SECTION XI
ELECTRICAL SYSTEM
11-1. INTRODUCTION. This section contains instructions and schematics for correcting difficulties which may
arise in the operation of the electrical system in the aircraft.
The instructions are organized so the mechanic can refer to: Description and Principles of Operation for a
basic understanding of the various electrical systems; Troubleshooting for a methodical approach in locating the
difficulty; Corrective Maintenance for removal, repair and installation of components; and adjustments and tests
for operation of the repaired system.
Schematics for the individual systems are located at the end of this section. For information concerning
electronic equipment, refer to Section Xll, Electronics.
11-2. DESCRIPTION Electrical power is supplied by a 14-volt. direct current. negative ground electrical system.
A 12-volt battery is incorporated into the system to furnish power for starting and as a reserve power source in
case of alternator failure. The battery is located forward of the firewall on the right side of the airplane. Access
to the battery is gained by releasing the cowl fasteners and lifting up the engine cowl
The electrical generating system consists of an engine driven 60 ampere alternator. A solid state voltage
regulator maintains the system bus voltage at 14 volts. Also incorporated is an over voltage relay,which prevents
damage to electrical and avionic equipment in case of regulator malfunction. The loads from the electrical bus
system are protected by manual reset type circuit breakers mounted on the lower right hand side of the instrument
panel.
The master switch must be on before any electrical equipment will operate. The master switch controls the
battery relay and field circuit. The switch is a double pole single throw type.
The lighting system for night time operation is optional equipment and consists of a landing light, anti-
collision lights and navigation lights.
11-3. TROUBLESHOOTING. Troubles peculiar to the electrical system are listed in Table XI-VI at the back of
this section along with their probable causes and suggested remedies. The wiring diagrams included in the back
of this section will give a physical breakdown of the different electrical circuits used in this airplane.
After the trouble has been corrected, check the entire system for security and operation of its components.
11-4. ALTERNATOR SYSTEM. The alternator is located on the front lower right side of the engine and utilizes
a belt drive from the engine crankshaft. Many advantages both in operation and maintenance are derived from
this system. The main advantage is that full electrical power output is available regardless of engine RPM.
The alternator has no armature or commutator and only a small pair of carbon brushes, which make contact
with a pair of copper slip rings. The rotating member of the alternator, known as the rotor, is actually the field
windings. The rotor draws only 1/20th of the current output. Therefore, there is very little friction and negligible
wear and heat in this area. The alternating current is converted to direct current by diodes pressed into the end
bell housing of the alternator. The diodes are highly reliable solid state devices, but are easily damaged if current
flow is reversed through them.
PIPER AIRCRAFT
PA-28-161 CADET
AIRPLANE MAINTENANCE MANUAL
Issued: FEBRUARY. 28, 1989
ELECTRICAL SYSTEM
2C20