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OBJECTIVES
After studying Chapter 20, the reader should be able to:
1. Prepare for ASE Electrical/Electronic Systems (A6)
certification test content area “D” (Charging
System Diagnosis and Repair).
2. List the parts of a typical generator (alternator).
3. Describe how a generator works.
4. Explain how the voltage regulator works to control
generator (alternator) output voltage.
Automotive Electricity and Electronics, 2/e
By James D Halderman
© 2009 Pearson Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
PRINCIPLES OF GENERATOR OPERATION
• All vehicles operate electrical components by taking
current from the battery.
• The amount of current generated can be increased
by the following factors.
1. Increasing the speed of the conductor through the
magnetic field
2. Increasing the number of conductors passing through
the magnetic field
3. Increasing the strength of the magnetic field
Automotive Electricity and Electronics, 2/e
By James D Halderman
© 2009 Pearson Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
ALTERNATING-CURRENT GENERATORS (ALTERNATORS)
• An alternator (AC generator) generates an
alternating current when the current changes
polarity during the generator’s rotation.
• Most manufacturers call an AC generator a
generator, but the most commonly used term in the
industry is alternator.
Automotive Electricity and Electronics, 2/e
By James D Halderman
© 2009 Pearson Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
GENERATOR CONSTRUCTION
• An alternator is constructed of a two-piece castaluminum housing.
• The rear housing, or the slip-ring end (SRE
housing), usually contains a roller-bearing support
for the rotor and mounting for the brushes, diodes,
and internal voltage regulator (if the generator is so
equipped).
Automotive Electricity and Electronics, 2/e
By James D Halderman
© 2009 Pearson Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
GENERATOR CONSTRUCTION
FIGURE 20-1 A typical generator
(alternator) on a Chevrolet V8 engine.
Automotive Electricity and Electronics, 2/e
By James D Halderman
FIGURE 20-2 The end frame toward the drive
belt is called the drive-end housing and the rear
section is called the slip-ring-end housing.
© 2009 Pearson Education, Inc.
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ALTERNATOR OVERRUNNING PULLEY
Purpose and Function
• Using a one-way clutch in
the alternator pulley allows
the belt to apply power to
the alternator in only one
direction thereby reducing
the fluctuations in the belt.
FIGURE 20-3 An OAP on a Jeep generator
with a diesel engine.
Automotive Electricity and Electronics, 2/e
By James D Halderman
© 2009 Pearson Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
ALTERNATOR OVERRUNNING PULLEY
Purpose and Function
• Another type of alternator pulley uses a dampener
spring inside, plus a one-way clutch.
• This unit is called an overrunning alternator
dampener (OAD).
Automotive Electricity and Electronics, 2/e
By James D Halderman
© 2009 Pearson Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
ALTERNATOR OVERRUNNING PULLEY
Purpose and Function
FIGURE 20-4A An OAD on a Chrysler
vehicle generator.
Automotive Electricity and Electronics, 2/e
By James D Halderman
FIGURE 20-4B An overrunning alternator
dampener (OAD) disassembled, showing all of
its internal parts.
© 2009 Pearson Education, Inc.
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ALTERNATOR OVERRUNNING PULLEY
Diagnosis and Service
• Overrunning alternator pulleys and overrunning
alternator dampeners can fail.
• In most cases, the entire alternator assembly will be
replaced because each OAP or OAD is unique for
each application and both require special tools to
remove and replace.
Automotive Electricity and Electronics, 2/e
By James D Halderman
© 2009 Pearson Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
ROTORS
• At both ends of the rotor
windings are heavy-gauge
metal plates bent over the
windings with triangular
fingers called claw poles.
• These pole fingers do not
touch, but alternate or
interlace
FIGURE 20-5 A cutaway of a General Motors
CS-130D generator showing the rotor and
cooling fans that are used to force air through
the unit to remove the heat created when it is
charging the battery and supplying electrical
power for the vehicle.
Automotive Electricity and Electronics, 2/e
By James D Halderman
© 2009 Pearson Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
ROTORS
• The magnetic fields are
created between the
alternating pole piece
fingers.
• These individual magnetic
fields produce a current by
electromagnetic induction
in the stationary stator
windings.
FIGURE 20-6 Rotor assembly of a typical alternator (AC generator).
Current through the slip rings causes the “fingers” of the rotor to
become alternating north and south magnetic poles. As the rotor
revolves, these magnetic lines of force induce a current in the stator
windings.
Automotive Electricity and Electronics, 2/e
By James D Halderman
© 2009 Pearson Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
STATORS
• The stator is the stationary
coil winding inside the
alternator.
• The stator is supported
between the two halves of
the generator housing and
there are three copper wire
windings wound on a
laminated metal core.
FIGURE 20-7 A cutaway view of a typical AC
generator (alternator).
