Balancing Circuit Operation; Preparation For Testing - Piper Navajo Chieftain PA-31-350 Service Manual

NAVAJO CHIEFTAIN SERVICE MANUAL
g. The LAMAR solid state regulator controls alternator field current to a steady value as required
by the electrical load conditions and engine speed. It does not continuously switch field current between
high and low values as do mechanical regulators and the switching type of electronic regulators.
h.
The design of this unit is such as to provide an alternator output voltage that does not vary with
ambient temperature.
11-21. BALANCING CIRCUIT OPERATION. (Considering two identical alternators and regulators having
the "PAR" terminals of the regulators connected.)
a.
Balancing circuit operation is initiated within one regulator whenever individual field voltages
delivered by the regulator units to their related alternators are not equal.
b.
When a difference in individual field voltages occurs, one-half the difference is impressed across
R 12 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 occuring in the collector circuit of Q6.
e.
Q6 collector current flows from regulator divider R1/R2 + R3 through limiting resistor R17 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 OPERATION OF REGULATOR, 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.
11-22. PREPARATION FOR TESTING. (Regulators may be tested using the aircrafts' 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 previously described.
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: 9/23/80
ELECTRICAL SYSTEM
3D5