ELECTRICAL SYSTEM. - TM-55-4920-424-13-P0011

TM 55-4920-424-13&P

console, thermocouple, tachometer generator, air inlet silencer, exhaust duct, speed increaser, and the fire extinguisher.

See figure 1-2 for Table of Leading Particulars.

1-9. ELECTRICAL SYSTEM.

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

instrument panel and relays, within the control console, are connected by cables to the battery. Cable connections from

the console attach to the engine control harness receptacle, to the ac generator output power cable, and to the do starter-

generator for operation of the APU.

1-11. BATTERY. (See figure 1-3.)

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

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. Refer to paragraph 7-45 for battery maintenance procedures.

1-13. CONTROL CONSOLE. (See figure 1-3.)

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. Four engine control harness

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

dc ammeter shunt, circuit breaker, rectifier, transformer, relays, contactor, resistors, voltage regulators, and wire

assemblies necessary to automatically control, regulate, and protect the APU through all phases of operation.

1-15. INSTRUMENT PANEL. (See figure 1-4.)

1-16. The instrument panel, housed in the top of the control console, simulates the aircraft controls. It contains manually-

actuated switches to operate the APU, and gages and lights to indicate conditions of the APU during operation. All

indicator lights and instruments are visible when the instrument panel cover is lifted. The panel is divided into three

groups of controls; ac generator control, turbine control, and dc generator control. The ac generator control group

contains the ac ammeter, voltmeter, frequency meter, LOAD CB OPEN light, LOAD CONTACTOR CLOSED light, AC

GEN FAILED light, VOLTS-AMPS phase selector switch, and the AC GEN ON-OFF-RESET-TEST switch. The turbine

control group contains the tachometer (percent speed indicator), pyrometer (exhaust temperature indicator),

OVERSPEED light, HIGH EXH TEMP light, LOW OIL PRESS light, 90% SEQ CHECK light, DC GEN CONTROLS circuit

breaker, TURBINE CONTROLS circuit breaker, TURBINE CONTROLS RESET switch, and the TURBINE START-ON-

OFF switch. The dc generator control group contains the dc volt-ammeter, OVERVOLTAGE DC light, DC GEN ON light,

and the DC GEN ON-OFF/RESET switch.

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