TM 9-8000
armature, which then decreases the charging current.
current does not flow through the regulator winding. The
When the current decreases to a predetermined amount,
winding on the core consists of a voltage coil of fine wire.
the current coil does not magnetize the core sufficiently
The two ends of the voltage coil are connected across
to overcome the pull of the spring, which then closes the
the generator brushes and in parallel with the battery
contacts. With the contacts closed, the resistance unit is
instead of in series with it. The iron core, regulator
once more short circuited and the full field strength is
points, and resistance unit, however, are practically the
restored, causing the charging current to increase again.
same; the only important exception is that the voltage
The regulator will continue to repeat this cycle. Under
regulator resistance is considerably higher than that used
operating conditions, the armature vibrates rapidly
with the current regulator.
enough to keep the generator output constant. As a
(2) The current flowing in the regulator coil and
result, the generator will never produce more than the
resultant magnetic pull of the core on the contact
predetermined rate (for example, 40 amperes), no
armature depend on the voltage developed by the
matter how high the speed of the car. This will be true
generator. For an example of regulator operation,
regardless of the connected electrical load.
assume that the regulator is adjusted to operate at 12.8
(3) This method of generator regulation is termed
volts. With increasing generator speed, the voltage
current regulation, because the current output of the
tends to rise above 12.8 volts. However, if this value is
generator is used for regulation. It is very important,
exceeded by a small amount, the increased magnetic
therefore, that no breaks occur in the charging circuit
pull of the core on the contact armature due to the
after the generator reaches a voltage that will operate the
current flowing in the voltage coil will overcome the
circuit breaker. If a break does occur, no current will flow
spring tension and pull the armature toward the core.
through the current coil to operate the vibrating points
This action will open the contacts and insert a resistance
and, due to lack of regulation, the generator will build up
in the generator field circuit. This added resistance
an excessive voltage at high speeds. A voltage regulator
decreases the current in the field winding, and the
is used to prevent excessive voltage.
voltage developed by the armature drops below 12.8
(4) The charging rate of the generator can be adjusted
volts.
easily in all electrical systems controlled by a vibrating
regulator. To increase the maximum charging rate, the
(3) When the voltage drops, the pull of the spring on
spring tension on the vibrating armature should be
the regulator armature overcomes the magnetic pull of
increased slightly. To decrease the maximum charging
the core and closes the contacts. This short-circuits the
rate, the spring tension should be decreased. Care must
resistance unit and allows the field current to increase.
be taken that the generator output does not exceed the
The cycle of operation is repeated rapidly, preventing the
value for which it was designed.
generator voltage from rising above that for which the
regulator is set. The regulator on most late-type military
b. Voltage Regulation.
equipment will prevent the generator from building up an
(1) A circuit diagram of a typical vibrating voltage
excessive voltage if a break occurs in the charging
regulator is shown in figure 13-11.
Although the
circuit. But this is not true on standard passenger cars
construction of this relay does not differ materially from
and light-duty equipment. In these, if a break occurs in
that of the current regulator, the principle of operation is
the voltage regulator circuit, regulation of the generator
somewhat different. With this regulator, the voltage
may be lost and at high speeds an excessive charging
output of the generator is used for automatic regulation.
rate will result.
By comparing both circuits, it will be seen that the
(4) It is obvious that increasing the tension of the
principal difference in the two regulators is in the winding
regulator spring will increase the output voltage of the
of the controlling coil and its connections. In the voltage
generator. Under no circumstances should the regulator
regulator, the charging
spring tension be increased in an attempt to have the
generator charge at a higher rate at lower speeds. The
generator cannot begin to charge until the circuit breaker
closes. The closing of the circuit breaker
13-10
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