Piper Navajo PA-31 Service Manual page 694

PIPER NAVAJO 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. One 24-volt battery is incorporated in the system 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 operating equipment for test purposes.
The electrical generating system consists of two engine driven alternators. They are
paralleled by the use of a voltage regulator to control field voltage of both units. Also
incorporated in the system is an overvoltage relay. Its function is to open and remove field
voltage to the unregulated alternators in the event of a failure of the voltage regulator. An
auxiliary voltage regulator and overvoltage relay is also furnished.
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 forward left side of bulkhead
81.00 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. 31-1 to 31-730096 1), 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. On Serial Nos. 31-649 to 31-7300961, white wing tip
strobes or red fuselage bottom and fin tip strobes may be used. These circuits are controlled by
a switch and circuit breaker located in the left side panel. Three strobe lights are incorporated
on aircraft with Serial Nos. 31-7300962 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.
31-7812001 and up) is located in the fin tip and inflight recognition lights (Serial Nos.
31-7812001 and up) are located in the wing tips. These circuits are controlled by switches
located in the overhead panel and circuit breakers located in the left side panel.
c. Two 250-watt landing lights, mounted on the nose gear, 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.
Reissued: 10/12/79
ELECTRICAL SYSTEM
4A16