External (Ground) Power Unit

CHAPTER NINE

T-34C AIRCRAFT SYSTEMS FAMILIARIZATION

CHANGE 3

WORKBOOK

Generator Control Panel

Monitoring and control of the generator is provided through the generator control panel. It

operates automatically to regulate the generator output voltage 27.0 to 29.5 volts, to provide

reverse current protection in the event of generator failure (output below 25-VDC), and provide

overvoltage protection should the regulator portion of the panel fail and generator output

increase to 34 volts. The voltage regulator is adjusted to provide a normal output of 28 volts.

Should a reverse current or overvoltage situation occur, a flashing MASTER CAUTION light

and the GENERATOR fault light illuminating will notify the pilot. The light will illuminate

when system voltage is below approximately 27.5 to 25-VDC. Depending on the setting of the

low voltage sensor, illumination of the generator light may indicate only low voltage output.

External (Ground) Power Unit

The external power unit is used to conserve the battery during maintenance functions and engine

start. A cable from the external power unit plugs into the aircraft on the right side of the fuselage

forward of the wing. For the aircraft to accept ground power, the battery switch must be ON and

battery voltage 18 volts or above. With external power applied, the GENERATOR fault light

will go out. If an external power unit is used to start the engine, the generator will not

automatically start operating when external power is disconnected, and the generator switch must

be pushed to the ON position to bring the generator into operation.

Volt/Ammeter

A volt/ammeter, located on the right side of the instrument panel in each cockpit, is a dual

indicator. The left side is the voltmeter, which indicates the highest voltage present on the DC

buses. The voltmeter scale reads 0 to 30 volts in two-volt increments. The right side is the

ammeter, which indicates the rate of current flow to and from the battery. The ammeter scale

reads battery amperes in a range of +60 to 0 to -60. With the pointer in the plus range the battery

is charging. In the minus range the battery is discharging, with one exception: With the external

power unit connected, a discharge is indicated even though the battery is being charged. This is

due to a design characteristic of the system.

Utility Bus Switches

Utility bus switches are located on the top row of the front cockpit circuit breaker panel. They

permit quick removal of nonessential loads from the DC power source by deenergizing utility

bus no. 1 and utility bus no. 2.

905.

AC POWER SYSTEM

The AC power system provides alternating current to various indicating systems. The source of

AC power is the inverters.

9-6 ELECTRICAL POWER SYSTEMS