Introduction; Description; Troubleshooting; Alternator System - Piper SENECA II Service Manual

11-1. INTRODUCTION.

This section contains instructions and schematics for correcting difficulties which may arise in the
operation of the electrical system.
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, see Table XI-I. For information concerning electronic equipment, refer
to Section XII, Electronics.

11-2. DESCRIPTION.

Electrical power is supplied by a 14-volt, direct current, negative ground electrical system. A 12-volt, 35
ampere hour battery is incorporated in the system to furnish power for starting and as a reserve power
source in case of alternator failure; it is located in the nose section of the airplane.
The electrical generating system consists of two engine driven 65 ampere alternators. Two solid state
regulators maintain effective alternator load sharing while regulating the system bus voltage at 14.0-
volts. Also incorporated in the system are overvoltage relays, one for each alternator circuit which
prevents damage to electrical and avionic equipment in case of regulator malfunction. A warning light on
the annunciator panel will illuminate if either alternator fails to produce current, accompanied by a zero
indication on the individual ammeter. The loads from the electrical bus system are protected by manual
reset type circuit breakers mounted on the lower right-hand instrument panel.

11-3. TROUBLESHOOTING.

Troubles peculiar to the electrical system are listed in Table XI-V at the back of this section, along with
their probable causes and suggested remedies. The wiring diagrams included at the end 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 electrical system for security and operation of its
components.

11-4. ALTERNATOR SYSTEM.

The alternators are mounted on the accessory case of each engine. Many advantages both in operation
and maintenance are derived from this system.
The altemators have 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.
The alternator system does not require a reverse current relay because of the high back resistance of the
diodes and the inability of the alternator to draw current or motorize. A current regulator is unnecessary
because the windings have been designed to limit the maximum current available. Therefore the voltage
control is the only control needed.
01/01/09
PIPER SENECA II SERVICE MANUAL
SECTION XI
ELECTRICAL SYSTEM
2F17
XI - ELECTRICAL SYSTEM