Automotive Electricity and Electronics, 2/e
By James D Halderman
© 2009 Pearson Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
STATORS
• As the rotor revolves,
its moving magnetic
field induces a current
in the stator windings.
FIGURE 20-8 An exploded view of a typical
generator (alternator) showing all of its
internal parts.
Automotive Electricity and Electronics, 2/e
By James D Halderman
© 2009 Pearson Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
DIODES
• AC generators use six diodes (one positive and
one negative set for each of the three stator
windings) to convert alternating current to direct
current.
• The symbol for a diode is shown.
FIGURE 20-9 A diode symbol.
Automotive Electricity and Electronics, 2/e
By James D Halderman
© 2009 Pearson Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
HOW A GENERATOR WORKS
• A rotor inside a generator is
turned by a belt and drive
pulley which are turned by
the engine.
• The magnetic field of the
rotor generates a current in
the stator windings by
electromagnetic induction.
FIGURE 20-10 Magnetic lines of force cutting
across a conductor induce a voltage and current
in the conductor.
Automotive Electricity and Electronics, 2/e
By James D Halderman
© 2009 Pearson Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
HOW A GENERATOR WORKS
• Field current flowing through the slip rings to the
rotor creates an alternating north and south pole on
the rotor, with a magnetic field between each finger
of the rotor.
• Therefore, the current generated is described as
being of a sine wave pattern.
Automotive Electricity and Electronics, 2/e
By James D Halderman
© 2009 Pearson Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
HOW A GENERATOR WORKS
FIGURE 20-11 Sine wave voltage curve
created by one revolution of a winding rotating
in a magnetic field.
Automotive Electricity and Electronics, 2/e
By James D Halderman
© 2009 Pearson Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
HOW A GENERATOR WORKS
• As the rotor continues to rotate, this sine wave current is
induced in each of the three windings of the stator.
FIGURE 20-12 When three windings (A, B, and C) are present in a stator,
the resulting current generation is represented by the three sine waves. The
voltages are 120° out of phase. The connection of the individual phases
produces a three-phase alternating voltage.
Automotive Electricity and Electronics, 2/e
By James D Halderman
© 2009 Pearson Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
WYE-CONNECTED STATORS
• The Y (pronounced “wye”
and generally so written)
type or star pattern is the
most commonly used
generator stator winding
connection.
FIGURE 20-13 Wye-connected stator winding.
Automotive Electricity and Electronics, 2/e
By James D Halderman
© 2009 Pearson Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
WYE-CONNECTED STATORS
• In a wye-type stator connection, the currents must
combine because two windings are always
connected in series.
FIGURE 20-14 As the magnetic field, created in the rotor, cuts across the windings of the
stator, a current is induced. Notice that the current path includes passing through one positive
(+) diode on the way to the battery and one negative (-) diode as a complete circuit is
completed through the rectifier and stator.
Automotive Electricity and Electronics, 2/e
By James D Halderman
© 2009 Pearson Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
DELTA-CONNECTED STATORS
• The delta winding is
connected in a
triangular shape.
• The delta-connected
generator produces
lower current at low
speed and must be
operated at high
speed to produce its
maximum output.
Automotive Electricity and Electronics, 2/e
By James D Halderman
FIGURE 20-15 Delta-connected stator winding.
© 2009 Pearson Education, Inc.
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GENERATOR OUTPUT FACTORS
• The output voltage and current of a generator
depend on several factors:
1. Speed of rotation.
2. Number of conductors.
3. Strength of the magnetic field.
Automotive Electricity and Electronics, 2/e
By James D Halderman
© 2009 Pearson Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
GENERATOR VOLTAGE REGULATION
• An automotive generator
must be able to produce
electrical pressure (voltage)
higher than battery voltage
to charge the battery.
• After generator output
begins, the voltage
regulator controls the
current flow through the
rotor.
Automotive Electricity and Electronics, 2/e
By James D Halderman
FIGURE 20-17 Typical voltage regulator
voltage range.
© 2009 Pearson Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
BATTERY CONDITION AND CHARGING VOLTAGE
• If the automotive battery is discharged, its voltage
will be lower than the voltage of a fully charged
battery.
• If a discharged battery is used during charging
system testing, tests could mistakenly indicate a
defective generator and/or voltage regulator.
Automotive Electricity and Electronics, 2/e
By James D Halderman
© 2009 Pearson Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
TEMPERATURE COMPENSATION
• A thermistor is used in the
electronic circuits of the
voltage regulator to control
charging voltage over a
wide range of under-the
hood temperatures.
FIGURE 20-18 A typical electronic voltage
regulator showing the connections and the
circuits involved.
Automotive Electricity and Electronics, 2/e
By James D Halderman
© 2009 Pearson Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
A AND B FIELD CIRCUITS
• When testing the generator,
using a bench-mounted test
unit, most test equipment
requires the technician to
select either A or B field
type.
