ELECTRICAL SYSTEM. - TM-55-4920-424-13-P0121

TM 55-4920-424-13&P

1-9.

ELECTRICAL SYSTEM.

1-10. The electrical system provides starting power for the APU, and the controls necessary for automatic operat ion. The

instrument panel and relays, within the control console, are connected by cables to the battery, and dc starter-generator

for operation of the APU.

1-11. BATTERY. (See figure E-1.)

1-12. A 24-volt, 34-ampere hour, nickel-cadmium battery, conforming to the requirements of MS24498-1, furnishes do

power for cranking the APU, and control power for the electrical controls. The battery is mounted on the right side of the

trailer, confined in a shallow frame (retainer) and secured to the retainer with studs and clamps. The battery is shipped

with electrolyte, and only a slight freshening charge prior to use is recommended. Bringing the battery up to full charge

can be accomplished during APU checkout operation.

1-13. CONTROL CONSOLE. (See figure E-1.)

1-14. The control console is located on the aft, left side of the trailer, and provides a weatherproof housing for the control

system components and the instrument panel. The check stand control system simulates the aircraft controls. The

console is bolted to two support channels which, in turn, are bolted to the top of the trailer frame. A door on the console

provides easy access to the electrical control system components. The top of the console houses the instrument panel; a

cover, hinged to the console structure, protects the instrument panel from the elements. Two engine control harness

assemblies are connected to the control component. The control system components include a reverse current relay,

engine crank relay, malfunction relay, ready-to-load relay, static voltage regulator, circuit breakers, monitor lights,

switches, DC voltage meter, electronic sequencing unit, OC shunt/resistor, terminal strip, and wire assemblies necessary

to automatically control, regulate, and protect the APU during operation. Space is also provided to install the Electronic

Sequencing Unit (ESU) multi-purpose test set (P/N 161226-200).

E-2 Change 2