 – Key switch interconnection chart.
Figure 3.28 – Komatsu four position key switch.
There are six terminals, "B," "BR," "R1," "R2," "C" and "AC". The "B" terminal comes from the
battery and is always hot. When the key switch is turned to the ON position, the contacts
between the "B" and "BR" terminals are completed and current for most machine electric
systems is available. Terminals "R1" and "R2" are used when preheating the engine during cold
weather starts. "R1" receives current when the key is held in the HEAT position. "R2" gets
current during cranking. When starting the engine, contacts between the "B" and "C" terminals
are complete so current can pass out of the switch "C" terminal to the starter motor solenoid for
cranking. "AC" is the accessory terminal. Current is fed to the instruments and lights from this
terminal so it receives current whenever the key is in the ON position.
Start Button - These are various key switches. Modern machines use a key switch to start the
engine. However, there are many seasoned machines, which use a simple push button for
cranking the engine. The push button should be released the instant the engine is started.
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Electrical symbol B in Figure 3.30 represents a
push button type starter switch.
Neutral Start Switch - The neutral start switch is
a safety device installed on Komatsu vehicles. It
is called a neutral start switch on Dresser,
Galion and Haulpak products. The similar
device found on Komatsu Products is called a
neutral safety switch. This apparatus prevents
the engine from starting unless the gearshift
lever is placed in the neutral position.
Figure 3.30 – Starter switch.
Figure 3.31 – Dresser neutral start switch.
Figure 3.32 – Komatsu neutral safety switch.
Typically these switches are found on the
gearshift lever or transmission linkage. Figure
3.33 shows a typical neutral safety switch
arrangement.
When a neutral start or neutral safety switch is
installed, it is placed in the circuit between the
starting switch or button and the starter solenoid
"C" or cranking terminal.
Figure 3.33 – Komatsu neutral safety switch
wiring diagram.
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Starting Motor - To start an engine it is
necessary to make electric current flow to the
starting motor. Figure 3.34 shows that the motor
consists of a motor, a pinion gear and a magnetic
switch.
Figure 3.34 – Starter motor.
Figure 3.35 – Starter circuit at beginning of
current flow.
The starting motor is actuated by pressing the
start button or by turning the starting switch key
to the START position. Current begins flowing to
the starting motor to bring it to a gradual turn.
See Figure 3.35.
Immediately after the motor starts, a pinion starts
engaging with a ring gear on the engine flywheel
so that the motor can drive the engine.
Current from the starting switch flows through
terminal "C" to the magnetic coil. A magnetic
force generated in coil 2 overcomes spring 4 and
pulls plunger 3 to the right. Notice that the
magnetic switch coil consists of two coils, a
pull-in coil and a holding coil. When the plunger
is pulled, overcoming return spring 4 requires a
large force so current flows to both coils. After
the plunger is pulled, the auxiliary contact cuts
off current to the pull-in coil and a small current
continues to flow through the holding coil to keep
the plunger to the right. These two coils are
used to prevent overheating of the coils and to
reduce consumption of electricity.
Figure 3.36 – Starter circuit immediately after the
motor starts.
Figure 3.37 – Starter circuit during cranking.
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When plunger 3 reaches the end of its stroke,
contacts 1 are closed and terminal "B" is
connected to terminal "M" of the switch. Now a
greater intensity of current can flow to the motor
via terminal "M", thereby increasing motor speed
up to its maximum.
When plunger 3 (Figure 3.39) is pulled to the
right, shift lever 5 (Figure 3.39) pushes shaft ring
6, clutch assembly 7 and pinion 8 to the left,
where the pinion engages the ring gear to begin
engine cranking.
Figure 3.38 – Starter magnetic switch.
Safety Relay - Komatsu designed starter circuits
include a safety relay. This item prevents the
flow of current into the starter after the engine is
running. Even if the starter switch is
inadvertently turned on while the engine is
running, no current will pass through the safety
relay so the starter pinion and flywheel ring gear
are protected from damage.
There are two types of safety relays. The
original version consists of coils and contact
points and the newer semi-conductor type.
Figure 3.39 – Starter motor.
The original safety relay looks very much like a
remote mounted battery relay. It has a shiny
black color and four marked terminals. These
terminals are labeled "B", "C", "A" and "S".
This type safety relay was remote mounted on
the engine compartment fire wall.
Figure 3.40 – Original safety relay containing coils
and contact points.
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The drawing in Figure 3.41 shows the contents of the original safety relay when the cover is
removed.
Figure 3.42 – Circuit diagram of original safety
relay. Key switch in ON position.
Figure 3.41 – Original safety relay.
The circuit diagram in Figure 3.42 shows the three coils, four contact points, two resistors and
five wiring terminals of the original safety relay.
When the starting motor switch is turned to START, current flows from terminal "C" of the
starting switch to terminal "S" of the safety relay → coil "L1" → switch "S1" and terminal "E".
When current flows to coil "L1", switches "A" and "B" are pulled down to make a circuit. Then,
current flows to the positive terminal of the battery at the "B" terminal of the safety relay → switch
"A" → switch "B" → terminal "C" of the safety relay → terminal "C" of the starting motor to rotate
the engine.
The drawing in Figure 3.43 shows current flow through the battery relay when cranking the
engine. The drawing in Figure 3.44 shows the same current flow using a schematic.
Figure 3.43 – Original safety relay – key in START
position and current passing from “B” to “C”
terminals.
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Figure 3.44 – Current through safety relay with
key switch in START position.
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If the key switch were held too long in the START position or if the starting motor switch were
inadvertently moved to the START position after the engine is running, current being generated
by the DC generator or by an alternator would cut the electricity to the starter motor to prevent
damage.
Figure 3.45 – Current from the alternator cuts the
circuit to the starter.
Figure 3.46 – Current through original safety relay
after the engine starts.
While the engine is running, the current generated by the DC generator or alternator flows to
terminal "A".
Alternator current entering terminal "A" flows through coil "L2" → resistor "R2" → terminal "E"
→ then to ground on the body. The flow of current through coil "L2" produces a magnetic force
which pulls switch "S1" to open its contacts. Therefore, when the engine is running and the
generator or alternator is generating electricity, the current which would normally flow from
terminal "S" to coil "L1" is cut off by switch "S1" and no magnetic force is produced in coil "L1".
Consequently, switches "A" and "B" do not contact and the starter does not rotate.
Semi-conductor type safety relay - There are
two designs of the semi-conductor type safety
relay, the combination type and the separated
type.
The combination type fits directly onto the starter.
As you can see in Figure 3.47 a bolt and holder
are provided for this purpose. Notice that there
are five wiring terminals. Each terminal is
attached as follows:
Figure 3.47 – Combination type safety relay.
Terminal
E
B
C
S
R
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Location
Ground
B terminal of starting motor solenoid
C terminal of starting motor solenoid
From stating key switch C terminal
From alternator R terminal
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The separated type can be attached to the starter or located nearby. Its appearance is different
from the combination type but it is attached to the starter circuit in the same manner as described
previously.
Figure 3.48 – Separated type safety relay.
Figure 3.49 – Composition of semi-conductor
type safety relay.
Both types are made up of the same type of parts.
Figure 3.49 shows the major parts of the semi-conductor type safety relay. These parts are the
safety circuit, a coil and a set of contact points.
Figure 3.50 shows the circuit diagram of the semi-conductor type safety relay.
The use of transistors "Q1" and "Q2" and diodes "D2", "D3", "D4" and "Z") have greatly increased
the life of safety relays.
Figure 3.51 – Current from starting switch
energizes the base of transistor “Q2”.
Figure 3.50 – Circuit diagram of semi-conductor
type safety relay.
When the starting (key) switch is turned to the START (cranking) position, the current flows from
the starting switch through resistor "R4" to the base of transistor "Q2", (see Figure 3.51). This
forms a circuit between collector "C" and emitter "E" which completes the circuit "S" → "L" →
"Q2" → "E". The flow through coil "L" makes it an electromagnet which closes contact "T". Now
current is able to flow from the "B" terminal of the starting motor to the "C" terminal to rotate the
starting motor. Figure 3.52 shows the complete current flow when cranking.
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Figure 3.52 – Current flow through semiconductor type safety relay when engine is
cranking.
