Charging and
Starting Systems
Unit 8
Charging and Starting Systems
Objective
Whether it’s a race car or an SUV, a crane or an excavator, electricity plays a key
role in how machines operate. Yet, in almost all vehicles, there is a similar, basic
electrical system to store electricity, draw on that stored electricity, and generate
new electricity.
When you have successfully completed this unit, you will understand how leadacid batteries operate and how the charging and starting systems work in almost all
combustion engine vehicles.
Overview
There is a similar basic electrical system in almost all vehicles that run by combustion
engines.
That basic electrical system involves a source for storing and dispensing electrical
power, a method of generating new electrical power, and a way to use the stored
electrical power to start the combustion engine.
In this unit, you will learn how a battery stores and dispenses electrical power.
You will learn about the alternator, which generates electricity and works with the
voltage regulator to charge the battery and supply electrical power to the rest of
the vehicle’s electrical system.
Figure 8.1 Basic components of a vehicle’s electrical system
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You will also learn about the starting system and the variations of components
in the two circuits of the starting system. And finally, you will be introduced to
remote start and stop functions associated with many mobile vehicles.
Battery Systems
Battery Basics
In mobile equipment, the battery system provides the electrical power to start
engines, turn on lights, run electrical accessories and control devices. A battery
stores electrical energy in the form of chemical energy (Figure 8.2). Storing energy
in a battery is called charging the battery. Drawing energy out of a battery is called
discharging the battery. When a battery is being charged, electrical energy is turned
into chemical energy. When a battery is being discharged, chemical energy is turned
into electrical energy.
Figure 8.2 Chemical energy processes occurring in a battery
Most mobile equipment uses lead-acid batteries. Some equipment uses more than
one lead-acid battery and connects them in series or series-parallel arrangements.
Most lead-acid batteries are twelve-volt batteries. Inside the polypropylene housing
of a twelve-volt battery are six cells, each responsible for producing just over two
volts of electrical energy.
The cells are physically separated by partitions but connected electrically in series
by metal connectors. Each cell is made up of lead plates separated by an electrolyte
solution. Some of the plates are called the anode plates and have a positive charge.
The other plates are called the cathode plates and have a negative charge. Each
plate is made of lead, hardened with antimony or calcium. The plates are coated
with chemically-active material. The positive plate is coated, or pasted, with lead
peroxide, sometimes also called lead dioxide. Each molecule of lead peroxide has
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Starting Systems
one lead atom and two oxygen atoms. The negative plate is coated with a porous
type of lead called sponge lead. It has only lead atoms. Separators keep the plates
apart to prevent short circuiting.
An electrolyte is a fluid that conducts electricity. An electrolyte has ions of electrons
that can be rearranged when electricity passes through the fluid. The electrolyte in
a lead-acid battery is sulfuric acid diluted with water. In a lead-acid battery, it is this
electrolyte that enables the chemical reaction. When a load is placed on a battery, a
chemical reaction occurs. The electrolyte releases its sulfate molecules to both of
the lead plates, and reacts with the positive plate to take the oxygen molecules. This
reaction works to coat the lead plates with lead sulfate and change the electrolyte
to H2O, or water as shown in Figure 8.3.
Figure 8.3 The chemical reactions that occur in a battery cell
When the battery is charged, the water molecules are broken into hydrogen and
oxygen. The sulfate molecules from the lead plates return to the electrolyte, and
the oxygen molecules from the water return to the positive plate. Gas is produced
inside a battery when the hydrogen and oxygen molecules are separated during
the charging cycle. Modern batteries have expansion and condensation chambers
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Starting Systems
to prevent the gas from escaping. However, care should still be taken to avoid any
sparks when working around a lead-acid battery.
In practical use, it is unlikely to fully charge or discharge a battery. Typically, a
battery is partially charged and partially discharged. For example, if a battery is ten
percent discharged, that means that ten percent of the chemical reaction has taken
place, and ninety percent of the battery is in the normal, charged state. A battery
may test at twelve-point-six volts, indicating that it is fully charged, but that does
not necessarily mean that the chemical state inside the cells is entirely charged.
