C01-01-08 5 Feb 2009 Page 7-11
Section 7
Aircraft & Systems
Model GA8-TC 320 Description
7.15 ELECTRICAL SYSTEM
The GA8-TC 320 has a 12/14 volt electrical system consisting of a 12 volt battery, starter motor,
self regulating alternator with a nominal 14 volt output, starter solenoid, electric fuel boost
pump, volts/amps meter, circuit breakers, stall and fuel warning systems, oil temperature gauge,
navigation, taxi, landing and instrument lights, switches and related wiring. The electrical system
is constructed as a dual bus system. Bus 1 provides power for electrical services such as the
landing lights, COMM 1, GPS and instrument lights. All other services are powered from Bus 2.
The bus that powers each service may be identied by examining the overhead panel. Bus 1
items are enclosed within a white line.
The master switches (mounted on the front left hand side of the overhead electrical panel)
individually connect the two main buses by solenoids. The Bus 1 Master Switch connects to the
battery, while the Bus 2 Master Switch simultan eously connects to both the alternator eld and
the battery. The feeds from the battery to the overhead electrical panel mounted main buses are
protected by 50 amp (Bus 1) and 70 amp (Bus 2) circuit breakers mounted at the battery box.
The master switch solenoids are protected by their own circuit breakers, as are the alternator
feed (100 amps) and alternator eld (10 amps). These circuit breakers along with the stall
warning circuit breaker (1 amp) can be found in the oor in front of the pilot’s seat under a kick
proof cover.
A combined volts/amps meter on the instrument panel provides information regarding the
electrical system. The voltmeter indicates the system voltage for Bus 1 and Bus 2 (each bus is
individually selected using a toggle switch), whilst the ammeter indicates the amount of electrical
energy produced by the alternator. An amber alternator failure caution light will illuminate if the
alternator is not delivering electrical power.
The self-regulating engine driven alternator delivers a regulated nominal 14 volts to the aircraft
electrical system. An over-volt relay is tted that will trip the alternator off line if the output
voltage exceeds approximately 16 volts. This system is designed to protect any avionics or
electrical equipment from damage due to excessive voltage as well as protecting the battery
from over-charge. The over-volt relay can be reset by momentarily turning the Bus 2 Master
Switch OFF, then ON again. If the over-volt relay trips the alternator off line a second time it
can be assumed that a fault denitely exists. The alternator can be taken off line at any time by
turning off the Bus 2 Master Switch, or if battery power is still required on both master circuits, by
pulling the 10-amp alternator eld circuit breaker. In the event that the aircraft battery goes open
circuit, the alternator will continue to function. A circuit incorporating a 47000mF 40V capacitor
will re-energise the alternator automatically whenever the Bus 2 Master Switch is turned OFF
then back ON.
The overhead panel contains circuit breakers (or switch breakers) for all circuits connected
to either bus, except for the stall warning breaker located in the oor. The overhead panel is
marked to show which circuits are on Bus 1 and which are on Bus 2, and is backlit for night
operations.
A ground power receptacle is tted externally on the fuselage skin below the pilots door. This
receptacle is wired with reverse and over voltage protection.
Refer to Figure 7-3 for a simplied schematic of the electrical system.
NOTE:
The master switches are not switch breakers and their circuits are protected by
circuit breakers found in the oor in front of the pilot’s seat.
01 Aug 2011
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