When the engine is started, the alternator starts
to generate electricity. The current from the
alternator passes through resistor "R2" to the
Zener diode. At about 600 RPMs the alternator
supplies sufficient electrical force for electricity to
pass through the Zener diode so current will then
pass through diode "D2" to energize the base of
transistor "Q1".
Now a circuit has formed between "Q1" collector
and emitter. The main current from the starting
switch will pass through resistor "R4" rather than
through coil "L" as it has less resistance. Also,
current passes easily through transistor "Q1"
because its base is now energized. Under these
conditions current flows from "S" → "R4" → "Q1"
→ "E". Consequently, current drops away from
coil "L" and it is no longer an electromagnet.
Contact points "T" are opened and current
cannot pass from terminal "B" to terminal "C".
Diodes - Diodes are used in two ways. These
ways are easily seen in Figure 3.53. Some
diodes are used like one-way electrical check
valves. This is how "D2" and "D4" are being
used. Zener diodes "Z" also act as electrical
check valves but they allow current to flow through them when the electrical force (voltage)
reaches a pre-determined value. Diodes such as "D3" in Figure 3.52 are wired parallel with coils.
Their job is to absorb high voltage surges which occur when the electrical system is shut down,
this increases the life of switches and other system components.
Figure 3.53 – Current flow through semiconductor type safety relay after engine is
started.
Some machines have an additional diode in their
engine starting system.
Diode "D10" in Figure 3.54 absorbs high voltage
when the starting switch is turned OFF. This
reduces wear of the starting switch and other
electrical components. If the internal circuit of
this diode is broken, the machine will not start
due to the open circuit. However, the most
frequent failure of this diode is that it will allow
current to pass in both directions and the engine
will not shut off when the start (key) switch is
turned to the OFF position.
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Figure 3.54 – Diode between starting switch and
battery relay.
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Fusible link - Many newer machines are using fusible links as an inexpensive type of
over-voltage protection.
Figure 3.55 - Starting circuit with fusible link.
Figure 3.55 – Starting circuit with fusible link.
Observe the fusible link at connector "M11" in
Figure 3.55. When the system is exposed to
excessive voltage (36 volts) this fuse will burn up
to save other system electrical components from
damage. When this happens there is no power
in the system until corrected by replacing the
fuse.
MAINTENANCE
Keeping the starting system in optimum working condition is absolutely necessary if
instantaneous engine operation is desired. The following maintenance checks will ensure that
system components do not fail prematurely.
Battery maintenance - Small, seemingly insignificant matters may affect battery life if neglected.
And when the battery is defective the engine cannot start. To prevent battery related problems
the following battery maintenance checks are recommended.
9 Check the battery case and cover for dust accumulation and corrosion. Thoroughly clean
with a baking soda and water solution. Fizzing of the solution indicates that acid is present;
this will continue until the area is clean. Dry the battery completely.
9 Check the terminal posts and clamps for corrosion and tightness. Clean as described above
if necessary. Cable clamps should be tightly fastened to terminals.
9 Use the proper tools for installing and removing battery cable clamps. Tapping cable clamps
onto the posts with a hammer, or prying them off with a screwdriver can cause the post to
break off inside the battery case and/or separate from the lid. If this occurs, it can cause a
spark with a resulting explosion. Battery clamp pullers for removing terminal clamps are
available, as well as battery clamp spreaders. Use the spreader to enlarge clamp holes to fit
posts before installation.
9 Check the battery support frames and hold down clamps for proper fit and tightness.
Looseness will cause cracking of the battery
case.
9 Check for proper electrolyte level, (see
Figure 3.56). When low electrolyte level is
observed, refill with distilled water.
Excessively high electrolyte level will cause
spouting of electrolyte during charging.
Figure 3.56 – Checking electrolyte level.
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9 Check specific gravity of electrolyte. The
chart in Figure 3.57 shows that if the specific
gravity of the electrolyte is 1.260, the battery
is fully charged. It also shows that when the
specific gravity drops to 1.20 the battery
should be recharged.
One of the simplest methods for checking
battery electrolyte specific gravity is using a
specially made refractometer. Simply put 1 or
2 drops of electrolyte onto the prism face
using the glass sampler and read the scale
where the shade changes. Be advised that
most of these devices have two scales, one
for specific gravity of electrolyte and the other
for cooling system antifreeze protection. Be
certain to read the correct scale.
Figure 3.57 – Specific gravity chart.
Wiring and connector maintenance - A recent Figure 3.58 – Using a refractometer to check
battery electrolyte specific gravity.
study showed that more than half of all electronic
system failures was due to faulty wiring or electrical connectors. These items may possibly be
the most neglected part of the electrical system.
9 Inspect wiring for cracks, broken and missing coatings and loose or missing connectors.
9 Be extremely careful when handling wiring
harnesses. Pulling on wires can damage the
soldering or the wiring may be broken. When
disconnecting the connectors, always hold
the connector instead of the wiring.
9 For connectors which have a lock stopper,
press down the stopper with your thumb and
pull the connectors apart.
Figure 3.59 – Handle wiring with care.
Figure 3.61 – High pressure water can enter
connectors.
Figure 3.60 – Press stopper when pulling
connectors apart.
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9 Connectors are made to resist the entrance
of water, but if high pressure water is sprayed
onto connectors, water may enter and cause
a short circuit. If any water should get in,
immediately dry the connector with a clean
dry cloth or blow dry with air. Avoid the use
of shop air because it may contain oil for
running pneumatic tools. This can cause a
defective contact.
After drying, spray
contacts with contact restorer.
Excessive grease and oil can be removed
with a dry cloth.
Figure 3.62 – Blow dry with air to remove
moisture.
Oil or grease on or in the connector may not
allow the electricity to pass, so there will be
a defective contact.
When wiping the
connectors, be careful not to use excessive
force or deform the pins.
9 After removing a connector, cover it with a
vinyl bag to prevent any dust, dirt, oil or water
from entering.
Figure 3.63 – Remove oil, grease and water with a
dry cloth.
9 When reconnecting a connector, insert it
securely. Connectors with a lock stopper
"click" when properly fitted into position.
Figure 3.64 – Protect connectors after removal.
Figure 3.65 – Stopper “clicks” when properly
positioned.
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Starter maintenance - Starters are generally maintenance free. The following checks may
prevent premature replacement of starters.
9 Check all wiring and connectors at the starter
for tightness.
9 Some manuals call for the replacement of
starter brushes every 2000 hours. Refer to
Figure 3.66. This is accomplished by
removing the connect bar plate between the
"M" terminals, and then the screws fastening
the brush cover in place. Lightly tap out the
cover with a wooden hammer to expose the
brushes. Lift up the spring holding the brush
in place and pick out the brush.
Figure 3.66 – Location of starter motor brushes.
Inspect the old brush contact surface and where it contacts the commutator. Rough surfaces
indicate distorted or loose brush holders.
When removing or installing the springs, take care not to deform them by applying excessive
force. Deformed or weak springs will not press the brushes securely against the commutator,
thereby causing sparks and low current flow. This leads to excessive wear of brushes and
commutator.
It is sometimes possible to clean up a roughened commutator or remove dust and carbon
build-up by sanding it with No. 400 to 800 grit sand paper.
TROUBLESHOOTING
Sluggish starting motor operation:
9 Low battery charge: Charge battery and check specific gravity. If battery does not respond
to charging, replace.
9 High resistance in circuit: Clean and tighten all connections. Repair or replace faulty wiring.
9 Defective starter motor: Service and repair. Starting motors have a short time rating of 30
seconds running and 30 seconds resting. Any operation that deviates from the short time
rating can cause the motor to burn out prematurely. On the other hand, any operation within
the short time rating such as 20 seconds running and 30 seconds resting will keep the motor
from burning out prematurely.
9 Starting motor bearings dry: Lubricate bearings with proper viscosity oil.
9 Engine oil to thick for ambient temperature: Replace with lower viscosity oil.
9 Extremely cold weather: Warm the battery before starting the engine.
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9 Poor engine over-haul procedures causing excessive engine drag due to tight bearings:
Recheck engine over-haul procedures.
