Piper SEMINOLE PA-44-180, Maintenance Manual

Page: 213 / 881

D.C. GENERATION.
ALTERNATOR SYSTEM.
The alternator is located on the front lower right side of the engine and utilizes a belt drive from the engine
crankshaft. 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.
There is one circuit breaker which controls the generating system. This circuit breaker, marked “Alternator
Field”. is for the voltage regulator and alternator field. If this breaker trips, it will result in a complete shutdown
of power from the generating system. After a one or two minute cool down period, the breaker can be reset
manually. If tripping occurs again, this indicates a short in the alternator circuit.
The ammeter does not indicate battery discharge, but displays the load in amperes placed on the generating
system. With all electrical equipment off. except the master switch, the ammeter will indicate the amount of
c h a rging current demanded by the battery. This amount will vary depending on the percent of charge in the
battery at the time. As the battery becomes charged the amount of current displayed on the ammeters will reduce
to approximately two amperes. The amount of current shown on the ammeter will tell immediately whether or
not the alternator system is operating normally, if the following principles are kept in mind.
— Note —
The amount of current shown on the ammeter is the total load, in amperes, that is
demanded by the electrical system from the alternator. As a check, take for example a
condition where the battery is demanding 10 amperes charging current, then switch on
the landing light. Note the value in amperes placarded on the circuit breaker panel for
the landing light circuit breaker (10 amps) and multiply this by 80 percent. You will
arrived at a current of 8 amperes. This is the approximate current drawn by the light.
Therefore, when the light is switched on there will be an increase of current from 10
to 18 amperes displayed on the ammeter. As each unit of electrical equipment is
switched on, the current will add up and the total, including the battery, will appear on
the ammeter.
A simulated load can be made by connecting 8 landing lights wired in parallel from the main bus to air-frame
ground or fourteen 3 ohm, 100 watt resistors. (See Figure 24-1)
PRECAUTIONS.
The following precautions are to be observed when testing or servicing the electrical system.
1. Disconnect the battery before connecting or disconnecting test instruments, except voltmeter, or before
removing or replacing any unit or wiring. Accidental grounding or shorting at the regulator, alternator,
ammeter or accessories, will cause severe damage to the units and/or wiring.
2. The alternator must not be operated on an open circuit with the rotor winding energized.
PA - 4 4 - 1 8 0 / 1 8 0 T
AIRPLANE MAINTENANCE MANUAL
2 4 - 3 1 - 0 1
Page 24-09
Revised: May 15, 1989
1I21
PIPER AIRCRAFT