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The alternator produces the electricity needed to charge the battery
and to operate electrical equipment. Its output, however, continues
to rise as its speed increases, so the charging system must be
provided with a voltage regulator.
Voltage regulators are in their third phase of development. First,
there were electromagnetic voltage regulators, which were used in
both dc and alternator charging systems. Then came electronic voltage
regulators, which are still used in most late model applications.
They are solid state devices, which did away with wire-wound coils,
contact points, and bimetallic hinges. They appear to be more
reliable, durable, and less affected by temperature change. Now, in
some cars, the voltage regulator function has become part of the
engine computer control system.
Regardless of the kind, the voltage regulator controls voltage and
current output of the alternator by automatically cutting resistance
in or out of the field circuit to keep it in a safe value. Varying
the resistance alters the amount of current passing through the
field. When the battery becomes fully charged, the resistance is cut
into the field circuit and the charging rate is decreased.
Electromagnetic regulators, which are used on many dc generator
charging systems, consist of three elements: cutout relay, current
regulator, and voltage regulator. Others may use a cutout relay and a
step-voltage control unit or a cutout relay with a vibrating voltage
regulator or a combination of the cutout relay with a current-voltage
unit.
In electromagnetic regulators, the voltage regulator unit limits
voltage output by controlling the amount of current applied to the
rotating field. The field relay on these regulators connects the
alternator field windings and voltage regulator windings directly to
the battery. The conventional cutout relay unit has been eliminated
by the diodes in the alternator. The current regulator has also been
eliminated by the current-limiting characteristic of the alternator
design.
Basically, in a transistorized or an electronic regulator, the
transistor is switched on and off to control the alternator field
current. The frequency of switching depends on the alternator speed
and accessory load, with the possibility that the on-off cycle may be
repeated as often as 7000 times per second. The transistorized units
have a voltage limiter adjustment. The electronic units are factory
calibrated and sealed. They are also nonadjustable. When the ignition
switch is turned off, the solid state relay circuit turns off the
output stage, and turns off all current flow through the regulator.
With that, there is no current drain on the battery. The field
current overprotection stage protects the regulator against damage
that could be caused by a "short" in the field circuit.
Voltage regulator units have been replaced by functions with two
engine computer modules on some late model Chrysler Corporation
applications. The regulator functions are shared by circuits in the
power and logic modules in the engine spark control computer. It is
claimed that this prevents the possibility of "blowing" computer
circuits if a charging system terminal is accidentally grounded. In
operation, the field is turned on by a driver in the power module.
The logic module also checks battery temperature as a means of
determining and controlling alternator output voltage to control the
amount of current allowed to pass through the alternator field
windings.
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