[kevin]

As you may have read in my Oshkosh trip report message, my charging system is still giving me problems. Both alternators stopped charging in the air on the way to Hibbing, MN, and any combination of alternator switches, plus turning of the master several times (along with the alternators) would not make it work for about five minutes. Then, with the front alternator switch off, the rear started charging, so I left it alone until landing at Hibbing. When I reduced power in Hibbing during the approach, the rear alternator went off line. I turned on the front alternator switch, and it started charging just fine.

My first theory was that the regulators were too far apart in voltage again. I found a mechanic, and we started the front engine, intending to start the rear, then balance the two regulators. But the front alternator would not put out anything at all, even with the rear engine shut down. So we shut down the front.

If you read the previous messages in this thread, you will note that at this time I had one new regulator, and one museum piece. I had brought the newer "bad" regulator that we removed with me, and I decided we would swap out the museum piece with the newer regulator, because that would at least make it easier to balance the two regulators (one adjusting screw on each). We changed the front regulator to the newer "bad" regulator, put the museum piece in the baggage compartment. Started both engines, but no matter how far we turned the adjusting screws on either regulator, we could not get any output out of either alternator.

Through a long series of turning things on and off carefully, I determined that if I turned the master and both alternators ON, then turned the master OFF, I would get balanced, correct power (voltage and amperage) from both alternators. But if I turned the master on, both alternators went to zero.

This made me think that there is a problem in the overvoltage protection circuit somewhere (even though I am not getting a light). I decided to give up and move to Minnesota.

After shutting down the engines, the mechanic inspected all the wires that go to the overvoltage/control circuit board. He did not find anything, although there were a couple of noise filter capacitors (large), one of which MAY have been in contact with something wrong. There are two 14A 32V fuses visible on this board, and I asked the A&P to ohm them. He inspected them visually by removing them, but ohmed them *in circuit*, which is not what I wanted, but he was holding the meter. We found nothing wrong with them, but put them back in swapped - one where the other was and vice versa.

Now I was SURE I was going to be in MN a while. We cowled the airplane again, and I decided to run it one more time, to make sure that moving the wires and fuses around had not changed the behavior.

Everything worked perfectly. I mean *really* perfectly, nearly balanced voltage and amperage out of both alternators, even a low RPM.

Hurray, I don't have to move to MN, but boo, I still don't know what is wrong with it.

The next morning, it still worked perfectly. On the trip back, I kept checking the amperage output from each alternator. During runup in Hibbing, it worked great. Early in the leg from Hibbing to Dickinson, the front alternator output went to zero, but the rear was fine at 20 amps. Later in that leg, the front started putting out 17 amps, the rear 3 amps. For the remainder of the trip, both alternators continued to work, with the share between each varying - sometimes high front/low rear, sometimes high rear/low front, sometimes (less often) balanced.

It got me home, for which I am very greatful. But now I am not sure how to proceed.

Anybody have suggestions?

Kevin