Electrical System Description; Introduction - Piper Navajo Chieftain PA-31-350 Service Manual

NAVAJO CIEFTAIN SERVICE MANUAL
SECTION XI
ELECTRICAL SYSTEM
11-1. INTRODUCTION. This section contains instructions for correcting difficulties which may arise in
the operation of the electrical system throughout the airplane. It includes a general description and
function of each part of the system along with test and adjustments of the various components. This does
not include any electronics installation such as AutoPilot or radios. For electronics information, refer to
Section XII of this manual.
11-2. DESCRIPTION. Electrical power is supplied by a 28 volt direct current, single wire, negative ground
electrical system. The system incorporates one 24 volt battery to furnish power for starting and as a reserve
power source in case of alternator failure. An external power receptacle is also provided in the nose of the
airplane for the use of external power during cold weather operation and when operating equipment for
test purposes.
The electrical generating system consists of the alternator paralleling system. This system incorporates
two engine driven alternators, however, the field voltage of each unit is controlled independently by its own
voltage regulator. These regulators are interconnected electronically so as to provide paralleled outputs
from their associated alternators under normal operating engine RPM ranges. The system incorporates
separate overvoltage relays. The overvoltage relay will open and remove field voltage to the unregulated
alternator in the event of a failure of the voltage regulator.
Electrical switches are located in a panel on the left side of the cockpit next to the pilot's knee, in an
overhead panel just above the windshield and in a panel along the lower section of the instrument panel. A
fuse block is located on the forward left side of bulkhead 57.00 for the alternator circuits. This airplane is
equipped with the following lighting circuits:
a. Position lights controlled by a single switch and thermal circuit breaker located in the left side
panel.
b. Two rotating beacons, (Serial Nos. 31-7305001 to 31-7305052), one mounted on the fin tip and one
mounted on the bottom of the fuselage, controlled by a single switch and thermal circuit breaker located in the
left side panel. Three strobe lights are incorporated on aircraft with Serial Nos. 31-7305053 and up. There is
one strobe light on each of the wing tips and one on the tail. As optional equipment, a ground recognition
beacon (Serial Nos. 31-7952001 and up) is located in the fin tip and inflight recognition lights (Serial Nos.
31-7852001 and up) are located in the wing tips. These circuits are controlled by switches located in the over-
head panel and a single circuit breaker located in the left side panel.
c.
Two 250 watt landing lights, mounted on the nose gear, are controlled by two separate switches
located in the left side panel. The switch placarded "Landing" activates both lamps and the switch
placarded 'Taxi" activates only one lamp. The lights are controlled by a solenoid located on the nose gear
and will not operate until the nose gear is down and locked. As optional equipment, one 50 watt wing
inspection light is located in the left engine nacelle aft of the firewall and is controlled by a switch located
in the left side panel. A single circuit breaker protects all these circuits.
d. Instrument panel lighting is accomplished through the use of lights located in various positions
adjacent to individual instruments in the panel and overhead. For aircraft with Serial Nos. 31-7305001 to
31-7952250 there are up to three rheostats in this circuit to give better area control. The main rheostat for the
pilot's flight panel (all instruments, placards and dials necessary for the pilot's flight operation) is located in the
left side panel. Another rheostat is located in the overhead switch panel to the pilot's left, for control of lighting
in that area. Still another rheostat (optional with dual instrumentation) is located on the right side of the in-
strument panel for control of lighting for the dual instruments. A single circuit breaker protects the aforemen-
tioned. A fourth rheostat is located in the radio junction box for controlling lighting of all radio equipment and
Reissued: 9/23/80
ELECTRICAL SYSTEM
3C13