I have an external alternator which is no longer charging the battery. Here are the symptoms and observations:
- The voltage and ammeters on the bus show the battery is not being charged
- The alternator field lamp light turns off when the field CB is closed
- The B+ cable has good continuity, as shown by a multimeter
- While in flight, the battery got as low as 12V
This would make me suspect a bad diode pack, but there are some anomalies I've listed below which (I don't think) can be explained by a bad diode pack:
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Anomalous observations:
1. Once, while the engine was off, I saw the alternator's lamp light LED flicker. After the engine was started the LED stopped flickering and stayed a solid red.
2. Once, in flight, the trim indicator (a simple LED bar), flickered. I turned it off and a few minutes later when I turned it back on it worked fine. The trim indicator is grounded through the avionics bus which in turn is grounded to the chassis.
3. Once, in flight, I saw the engine instruments twitch. They are powered by the battery bus, but grounded through the engine.
4. Once, while taxiing, I saw the voltmeter and ammeter show a positive charge, but at around 13V instead of the typical 14V.
With the above anomalies, I would suspect a failing ground, except that the engine has no trouble starting. So if there's enough ground to crank on the starter, there's enough ground to charge a battery.
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What explains all these electrical gremlins?