Starting motor will not operate:
9 Low battery charge: Charge battery and check specific gravity. Install a new battery if it does
not respond to charging.
9 Starter safety switch open: Put shift lever in neutral or park.
9 Improperly adjusted or defective starter safety switch: Adjust or replace.
9 Defective starting switch: Replace.
9 High resistance in starting circuit or defective wiring: Clean and tighten all connections and
replace faulty wiring.
9 Faulty magnetic (solenoid) switch on starting motor: Repair or replace.
9 Faulty starting motor: Service and repair.
Starting motor solenoid sounds like a machine gun:
9 Low battery charge: Charge battery and check specific gravity. Replace the battery if it does
not respond to charge.
9 High resistance in circuit: Clean and tighten all connections and replace faulty wiring.
9 Open circuit in starter solenoid hold-in winding circuit: Repair or replace solenoid or wire.
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Chapter 3 - Assessment
Starting System
Instructions:
There is only one correct answer to each question. If there appears to be more
than one answer, select the most correct answer.
If an in-house instructor is administering this test, turn your answers in to the
instructor when you are finished. Your instructor will input your scores into the
Komatsu Learning Management System.
If you are taking the Basic Electric course as self-study, mark your answers in
the appropriate space on the answer sheet provided in the back of the booklet.
When you have completed all of the assessments for the entire book, either:
a.
Turn the assessments into your instructor along with your Answer Sheet.
The instructor is provided with an answer key and will grade your
assessment and also input your scores into the Komatsu Learning
Management System. Or,
b.
Log-in to the Komatsu Learning Management System (LMS), using your
extranet username and password. Go to the LMS site, enroll in this Basic
Subject course, after your enrollment has been approved, you can launch
the course, then click on the Assessment link and answer each question.
Your grade will be scored and tracked automatically. Note: The online
assessment questions are in random order.
1. What is the short time rating of a starter motor?
a. 10 seconds running and 10 seconds resting.
b. 20 seconds running and 20 seconds resting.
c. 30 seconds running and 30 seconds resting.
d. 20 seconds running and 30 seconds resting.
2. What is the recommended method for servicing a roughened commutator at its
surface, which contact the brushes?
a. Replace the starter in such a case. A roughened commutator can never be adequately
serviced.
b. Sand the contact surface with No. 400 to 800 grit sand paper.
c. First remove burrs with a rough-cut file, and then sand the contact surface with No. 400 to
800 grit sand paper.
d. First remove burrs with a fine tooth file, and then sand the contact surface with No. 400 to
800 grit sand paper.
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Chapter 3 Assessment
3. Which of the following statements is false regarding electrical connectors?
a. Remove moisture with a blow dryer.
b. Avoid spraying high-pressure water onto connectors.
c. Ensure that connectors fitted with a lock stopper “click” when being reconnected.
d. Oil and grease can be removed with warm soapy water solution, then blow dry and coat
contacts with a light oil.
4. Which of the following is not an advantage of using hydraulics?
a. 1.20.
b. 1.22.
c. 1.24.
d. 1.26.
5. What is the purpose of the safety relay?
a. It prevents the engine from being started if the safety lever is locked.
a. It prevents the engine from being started except when the transmission is in neutral.
c. It prevents the flow of current to the starter after the engine is running.
d. It protects the starting circuit from over voltage (36 or more volts).
6. Which of the following Komatsu starting switch terminals receive current only when
the key is placed in the START position?
a. AC
b. C
c. B
d. BR
7. What is the functioning difference between a Dresser four position key switch and a
Komatsu four position key switch?
a. Dresser does not use a four position key switch. Instead, they use a two position key
switch and a starter button.
b. The Dresser switch does not have a “heat” position.
c. The accessories receive current when the Dresser switch is in the OFF position.
d. There is no difference between the Dresser and Komatsu four-position switch.
8. What is the function of the battery relays found in the starting circuit of Komatsu
designed machines?
a. These are anti-vandalism devices.
b. They protect the machine electrical system from aver-voltage (36 or more volts).
c. They prevent the starter from receiving current after the engine is running.
d. They eliminate the possibility of short circuit or getting shocked when repairing or
replacing electrical components.
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Chapter 3 Assessment
9. When does the greatest intensity of current flow to the starter motor?
a. When the key switch is placed in the ON position.
b. When the key switch is placed in the START position and during the time that the starter
motor first begins to rotate and the pinion gear starts to engage the ring gear.
c. When the key switch is placed in the START position and the pinion gear and the ring
gear have completed their engagement.
d. When the key switch is held in the START position after the engine is running.
10. Which of the following suggestions will minimize the self-discharge of a battery?
a. Remove batteries from vehicles not in operation and store in a cool place..
b. Keep the tops of batteries clean and dry.
c. Use only distilled water to replenish electrolyte level that has diminished due to
evaporation.
d. All of the above can minimize the self-discharge of a battery.
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Chapter 3 Assessment
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Chapter 4
Charging System
INTRODUCTION
The charging system is needed to replenish the positive charge of the battery. This is important
to ensure that the engine can be easily started and that other machine electrical devices can be
used.
Field Service Specialists need to have a complete understanding of the charging system so that
they can easily repair the system should it become defective.
Chapter 4 will examine the structure and function of the charging system and its components.
The contents of this chapter will be presented in the following order:
•
•
•
•
Charging Circuit Diagram
Component Construction
- Generator
- Voltage Regulator (for generator)
- Alternator
- Rectifier (for alternator)
- Voltage Regulator (for alternator)
- Semi-conductor Type Regulator
- Ammeter
Maintenance
Troubleshooting
CHARGING CIRCUIT DIAGRAM
A typical charging circuit is illustrated in Figure 4.1. It consists of a generator or alternator which
charges the battery and provides current to
electrical devices, a regulator, an ammeter or
charge lamp to indicate the charging level, and
the wiring between them.
Figure 4.1 – Charging circuit diagram.
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The charging circuit is integrated with the
starting system. Figure 4.2 shows how they are
connected. The blue line serves to show that the
battery (+) positive terminal is always connected
via the fuse box to the "B" terminal of the starter
switch.
When the key switch is turned "ON", current
flows as shown in Figure 4.3.
When the key switch is turned "ON", current
Figure 4.2 – Integrated starting and charging
flows from starter switch "B" terminal to its "BR"
circuit.
terminal to a diode. From this diode current
flows in two directions. First it goes to the BR (+)
of the battery relay coil and ground. This closes the main battery relay switch to make stored
battery current available to the rest of the machine as needed.
Figure 4.3 – Activation of battery relay.
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The other route is to another diode where it is stopped. It is important to see that on the other
side of this second diode is the “R” terminal of the starter safety relay and alternator, the monitor
panel charge indicator and the service meter. This observation is important so that one can
realize that should the diode become defective, the starter may not work or electric defects may
be noticed with the monitor.
When the battery relay solenoid has been energized, a path is completed for current to flow from
the battery (+) → battery relay "B" → battery relay "M" → starter & safety relay "B" → alternator
"B".
Figure 4.4 shows this flow. Current is now available for all machine electrical circuits.
Figure 4.4 – Switch “ON”, current to machine circuits.
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Figure 4.5 – Current flow during cranking.
When the key switch is placed in the “START" position, current flows from the starter switch "C"
terminal to the safety relay.
This completes the circuit of the safety relay from its "B" terminal to its "S" terminal so cranking
current is delivered to the starter. At the same time the start signal of the monitor panel is
energized. (See Figure 4.5.)
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Figure 4.6 – Current leaving the alternator ”R” terminal when engine is running.
After the engine is running and the alternator begins generating electricity, current flows from the
alternator "R" terminal to the starter relay "R" terminal. This cuts the safety relay's connection
between its "B" and "C" terminals to prevent accidental cranking when the engine is running.
At this time current also flows through a diode to the battery relay (+) "BR" terminal to keep the
solenoid energized during the time that the key switch is being returned to the "ON" position.
Also notice that current goes to the charge signal of the monitor and to the service meter.
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Figure 4.7 – Recharging the batteries.
Figure 4.7 shows how current reaches the battery to recharge it when the engine is running.
The batteries are recharged when the engine is running. The current flow is from the alternator
"B" terminal → starter "B" → battery relay "B" → battery + terminal.
