Download Heavy-Duty Truck Sytems Chapter 08

Chapter 8
Charging Systems
Objectives (1 of 2)
• Identify charging circuit components.
• Navigate a charging circuit schematic.
• Voltage drop-test charging circuit wiring and
components.
• Describe the construction of an alternator.
• Explain full-wave rectification.
Objectives (2 of 2)
•
•
•
•
Full-field an alternator.
Measure AC leakage in the charging circuit.
Verify the performance of an alternator.
Use Intelli-check to assess charging circuit
performance.
• Disassemble and reassemble a Delcotron
40SI alternator.
Charging Systems
Alternator Construction (1 of 2)
Alternator Construction (2 of 2)
• To generate electricity, the alternator uses this basic
law of physics:
– When magnetic lines of force move across a
conductor (such as a wire or bundle of wires), an
electrical current is produced in the conductor.
• Actual current flow induced depends on several
factors:
– The strength of the magnetic field
– The speed of the wire passing through the field
– The size and number of wires
Rotor
• The rotor is the only moving component within the
alternator.
• It is responsible for producing the rotating magnetic
field.
• The rotor consists of a coil, two pole pieces, and a
shaft.
• The magnetic field is produced when current flows
through the coil; this coil is simply a series of
windings wrapped around an iron core.
• Increasing or decreasing the current flow through the
coil varies the strength of the magnetic field, which in
turn defines alternator output.
Slip Rings and Brushes
• The wiring of the rotor coil is connected to
slip rings.
• The slip rings and brushes conduct current to
the rotor.
• Most alternators have two slip rings mounted
directly on the rotor shaft; they are insulated
from the shaft and from each other.
– A spring-loaded carbon brush is located on
each slip ring to carry the current to and from
the rotor windings.
Stator
• The stator is made up of many conductors, or wires,
into which the spinning rotor induces voltage.
• The wires are wound into slots in the alternator
frame, with each wire forming several coils spaced
evenly around the frame.
• The wires are grouped into three separate bundles,
or windings.
• The coils of the three windings are staggered in the
alternator frame so that the electrical pulses created
in each coil will also be staggered.
• This produces an even flow of current out of the
alternator.
Alternator Operation
Voltage Regulators
• Microprocessors and electronic sensors and
switches are easily damaged by voltage spikes and
high voltage levels.
• The voltage regulator receives battery voltage as an
input.
– This is called the sensing voltage; it allows the
regulator to sense and monitor the battery voltage
level.
– When the battery voltage rises to a particular level
(approximately 13.5 volts), the regulator will turn the
field current off.
Types of Field Circuits
• The field circuit, which is controlled by the voltage
regulator, might be one of two types.
– “A” circuit
– “B” circuit
• With an “A” circuit, the regulator is on the ground
side of the rotor. The regulator turns the field circuit
off and on by controlling a ground.
• With a “B” type, voltage regulator is positioned on the
feed side of the alternator. Battery voltage is fed
through the regulator to the field circuit, which is then
grounded in the alternator.
Charging System Failures and Testing
• A malfunction in the charging system results
in either:
– An overcharged battery
– An undercharged battery
Overcharging
• An overcharged battery will produce water
loss, eventually resulting in hardened plates
and the inability to accept a charge.
• Overcharging can be caused by one or a
combination of the following:
– Defective battery
– Defective or improperly adjusted regulator
– Poor sensing lead contact to the regulator or
rectifier assembly
Undercharging (1 of 2)
• An undercharged battery will result in slow
cranking speeds and a low specific gravity of
the electrolyte.
– A loose drive belt
– Loose, broken, corroded, or dirty terminals on
either the battery or alternator
– Undersized wiring between the alternator and
the battery
– Defective battery that will not accept a charge
Undercharging (2 of 2)
• Undercharging can also be caused by one or a combination of the
following defects in the alternator field circuit:
– Poor contacts between the regulator and brushes
– Defective diode trio
– No residual magnetism in the rotor/shorted, open, or grounded
rotor coil
– Defective or improperly adjusted regulator
– Damaged or worn brushes/damaged or worn slip rings
– Poor connection between the slip rings and field coils
• Undercharging can also be the result of a malfunction in the
generating circuits:
– One or more of the stator windings (phases) can be shorted,
open, or grounded.
– The rectifier assembly might be grounded.
– One or more of the diodes might be shorted or open.
Charging System Testing
• The battery must be at least 75 percent charged
before the alternator will perform to specifications.
• The output of the alternator is first tested.
• If the output is below specifications, the voltage
regulator is bypassed and battery current is wired
directly to the field circuit of the rotor.
• This is called full-fielding the rotor.
– If this corrects the problem, the fault is in the
regulator.
– If the output remains low with the regulator bypassed
by full-fielding, the alternator might be defective.
Full-field Testing
the Alternator (1 of 2)
• By applying full battery voltage directly to the
field windings in the rotor, it can be
determined whether or not the regulator is
the cause of the undercharging condition.