• An A circuit is the most
commonly used.
FIGURE 20-19 Diagram of a A-type field circuit.
Automotive Electricity and Electronics, 2/e
By James D Halderman
© 2009 Pearson Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
A AND B FIELD CIRCUITS
• In a B-circuit field, the
voltage regulator controls
(opens and closes) the
power side of the field
circuit, and the circuit is
grounded inside the
generator.
FIGURE 20-20 Diagram of an B-type field circuit.
Automotive Electricity and Electronics, 2/e
By James D Halderman
© 2009 Pearson Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
ELECTRONIC VOLTAGE REGULATORS
• The electronic circuit of the voltage regulator cycles
between 10 and 7,000 times per second as needed
to accurately control the field current through the
rotor, and therefore control the generator output.
• Whether mounted inside the generator or externally
under the hood, electronic voltage regulators are
mounted where normal airflow can keep the
electronic components cool.
Automotive Electricity and Electronics, 2/e
By James D Halderman
© 2009 Pearson Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
HOW AN ELECTRONIC VOLTAGE REGULATOR WORKS
• Depending on the
generator RPM, vehicle
electrical load, and state of
charge of the battery, this
controlled switching on and
off can occur between 10
and 7,000 times per
second.
FIGURE 20-21 Typical General Motors SI-style AC
generator with an integral voltage regulator. Voltage
present at terminal 2 is used to reverse bias the zener
diode (D2) that controls TR2. The hot brush is fed by
the ignition current (terminal 1) plus current from the
diode trio.
Automotive Electricity and Electronics, 2/e
By James D Halderman
© 2009 Pearson Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
COMPUTER-CONTROLLED GENERATORS
• Computers can interface with the charging
system in three ways.
1. The computer can activate the charging system by
turning the field current to the rotor on and off.
2. The computer can monitor the operation of the
alternator and increase engine speed if needed during
conditions where a heavy load is demanded by the
alternator.
3. The computer can control the generator by controlling
alternator output to match the needs of the electrical
system.
Automotive Electricity and Electronics, 2/e
By James D Halderman
© 2009 Pearson Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
COMPUTER-CONTROLLED GENERATORS
• A typical system used on
some General Motors
vehicles is called electrical
power management
(EPM).
• It uses a Hall effect sensor
attached to the negative
battery cable to measure
the current leaving and
entering the battery.
Automotive Electricity and Electronics, 2/e
By James D Halderman
FIGURE 20-22 A Hall-effect current sensor
attached to the negative battery cable is used as
part of the EPM system.
© 2009 Pearson Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
COMPUTER-CONTROLLED GENERATORS
• The engine control module (ECM) controls the alternator
by changing the on-time of the current through the rotor.
• The on-time, called duty cycle, is varied from 5% to 95%.
Automotive Electricity and Electronics, 2/e
By James D Halderman
© 2009 Pearson Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
COMPUTER-CONTROLLED GENERATORS
• This system has six modes of operation,
including:
–
–
–
–
–
–
Charge mode.
Fuel economy mode.
Voltage reduction mode.
Start-up mode.
Battery sulfation mode.
Headlight mode.
Automotive Electricity and Electronics, 2/e
By James D Halderman
© 2009 Pearson Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
GM CS GENERATORS
• Beginning in the mid-1980s, General Motors introduced a
smaller, yet high-output series of generators.
FIGURE 20-23 General
Motors CS generator. Notice
the use of zener diodes in the
rectifier to help control any
high-voltage surges that could
affect delicate computer
circuits. If a high-voltage surge
does occur, the zener diode(s)
will be reverse biased and the
potentially harmful voltage will
be safely conducted to
ground. Voltage must be
preset at the L terminal to
allow the generator to start
producing current.
Automotive Electricity and Electronics, 2/e
By James D Halderman
© 2009 Pearson Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
GM CS GENERATORS
FIGURE 20-24 The components inside a GM CS generator.
Automotive Electricity and Electronics, 2/e
By James D Halderman
© 2009 Pearson Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
GM CS GENERATORS
• The voltage regulator switches the field voltage on and off
at a fixed frequency of about 400 times per second.
FIGURE 20-25 The alternator field (rotor) current is controlled by the
computer. SMEC stands for single module engine controller.
Automotive Electricity and Electronics, 2/e
By James D Halderman
© 2009 Pearson Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
GM CS GENERATORS
Types of Computer Controlled Charging
Systems
• Computer control of the charging system has the
following advantages.
1. The computer controls the field of the generator, which
can pulse it on or off as needed for maximum efficiency,
thereby saving fuel.
2. Engine idle can also be improved by turning on the
generator slowly, rather than all at once, if an electrical
load is switched on, such as the air conditioning system.