Charging System
Charging System Basics
The charging system (Figure 8.4) includes the battery, or in some cases multiple
batteries, an alternator, a voltage regulator, the loads of the vehicle, and the wiring
between all of these parts.
The charging circuit has two main jobs: first, to recharge the battery, and second,
to provide most of the current needed to power all of the electrical components
of the vehicle, once the engine is running.
Figure 8.4 The components of a simple charging system
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The battery is like a reservoir of energy. It stores energy in the form of chemical
energy. When a load is placed on this chemical energy, it quickly starts turning into
electrical energy and electrons flow through the circuit.
The alternator is the workhorse of the charging system. It is usually connected to
the crankshaft of the engine by a belt. Once the engine is running, the rotation of
the engine’s crankshaft becomes mechanical energy in the rotation of the belt. The
belt transfers this mechanical energy to turn the rotor inside the alternator. The
alternator changes this mechanical energy into electrical energy. Then the alternator
acts like an electron pump, pushing electrons through the circuit to supply current
for the lights, radio, heater, ignition, and other components in the electrical system.
The alternator also pumps electrons back into the battery to keep it charged.
The electrical charge in a battery, called voltage, acts like pressure. A heavy-duty
twelve-volt battery (Figure 8.5) is considered fully charged when it has twelvepoint-six volts of electrical pressure available. As the battery sends out current
and discharges, the voltage or electrical pressure drops. The more discharged the
battery, the lower the voltage or electrical pressure, and the easier it is for the
alternator to pump in electrons against the remaining pressure. The higher the
voltage or electrical pressure in a battery, the harder the alternator has to work
against that pressure to charge the battery.
In a twelve-volt system, the alternator generally sends 14.2 volts of electricity to the
battery. In a twenty-four-volt system, the alternator generally sends between 27.5
and 29.5 volts to the battery.
Figure 8.5 The voltage regulator detects when there is a load on the system
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Starting Systems
The voltage regulator is the traffic cop of the charging system. It directs the amount
of electrical traffic from the alternator to the battery and to the rest of the vehicle’s
electrical system. The regulator senses when the vehicle’s electrical needs increase
or when the battery needs charging. The regulator then adjusts the alternator’s
electrical output to the system or the battery.
An alternator can make hundreds of instantaneous adjustments each minute. The
battery, alternator, and regulator work together to keep the vehicle’s electrical system
supplied. When the engine is not running, and at start-up, the battery supplies all of
the current for the loads. When the engine is running and the vehicle is operating
with normal loads, the alternator supplies current to the system and charges the
battery as needed. When the engine is running and the vehicle is operating with
low loads, the regulator may direct more current flow from the battery and allow
the alternator to freewheel for fuel economy, since a one-hundred-amp alternator
can consume up to seven horsepower. When the vehicle is operating with peak
electrical loads, the regulator directs the alternator and the battery to work together
as a team to supply all of the needed current.
Starting System
Starting System Basics
One of the most important systems in a vehicle is the starting system. Its work
is occasional and short, but critical. When the starting system isn’t working, the
vehicle won’t work.
The starting system works by taking electrical power stored in the battery, sending
that power to a starter motor, where the electrical power is converted to mechanical
power, and using that mechanical power as rotation to crank the engine and get the
engine up to speed to operate on its own. When the engine is operating, the work
of the starting system is completed and other systems take over the operation of
the vehicle.
The basic components in the starting system (Figure 8.6) include: the battery, which
supplies the energy, heavy-gauge electrical cables, which transfer the energy to the
starter motor, the starter solenoid, which engages the starter motor drive with the
engine flywheel, the starter motor, which drives the flywheel to crank the engine,
and the starting, or ignition switch, which activates the starting circuit.
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Figure 8.6 The basic components of a starting system
The first component to activate is the starting switch. This could be a key switch
or a start button.
When the starting switch is activated, a circuit is closed and electricity flows from
the battery, through the cables, to the starter solenoid.
When the starter solenoid receives electricity in its coils, a magnetic field is created,
and this magnetic field moves the solenoid plunger. The movement of the solenoid
plunger accomplishes two things: it engages the starter pinion with the flywheel of
the engine, and it completes the circuit between the battery and the starter motor.
