Beechcraft C-12C Operator And Technical Reference Manual page 124

TM 1-1510-218-10
or voltage is insufficient to keep it connected to the
power distribution system.
The Ground Power Unit (GPU) shall be
adjusted to regulate at 28-volts maximum
to prevent damage to the aircraft. Do not
turn generators on when GPU is supplying
power.
j. DC External Power Source.
power can be applied to the aircraft through an
external power receptacle on the underside of the right
wing leading edge just outboard of the engine nacelle.
The receptacle is installed inside of the wing structure
and is accessible through a hinged access panel. DC
power is supplied through the dc external plug and
applied directly to the battery bus after passing
through the external power relay. Turn off external
power while connecting the power cable to, or
removing it from, the external power supply receptacle.
The holding coil circuit of the relay is energized by the
external power source when the keylock and BATT /
BATTERY switches are in the ON position. The GPU
shall be adjusted to regulate at 28-volts maximum to
prevent damage to the aircraft battery and electronics.
k. Security Keylock Switch. The aircraft has a
security keylock switch installed on the overhead
control panel, placarded OFF / ON.
connected into the battery relay and external power
circuits, in series with the battery master power switch.
The key cannot be removed from the lock when in the
ON position. The key will not fit the keylocks on other
Army aircraft.
l. Circuit Breakers.
breaker panel contains circuit breakers for most
aircraft systems. The circuit breakers on the panel are
grouped into areas, which are placarded as to the
general function they protect. A dc power distribution
panel is mounted beneath the floor forward of the main
spar. This panel contains higher current rated circuit
breakers and is not accessible to the flight crew under
normal conditions. Refer to Figure 2-16, Sheet 1 for
configuration, Sheet 2 for D1, Sheet 3 for D2, and
sheet 4 for T .
2-84. AC POWER SUPPLY.
a. Description C D1
is supplied by inverter units, numbered #1 and #2,
which obtain operating current from the dc power
system. Refer to Figure 2-29. Both inverters are rated
at 750 VA and provide single-phase output only. Each
inverter provides 115-volt and 26-volt 400 Hz ac
output. The inverters are protected by circuit breakers
2-108
CAUTION
External dc
The switch is
The overhead circuit
. AC power for the aircraft
mounted on the dc power distribution panel mounted
beneath the floor. Aircraft equipment operating from
single-phase ac include the following: autopilot
navigation receivers, the tuning portion of the ADF
receiver, gyro
instruments for fuel flow and torquemeters. Controls
and indicators of the ac power system are located on
the overhead control panel and on the caution/
advisory annunciator panel.
sources using the two inverter select switches located
on the overhead control panel.
AC Power for ANVIS cathode tube lighting
is provided by cathode power packs totally
independent of the #1 and #2 aircraft
inverters.
b. Description
is supplied by inverter units, numbered #1 and #2, that
obtain operating current from the dc power system.
Refer to Figure 2-29, Sheets 2 and 3. Both inverters
are rated at 750 VA and provide single-phase output
only. Each inverter provides 115-volt and 26-volt
400 Hz ac output.
circuit breakers mounted on the dc power distribution
panel mounted beneath the floor. Aircraft equipment
operating from single-phase ac include the following:
autopilot/flight director, the tuning portion of the ADF
receiver, gyro
altimeter, transponder IFF computer, and engine
instruments for fuel flow and torquemeters. Controls
and indicators of the ac power system are located on
the overhead control panel and on the caution/
advisory annunciator panel.
sources using the two inverter select switches located
on the overhead control panel.
c. AC Power Warning Lights.
MASTER CAUTION lights and the illumination of an
annunciator caution light #1 INVERTER or #2
INVERTER, indicate an inverter failure.
d. Inverter Control Switches. Two switches,
placarded INVERTER #1 or #2 on the overhead
C
control panel give the pilot a choice of inverters to
provide single-phase ac power.
involved in this selection.
e. Volt-Frequency Meters
volt-frequency meters are mounted in the overhead
control panel to provide monitoring capability for both
115 Vac buses. Normal display on the meter is shown
in frequency (Hz). To read voltage, press the button
located in the lower left corner of the meter. Normal
output of the inverters will be indicated by 115 Vac and
400 Hz on the meters.
magnetic compass,
The pilot selects ac
NOTE T2
D2 T . AC power for the aircraft
The inverters are protected by
magnetic compass,
The pilot selects AC
Two flashing
Two inverters are
C D
and engine
RMI, pilot's
T1. Two