TM 5-3895-346-14
REGULATOR
ENGINE OVERHAUL
created in the winding causes the voltage contacts to open, thus causing the transistor to shutoff the field
current. The generator voltage then decreases and the voltage contacts reclose. This cycle repeats many
times per second, thereby limiting the generator voltage to the value for which the regulator is set.
The magnetism produced in an accelerator winding, when the voltage contacts are closed, aids the shunt
winding in opening the contacts.
When the contacts are open, the absence of the magnetism in the accelerator winding allows the spring to
immediately reclose the contacts. This action speeds up the vibration of the contacts.
CAUTION
Do not short across or ground any of the terminals on the regulator or the
generator and DO NOT attempt to polarize the generator.
TRANSISTOR REGULATOR
The transistor regulator is composed principally of transistors, diodes, capacitors, and resistors to form a
completely static electrical unit containing no moving parts.
The transistor is an electrical device which limits the generator voltage to a preset value by controlling the
generator field current. The diodes, capacitors, and resistors act together to aid the transistor in performing this
function, which is the only function that the regulator performs in the charging circuit.
The voltage at which the generator operates is determined by the regulator adjustment. Once adjusted, the
generator voltage remains almost constant, since the regulator is unaffected by length of service, changes in
temperature, or changes in generator output and speed.
A separately mounted field relay connects the regulator POS terminal and the generator field windings to the
battery when the engine starting switch is closed.
The voltage regulator illustrated in Fig. 2 is designed for negative ground battery-charging circuits only. It has
two exposed terminals. The voltage setting may be adjusted by relocating a screw in the base of the regulator.
The voltage regulator shown in Fig. 3 has shielded plug-in connections and requires a cable and plug assembly
to connect the regulator into the battery charging circuit. This type of regulator may be used in negative
ground, positive ground, and insulated charging circuits. The voltage setting may be adjusted by removing a
plug in the cover and turning a slotted adjusting button inside the regulator.
Operation
When the engine starting switch is closed, the field relay winding is energized, which causes the relay contacts
to close.
In the negative ground circuit with the field relay contacts closed and the engine not running, generator field
current can be traced from the battery through the relay contacts to the regulator POS terminal. Current then
continues through the back-bias diode (D-1) and power transistor (TR-1) to the regulator FLD terminal, and then
through the generator field winding to ground, completing the circuit back to the battery.
When the generator begins to operate, ac voltages are induced in the stator windings. These voltages are
changed, or rectified, to a dc voltage which appears at the output, or BAT, terminal
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