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:


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.


What explains all these electrical gremlins?

10015_1_Stemme S6 alternator bus.pdf (You do not have access to download this file.)
You do not have permissions to reply to this topic.