CHAPTER
7
Charging Systems
Instructor Name: (Your Name)
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Learning Objectives
• Explain how an alternator produces a
regulated DC voltage
• Describe how electrical contact is made
through the rotating rotor windings
• Trace the current flow from the stator
winding through a rectifier bridge
• Explains haw a voltage regulator controls
the strength of the rotors magnetic field
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Learning Objectives (continued)
• Define the purpose of the diode trio or the
field diode assembly
• Perform a preliminary inspection of a
charging system
• Disassemble and inspect the internal
components of a typical alternator
• Test a truck charging system
• Perform a parasitic current draw test
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Alternators Role in the Electrical System
• Recharges the trucks batteries
• Primary power source when the truck is
running
• Produces AC voltage and converts it to DC
with diodes
• Regulates the voltage supplied to the
system and the battery
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Cutting Magnetic Lines of Force with a
Conductor to Produce a Positive Voltage
Figure 7-1 Cutting
magnetic lines of
force with a
conductor to induce
a voltage: conductor
is moving from right
to left through the
magnetic field.
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Cutting Magnetic Lines of Force with a
Conductor to Produce a Negative Voltage
Figure 7-2
Conductor has
been moved
from left to right
through the
magnetic field
causing a reversal
of polarity of
induced voltage.
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Inducing More Voltage
• The greater the number of magnetic lines
of force that are cut by a conductor per
second, the greater the voltage that is
induced in the conductor
• Increase the speed of the conductor that
moves through the magnetic field
• Increase the strength of the magnetic field
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Voltage Waveforms
• An oscilloscope displays voltage amplitude on
the y-axis and the time on the x-axis
• The oscilloscope can be adjusted to change the
values of each division of both the horizontal
and vertical axis
• 120 VAC from a wall socket would form a sine
wave on the oscilloscope
– The sine wave would alternate between positive and
negative
– This alternating polarity is where the term alternating
current came from
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Voltage Waveforms (continued)
• The number of times a wave form repeats
per seconds is called frequency and is
measured in hertz
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Simple Alternator
Figure 7-8 Simple alternator.
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Single Loop Rotating
Through a Magnetic Field
Figure 7-9 Single loop rotating in magnetic field at six different positions.
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Voltage Wave Form
Figure 7-10 Voltage waveform produced by a single loop rotating in a magnetic field.
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Magnets Rotating Inside a
Conductive Loop
Figure 7-11 Magnet
rotating inside of
conductive loop
induces an AC
voltage in the loop.
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Magnetic Field Lines of Force Flow
Through a Stator
Figure 7-12 Magnetic field lines of force flow through stator.
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Electromagnet Rotating Inside
Conductive Loop
Figure 7-13 Electromagnet rotating inside of conductive loop induces an AC voltage in the loop.
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Sine Wave Produced by Magnet
Rotating Inside Conductive Loop
Figure 7-14 Sinusoidal AC voltage
waveform produced by rotating
electromagnet inside of a conductive loop.
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Three-Phase Power
• Three-phase alternators have three
conductive loops
• Each loop is place 120° apart
(360°÷3=120°)
• Each loop will form a single sine wave
voltage form with every revolution of the
rotor
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Three Conductor Stator and Output Sine Wave
Figure 7-16 Three
conductive loops
connected together and
spaced around the stator.
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Three-Phase Sine Waveform Voltage Trace
Figure 7-17 Three-phase sine
waveform voltage trace.
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Delta and Wye Wound Stators
Figure 7-20 Stator winding
arrangements.
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Rotor Components
Figure 7-21 Rotor components consist of coil and pole pieces installed on rotor shaft.
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Alternating North and South Poles of Rotor
and Magnetic Field Between Them
Figure 7-22 Alternating north and south
poles of rotor pieces produce a rotating
magnetic field.
Figure 7-23 Magnetic fields
between adjacent rotor pole pieces
surround the rotor.
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Three-Phase Stator Winding
Figure 7-24 Three-phase
stator windings installed in
laminated iron frame.
