THEORY OF OPERATION -- CONTINUED
AUXILIARY POWER UNIT (HATZ)
Voltage Regulator (1) -- voltage regulator receives 28 V dc from the starter/generator (3) and provides
28+0.7 V dc to charge the vehicle batteries. Voltage regulator (1) is equipped with a resettable circuit
breaker. If the circuit breaker opens due to an over voltage condition, the reset button (5) can be pushed
to reset the circuit breaker.
Engine (2) -- burns fuel drawn from the right rear fuel tank. Engine drives starter/generator (3) and auxilia-
ry hydraulic pump (4).
Starter/Generator (3) -- connected to the APU engine (2) by a chain. Chain driven by the APU engine (2),
the 300--amp 28--volt generator functions as the starter motor. Power from the batteries is used to power
the starter/generator when starting the APU. Once the APU is started, the starter/generator generates 28
V dc and delivers it to the voltage regulator (1) to charge vehicle batteries and supply electrical power to
Auxiliary Hydraulic Pump (4) -- supplies hydraulic pressure to run the impact wrench and refuel/defuel
pump under normal operations, or raise/lower the spade or boom, and retrieve cables under no load con-
ditions under emergency operations.