The starter motor is an electric motor designed to deliver high power for a short
time. When the motor is energized, it creates torque to drive the rotation of the
starter pinion, and the starter pinion turns the flywheel, which cranks the engine
into operation. When the starter button is released, or the ignition switch key is
released from the start to the run position, the solenoid is deactivated. Springs force
the solenoid plunger to return, and this draws the pinion away from the engine’s
flywheel and opens the starter motor circuit, which stops the starter motor.
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Starting Systems
Control and Crank Circuits
There can be many other types of components included in a starting system. The
components are arranged in two interconnected circuits: the cranking circuit and
the control circuit.
A large starting motor can draw more than three-hundred amps of current from
the battery. That is why heavy-gauge cables connect the battery directly to the
starter motor. This is the basic cranking circuit, from the battery to the starter
motor.
The control circuit is set up as a separate circuit, but interconnected with the
cranking circuit. This allows a small amount of battery current in the control
circuit to control a larger amount of current in the cranking circuit. Since the
control circuit is not directly part of the cranking circuit, there is less resistance to
be overcome than in the very large power needs of the cranking circuit.
Figure 8.7 Cranking circuit showing large
current from the battery to the starter
Starting Components
Different manufacturers use different configurations of components. In this
course, we are covering the basic system, and only touch on some of the variations.
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Starting Systems
When working on a system, make sure to refer to the specific shop manual for that
equipment. Typical components (Figure 8.8) may include: a neutral safety switch,
a starter relay, also called a magnetic switch, a safety relay, a battery relay, a master
switch, a fusible link, and a thermostat.
A neutral safety switch is a safety device. If you try to start the engine when the
vehicle is in gear, the vehicle could suddenly lurch forward or backward. If the
vehicle is in gear when you turn the key, the neutral safety switch is open and
no electricity flows through the control circuit. When the vehicle is in park or
neutral, the neutral safety switch is closed and electricity can flow through the
control circuit. Generally, the neutral safety switch is located on the gearshift lever
or transmission linkage.
Figure 8.8 Various starting system components
The starter relay is also called the magnetic switch. It enables a small current in
the control circuit to open and close the larger current in the cranking circuit. The
starter relay is either built into the front end of the starter’s solenoid assembly, or it
is remote mounted either close to the battery or close to the starter.
A safety relay prevents current from going to the starter motor after the engine
is running. This prevents damage to the pinion and flywheel by preventing them
from making contact when the flywheel is activated. There are two main types of
safety relays (Figure 8.9): the older mechanical type, which uses coils and contact
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Starting Systems
points, and the newer semi-conductor type. Safety relays can be mounted in various
places, so check the shop manual for the exact type and location.
Figure 8.9 A mechanical safety relay and a semi-conductor safety relay
A battery relay removes electricity from wires that are not in use. This prevents
possible short circuits. It also prevents electrical shock when you are making repairs
or replacing components. A battery relay can be located on either the positive or
negative side of the battery.
A master switch is another type of device to remove electricity from wires that are
not in use. It is a manually operated battery disconnect switch. The master switch
is located between the battery and the chassis ground.
A fusible link is an over-current protection device for the system. The most
common type of fusible link is a section of wire covered with nonflammable
insulation. Generally the wire is two sizes smaller than the wiring of the circuit it
is designed to protect. When a system is heated with overcurrent, the fusible link
breaks and opens the circuit. Usually, the insulation will appear charred. However,
you should do a continuity test on it to make sure. Typically, the largest fusible link
is located at the starter solenoid battery terminal. There is often another fusible
link between the battery terminal and the main body harness. This link protects the
complete wiring of the vehicle.
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Some starter motors have a thermostat to monitor the temperature of the
starter motor. If the starter motor is run too long, the temperature builds and
the thermostat breaks the circuit. When the thermostat senses that the motor has
cooled sufficiently, it will again close the circuit.
Remote Start & Stop
On some vehicles, such as bucket trucks, some fire trucks, digger derricks, and
other utility vehicles, there is a need to interact with the starting system from
outside of the cab. A remote start/stop unit allows operators to start and stop the
engine without re-entering the cab.