COMPONENT CONSTRUCTION
The major component of the charging system of a typical piece of construction equipment is a
generator or alternator, a voltage regulator, a rectifier when an alternator is used and an
ammeter. Next, we will examine the structure of these items.
Generator - Figure 4.8 shows the parts of a generator. The coils are used to set up north and
south magnetic poles. When the armature is rotated, the magnetic fields of force are broken and
electricity is generated. This generated electricity is transferred from the commutator to the
brushes and sent to the machines electrical appliances and battery as needed.
The current produced by a generator flows in only one direction and is called "direct current"
(DC).
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Figure 4.8 – Generator construction.
The current flowing through the coils also generates heat and due to the speed the generator is
driven. The higher the rpm's the greater the heat and too high temperature can deteriorate the
coil wire insulation. To prevent this, a cooling fan is installed.
Figure 4.9 - Armature
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Figure 4.9 shows the armature. It consists of
coils of wire around an iron core. Wire loops are
wound parallel with the drum drive shaft. As the
armature is rotated, each of its segments cuts
across fields of force caused by electromagnetic
north and south poles. This causes electricity to
be produced.
The amount of electricity
produced depends upon the intensity of the
electromagnetic fields and the speed at which
the armature is driven. If the drive belts are
loose, the amount of electricity generated may
not be sufficient to charge the batteries.
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The current generated by the rotating armature is transferred to the brushes through the
commutator.
The commutator is made of copper and divided into a number of segments. The gaps between
these segments are filled with mica to insulate them from each other. The brushes are made of
carbon and are held in place against the rotating armature by springs. These brushes wear so
they should be inspected for serviceability every 1,000 hours of operation.
Voltage regulator for generator - A generator generates electric current, which may be
directed to the battery to charge it or to the machines electric accessories. The generated
voltages are proportional to the speed of the engine and there often is high intensity of current
and excessively high voltages, which, if not controlled, could cause damage to or shorten the life
of electrical components. The device we use to keep generated voltages and current within
acceptable ranges is the regulator.
The generator regulator consists of three electromagnets. The "cut-out relay" (at the right in the
Figure above) is used to open the circuit leading
to the "B" terminal whenever the voltage of the
generator reduces to a level lower than that of
the battery. This prevents current from flowing
back from the battery to the generator. The
center part of the regulator is the current
regulator.
Figure 4.10 – Brush and commutator.
Current, which flows out of the regulator to the
vehicle electric appliances, is limited to a
specified value by this apparatus. The left hand
item shown in Figure 4.11 is the voltage regulator.
It directs current to the generator field coil. In
addition, the voltage regulator limits the current
in the field coil within the specified value even if
the generator rotates at excessively high speed.
Regulated voltage in most Komatsu, Dresser or
Galion product lines is between 25 and 29.5 volts
depending upon the speed of the engine, the
condition of the battery and the amount of
electrical accessories being used.
Figure 4.11 – Generator regulator.
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Figure 4.12 is a graph, which shows that as a
generator begins to rotate, the voltage it
generates rises proportionally to the increase of
rotational speed. In the case illustrated, the
voltage is allowed to rise to 29V. Thereafter, the
voltage is controlled between 28 and 29 volts.
Setting of this voltage is variable by adjusting the
voltage regulator.
Figure 4.12 – Generator regulated voltage.
Figure 4.13 shows the set up of a typical
electromagnet used for regulating voltage.
When the coil is energized, the magnetized core
at the top begins to attract the plate, which has
one half of the contact points attached.
When the strength of the generated electricity
increases to a point where the intensity of the
electromagnet is strong enough to overcome the
force of the spring that is attached at the other
end of the plate, the contact points are separated
and the circuit is broken.
The contact points of all three electromagnets in
a voltage regulator can be adjusted by turning the
appropriate screws.
Figure 4.14 – Regulator adjustment screws.
Figure 4.13 – Regulator electromagnet
functioning.
Figure 4.15 – Resurfacing contact points.
The contact points within a regulator will in time become burned. Burned points have decreased
contact surface and consequently deteriorated functioning. Burned regulator points can be
resurfaced by burnishing each point separately until every point gets a refreshed, flat,
conductible surface.
Use number 400 sand paper or equivalent. After burnishing, wipe the dust from contact points
with a dry, clean rag.
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Alternator - All recently built Komatsu machines are equipped with an alternator rather than a
generator. Alternators generate alternating current (AC) rather than direct current (DC).
An alternator and a DC generator produce electricity in different ways. In a DC generator, a wire
coil is rotated near fixed magnets; in an alternator, a magnet is rotated in a fixed coil.
The electromagnet of an alternator is an iron core wound with wire. In the following diagram,
when the polarity of the magnet on one side is south, the polarity on the opposite side is north.
Figure 4.16 – Alternator construction.
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Actually there are claw-like iron cores of
alternate polarity above the coil of wire. Turning
these cores has the same effect as turning a
number of magnets simultaneously.
In this set up, during a single turn of the shaft,
electricity is generated in the stator coil several
times.
Figure 4.17 – Alternator interior components.
The section rotating inside the alternator is
called the rotor, and the coil of the rotor is called
the rotor coil. (Figure 4.18.)
When the rotor or electromagnet turns slowly, the voltage generated is low. Therefore, if the
engine rotates at low speeds or if the V-belt slips, the voltage generated may not be sufficient to
charge the batteries. In this case the ammeter pointer does not move toward the + (plus) side
(charging).
The brush is carbon and is inserted in a holder. Since it is pressed against the slip ring by
springs, it wears over time. A worn brush sparks between it and the slip ring and this adversely
effects both brush and slip ring. The same phenomenon occurs if the brush holder is loose or the
brush is unevenly worn. Because of this, the brushes and slip rings should be checked at the
specified intervals. If the surface is badly roughened, polish with #400-#800 sand paper, then
wipe the surface clean with a cloth. Replace a deformed or rusty spring. If the bearing makes
noise it is probably worn so replace it. These bearings are sealed with grease so lubrication is
not necessary.
Figure 4.18 – Alternator terminals and parts.
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Lets review how the alternator generates electricity.
When a wire is across the fields of force of a magnet, an electric current is generated in the wire
(by induction).
A current is also generated when a magnet is moved near a fixed wire. Notice that the
relationship between the movement of the
magnet and the direction of electric current
flowing through the wire is shown in Figure 4.19.
Thus, even though the magnet is moved in the
same direction, the direction of flow of the
current varies depending on whether the polarity
of the magnet is north or south.
Sense the polarity of the magnet reverses each
time the magnet rotates a half turn, the direction
of the current flowing through the loop reverses
(i.e. alternates) as well.
Figure 4.19 – Rotating magnet and fixed wire.
As the magnet's rotating speed increases, or as
the force of the magnetic field increases, the
voltage becomes higher and more electricity is
generated.
In the alternator, the wire loop through which the generated electric current passes is called the
stator coil.
In reality, an alternator uses an electro-magnet consisting of an iron core, on which wire is wound.
When an electric current is passing through the coil windings, the iron core is magnetized.
Figure 4.21 – Electromagnet of alternator.
Figure 4.20 – In an alternator, the wire loop is the
stator coil.
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If the magnet turned in the setup shown in Figure
4.21, the wire would twist and become entangled.
To prevent this, a couple of insulated rings are
fitted to the shaft and each end of the core wire is
connected to a ring. Each ring contacts a brush,
through which an electric current is fed to the
core wire. These rings are called the slip rings.
(See Figure 4.22.)
The intensity of electricity varies depending on
the magnet position as shown in Figure 4.23.
Figure 4.22 – Alternator slip rings and brushes.
Figure 4.23 – Strength of a single-phase alternating current.
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Figure 4.24 – Wave pattern of a three-phase alternator.
If three loops are positioned around a magnet at intervals of 120°, electricity is generated in all
three loops as the magnet turns. In this case, the waveform becomes more complicated than
with only a single loop. (Figure 4.24)
By connecting one end of each of the three loops together and then connecting wires to the other
ends, it is possible to collect a three-phase alternating current.
There are two methods for connecting the
stator wires and these two types are
illustrated in Figure 4.25. One way is called
the Star or “Y" type connection and the other
is called the Delta type connection.