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Converting AC to DC
• AC current from alternator must be
converted to DC current
• Diodes, often called rectifiers, convert AC
current to DC current
• The output of the alternator stator
windings is connected to a four diode
bridge rectifier
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Four Diode Bridge Rectifier
Figure 7-27 Single-phase AC rectifier bridge.
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Full Wave Rectification
Figure 7-28 Full wave rectification reverses the
polarity of the negative portion of a sine
waveform.
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Three-Phase Rectifier Requiring Six Diodes
Figure 7-30
Three-phase
rectifier requires
six diodes.
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Rectified Three-Phase Voltage
Figure 7-31 Rectified three-phase voltage.
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Voltage Regulation Fundamentals
• Modern truck alternators are designed to
maintain a 14.2V output for a 12V system
• Voltage regulators maintain alternator
output by controlling the current flow
through the rotor field coil windings
• If the alternator output is low, current to the
rotor field coil is increased
• If the alternator output is high, current to
the rotor field coil is decreased
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Switch Controlling Current Flow
Figure 7-36
Switch shown as
controlling
current through
rotor field coil
through slip rings
and brushes.
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Voltage Regulation Fundamentals
(continued)
• Modern truck voltage regulators use pulse
width modulation to control current flow to the
rotor field coil
• Pulse width refers to the on portion of a pulse
compared to the off portion of a pulse
• The longer the on portion a pulse has the
more current supplied to the rotor field coil
• The shorter the on portion a pulse has the
less current supplied to the rotor field coil
• Voltage for the rotor field coil is supplied by
the diode trio or a field diode
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Pulse Width Modulation Duty Cycle
Figure 7-37 (A) Lights on for one time period and off for two time periods resulting in dim lamp output.
(B) Lights on for two time periods and off for one time period resulting in brighter lamp output.
Figure 7-38 Pulse width modulation (PWM). Duty cycle is the percentage of on-time per cycle.
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Alternator Terminals and Circuits
• Positive Output Terminal – insulated terminal
marked BAT or B+. Normally connected to
battery terminal of started and battery
positive
• Ground Terminal – Most truck alternators
have a ground terminal that connects to the
starter ground or frame. Some alternators
ground through the alternator mounting bolts
• Relay Terminal – Marked R or AC. Used on
some systems to power relay only when
engine is running
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Alternator Terminals and Circuits
(continued)
• Indicator Light Terminal – Available on
some alternators. Dash indicator will light if
alternator in not functioning.
• Remote Sensing Terminal – Provides an
indication of the battery voltage to the
voltage regulator
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Brushless Alternator
Figure 7-42 Brushless alternator rotor and field coil.
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Charging System Problems
Complaints of High
Charging Voltage
Complaints of Low
Charging Voltage
• Voltmeter reads high
• Sulfur smell
• Wet batteries and high
water usage
• Lamps that are too bright
and burn out quickly, turn
signals that flash too
rapidly
• Decreased battery life
• Voltmeter reads too low
• Slow cranking speed or
no crank
• Lamps that are too dim
and turn signals that flash
too slowly
• Decreased battery life
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Tech Tip
Testing a charging system using batteries
that are not fully charged may lead you to
an incorrect diagnosis. Recharging
batteries can take a considerable amount
of time. Having sufficiently charged
batteries that you can temporarily install
for testing can save you and your
customer valuable time.
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Delco Remy 28SI Alternator
Figure 7-46
Delco Remy 28SI
pad-mount alternator
with serpentine drive
belt and automatic
tensioner.
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CAUTION
Each OEM has procedures for testing the
charging system that should always be
followed. Procedures listed are only
examples and can not be performed on all
vehicles.
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Testing Alternator Charging Circuit Voltage Drop
Figure 7-47
Testing alternator
charging circuit
voltage drop using
carbon pile load
tester, engine off.
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Determining Individual Alternator
Cable Voltage Drops
Figure 7-48 Determining
individual alternator
cable voltage drops,
engine off.
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Alternator Output Test, No Load
1.
2.
3.
4.
Connect voltmeter across the alternator output positive and
negative leads. Connect ammeter probe to alternator output
lead.
Start engine, run at 1500 rpm for 2 minutes.
Observe voltage and current reading with all electrical loads
off and engine running.