A remote control system can be as simple as only starting and stopping the vehicle
or as complicated as operating all of the functions of the vehicle. The remote
control unit can be mounted on the vehicle, with signals sent to the vehicle’s
electrical system through electrical cables or fiber optic cables. The remote control
station can also be a mobile transmitter that sends radio wave signals to a receiver
connected to the vehicle’s starter system and other electrical systems.
Always refer to the remote control manual when working with a vehicle equipped
with a remote control device.
Figure 8.10 Examples of remote start and stop controls
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SUMMARY
The battery system provides the electrical power to start engines, turn on lights,
run electrical accessories and control devices.
A battery stores electrical energy in the form of chemical energy.
The charging system includes the battery, an alternator, a voltage regulator, the
loads of the vehicle, and the wiring between all of these parts.
The starting system works by taking electrical power stored in the battery, sending
that power to a starter motor, where the electrical power is converted to mechanical
power, and using that mechanical power to crank the engine.
There can be many types of components included in a starting system. The
components are arranged in two interconnected circuits: the cranking circuit and
the control circuit.
Typical starting components include: a neutral safety switch, a starter relay, also
called a magnetic switch, a safety relay, a battery relay, a master switch, a fusible
link, or a thermostat.
QUESTIONS
Battery Basics
1. Batteries store energy in which form?
a. electrical energy
b. chemical energy
c. mechanical energy
d. light energy
2. How much potential does each cell
within a 12 volt battery produce?
a. just under three volts
b. just over two volts
c. just under two volts
d. It depends on the number of
cells present.
3. What material is used to coat the
positive, or anode, plate of a battery?
a. lead peroxide
b. sponge lead
c. sulfuric acid
d. aluminum
4. In a lead-acid battery, it is the electrolyte
that enables the chemical reaction.
a. True
b. False
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Starting Systems
Charging System
Starting System & Remote
Start and Stop
5. Which is NOT typically part of a
charging system?
a. battery
b. voltage regulator
c. capacitor
d. alternator
10. Which is NOT a basic component of
the starting system?
a. alternator
b. heavy-gauge electrical cables
c. starter solenoid
d. ignition switch
6. Which part controls the amount of
electricity flowing into the vehicle’s
electrical system?
a. solenoid
b. crankshaft
c. regulator
d. alternator
7. The only job of the charging system is to
charge the battery.
a. True
b. False
8. The alternator converts ________
energy into ________ energy.
a. mechanical, electrical
b. chemical, mechanical
c. electrical, mechanical
d. electrical, chemical
11. What is the purpose of the neutral
safety switch?
a. It prevents current from going
to the starter motor after the
engine is running.
b. It removes electricity from wires
that are not in use.
c. It prevents the engine from
starting if the vehicle is in other
than neutral or park.
d. It allows a circuit to be
grounded to the frame.
12. What is the purpose of a safety relay?
a. It prevents current from going
to the starter motor after the
engine is running.
b. It removes electricity from wires
that are not in use.
c. It prevents the engine from
starting if the vehicle is in other
than neutral or park.
d. It allows a circuit to be
grounded to the frame.
9. In a twelve-volt system, how many volts
does an alternator generally send to the
battery?
a. 12 V
b. 12.6 V
c. 13 V
d. 14.2 V
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13. What is the purpose of a battery relay?
a. It prevents current from going
to the starter motor after the
engine is running.
b. It removes electricity from wires
that are not in use.
c. It prevents the engine from
starting if the vehicle is in other
than neutral or park.
d. It allows a circuit to be
grounded to the frame.
14. Generally, how would you compare the
size of a fusible link wire to the size of
the wiring of the circuit it is designed
to protect?
a. It is the same size.
b. It is two sizes bigger.
c. It is two sizes smaller.
d. It is three sizes bigger.
15. What is a benefit of a remote start/stop
system?
a. It breaks the starter motor
circuit if the temperature is too
high.
b. It prevents electrical shock
when you are making repairs or
replacing components.
c. It saves wear and tear on the
brake system.
d. It allows you to start and stop
the engine without re-entering
the cab.
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