Piper PA-24 Comanche, Service Manual

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PIPER SENECA SERVICE MANUAL
04/01/09 IX - ELECTRICAL SYSTEM
3A11
SECTION IX
ELECTRICAL SYSTEM
9-1.
General.
9-2. Electrical power for the Comanche is supplied by a 12-volt, direct current, single wire, negative ground
electrical system. A 12-volt battery is incorporated in the system to furnish power for starting and a
reserve power source in case of generator or alternator failure. An external power receptacle can be
provided as optional equipment in the fuselage to permit the use of an external power source for cold
weather starting. On the PA-24-180 and PA-24-250 models, a 35-ampere or 50-ampere generator is
installed. With the generator is a regulator assembly, composing of a voltage regulator, and current
regulator to prevent over-loading of the battery and electrical circuits. Also, with the regulator is a
reverse current cutout to prevent the generator from being motorized, by the battery, when the generator
output drops below the battery voltage. On the PA-24-260 and PA-24-400 models, a 70-ampere
alternator is installed. It is controlled by a voltage regulator within the field circuit to control field
voltage. Also, in the field circuit is a 5-ampere thermal circuit breaker, master switch, radio noise filter
and an over-voltage regulator. The output circuit consists of a radio noise filter and a 90-ampere magnet
circuit breaker ganged to the 5-ampere circuit breaker in the field circuit. The generator or alternator is
located on the front lower right side of the engine and utilizes a belt drive from the engine crankshaft.
The generator voltage regulator is located on the engine firewall and the alternator voltage regulator and
relay is located within the aft section of the fuselage. Electrical switches are located on the left lower
side of the instrument panel. Circuit breakers for the individual circuits are mounted in a cluster below
the left side of the instrument panel.
CAUTION: THE ALTERNATOR CIRCUIT BREAKER SHOULD NOT BE OPENED UNDER ANY
CIRCUMSTANCES. OTHER THAN AN EMERGENCY, WHILE THE ENGINE IS
RUNNING. STANDARD LIGHTING ON THE COMANCHE ARE NAVIGATION
LIGHTS. LANDING LIGHTS. ONE ON THE OUTBOARD LEADING EDGE OF EACH
WING. COCKPIT LIGHT AND INSTRUMENT SPOT LIGHTING. AS OPTIONAL
EQUIPMENT. A ROTATING BEACON IS MOUNTED ON TOP OF THE FUSELAGE
AND INDIVIDUAL INSTRUMENT LIGHTS.
9-3.
Generator System.
9-4
General.
The generator supplied with the Comanche is of the two brush, shunt type and is controlled by a
regulator operating on the principal of inserting resistance into the generator field circuit to cause a
reduction of generator voltage and current output. The best assurance of obtaining maximum service
from the generator with minimum trouble is to follow a regular inspection and maintenance procedure.