ARMY TM 9-6115-670-14&P
1-6
1.13.
LOCATION AND DESCRIPTION OF MAJOR COMPONENTS.
1.13.1. Engine (1, Figure 1-1). The APU power source is a three cylinder, four cycle, turbo charged, fuel
injected, liquid cooled diesel engine. The engine's electrical system contains a starter and a battery charging
alternator with integral rectifier and voltage regulator. The APU control and starting voltage of 28 volts is
provided from the host vehicle battery and from a 20 ampere DC alternator when the engine is running. The
engine is also equipped with a fuel filter, oil filter, and an air filter. Coolant is circulated through the engine by
a water pump. Safety devices automatically stop the engine during conditions of high coolant temperature,
low oil pressure, low fuel, over-speed, or over-voltage.
1.13.2. Generator (2). The AC generator is a single bearing, drip-proof, synchronous, brushless, single
phase, fan-cooled generator. Rated voltage is maintained by excitation of the generator-excitation field by a
static exciter. The fan, located at the front of the generator, impels air which enters the generator and passes
over the windings. Safety devices are provided to protect the generator in the event of overload and over-
voltage.
1.13.3. Governing System (3). The APU governor system senses speed and load electrically and provides
the controls and load responses necessary to maintain the APU frequency requirements for efficient APU
operation.
1.13.4. Lubrication System (4). The APU engine has a lubrication system which consists of an oil pump, oil
filter, oil strainer, relief valve, oil pressure switch, and oil lines necessary to provide adequate oil circulation for
all APU operating conditions. This engine can be operated up to 100 hours between oil changes. An oil
pressure transducer sends a signal to the APU control panel, where a corresponding status light provides the
operator with a warning indication when adequate oil pressure is lost. Lack of adequate oil pressure will cause
the engine to shut down, unless the APU is operating in the BATTLE SHORT ON mode.
1.13.5. Fuel System (5). The APU engine operates on diesel fuels DF-1, DF-2, and DF-A (when operating
in an arctic climate). The APU is equipped with a small fuel reservoir having two fuel sensors. Sensor one
senses the need for more fuel and, when required, energizes the fuel transfer pump. Sensor two senses that
a critical low fuel level has occurred, and sends a signal to the control panel which energizes a status light
and shuts down the engine prior to complete fuel starvation, preventing the need to prime the fuel system.
1.13.6. Cooling System (6). The APU is equipped with a pressurized liquid cooling system consisting of a
radiator, centrifugal water pump, suction fan, thermostat, temperature sensor (high coolant temperature),
coolant drains, and a filler cap. Coolant circulation is controlled by the thermostat (which operates at a coolant
temperature of approximately 180°F (82.2°C) to maintain safe engine operating temperatures. The
temperature sensor monitors the coolant temperature and sends a signal to the coolant temperature indicator
on the control panel. When the coolant temperature reaches a level at which the engine will over heat 230°F
(110°C), a signal is sent to shut down the APU before engine damage can occur. As with the low oil pressure
condition, the APU will not shut down at the high coolant condition when operating in the BATTLE SHORT
ON mode.
1.13.7. APU Control Unit (7). The APU controller contains instrumentation and controls for operating the
engine and the generator. The control panel is grounded to protect the operator from electrical shock in the
event of a short in the electrical system. The APU controller contains meters for monitoring APU output, an
adjustment for increasing and decreasing voltage, a circuit breaker switch for interrupting output from the
APU, and switches for preheating, starting, and stopping the APU. An ammeter is also provided for monitoring
the 20 AMP DC alternator.
1.13.8. Wiring Harness Control Cable (8). A wiring harness control cable is provided with the APU to
connect the APU to the control panel. This cable contains 25 leads with a 25-pin connector at each end. As
installed in SICPS shelters, the APU and the APU controller are not directly connected. One end of the control
cable is plugged into a receptacle on the rear of the APU. The other end of the control cable is connected to
the shelter power distribution vault where the signals are passed through EMI filters. The APU controller,
which is panel mounted inside the shelter, is connected to the power distribution box by internal SICPS
cabling. In JTACS shelters, the control cable connects the APU to a bulkhead connector next to the power
entrance box. A second cable (interconnect harness) connects the bulkhead connector to the control unit (9).
