ARMY TM 9-6115-604-12
NAVY NAVFAC P-8-633-12
Engine run relay K15B will energize to latch in the engine start circuit so that battery positive remains
available after MASTER SWITCH S9 is released from START to RUN. A second set of K15B contacts
closes to apply battery positive to engine fuel solenoid L1. Engine fuel solenoid L1 energizes to open a
fuel line into the fuel block manifold.
DC operating power is applied to synchronizer A105, load sharing panel A104, LUBE OIL PRESSURE
gage M1, LUBE OIL TEMP gage M2, COOLANT TEMP gage M3, FUEL LEVEL gage M4, and TIME
TOTALIZING meter M5.
Engine run relay K15A is energized Its normally closed contacts open to remove 240 V ac power from
generator GI heaters H109 and H110 (K15A contact sets are shown on the AC schematic, FO-2.).
Engine run relay K15C is energized. Its normally closed contacts open to remove 120 V ac power from the
coils of coolant and lube oil heater contactors K104A and K104B (K15C contact sets are shown on the AC
Engine run relay K15D is energized. Its normally closed contacts open to remove battery positive from the
trip coil of load circuit breaker CB101. This action prepares CB101 for arming. Arming of the circuit
breaker is accomplished by synchro-check relay K116. The operation of synchro check relay K116 is
explained in paragraph 4-34.
Battery positive is applied to coolant level warning switch S13 and coolant level shutdown switch S14.
Unless coolant level is low, both switches will be open if not, a warning circuit and possibly a shutdown
circuit will be activated in accordance with step d, below.
Battery positive is applied to OVERCURRENT relay K114. The operation of K114 is explained in
Crank cycle timer relay M7 receives battery positive and begins to operate as described in step c, below.
Engine Cranking. Crank cycle timer relay M7 controls starter motors B1 and B2. The timer will cause the starter
motors to crank for 15 seconds (nominal), then rest for 15 seconds (nominal), for a total of four crank cycles. If
at the end of the fourth cranking cycle the engine has not started, the EXCESSIVE CRANKING fault circuit will
trip, putting the generator set into a fault shutdown condition. The circuit works as follows:
Battery positive is applied to M7 pin 4 when MASTER SWITCH S9 is set to START and released to RUN.
When this occurs, battery positive appears immediately at M7 pin 7, energizing crank relay K3.
Normally open contacts of crank relay K3 close to apply battery positive to the field flashing terminals (F+
and F-) of voltage regulator VR101. Voltage regulator VR101 applies field flashing current to the exciter of
A second set of normally open contacts In crank relay K3 closes to apply battery positive to starter slave
relays K1 and K2. The normally open contacts of starter slave relays K1 and K2 close to apply battery
positive to starter solenoids L3 and L4, respectively.
Starter solenoids L3 and L4 energize and their normally open contacts close to apply battery positive to
starter motors B1 and B2, respectively. The starter motors begin cranking the engine for 10 to 20
seconds. The engine accelerates.
If the engine fails to reach 600 rpm before M7 times out (10 to 20 seconds), battery positive will be cut off
from M7 pin 7, and crank relay K3 will deenergize. The contacts of relay K3 will open, cutting off battery
positive from the voltage regulator field flashing terminals and from starter relays K1 and K2. The contacts
of relays K1 and K2 will open, cutting off battery positive from starter solenoids L3 and L4. Solenoids L3
and L4 will cut off starter motors B1 and B2, ending the cranking cycle. The starter motors will then have
10 to 20 seconds to cool down before M7 pin 7 again delivers battery positive to crank relay K3,
whereupon steps (2), (3), and (4), above, are repeated. Note that if the generator set enters a second,
third, or fourth crank cycle, the operator should use START AID switch S10 to inject ether into the engine
intake manifold. Ether will not be injected, however, if the ambient engine temperature is above 40°F
(4 C) because thermoswitch S17 will be open. If the engine fails to start after four crank cycles, the
generator set will go into a fault shutdown condition.