ARMY TM 9-6115-639-13
AIR FORCE TO 35C2-3-386-51
MARINE CORPS TM 10155A-13/1
Section III. PRINCIPLES OF OPERATION
1-15. PRINCIPLES OF OPERATION.
The theory behind the operation of the generator set is described in the following paragraphs. Each system
is dependent upon the other for efficient operation of the generator set. The information contained herein will
assist direct support and general support maintenance personnel in understanding how the generator set
functions. This knowledge will assist in isolating components which have failed.
1-16. ELECTRICAL SYSTEM.
The generator set has two electrical systems, direct current (DC), and alternating current (AC) (Figure FO-
1). The DC system provides generator control circuitry, relay logic, and engine cranking. The AC system
produces voltage for load application. Five test points (on terminal board TB3) provide malfunction isolation
for critical components of the generator set.
1-17. DIRECT CURRENT SYSTEM. (Figure FO-1)
a. The direct current system (Figure FO-1) is powered by a 24 VDC battery (BT1). The battery is
charged by the battery charging regulator (A9) when the engine is running. Engine cranking is initiated by
placing the START / RUN / STOP switch (Sl, located on the control panel) in the START position. This signals
engine start contactor (K2) to actuate the engine start solenoid (L4) and energize the starter motor (Bl).
b. With the START / RUN / STOP switch (Sl) in the START or RUN position, the engine fuel transfer
pump (E2) is energized, allowing fuel to be injected into the engine. Placing the START / RUN / STOP switch
in the RUN position de-energizes the starter motor (Bl). Placing the START / RUN / STOP switch in STOP
position opens the circuit to the engine fuel transfer pump (E2) and the governor control (A5), stopping fuel
flow to the engine. DC voltage is removed from the AC circuit interrupter coil, causing the contactor to open.
c. Pressing the EMERGENCY STOP switch (S19, located on the control panel) opens the AC circuit
interrupter (K1) and disconnects power to the governor control (A5), which causes the generator set to shut
down.
d. The generator set is equipped with an engine preheat system to help in cold-weather operation (below
+20F (-6.6C)). Prior to starting the engine, the preheat mode may be actuated by placing the PREHEAT
switch (S18, located on the control panel) in the ON position. This signals the engine preheat contactor (K13) to
energize air heaters (H1 and H2). The air heater heats intake air which, in turn, assists in igniting fuel when
injected into the engine combustion chamber.
e. Should engine oil temperature exceed normal operating temperature (+265F), a heat sensitive
temperature switch (HT) closes the circuit to energize the fault lockout relay (K12) and shut down the engine.
The ENGINE HIGH TEMP indicator on the malfunction indicator module (A2) will illuminate. The fault
lockout relay (K12) will lockout power to the engine until the FAULT RESET / LAMP TEST button on A2 is
depressed. This safety mechanism prevents the operator from using the generator set until the malfunction has
been corrected.
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