• There are two variations of this procedure
that apply to alternators with external
regulators.
Caution
• When testing the output of a full-fielded alternator,
carefully observe the rise in system voltage.
• Because the current output is not regulated, battery
voltage can quickly rise to an excessive level, high
enough to overheat the batteries, causing electrolyte
to spew from the vent holes, and possibly damage
sensitive electronic components.
• Do not allow system voltage to rise above 15V.
Shop Talk
• Some alternators with remote-mounted electronic
regulators are connected to the regulators by a
wiring harness and a multi-pin connector.
• Full-fielding the field circuit is accomplished by
removing the connector from the regulator and
connecting a jumper wire between two pins
(terminals) in the harness connector (consult OEM
service literature to correctly identify the pin
assignments). Doing so bypasses the regulator,
sending battery current directly to the field circuit.
Caution
• Never full-field an alternator without applying
an electrical load to the batteries.
• Whenever the voltage regulator is bypassed,
there is nothing to control peak alternator
output; this can cause voltage spikes that can
damage both electrical and electronic
components.
Full-field Testing
the Alternator (2 of 2)
• If the field circuit is grounded through the
regulator (an A circuit), the regulator is
disconnected from the field terminal on the
alternator and a jumper is connected
between the terminal and a ground.
• If the alternator receives battery voltage
through the regulator (a B circuit), the
regulator is disconnected from the field (F)
terminal and a jumper is connected to the
terminal and to the insulated battery terminal.
Full-fielding Internally
Regulated Alternators
• Full-field testing is not possible on some
alternators with internal voltage regulators.
• To isolate and test the regulator on these
types of alternators, the alternator must be
removed from the truck and disassembled.
• Other internally regulated alternators have a
hole through which the field circuit can be
tested.
AC Leakage Test
• Over time, the diode bridge can start to “leak”
AC current to ground.
• Typically AC leakage should not exceed 0.3
volts AC.
• Use a DMM set to the AC voltage scale.
• Place one test lead on the alternator
insulated terminal and connect the other lead
to chassis ground.
Intelli-Check™
• Intelli-check™ should first be plugged into the twoway connector attached to the alternator output and
ground terminal.
• Next, the engine should be started and run with no
chassis electrical loads turned on.
• Rev up the engine once to high idle.
• Then turn on the lights and the heater blower to high,
and once again rev up the engine again to high idle.
• This completes the test, and the charging circuit
condition will be displayed by illuminating one of five
LEDs.
Scope Testing (1 of 2)
• Oscilloscopes can be used to diagnose
alternator conditions.
• The scope used may be either a full-sized
oscilloscope or a good-quality, hand-held lab
scope.
• Use the scope manufacturer’s instructions to
make the connections.
Scope Testing (2 of 2)
Caution
• Truck alternators are not provided with
reverse-polarity protection.
– Reverse-polarity connections such as those
caused by jump-starting can destroy alternator
diodes and numerous other chassis solidstate devices.
Shop Talk
• Alternators that energize the field circuit with current
produced by the stator windings rely on residual
magnetism in the rotor to initially energize the stator
when the engine is being started.
• During handling or repair, this residual magnetism
can be lost.
– It must be restored before testing the system. This is
done by connecting a jumper wire between the diode
trio terminal and the alternator output terminal as
shown in the following figure.
Summary (1 of 4)
• A truck charging system consists of batteries,
alternator, voltage regulator, associated wiring, and
the electrical loads of the chassis.
• The purpose of the charging system is to recharge
the batteries whenever necessary and to provide the
current required to power the electrical components
on the truck chassis.
• A malfunction in the charging system results in either
undercharged or overcharged batteries.
• The subcomponents of an alternator consist of stator,
rotor, slip rings, brushes, and rectifier.
Summary (2 of 4)
• A magnetic field is established in the rotor windings,
and this is used to induce current flow in a stationary
stator.
• Slip rings are used to conduct current to the rotor to
establish a magnetic field.
• Because the brushes in slip rings conduct very low
current to the rotor windings, they significantly outlast
the brushes used in now-obsolete generators.
• The alternator rectifier is located in the end frame
assembly.
Summary (3 of 4)
• Most current truck alternators use a delta
configuration of diodes in the rectifier to achieve full
wave rectification.
• Current truck alternators use solid-state, electronic
voltage regulators.
• TR-type alternators use electronic switching in
12/24V systems, eliminating the need for
electromechanical series-parallel switches.
• When the voltage regulator is shorted out of the
circuit, the alternator is full-fielded and will produce
maximum output.
Summary (4 of 4)
• The sensing voltage of the charging system should
be battery voltage at any given moment of operation.
• AC leakage testing can verify the performance of the
diodes in the rectifier and help predict imminent
alternator failures.
• Scope testing can graphically identify rectifier solidstate component failures.
• Delco-Remy’s Intelli-check™ tool enables
technicians to make a rapid test of charging system
performance.