Overvoltage Control; Purpose And Operation - Piper Navajo PA-31 Service Manual

e. Shutdown the system, including the master electrical switch. Connect a portable
voltmeter (non-precision) such as Simpson No. 260 or equivalent between the "FIELD"
terminals of the left and right regulators in addition to the aircraft system wires already on
these terminals. The positive terminal of the meter is to be on the right regulator terminal.
Use a 30-volt or 50-volt meter range initially.
f. Restore operation of the right engine and alternator system using load and RPM as
in step d, and turn on the left alternator system switching. (HOWEVER, THE LEFT
ENGINE IS NOT OPERATING.)
g. Now slowly rotate
the left regulator voltage adjustment while observing the
voltmeter connected between the field terminals. If a reverse (downscale) reading is
obtained with meter polarity as specified, turning the "LEFT" regulator adjustment
counterclockwise will bring the meter up scale. Then slowly set the "LEFT" adjustment to a
point where the voltmeter will read a low value. Any reading from zero to 8-volts is
acceptable. A stable reading should not be expected. A lower meter range such as 10-volts
may be used for this adjustment. Now reconnect the wire to join the "PAR" terminals of
the two regulators and observe that the voltmeter drops to a very low value (0.2 to 0.5-volt)
and it will be stable. Continue operation in this manner for 5 to 10 minutes to establish
initial warmup of the "LEFT" regulator and alternator system. After the warmup period
make a final adjustment of the balance. This is done by again briefly opening the "PAR"
circuit between regulators and touching up the "LEFT" adjustment for a low reading of the
voltmeter between field terminals. Again any value from zero to 8-volts is acceptable; and
again it will not be stable while the "PAR" circuit is open. Remove the adjustment
screwdriver and replace the snap plug in the "LEFT" regulator adjustment hole.
h. Shutdown the "RIGHT" engine and mas ter switch. Remove all voltmeter leads.
Reconnect the "PAR" circuit wire removed in step b and check all terminal screws for
security.
11-52. OVERVOLTAGE CONTROL.
11-53. PURPOSE AND OPERATION.
a. The overvoltage control is used to protect electrical circuits and electronic
equipment from excessive voltage in the event of a charging circuit malfunction.
b. The overvoltage control consists of a mechanical relay and a solid state triggering
device. The solid state triggering device activates the mechanical relay, when the voltage
reaches a preset value, thereby opening the relay contacts and disconnecting the field circuit
of the alternator.
c. The relay contacts will remain open until the alternator switch is turned off. Figure
11-37 illustrates the overvoltage control connected in a typical Prestolite insulated field
alternator.
Revised: 9/23/80
ELECTRICAL SYSTEM
PIPER NAVAJO SERVICE MANUAL
4C13