Preparation For Testing - Piper Navajo PA-31 Service Manual

PIPER NAVAJO SERVICE MANUAL
b. When a difference in individual field voltages occurs, one-half the difference is
impressed across R12 within each regulator and is thus applied to the input of Q5.
c. In that regulator which is delivering the lower field voltage, the polarity of R12
voltage drop causes Q5 collector current flow.
d. Q5 collector current flow results in conduction occurring in the collector circuit of
Q6.
e. Q6 collector current flows from regulator divider R1/R2+R3 through limiting
resistor R 17 to ground.
f. Conduction through R17 effectively alters the ratio of the regulator divider
R1/R2+R3 in the direction to increase Q1 collector current flow.
g. As described above under REGULATING CIRCUIT OPERATION, increased Q1
current results in increased output from the regulator to the field of its related alternator.
h. Feedback action results in Q6 collector current stabilizing at a value that results in
nearly equal field voltage being delivered by the two regulators to their respective alternator
fields.
i. The balancing circuit will thus automatically maintain, at a low value, the difference
voltage applied to the alternator fields. In a parallel system having identical alternators
operating at the same RPM, the output currents of the alternators will thus be maintained
nearly equal.
j. In whichever regulator of a pair is set to deliver the highest voltage, the balancing
circuits are inactive. Thus system voltage is determined by the regulator of a pair which is
set to higher voltage. The lower set regulator will adjust itself automatically, as described
above, to deliver the same field voltage as the one which is set higher, within the limits of its
design capability.
k. The balancing regulator system as described provides for automatic load balancing of
parallel operated alternators having independent field excitation circuits. The pilot can,
while in flight, remove either alternator system completely from the aircraft system and
maintain operation of the other system.
11-47. PREPARATION FOR TESTING. (Regulators may be tested using the aircraft's
alternator or an alternator test stand.)
CAUTION
Do not interchange regulator leads. This will destroy
regulator and void warranty.
a. The aircraft technician or other electrical systems specialist, must disconnect the
battery ground cable at the battery before connecting or disconnecting a test ammeter or
other test equipment or before making wiring changes in the electrical system.
b. Voltmeters with test probes or clips are not recommended. Fully insulated bolted
terminal connections are best, and these should be attached when all power is removed as
described above.
c. When installing a battery in an aircraft, be sure that the battery negative terminal is
in a position so that this terminal can be connected to the battery ground cable for negative
ground systems.
Reissued: 10/12/79 ELECTRICAL SYSTEM
4C8