Usually, an alternator uses a star or Y
connection since it permits charging a
battery at lower magnet speeds than a delta
connection. Since alternating current is
generated in the stator coil, it must be
rectified (changed from AC to DC).
Figure 4.25 – Star and Delta connections.
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Figure 4.26 – A three-phase alternator uses six diodes for rectification.
Rectifier - A three-phase alternator uses two types of diodes (three each). These six diodes are
used for rectification.
Three similar diodes used for alternator rectification are set in a single holder to allow current to
pass from the body to the terminals.
The other three diodes are set in another holder allow current to pass in the opposite direction.
When replacing or checking the diodes, be careful not to confuse the different types of diodes.
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Figure 4.27 – Installation of diodes in alternator.
The diodes are adversely effected by heat, and at high temperatures their rectification drops
substantially. For this reason, the holders have a plate to insulate the stator coil. Avoid applying
steam to the alternator when cleaning. Also, when soldering the diode terminal, use an
appropriate plate to draw heat from the terminal.
The diodes prevent current from flowing from the battery to the stator coil. However, excessive
voltage may damage the diodes. If this occurs, current may flow from the battery to the stator
coil. Therefore, when quick charging the battery, be sure to remove the battery from the vehicle
or disconnect the alternator B terminal.
It should now be clear how three-phase alternating current is generated.
Voltage Regulator (for alternator) - The
voltage regulator of an alternator differs from that
of a generator because no current limiting relay
is required since the alternator itself has a
current limiting function. It has only a voltage
regulator and a field relay.
The field relay is an electromagnet. When
current flows through its coil, the electromagnet
attracts a spring-loaded plate. As shown in
Figure 4.29, the plate operates an electric
contact. This contact closes a circuit to the
electromagnet when the plate is pulled to the
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Figure 4.28 – External regulator for alternator.
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magnet, and opens the circuit when the plate is
released.
The coil ends of the field relay are connected to
terminals N and E, which are connected to the
alternator N and E terminals.
Electricity
generated by the alternator passes through the
coil to actuate it.
When the starter switch is turned on while the
alternator is inactive, battery current flows to the
regulator terminal I, then to the alternator rotor Figure 4.29 – Field relay construction.
coil through a resistor and the F terminal, and
magnetizes the rotor. When the rotor starts
rotating, electricity is generated. This electricity flows to the coil of the regulator field relay from
terminal N, and then returns to the alternator through terminal E. However, at this time the
voltage coming from the alternator is small, so the contact circuit of the electromagnet is open
because the magnetic attraction is insufficient to move the spring-loaded plate.
As the voltage generated by the alternator rises and the current flowing from terminal N to the
coil increases, the magnetic attraction also increases, enabling the magnet to attract the plate
and close the contact circuit. This causes the current from terminal I to bypass the resistor. That
is, the current from terminal I flows to the rotor coil directly through terminal F. As a result, the
current flowing through the rotor coil rapidly increases.
Figure 4.30 – Current flow through field relay
when alternator output is low.
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Figure 4.31 – Current flow through the field relay
when alternator output is high.
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Figure 4.32 – Alternator voltage regulator construction.
When the voltage generated by the alternator rises rapidly above battery voltage, the current
flows from the alternator terminal B to the battery charge it. With this type of alternator, the
voltage generated at terminal N is about 5 volts. The other electromagnet in an external
regulator for an alternator is the voltage regulator relay.
Like the field relay, this relay consists of an electromagnet with a spring-loaded plate operating
a contact. Current generated by the alternator enters the electromagnet coil from terminal I. The
other end of the coil is connected to terminal E.
When the current flowing through the coil is small, the spring-loaded plate is not moved. When
the current increases to a certain level, the strength of the electromagnet becomes strong
enough to overcome the spring force and the plate is moved.
The plate has a moving contact. (See Figure 4.32.) When the spring force is greater than the
electromagnet, the circuit to the low speed contact is complete. When the strength of the
electromagnet is greater, the plate is moved, the low-speed circuit is broken and the circuit to the
high-speed contact is closed.
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Figure 4.33 – Current flow in the low-speed circuit.
Figure 4.33 shows the current flow when the low-speed contact circuit is complete (current flows
to the rotor coil via terminal I). This magnetizes the alternator rotor.
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Figure 4.34 shows the current flow when the alternator voltage rises to about 29 volts. The coil
current increases, so the magnet strength is great enough to move the plate, which separates
the low speed contact points.
Figure 4.34 – Current flow when alternator voltage reaches 29 volts.
Notice that the current flows through a resistor when the alternator voltage reaches 29 volts. As
a result of the added resistance, the rotor coil current decreases and the voltage generated
drops. Therefore, the voltage coil magnetic intensity also decreases. When the voltage
decreases to 28 volts, the plate is separated from the magnet by the spring force and the
low-speed contacts are connected again. Now, the current flows to the rotor coil in the same
manner as before and the voltage rises.
This process repeats itself over and over to
maintain the voltage between 28 and 29 volts.
(See Figure 4.35.)
Figure 4.35 – Regulated voltage.
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The regulated voltage of an alternator with an externally mounted regulator can be adjusted by
turning the screw shown in Figure 4.36. To adjust, connect two-volt meters as shown. The
voltmeter connected to terminal I should read 28.5 V.
Figure 4.36 – Adjusting voltage.
It should also read 28.5 V when the voltmeter
connected to terminal F indicates 7 V or less
(the high speed contact points connect). If not,
adjust by turning the adjusting screw or by
cleaning the contact points. If necessary,
adjust the point retainer position. The adjusted
voltage should be between 28 and 29 volts.
If the moving contact remains with the
low-speed contacts engaged due to a coil wire
disconnection or the moving contact does not
contact the high-speed points correctly, the
voltage rises abnormally, damaging the
alternator and battery and/or burning out lamps.
A defective low-speed contact point prevents
the voltage generated by the alternator from
rising, which may cause insufficient battery
charging.
Figure 4.37 – Polishing regulator contacts.
If contacts are defective, they can sometimes be corrected by polishing them to get a smooth
contact surface. Use # 400 emery paper between the contacts points to smooth the surfaces.
After polishing, remove the residue with a clean dry cloth, and then adjust the relay.
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Some of these regulators have a terminal marked W. This type is used on machines, which have
a charge lamp on the monitor panel rather than an ammeter. This lamp lights when the battery
is not being charged and goes off when the battery is being charged.
Semi-conductor type regulator - All newer alternators have built-in semi-conductor type
regulators. They have replaced the older models because these regulators do not have contact
points, which require polishing, and their operating life is much longer.
A circuit diagram of a typical semi-conductor type regulator is found in Figure 4.38.
1.
2.
3.
4.
Brush, commutator ass’y
Field coil (Alternator)
Rectifier ass’y
Semiconductor
regulator ass’y
5. Armature coil
(Alternator)
6. Starting motor switch
7. Battery
Figure 4.38 – Circuit diagram of semi-conductor type regulator.
Figure 4.38 identifies the major components in a semi-conductor type regulator. Notice that the
regulator consists of two transistors, a zenor diode, a regulator diode, three capacitors and
several resistors.
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Figure 4.39 – Current flow when key switch is turned “ON”.
Figure 4.39 shows the current flow when the key switch is turned "ON". Current comes from the
batteries to the alternator field coil to excite it. This circuit is completed through transistor T1 in
the regulator.
Figure 4.40 – Current flow in semi-conductor regulator when charging.
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The three-phase current generated in armature coil 5 is rectified to direct current by rectifier
assembly 3. DC current flows in two directions. First it goes to the batteries to charge them.
Figure 4.41 – Current flow in semi-conductor regulator when not charging.
Secondly, it flows to the base of transistor T1 to turn it on and make a complete circuit for the field
coil.
As current flows through the field coil, the generated output increases to raise the voltage at
terminal B, thus the charging rate to the batteries increases.
When the batteries become fully charged, they have more resistance to current flow then the
combined resistance of resistors R2, R3 and the zenor diode of the regulator. (Voltage at
terminal B exceeds the specified level.) As a result, the zenor diode allows current to pass
through it to the base of transistor T2 to turn it on. When transistor T2 is turned on, it opens a new
path for the current that had been energizing the base of transistor T1 to ground. This turns
transistor T1 off.
