Intermittant Alternator

[Kittiwake]

I'm trying to sort out a problem that's developed over the last couple of days that so far has me baffled. After an especially rough crossing of St Andrew's Sound about 10 days ago, I noticed that my alternator had stopped putting out juice late in the afternoon. About 2 hr after shutting the Volvo down, it would work again. This has been repeated daily since - nothing that I can pinpoint associated with it (rough water, rain, battery voltage, etc).
The alternator is the new version of the original, 35 amp generator, about a year old without previous problems in approx 500 hr of use. Batteries are 2 Lifeline AGM group 24s, are holding charge well, and I don't use much juice as you can imagine.
Thinking that it must be a short in the wiring which happens when things heat up, or maybe get wet, or something?
Any ideas, or similar past experiences?
Thanks

[sharkbait]

The internal regulator in an alternator has a nasty habit of working intermittently. Depending upon the type of regulator you might be able to just replace the regulator.

[Jeff Barnes]

I too would suspect the regulator, particularly if it's the internal version. With the AGMs I would definitely invest in an external 3-stage regulator which has adjustable charging voltages and times. They are also more reliable.

I have 4 6-volt AGMs (400 Ah) on my CD36 with a Heart Interface regulator and haven't had a problem in five years.

Jeff

[Kittiwake]

I've just finished putting the old alternator back in, and will take the "new" alternator in to have it checked out tomorrow. With more experimentation observation - think it was heat related, so maybe a diode or something? Thanks for the ideas, if this doesn't do it, will be going to external regulator, hopefully later rather than sooner...

[Jeff Barnes]

Bill,

Good lick with the testing. These types of problems can be challenging to diagnose. Your AGMs will ultimately be happier with a three stage external regulator with adjustable charging pahses.
Let us know what they find with the new alternator.

Jeff

[Bob L]

Bill,

Last year as we exited the Cape May Channel, heading back to the Chesapeake, I noticed our alternator was not charging the batteries. We anchored near the beach by the channel and I did some measurements. The alternator was putting out a good voltage, measured at the starter motor, but nothing was getting to either battery. I tried all sorts of things, wiggling wires, checking and cleaning various connections, but nothing worked. Eventually, I figured we'd head back into Cape May and get some help.

The ONLY change that I had done to the alternator was the day before when I tightened the belt. While anchored working on the problem, and in desperation, I slacked off on the belt a bit. This was the last thing I did before heading back to Cape May, and after starting the engine, I saw we were charging again. I doubt that my changing the belt tension had an effect, although some stress might have been put on the bearings (which is improbable to kill the charging).

Since then I have had no problem with the alternator, but live in some fear it will show up again.

Bob