Automotive Electricity and Electronics, 2/e
By James D Halderman
© 2009 Pearson Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
GM CS GENERATORS
Types of Computer Controlled Charging
Systems
3. Most computers can also reduce the electrical load on
the electrical system if the demand exceeds the capacity
of the charging system by reducing fan speed, shutting off
rear window defoggers, or increasing engine speed to
cause the alternator to increase the amperage output.
4. The computer can monitor the charging system and set
diagnostic trouble codes (DTCs) if a fault is detected.
5. Because the charging system is computer controlled, it
can be checked using a scan tool.
Automotive Electricity and Electronics, 2/e
By James D Halderman
© 2009 Pearson Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
SUMMARY
1.
Generator output is increased if the speed of the generator is
increased.
2.
The parts of a typical generator (alternator) include the drive-end
housing (DE), slip-ring-end (SRE) housing, rotor assembly, stator,
rectifier bridge, brushes, and voltage regulator.
3.
The magnetic field is created in the rotor.
4.
The current is created in the stator windings.
5.
The voltage regulator controls the current flow through the rotor.
Automotive Electricity and Electronics, 2/e
By James D Halderman
© 2009 Pearson Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
REVIEW QUESTIONS
1.
Describe how a small electronic voltage regulator can
control the output of a typical 100 ampere generator.
2.
List the component parts of a typical generator (alternator).
3.
Explain how the computer is used to control a generator
(alternator).
4.
Why do voltage regulators include temperature
compensation?
Automotive Electricity and Electronics, 2/e
By James D Halderman
© 2009 Pearson Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
CHAPTER QUIZ
1. Technician A says that the diodes regulate
the generator output voltage. Technician B
says that the field current can be computer
controlled. Which technician is correct?
a)
b)
c)
d)
Technician A only
Technician B only
Both Technicians A and B
Neither Technician A nor B
Automotive Electricity and Electronics, 2/e
By James D Halderman
© 2009 Pearson Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
CHAPTER QUIZ
2. A magnetic field is created in the _____ in a
generator (AC generator).
a)
b)
c)
d)
Stator
Diodes
Rotor
Drive-end frame
Automotive Electricity and Electronics, 2/e
By James D Halderman
© 2009 Pearson Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
CHAPTER QUIZ
3. The voltage regulator controls the current
through _____.
a)
b)
c)
d)
The generator brushes
The rotor
The generator field
All of the above
Automotive Electricity and Electronics, 2/e
By James D Halderman
© 2009 Pearson Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
CHAPTER QUIZ
4. Technician A says that two diodes are required for
each stator winding lead. Technician B says that
diodes change alternating current into direct
current. Which technician is correct?
a)
b)
c)
d)
Technician A only
Technician B only
Both Technicians A and B
Neither Technician A nor B
Automotive Electricity and Electronics, 2/e
By James D Halderman
© 2009 Pearson Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
CHAPTER QUIZ
5. The generator output current is produced in
the _____.
a)
b)
c)
d)
Stator
Rotor
Brushes
Diodes (rectifier bridge)
Automotive Electricity and Electronics, 2/e
By James D Halderman
© 2009 Pearson Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
CHAPTER QUIZ
6. Generator brushes are constructed from
_____.
a)
b)
c)
d)
Copper
Aluminum
Carbon
Silver-copper alloy
Automotive Electricity and Electronics, 2/e
By James D Halderman
© 2009 Pearson Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
CHAPTER QUIZ
7. How much current flows through the
generator brushes?
a) All of the generator output flows through the
brushes
b) 25 to 35 A, depending on the vehicle
c) 10 to 15 A
d) 2 to 5 A
Automotive Electricity and Electronics, 2/e
By James D Halderman
© 2009 Pearson Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
CHAPTER QUIZ
8. Computers can be used in charging system
in which way(s)?
a)
b)
c)
d)
Activate the charging system
Monitoring the operation of the charging system
Control the charging system
Any of the above
Automotive Electricity and Electronics, 2/e
By James D Halderman
© 2009 Pearson Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
CHAPTER QUIZ
9. Operating a generator (alternator) in a
vehicle with a defective battery can harm
the _____.
a)
b)
c)
d)
Diodes (rectifier bridge)
Stator
Voltage regulator
Brushes
Automotive Electricity and Electronics, 2/e
By James D Halderman
© 2009 Pearson Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
CHAPTER QUIZ
10. Technician A says that a wye-wound stator
produces more maximum output than the same
generator equipped with a delta wound stator.
Technician B says that a generator equipped with
a delta-wound stator produces more maximum
output than a wye-wound stator. Which technician
is correct?
a)
b)
c)
d)
Technician A only
Technician B only
Both Technicians A and B
Neither Technician A nor B
Automotive Electricity and Electronics, 2/e
By James D Halderman
© 2009 Pearson Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
END
Automotive Electricity and Electronics, 2/e
By James D Halderman
© 2009 Pearson Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458