When transistor T1 is turned off, the circuit of the field coil is broken to decrease alternator output.
As the output voltage drops, the battery charging current decreases.
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Ammeter - An ammeter is used
to measure the amount of
current flowing in the charge
circuit. It is always connected in
series between the load and the
source of current.
The
discrimination between positive
and negative is important.
Figure 4.42 – Ammeter connection.
Figure 4.43 – Ammeter connection in construction equipment.
If a DC ammeter is connected wrong, its indicator can be damaged as it bounces against its end
of stroke stopper.
Figure 4.43 shows how the ammeter is connected in construction equipment.
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MAINTENANCE
The charging system does not require much maintenance. The following checks will insure
normal functioning for many hours of operation.
1.
Check the alternator or generator belt tension periodically. The amount of belt deflection at
a specified tension will be shown in the operator’s manual.
2.
Check the condition of the fan belt. It should not have cracks in the rubber, frayed edges or
glazing. Remember that a V-belt should ride on the sides of the pulley groove, not the
bottom. If the belt bottoms in the pulley, the pulley as well as the belt may be worn.
3.
Inspect the brushes and commutator on generators and alternators that have brushes every
2000 hours of operation.
4.
Periodically check the wiring of the charging circuit. Loose connections may not allow
current to pass.
5.
Never disconnect or connect any alternator or regulator wiring with the batteries connected,
or with the alternator operating.
6.
Repair frayed wires properly. Solder broken wires together and seal splices with shrink tube.
Don’t expect black electrical tape to keep moisture out of joints.
7.
If wiring needs replacement, use the size recommended by the manufacture. A wire that is
too small will soon fail.
TROUBLESHOOTING
The following checklist can help identify possible causes of charging system problems.
Low Charging Circuit Voltage:
9
High resistance in the charging circuit connections. Check the voltage drop to locate
resistance.
9
Defective wiring. Check voltage drops in wire to locate broken strands or undersized wire.
9
Dirty voltage regulator contact points. Polish the points to get a flat, conductible surface.
9
Regulator out of adjustment. Adjust as described on page 4.20.
9
Poor regulator ground. Clean and tighten.
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Low Charging Circuit Output:
9
Slipping drive belts: Adjust belt tension.
9
Excessive wore or sticking brushes: Repair or replace.
9
Dirty current regulator contact points: Polish contacts to obtain a flat, conductible surface.
9
Defective alternator diodes: Replace diode or diode plate assembly.
9
Defective electrical windings in generator or alternator: Repair or replace.
Noisy Generator or Alternator:
9
Misaligned drive belt or pulley: Check pulley and alternator mounting bracket condition.
Repair or align as necessary.
9
Loose mounting or loose drive pulley: Tighten pulley and mounting.
9
Worn or defective bearings: Replace.
9
Generator or alternator brushes not seated: Dress the commutator with #400 sand paper,
install new brushes and ensure brush springs have even tension at center top of brushes.
9
Defective or badly worn drive belt: Replace belt and adjust properly.
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Chapter 4 - Assessment
Charging System
Instructions:
There is only one correct answer to each question. If there appears to be more
than one answer, select the most correct answer.
If an in-house instructor is administering this test, turn your answers in to the
instructor when you are finished. Your instructor will input your scores into the
Komatsu Learning Management System.
If you are taking the Basic Electric course as self-study, mark your answers in
the appropriate space on the answer sheet provided in the back of the booklet.
When you have completed all of the assessments for the entire book, either:
a.
Turn the assessments into your instructor along with your Answer Sheet.
The instructor is provided with an answer key and will grade your
assessment and also input your scores into the Komatsu Learning
Management System. Or,
b.
Log-in to the Komatsu Learning Management System (LMS), using your
extranet username and password. Go to the LMS site, enroll in this Basic
Subject course, after your enrollment has been approved, you can launch
the course, then click on the Assessment link and answer each question.
Your grade will be scored and tracked automatically. Note: The online
assessment questions are in random order.
1. Which of the following statements is correct regarding the zenor diode in an
alternator’s semiconductor regulator?
a. Voltage passes through the zenor diode to permit current to flow in the field coil. This
increases alternator output.
b. Voltage passes through the zenor diode at a predetermined voltage to cut the flow of
current to the field coil. This decreases alternator output.
c. Voltage never passes through the zenor diode.
d. The zenor diode protects the transistors from over voltage.
2. Regulated voltage from external alternator regulators can be adjusted. What is the
correct voltage adjustment?
a. Between 26 and 27 volts.
b. Between 27 and 28 volts.
c. Between 28 and 29 volts.
d. Between 29 and 30 volts.
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Chapter 4 Assessment
3. What is used in an alternator as a rectifier?
a. A diode.
b. A transistor.
c. Three diodes.
d. Six diodes.
4. There are two different ways to connect stator wires in a three-phase alternator. Why
are Komatsu alternators normally connected in a “Star or Y” type connection?
a. Y connections produce more voltage than Delta types.
b. Y connections permit charging at lower speeds.
c. Y connections are easier and cheaper to produce.
d. Both “a” and “b” are correct.
5. Some alternators have brushes. What do these brushes do?
a. They are located in the end plates and keep dirt from entering the alternator body.
b. They allow electrical current to pass into the stator to turn it into an electromagnet.
c. They allow electrical current to enter and leave the rotating electromagnet of the
alternator.
d. They allow electrical current to enter and leave the stationary electromagnet of the
alternator.
6. Some alternators have slip rings. How can badly roughened slip ring surfaces be
reconditioned?
a. Polish with #400 - #800 sand paper, then wipe the surface clean with a cloth.
b. Remove rough spots with a rough tooth file, then polish with #400 - #800 sand paper, then
wipe the surface clean with a cloth.
c. Remove rough spots with a fine tooth file, then polish with #400 - #800 sand paper, then
wipe the surface clean with a cloth.
d. Alternator slip ring surfaces can never be reconditioned.
7. What is the regulated voltage in most Komatsu, Dresser, or Galion construction
equipment?
a. Between 25 and 29.5 volts.
b. Between 27 and 32.5 volts.
c. Between 24 and 27 volts.
d. Between 19.5 and 24 volts.
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Chapter 4 Assessment
8. Which of the following best describes the function of the transistors within a
semi-connector type regulator?
a. They are used to change alternating current to direct current.
b. They are used to direct current into the field coil.
c. They are used like switches to control the strength of the field coil.
d. They provide rectification.
9. Which of the following could be the cause of low output of a charging system?
a. Slipping fan belt.
b. Misaligned drive belt or pulley.
c. Worn bearings.
d. Strong brush springs.
10. Which of the following charging system items do not require periodic maintenance or
checking?
a. Checking the drive belt.
b. Inspection the alternator brushes for serviceability.
c. Check for loose electrical conditions.
d. Inspecting the alternator diodes for serviceability.
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Chapter 5
Air Preheat Circuits
INTRODUCTION
Three elements are needed to create combustion in a diesel engine. These ingredients are fuel,
oxygen and heat. When the intake valves open, air with the necessary oxygen is drawn or
pumped into the combustion chamber. Then the intake valves close trapping, air inside.
Cranking the engine over to quickly compress the air creates the necessary heat. Combustion
then begins when fuel is injected. If the air is too cool or the engine cranks too slowly, the engine
may not start. The purpose of the preheat circuit is to warm the intake air during cold weather to
insure that the air is hot enough during compression to start combustion.
This chapter will discuss the structure and functions of the various preheat circuits and their
components. The contents of this chapter will be presented in the following order:
•
•
•
•
•
•
•
•
Preheater System
Glow Plug Systems
Ribbon Heater Systems
Thermo start System
Automatic Priming System
Automatic Preheating System
Maintenance
Troubleshooting
Preheater Systems
The preheater circuit consists of a glow plug type preheater, heater signal, resister and circuit
breaker. The preheater is different from a glow plug due to location and capacity. One or two
pre-heaters with the capability to heat all the air in the intake manifold rather than one per
cylinder as is found in a glow plug system. Figure 5.1 shows this circuit outline. When actuated,
current flows from the battery to the starter switch B terminal. The key switch is held in the
preheat position and current flows to the R1 and R2 contacts of the switch. From the R1 terminal
current flows through the heater signal to the resister. Also, current comes to the resistor from
the R2 terminal. The current to this point is 24 volts.
