ARMY TM 9-8115-842-24
AIR FORCE TO 35C2-3-455-12
MARINE CORPS TM 09247A/09248A-24/2
1-12.8 Generator Set Controls.
1-12.8.1 Engine Starting System.
1-12.8.1.1 Engine starting (FIGURE 1-9) is accomplished primarily with two 12-volt batteries, connected in series to
provide 24 VDC power, and a starter. The starter includes a cranking motor and solenoid. To permit engine starting, the
DC CONTROL POWER circuit breaker must be pushed in, the DEAD CRANK switch must be in the NORMAL position
and the BATTLE SHORT switch must be in the OFF position. In addition, any ENGINE SHUTDOWN fault previously regis-
tered on the malfunction indicator panel must have been corrected, and the rnalfunction indicator panel must have been
reset. When the MASTER SWITCH is then placed in the START position, the starting circuits supply 24 VDC power to
the starter. As the engine accelerates to approximately 900 rpm, the starting circuits disconnect power from the starter
and energize the field flash relay. After the needle of the AC voltmeter (VOLTS AC) reaches rated voltage, indicating that
the generator is producing power, the MASTER SWITCH can be moved to one of the two RUN positions for generator
operation.
1-12.8.1.2 When the MASTER SWITCH is first moved to the START position, the various instrument and control circuits
including two starting control circuits are energized. One starting control circuit supplies 24 VDC power directly to the con-
trol function of the crank disconnect switch and also energizes the coil of the crank disconnect relay through closed con-
tacts of BATTLE SHORT switch and crank disconnect switch. The other starting control circuit directly energizes the coil
of the field flash relay and also energizes the cranking relay coil through closed contacts of the engine fault relay and crank
disconnect relay. With the cranking relay energized, power passes from the batteries through closed contacts of the crank-
ing relay to energize the solenoid and the pulling coil of the fuel solenoid. With the solenoid energized, power passes from
the batteries through closed contacts of the solenoid to the cranking motor. The cranking motor then cranks the engine.
As the engine accelerates to approximately 900 rpm, the magnetic pickup, which senses engine speed, causes the crank
disconnect switch to break the circuit to the coil of the crank disconnect relay and close the contacts of the field flash relay.
When the MASTER SWITCH is moved to one of the RUN positions, both starting control circuits are deenergized while
the instrument and other control circuits remain energized. The fuel solenoid holding coil remains energized.
1-12.8.1.3 The engine may be cranked without starting by use of the DEAD CRANK switch. With the DEAD CRANK
switch in the CRANK position, the cranking relay coil is energized to initiate engine cranking without energizing any other
starting or control function.
1–12.8.1.4 The generator set can be started without batteries by connecting an external 24 VDC power source to the
NATO SLAVE RECEPTACLE. The generator set can also supply starting power to another set through the NATO SLAVE
RECEPTACLE.
1-12.8.1.5 The batteries are charged by the battery charging alternator that is belt driven by the engine. Generator set
control system power is also supplied by the battery charging alternator. The BATTERY CHARGE ammeter indicates the
charge rate of the batteries, from -10 to +20 amps. The ammeter is connected to a shunt which provides a DC voltage
signal, which is directly proportional to the battery current flow, to the BATTERY CHARGE ammeter. Normal operating
indication depends on the state of charge in the batteries. A Iow charge which can exist immediately after engine starting,
will cause a high reading (needle moves toward CHARGE area). When the charge in the batteries has been restored,
the indicator moves near zero (0). The battery charging system is protected from a reverse polarity when connecting the
batteries by a fuse and diode.
1–12.8.2 Field Flash. When the engine reaches sufficient speed (900 rpm), the magnetic pickup causes a set of contacts
in the crank disconnect switch to open and deenergize the crank disconnect relay. A set of contacts in the crank disconnect
relay then closes and energizes the Field Flash circuit through closed contacts of the field flash relay (refer to
FIGURE 1-9). This provides current to the AC generator exciter field windings which sets up an electromagnetic field.
The field current is necessary for the set to generate sufficient voltage for the voltage regulator (refer to FIGURE 1-11)
to begin controlling the output voltage of the generator set. The Field Flash circuit is maintained until the MASTER
SWITCH is released from the START position.
1-12.8.3
Ope ration. Placing the MASTER SWITCH in the PRIME& RUN or PRIME RUN AUX positions keeps the fuel
solenoid energized, and fuel will be supplied to the engine as long as no fault condition exists. During operation, the opera-
tor should periodically check the set’s instruments to ensure they are reading in the normal operating ranges. The VOLT-
AGE and FREQUENCY adjust controls are adjusted as required to maintain the desired frequency and voltage output.
1-12.8.4 Applying the Load.
The load is applied by closing the AC CIRCUIT INTERRUPTER switch (refer to -
FIGURE 1-8). This is a momentary contact switch that returns to the neutral, or center position. The AC circuit interrupter
relay is energized by this momentary contact, and a holding circuit keeps it closed, bringing the load on line.
1-18