Conduct next test based on the results of test and chart
below:
Figure 7-49 Determining individual alternator cable voltage drops.
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Test 1, Acceptable Unloaded
Charging Voltage
1. Connect ammeter current probe to output
lead of alternator
2. Connect carbon pile load tester across
the battery terminal
3. Start engine, run at 1500 rpm, turn off all
loads
4. Run 2 minutes with no electrical load
5. Adjust carbon pile until ammeter reads
highest value. Quickly return carbon pile
to the unloaded position.
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Test 2, Low Alternator Output Voltage
• Rotor lost residual magnetism. “Flashing
the Field” may be required to start
alternator charging.
• Voltage regulator may be set too low
• Full field the alternator to determine if the
voltage regulator is faulty or if the
alternator is faulty
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WARNING
Only perform a full field test if specified by
the OEM. Use extreme caution when full
fielding an alternator. The output voltage
can rise to a very high level in a brief time
and cause damage to the electrical
system. It may also be very difficult to
access the full fielding access hole on
some alternators. Be careful when working
around rotating components to avoid
injury.
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Test 3, High Charging Voltage
•
•
•
•
Possible faulty voltage regulator
Internal short to ground in the field coil
Voltage regulator set too high
Check OEM information for specific test
for high charging voltage
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CAUTION
Never disconnect any battery or alternator
cable when the engine is running. The
rapid change in alternator output current
can result in a very high alternator output
voltage, which can destroy modern truck
electronics. Never operate an engine
without the batteries connected in parallel
with the alternator output. This batteryless operation will cause the alternator
output voltage to become very unstable,
which could result in damage to electronic
components.
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Parasitic Draw Test
1. Turn off all electrical loads on truck.
2. Connect current ammeter probe on negative
lead of battery. All other batteries may need
to be disconnected.
3. Watch as the various modules power down.
After a couple of minutes observe parasitic
load current.
4. Using circuit diagram as a guide remove
circuit protection devices one at a time until
the parasitic load on ammeter drops off.
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Testing Rotor With an Ohm Meter
Figure 7-52 Testing for rotor field winding
resistance.
Figure 7-53 Testing for a short to ground
field winding.
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Testing Stator with an Ohmmeter
Figure 7-54 Testing the stator for
open circuits.
Figure 7-55 Testing the stator for shorts
to ground.
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Testing The Rectifier with an
Ohmmeter
Figure 7-56
Testing the
rectifier
diodes.
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Testing Diode Trio with an Ohmmeter
Figure 7-57
Testing the field diode or diode trio.
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Simplified Regulator Circuit
Figure 7-58 Simplified electronic voltage regulator schematic – zener diode D2 is the
primary component.
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Summary
• The charging system supplies the energy to
recharge the truck batteries.
• The alternator produces a three-phase
alternating current through the principles of
electromagnetic induction. The alternating
current is rectified to direct current.
• The rotor is an electromagnet that produces
a rotating magnetic field inside of the
stationary windings called the stator. The
magnetic lines of force produced by the rotor
cut through the stator winding to induce a
sine wave voltage in the stator windings.
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Summary (continued)
• The three-phase stator winding may be
connected in a delta or wye (y) configuration.
Either configuration produces a three-phase
alternating current wave form.
• The means of making electrical contact with
the rotor field windings is through slip rings
and brushes.
• The alternator output voltage is controlled by
regulating the current flow through the rotor
field windings. The voltage regulator uses
PWM to control the field winding current
level.
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Summary (continued)
• The rectifier uses a series of diodes to transform
the negative half of the sine wave into a positive
wave form. The pulsating positive polarity wave
form is smoothed by a capacitor. The small
amount of pulsation that remains in the wave
form is called ripple voltage.
• Testing the charging system includes testing the
batteries, making a visual inspection, and
measuring charging system circuit resistance.
Circuit resistance testing is performed by
measuring the voltage dropped on the charging
circuit at rated alternator current flow in the
circuit.
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Summary (continued)
• Parasitic current draw is the key-off
current draw of the trucks electrical
system. Parasitic current is measured with
an ammeter. The source of the current
draw can be determined by removing
fuses one by one.
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