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Heater Signal - The heater signal is a pilot lamp, which indicates heating of the preheater. If the
heater signal does not light it is assumed that the preheater is broken.
Figure 5.1 Preheater system.
Resistor - The resister drops the power supply voltage from 24 volts to the voltage setting of the
glow plugs. It is desirable to use low voltage glow plugs because they use less electricity to
generate heat. This reserves electricity for cranking the engine. From the resistor, lower voltage
(18V, 12V or 6V) continues to the circuit breaker.
Circuit breaker - The circuit breaker has two
purposes:
1) It prevents the preheater from overheating due to
excessive current flow.
2) It protects equipment and wiring in the preheater
circuit against damage due to short circuit.
Figure 5. 2 – Circuit breaker (normally closed
contacts)
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When excessive current flows through the circuit
breaker, excess heat is generated. The heat causes
the bimetal material to straighten, opening the contact
points to cut off the circuit. After the cause is found and
corrected, press the reset button to complete the
circuit again.
From the circuit breaker current flows to the heater
switch, then to the glow plug and ground.
Figure 5.3 – Circuit breaker (contacts open
by heat).
Glow Plug Systems
One glow plug is installed in each pre-combustion chamber of Komatsu 120 and 130 Series
engines. The glow plug circuit consists of the glow plugs, heater signal, resistor, and preheater
switch. The flow of current is as shown below.
Figure 5. 4 – Glow plug current flow
Glow plugs can be connected in either a series or
parallel circuit. The earliest systems used a series
circuit similar to that shown in Figure 5.5. Notice that
there is one ground for the entire system.
The series method of wiring glow plugs was
abandoned after a few years because if one of the
glow plugs became defective, the entire system
Figure 5.5 – Glow plugs connected in series
would not work.
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Later glow plug systems have their glow plugs wired
parallel as shown to the right. Each glow plug has a
separate ground so if one of them becomes defective
the others will still function.
Figure 5.6 – Glow plug connected in parallel.
Glow Plugs - There are two types of glow plugs, coil
type and sheath type.
The coil type glow plugs were used in the series
circuits. They are not popular today because when
they get old the coil sometimes brakes off and
contaminates the combustion chamber.
Figure 5.7 – Coil type glow plug.
Sheath type glow plugs are used in parallel circuits.
Because of the sheathing, if the coil brakes, it doesn’t
wind up in the combustion chamber.
Figure 5.8 – Sheath type glow plug.
RIBBON HEATER SYSTEMS
Today, most Komatsu small bore engines use ribbon
heaters. Ribbon heaters are more reliable and
durable then glow plugs.
Small engines use a single ribbon heater. It is usually
installed between the turbocharger and intake
manifold. The one shown in Figure 5.9 has a rating of
110 A/22V.
Figure 5.9 – Ribbon heater for (S)6D105 series
engine.
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Medium sized engines might use a ribbon heater like
that used in the Komatsu 110 series engines.
Figure 5.10 – Ribbon heater for Komatsu 110
series engine.
The 110 series engine ribbon heater is rated
173A/22V. It is wired like a six heaters in two parallel
circuits.
Figure 5.11 – Schematic of 110 series ribbon
heater.
Notice that with the 110 series ribbon heater, if one of the two elements were broken, the other
would still function. However, if the common inlet wire or ground wire is broken, neither element
will function.
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THERMO START SYSTEM
The thermo start system is found only in the Komatsu 92, 105, and early 155 series engines.
The thermo start is found in the air intake manifold. This circuit consists of a preheating switch,
heater signal, resistor, and thermo start(s). Flow of the circuit in this circuit is as follows:
Battery Î starting switch Î heater signal and resistor Î preheating switch Î thermo start(s)
Î ground.
See Figure 5.12.
Figure 5.12 – Thermo start system.
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AUTOMATIC PRIMING SYSTEM (APS)
Figure 5.13 – APS components.
The automatic priming system is found on Komatsu 155 and 170 series engines. It heats the
intake air by burning fuel in the intake manifold.
The components of this system are the key switch; the APS panel switch, the relay box (with
three heater relays, bi-metal timer, two resistors and APS controller), the APS indicator light of
the monitor panel, two glow plugs, two fuel nozzles, and a water temperature sensor.
Figure 5.14 is used to explain what occurs when using the APS. The "flow of time" begins when
the ignition switch is turned ON. This chart should be used to explain to the operator how the
APS system is used. This entire system is controlled electronically. The entire system has one
ground and that is the water temperature sensor. These engines have two water temperature
sensors, one for the APS and another for the water temperature gauge on the monitor panel.
The temperature sensor with one wire connection is for the APS. The engine coolant
temperature must be below 20°C (68°F) for the temperature sensor to complete the APS circuit
to ground. In other words, if the engine coolant temperature is above 20° C (68°F), the system
will not operate.
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Figure 5.14 – APS current flow when coolant is cold and ignition switch is ON.
When the engine coolant is cold enough the water temperature sensor contacts will close,
actuating the preheater relay. Current will flow as shown in Figure 5.15.
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Figure 5.15 – Items ON when coolant is cold and ignition switch is turned ON.
To start the APS under the previously mentioned conditions, press the preheat panel switch.
This causes the monitor panel pre-heat indicator to light up.
The large capacity heater relay is now energized. Because of this, current now flows through the
resistors to the glow plugs and B terminal of the APS controller. The resistors lower the voltage
to 18V to meet the rated voltage of the glow plugs. At the same time current passes through the
bi-metal timer to the APS pilot lamp. Figure 5.16 illustrates the current flow described in this
paragraph.
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Figure 5.16 – APS start – glow plug preheating.
Figure 5.17 describes the conditions above as glow plug preheating. The glow plugs are heating
the intake air before cranking the engine. One of two necessary electric signals has reached the
APS controller.
Figure 5.17 – Glow plugs preheating.
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When the glow plug preheating time is up, the bimetal contacts will open and the pilot lamp will
go OFF. This indicates to the operator that the optimum time has come for cranking the engine.
After the APS pilot lamp goes OFF, turning the ignition switch to START activates the APS
controller. Now the second electric signal required to start the APS controller is sent to the
controller C terminal. The APS controller now sends intermittent (10 times per second) electric
current to the fuel nozzles in the intake manifold. The intermittent opening and closing of the
nozzles ensures good atomization of the fuel.
Figure 5.18 – Current flow during cranking.
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At the same time, when the ignition switch is in the START position, the preheater back-up relay
is actuated. This allows current to the glow plugs to by-pass the resistors. During cranking the
amperage draw of the starter motor is sufficient to lower the voltage to the rating of the glow
plugs so the resistors are not needed.
Figure 5.19 – Starting motor running.
When the engine is started, the ignition switch is returned to the ON position. Consequently, the
preheater back-up relay is turned OFF and current again reaches the glow plugs via the
resistors.
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Figure 5.20 – Current flow after engine is running.
The APS controller continues to operate the fuel nozzles because the second required electric
signal comes from the alternator when the engine is running.
Figure 5.21 – Heating with glow plugs and nozzles functioning.
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When the engine coolant temperature rises above 20°C (68°F), the APS water temperature
sensor contacts open and the heater relay is turned OFF. This shuts off the entire system so the
glow plugs stop heating and the fuel injection nozzles stop injecting fuel.
Figure 5.22 – Current flow when coolant temperature exceeds 20°C (68°F)
Figure 5.23 – Engine coolant reaches 20°C (68°F)
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AUTOMATIC PREHEATING CIRCUIT
Figure 5.24 – Preheating and after heating with the heater switch.
The automatic preheating system discussed here is typically found on wheel loaders. The
components of this system is the ignition switch, preheat switch, bimetal timer, heater relay, air
intake heater, and pilot lamp display of the monitor panel.
When the ignition switch is ON, and the preheat switch is set to ON, the following circuit is
formed.
1) Ignition switch BR Î heater switch Î heater relay signal terminal Î heater relay coil Î
ground connection.
The heater relay is closed.
