ARMY TM 9-6115-673-13&P
AIR FORCE TO 35C2-3-512-1
1.20.
DIESEL ENGINE ELECTRICAL STARTING SYSTEM.
1.20.1 Electrical Starting. The diesel engine electrical starting system (Figure 1-6) can be used to start the diesel
engine whenever there is an external 24 VDC power source connected to the NATO slave receptacle. The electrical
starting system will be required when starting the diesel engine in extremely cold weather or as a backup to the manual
starting system (recoil mechanism failure). The electrical system also provides a means for warming diesel engine
intake air which also helps to start the engine in cold weather. The system consists of a NATO slave receptacle (SR1),
START-PREHEAT/PREHEAT/OFF/START switch (S2), diode (CR1), an engine-mounted starter motor (B1) with
solenoid (L5), and two resistance heater elements (HTR1 and HTR2).
1.20.2 When connected to a 24 VDC power source via a power cable, the NATO slave receptacle (SR1) provides
power to the START-PREHEAT/PREHEAT/OFF/START switch (S2) at pin B and to the starter solenoid (L5) at pin S.
When the operator places switch (S2) in the START position, power is applied through the switch at pin S to the starter
solenoid (L5) pin C. This energizes the coil in solenoid (L5) which pulls in the solenoid's plunger and pushes the
starter drive pinion attached to the plunger toward the engine flywheel. This movement engages the starter pinion
drive with the ring gear teeth on the diesel engine flywheel. As the solenoid plunger pulls in, the power available at
solenoid pin S is applied via a jumper to the starter motor (B1) which rotates the starter pinion drive (part of the starter
motor) and turns over the flywheel engaged with the pinion drive to start the diesel engine. Immediately after the diesel
engine starts, the generator set operator releases the START-PREHEAT/PREHEAT/OFF/START switch (S2). This
opens the solenoid-starter circuit causing the solenoid plunger to release the starter pinion drive disengaging it from the
engine flywheel ring gear. At the same time, the starter motor (B1) is de-energized. The starter pinion will return to its
normal position as the starter motor (B1) slows to a stop.
Diode (CR1) protects the diesel engine electrical starting circuit. It prevents any inductive surges in the grounded side
of the circuit from damaging the contacts of START-PREHEAT/PREHEAT/OFF/ START switch (S2) and the starter
solenoid (L5).
1.20.3 Preheat Circuit. The diesel engine features two 12-VDC resistance-type heaters (HTR1 and HTR2) wired in
series and located in the engine air intake piping between the intake manifold and the air cleaner. The heaters warm
the air intake piping and manifold in order to warm up the intake air during attempted cold weather starts.
1.20.4 With an external power cable connected to the NATO slave receptacle and the START-
PREHEAT/PREHEAT/OFF/START switch (S2) in the PREHEAT position, power exiting switch S2 at pin H energizes
the two resistance-type heaters (HTR1 and HTR2). Normally, the heaters are allowed to remain energized for several
minutes to warm up the air intake piping and manifold in preparation for starting the engine. The heaters are then de-
energized just prior to the engine startup sequence. However, during periods of extreme cold, it may be necessary to
leave heaters HTR1 and HTR2 on during the start sequence. This is accomplished by placing switch S2 in the
PREHEAT-START position so that heaters HTR1 and HTR2 remain energized during the engine startup sequence.
