Twins, 3 batteries (1 for each engine and a house), isolator, 3 bank charger. Voltmeters (both) occasionally peg (over 15 volts), stay there for a while, pull a big load on the engines and then back to normal. This happens with 1 engine running, or the other or both. Batterys are definitely overcharging when this happens.

Any ideas? I think its unlikely that both alternators are bad. Someone suggested I disconnect the charger from the system and then one battery at a time.

Im on the road this week and sure could use some good ideas before I work on it this weekend. At least to order any parts I might need.

Thanks,
Tom

Not sure how your set up is going on, but if one of your regulators are messed up then it will show a high voltage on all your batteries.

Jon

Audio is right, so you should try to disconnect one alternator at a time if you don't need both, and see if one of them causes the problem and not the other. If you still have the problem maybe the isolator is goofy.

I think AUDIO is right,bad voltage regulator,if there prestolites you should be able to dissconnect the purple ignitor wire on the regulators and see if the voltage returns to normal.

You should not have to disconnect anything on the motors, just start one motor, then the next.

This will help issolate the motor with the trouble. Then I would swap the alternators if I thought I had a issue with the alternator. See you can still show high voltage on one engine and have a problem with your Issolator. By changine engines if the problem fallows you have a bad alternator, if not you have a bad issolator This is of course assuming that when you start one motor one side is good and the other is high.

Jon

Don't forget about the possible junk (shorted batt.) Make sure they have a full charge and do a load test.

I would start by checking the battery cable connection at the starter and the ground on the engine.Ussally an overcharge is caused by loose or corroded connections.The alternator will see low voltage due to the loose connection and overcharge to compensate for the voltage loss.

Thanks for the replies, as per the post, it happens with either engine running. I will replace batterys one at a time when I get home this weekend. I did check connections as good as I could without pulling engines. They also crank and start very well so I think wiring is OK.

Both gauges read the same whether one engine is running or both or the other engine is running. Would that then point to the Isolator?

Yes it could be the isolator,it can cause a tempoary disconection and cause a voltage spike.Bypass it and see if the problem goes away.

Geez, now Ive seen everything. BOTH voltage regulators were bad. Everything else electrical checks out OK.