Thread: over-voltage
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Unread 03-13-18, 03:17 PM
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rhurt rhurt is offline
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Had the issue yesterday

Both alternators failed yesterday when I was ferrying a 337H from PA. In heavy haze over the mountains and the radio lights started getting dim. Neither alternator out light was energized, or the hi/lo voltage lights. The engine monitor showed 14 volts on the bus and there was enough power to cancel IFR before shutting off the master.

Got to better visibility and continued the flight while troubleshooting, finding the system would charge if the rear alternator was on, but would overvolt and pop off line if both alternators were on. The front would not charge by itself. The plane had voltage pulsing issues before and after the failure.

I suspect the front diode is bad and will let you know if that's correct. Maybe it will stop the pulsing issue also.

My 337C has diodes on the middle of the firewall just under the cowling. One diode/relay assembly and the over/under voltage assembly was replaced and the voltage flicker went away. It was likely the relay, but it is interesting the hi/lo voltage assembly is mounted under the rudder trim chain and lube drops on it after the chain is serviced.
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