Piper COMANCHE PA-24-180 Service Manual page 579

PIPER COMANCHE SERVICE MANUAL
FIGURE 9-2r. APPLICATION OF FIGURE 9271. TESTING OVERVOLTAGE
OVERVOLTAGE CONTROL CONTROL
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c. Caution Notes:
1. Use only with insulated (ungrounded) field alternators.
2. Regulator base must have a good ground connection.
3. Do not connect ground power to aircraft until voltage regulator "I" terminal has been
disconnected from electrical system.
4. Do not (even momentarily) connect the two voltage regulator termunals together.
5. Do not connect battery into system with oolarity reversed.
6. Do not force the voltage adjustment screw.
7. Th is a sealed unit and not repairable. Replace with a new unit.
9-61s. Overvoltage Control.
9-61t. 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 de-
vice. 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 alternatot
c. The relay contacts will remain open until the alternator switch is turned off. Figure 9-27r
illustrates the overvoltage control connected in a typical Prestolite insulated field alternator.
9-61u. Test Procedure. Connect the relay as shown in Figure 9-27s. Use a 100-ohm potenti-
ometer of IS-watt rating, or more, to adjust the voltage. The voltmeter is used to read the voltage
until the relay opens. at which time the voltmeter reading will drop to zero. See tabulation for
voltage reading. Test figures are at 75 degrees Fahrenheit. These units are not adjustable. Re-
place the overvoltage control if it does not test to specifications.
Relay contacts open between 16.2 and 16.8-volts. Use 18 or 24-volts to test.
ELECTRICAL SYSTEM
ISSUED: 8/18/72
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