Alternator Paralleling System; Alternator Test Specifications (Prestolite); Description; Alternator Service Test Specifications - Piper Navajo Chieftain PA-31-350 Service Manual

NAVAJO CHIEFTAIN SERVICE MANUAL
11-4. ALTERNATOR PARALLELING SYSTEM.
11-5. DESCRIPTION OF ALTERNATOR PARALLELING SYSTEM. The positive output terminal of
each alternator is connected to the aircraft electrical bus through separate 90 ampere circuit breaker
switches. Each alternator has a shunt installed between aircraft electrical bus and its positive output
terminal in order to monitor output current on an ammeter.
The field circuit for each alternator is wired through a section of a Dual Master Switch (L or R as
appropriate), an auxiliary switch which is ganged to the circuit breaker switch, an overvoltage relay and a
voltage regulator. Field voltage can be manually disconnected from either alternator by turning off the
appropriate section (L or R) of the Dual Master Switch. Turning both sections of the master switch off
completely disconnects all electric power from the aircraft bus bar. Field voltage will be automatically
removed from an alternator whenever its overvoltage relay actuates or its circuit breaker switch trips.
The system has one ammeter installed to measure system currents. The output current of either
alternator may be checked by pressing the appropriate button "LEFT" or "RIGHT" located above the
ammeter on the overhead switch panel. A shunt is installed between aircraft electrical bus and the positive
terminal of the battery to allow measuring of the battery charge and discharge current with its ammeter.
An alternator inoperative "INOP" warning light is provided for each alternator. The appropriate light
will illuminate whenever its respective alternator fails to provide output voltage.
The 90 ampere circuit breaker switches should not be turned off when their associated alternator is
operating normally. Turning "OFF" one of these switches while it is carrying current could cause a high
voltage transient to occur on the electrical bus with possible subsequent damage to the semiconductor
equipment attached to it.
11-6. ALTERNATOR SERVICE TEST SPECIFICATIONS. Prestolite specifications for the 28 volt
alternators installed as standard equipment on PA-31-350 series airplanes are as follows:
TABLE XI-I. ALTERNATOR TEST SPECIFICATIONS
(PRESTOLITE)
I
Alternator Model
Voltage
Rated Output
Ground Polarity
Rotation
Rotor:
Current Draw (77°F)
Resistance (77°F)
Output Test (77°F)
Volts
Amperes Output
Field Amperes
Alternator RPM
ALU8403 or ALU8421
24 volts
70 amperes
Negative
Bi-Directional
2.0 to 2.2 amps @ 24.0 volts
11.3 to 11.9 ohms
26.3
10.0
2.05
28.4
51.0
2.05
3220 min. 5000 min.
Revised: 10/5/83
ELECTRICAL SYSTEM
3C18