Piper SEMINOLE PA-44-180, Maintenance Manual

Page: 224 / 881

2. Lift the wire from the PAR terminal of either regulator and insulate the free end so it will not contact
other circuits or ground during the adjustment procedure. Breaking this circuit will disable the balancing
circuits in both regulators.
3. Position the RIGHT alternator field switch OFF. Select all LEFT alternator switches ON.
4. Operate the LEFT engine and alternator system with a load of at least 15 amperes and the engine s p e e d
at 920 to 1,250 RPM to obtain 3,000 to 4,000 alternator RPM for at least one minute. If required, caref u lly set
the LEFT regulator voltage adjustment to 14.0 ±0.1 volts as measured with the precision voltmeter connected
to the regulator terminals. Replace the snap plug in the LEFT regulator adjustment access hole.
— CAUTION —
DO NOT MAKE ANY FURTHER ADJUSTMENT OF THE
LEFT REGULATOR.
5. While continuing LEFT engine operation with the same electrical load as in item 4, and the RIGHT
engine NOT operating, turn on the RIGHT alternator system switches.
6. Very slowly rotate the RIGHT regulator voltage adjustment clockwise while observing the field circuit
voltmeter. (Suggested range 0-50V.) If a reverse (down scale) reading is obtained, turn the RIGHT regulator
adjustment counterclockwise to bring the meter up scale. Very slowly turn the RIGHT regulator adjustment
clockwise to make the field voltmeter read near zero. Do not expect a stable reading . The adjustment is
c o rrect when the meter remains briefly in the vicinity of zero, swinging both upscale and down scale. Use a
low range on the voltmeter (0-50V) for the final adjustment.
7. Replace the snap plug in the RIGHT regulator adjustment hole.
8. Shut down the LEFT engine and position master switch OF.
9. Replace the connection to the PAR terminal. Remove all voltmeter leads and test equipment.
BALANCING CIRCUIT OPERATION OF LAMAR MODEL NO. B-00288-1 REGULATOR.
(Considering two identical alternators and regulators having the “PAR” terminals of the regulators con-
nected. )
1. Balancing circuit operation is initiated within one regulator whenever individual field voltages deliv-
ered by the regulator units to their related alternators are not equal.
2. 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.
3. In that regulator which is delivering the lower field voltage, the polarity of R 12 voltage drop causes
Q5 collector current flow.
4. Q5 collector current flow results in conduction occurring in the collector circuit of Q6.
5. Q6 collector current flows from regulator divider R1/R2+R3 through limiting resistor R17 to ground .
6. Conduction through R17 effectively alters the ratio of the regulator divider R1/R2+R3 in the direction
to increase Q1 collector current flow.
7. As described above under REGULATING CIRCUIT OPERATION, increased Q1 current results in
increased output from the regulator to the field of its related alternator.
8. Feedback action results in Q6 collector current stabilizing at a value thai results in nearly equal field
voltage being delivered by the two regulators to their respective alternator fields.
9. 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.
PIPER AIRCRAFT
PA - 4 4 - 1 8 0 / 1 8 0 T
AIRPLANE MAINTENANCE MANUAL
24 -23-08
Page 24-20
Revised: June 20, 1995
1J8