The ignition switch is ON, and the battery relay is also closed, so electric current flows in the
following circuit.
2) Battery (+) Î battery relayÎ heater relay Î electric air intake heater Î ground connection
and the engine is preheated (or after-heated).
If the heater switch is released, it automatically turns OFF and the preheating is stopped.
Basic Electric - 4005
Page 5-16
KT800895-R1
March 2005
Figure 5.25 – Preheating with ignition switch.
If the ignition switch is turned one stage to the left from the OFF position to the HEAT position,
the electric current from terminal B flows to terminals BR and R1. The electric current from
terminal BR flows in the following circuit.
1) Ignition switch terminal BR Î battery relay terminal BR Î battery relay coil Î ground
connection, and the battery relay is closed.
The electric current from terminal R1 flows in the following circuit.
2) Starting switch terminal R1 Î heater relay signal terminal Î heater relay coil Î ground
connection and the heater relay is CLOSED.
Because of circuits 1) and 2), the electric current from the battery flows through the following
circuit.
3) Battery (+) Î battery relay Î heater relay Î electric air intake heater Î ground connection
and the engine is preheated.
KT800895-R1
March 2005
Basic Electric - 4005
Page 5-17
Figure 5.26 – Preheating with heater switch in the automatic position.
In cold weather (-5°C or 23°F), when the ignition switch is turned ON and the preheater switch is
in the AUTO position, the bimetal timer is at low temperature, so the contacts are closed. As a
result, electric current flows in the following circuit.
1) Battery (+) Î starting switch terminal B Î starting switch terminal BRÎ bimetal timer
terminal "2" Î 2) and 3).
2) Bimetal timer terminal "3" Î ground connection.
3) Bimetal timer terminal "1" Î preheat switch "auto" Î preheat switch "ON" Î heater relay
signal terminal Î heater relay coil Î ground connection.
The electric current in circuit (3) closes the heater relay. As a result, electric current flows in
the following circuit.
4) Battery (+) Î battery relay Î heater electrical air intake heater Î ground connection and
the engine is preheated.
Basic Electric - 4005
Page 5-18
KT800895-R1
March 2005
Figure 5.27 – Automatic preheating with engine running.
As the engine is being preheated, circuit is passing through the resistor of the bimetal timer, so
the resistor heats up and the bimetal between its terminals "1" and "2" is heated. As a result, after
a time (the time depends upon on ambient temperature), the bimetal bends. Current is stopped
to the heater relay so its contacts are opened and preheating is stopped.
Even after preheating is stopped, current continues to flow between terminals "2" and "3" of the
bimetal timer so the bimetal is continually heated. This prevents the bimetal contacts from
closing. Therefore, the bimetal cannot be straightened until the ignition switch is turned OFF.
This means that preheating is not possible after the engine is started.
KT800895-R1
March 2005
Basic Electric - 4005
Page 5-19
Basic Electric - 4005
Page 5-20
KT800895-R1
March 2005
Chapter 5 - Assessment
Air Preheat Circuits
Instructions:
There is only one correct answer to each question. If there appears to be more
than one answer, select the most correct answer.
If an in-house instructor is administering this test, turn your answers in to the
instructor when you are finished. Your instructor will input your scores into the
Komatsu Learning Management System.
If you are taking the Basic Electric course as self-study, mark your answers in
the appropriate space on the answer sheet provided in the back of the booklet.
When you have completed all of the assessments for the entire book, either:
a.
Turn the assessments into your instructor along with your Answer Sheet.
The instructor is provided with an answer key and will grade your
assessment and also input your scores into the Komatsu Learning
Management System. Or,
b.
Log-in to the Komatsu Learning Management System (LMS), using your
extranet username and password. Go to the LMS site, enroll in this Basic
Subject course, after your enrollment has been approved, you can launch
the course, then click on the Assessment link and answer each question.
Your grade will be scored and tracked automatically. Note: The online
assessment questions are in random order.
1. What is the purpose of a resistor in an engine intake air heating glow plug circuit?
a. To generate the heat required to quickly start the engine.
b. To increase the voltage to the glow plugs so the intake air will be heated quickly.
c. To lower the supply voltage to the voltage setting of the installed glow plugs.
d. Resistors are never installed in glow plug circuits because their increased amperage draw
would nullify any benefit of having glow plugs.
2. Which of the following Komatsu Automatic Priming System parts must be functional
before any other component will work?
a. APS controller.
b. Water temperature sensor.
c. Bi-metal timer.
d. Preheater relay.
KT800895-R1
March 2005
Basic Electric - 4005
Page 5-21
Chapter 5 Assessment
3. What is the purpose of the bi-metal timer found in the Komatsu APS?
a. Signals the operator that the optimum time has come for cranking the engine.
b. It prevents the possibility of preheating after the engine is running.
c. It controls current flow to the electrical air intake heater when the preheat switch is in the
auto position.
d. It limits the duration of cranking in cold weather operations.
4. What is the purpose of the bi-metal timer found in the automatic preheating circuit of
Komatsu and some Dresser wheel loaders?
a. Signals the operator that the optimum time has come for cranking the engine.
b. It prevents the possibility of preheating after the engine is running.
c. It controls current flow to the electrical air intake heater when the preheat switch is in the
auto position.
d. It limits the duration of cranking in cold weather operations.
5. At what temperature will automatic preheating occur in the automatic preheat system
found on Komatsu and some Dresser wheel loaders?
a. Above water’s freezing point at 45° F.
b. Above water’s freezing point at 35° F.
c. At water’s freezing point at 32° F.
d. Below water’s freezing point at 23° F.
6. What is the purpose of the circuit breaker in a glow plug circuit?
a. It prevents the preheater from overheating due to excessive current flow.
b. It protects equipment and wiring in the preheat circuit against damage due to a short
circuit.
c. It does both things described in “a” and “b”.
d. None of the above is true.
7. What is the amp rating of the ribbon heater found in the 110 series engine?
a. 10 amp.
b. 110 amp.
c. 17 amp.
d. 173 amp.
8. At what engine coolant temperature does the Komatsu APS become operational?
a. Any coolant temperature.
b. Below 20° C (68° F).
c. Below 0° C (32° F).
d. Below -5° C (23° F).
Basic Electric - 4005
Page 5-22
KT800895-R1
March 2005
Chapter 5 Assessment
9. How many electrical input signals must the APS controller be receiving before it will
begin generating output voltage to the APS fuel nozzle solenoids?
a. One.
b. Two.
c. Three.
d. Four.
10. Most Komatsu wheel loaders have an electronic vehicle monitoring system that
contains a preheat pilot display lamp. During preheating, what does it mean when this
lamp turns OFF?
a. Preheating has stopped.
b. The optimum time has arrived for starting the engine.
c. The circuit to the air intake heater has been broken or is defective.
d. Now is the time to inject ether into the combustion chamber.
KT800895-R1
March 2005
Basic Electric - 4005
Page 5-23
Chapter 5 Assessment
Basic Electric - 4005
Page 5-24
KT800895-R1
March 2005
For Instructor Use Only
Score: ________
IMPORTANT:
This is a multi purpose answer sheet designed especially for the Basic Service Training Materials series. This
answer sheet can be used for in-house and/or self study manuals. This answer sheet is used to validate your
study of each chapter or lesson.
BASIC SUBJECT TITLE:
BASIC ELECTRIC-4005
DISTRIBUTOR NAME:
_______________________________ DISTRIBUTOR BRANCH: ______________________________
STUDENT’S NAME: __________________________________
INSTRUCTIONS:
NOTE: If you are taking this Basic Subject course online – you will not need to use this form.
A.
All answers are based upon the contents of the Basic Service Training Manual.
B.
Read each question and all answers carefully.
C.
When there are fewer than 12 questions, mark your answer for the number of questions asked per chapter and leave remaining boxes
blank.
D.
There is only one correct answer for each question. If there appears to be more than one correct answer - select the most correct answer.
E.
Please circle the appropriate letter for each answer.
F.
Make corrections by drawing a BOLD "X" through any incorrect answer and place a circle around new selection.
G.
Upon completion, turn the answer sheet in to your instructor or KLMS Administrator.
H:
DO NOT MAIL YOUR ANSWER SHEET TO KOMATSU.
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