Alternator Exciter Problem

[svstrider]

I have two 3GM30 Yanmars with 55 amp alternators . As part of an electrical upgrade by PO both alternators were fitted with external voltage regulators. One of the alternators stopped charging and I went to the hassle of taking the alternator off and pedalled 90 mins to a marine elctrician (Oh How I wish I had not sold my car to go cruising ). Electrician tested alternator on bench belt and found it was OK - WTF!!

I returned to the boat and refitted the alternator & checked the external voltage regulator. The two green lights were on when I ran the engine, just like on the other engine whose alternator was working fine. I did notice that the 15 amp fuse in the wire from the ext regulator had blown. I replaced it and the alternator worked for a couple of hours but has again stopped BUT the fuse checks as OK this time.

When I get back to the boat in 2 weeks after this work stint is over, I was considering doing the following in order of ease of accomplishment

1. change the fuse anyway (BUT why did it blow in the first place - thoghts, any one??)
2. clean the small contact spade on the back of the alternator where the excitator wire inserts
3. check the current coming down the excitator wire at the external voltage regulator and at the alternator
4 swap alternators between the engines

Does anyone have any thoughts /ideas / suggestions??

[Pblais]

The regulator could be bad. You may have a short that triggers with vibration or heat. While my boat is totally different I had an external regulator and a 100 amp alternator and both were old yet delivered great service all season. The regulator died but not totally and it was not obvious visually. In the end we proved the regulator would work some and not work most of the time. The indicator lights worked and gently tapping the regulator would cause the lights to blink on and off. That proved the regulator was bad. They shouldn't do that.

Fuses never blow more than once without cause. Go over all the electrical connections from the engine to the alternator and probably beyond. Look also at ground connections and look for fatigue, chafe, or other external signs to wires and connections. A loose crimp or other physical signs would be nice to find only to be certain it was the real problem.

Having a spare regulator given you have two identical engines just can't be a bad idea and you could swap it out. I wouldn't swap it out until you give everything a good going over. The process of swapping it out might conceal the real cause and it would be better to really know why it happened. It could be a problem damaged the regulator so repeating the process would not be good news. The fuse is probably the key to finding the cause. The fix is usually obvious though finding the problem can take a while.

[svstrider]

Thanks Paul
Good advice. I have cut & paste your sagaciousness to my ever growing BJL (boat job list) for when I return home.

I also have to overhaul the engine wiring harness on that same engine as it has developed the "aging Yanmar ignition key click, click, etc, etc then engine firing affliction". Apparently, from my CF research, a common problem with old Yanmars. Wish I had looked on CF before I bought a new solenoid.

Both problems may well be But as you say, with two engines, having spares is a good idea.

CF is a great resource for figgering out these "weird" happenings.
Have any other cat owners noticed that when you have two engines, the same one always is the one that plays up. On my last cat, "Starbie" was always the bad apple but now on this boat it is "Portos" turn to be a PITA.

[daddle]

I hate those little fuses. Check the fuse contacts. They can be poor, which can heat the fuse, and can cause it to blow (or rather melt the solder inside). Worth a check since the fuse was a problem before.

There is only one (little) fuse on my boat. On the windlass control. Every few months it's wiggle, wiggle, twist, twist to get it to work.

[imagine2frolic]

You can jump one key to the other if a problem does arise on the click click issue. Are you sure you are getting enough to excite the alternator?......i2f