Only a Loose Connector, not a Bad Voltage Regulator

Discussion of aircraft electrical system design, construction, and problems.

Only a Loose Connector, not a Bad Voltage Regulator

Postby sonex1374 » Mon Dec 19, 2016 6:01 pm

I had an interesting electrical problem in my Jabiru powered Sonex over the past couple flights. I initially thought (feared) my voltage regulator was failing, but it turns out it was simply a loose connection at the large capacitor-filter connected to the +12V output of the voltage regulator.

I was getting a high voltage warning coming into my electrical bus. Troubleshooting the problem showed that turning off the alternator (permanent magnet charging coil on the Jabiru is probably a better description, really) eliminated the high voltage. Furthermore, the voltage was erratic, starting at 12.9-13.5 volts (normal for my system) but climbed after several minutes to over 15 volts before my crowbar over-voltage module shut down the alternator. I thought that the regulator connections might have been loose, dirty or corroded, or had a burnt connector, but close inspection showed them to be fine. I didn't find the loose ring terminal on the large blue capacitor until the second inspection. It wasn't totally disconnected, but the terminals could rotate on the screw.

I guess the poor connection caused the regulator to push an overly-high voltage level into the system. Cleaning and reinstalling the connectors on the capacitor solved the problem. A quick test flight showed the voltage right where it normally is, and it held rock steady.

For anyone having unusual voltage problems, make sure to inspect the electrical system very closely before simply replacing parts like the voltage regulator. The problem could be a simple as a loose connection, overlooked despite your efforts to find it!

Jeff Shultz
Jackson, MS
Sonex TD, 3300, AeroInjector
Posts: 183
Joined: Thu Mar 27, 2014 1:02 am

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