Alternator keeps burning up!

[Chad Flaugher]

1974 Cobalt I/O with an OMC 302 Ford 190 HP. So when I got the boat last year, it wouldn't charge. I had the alternator rebuilt, and still nothing. The problem ended up being a fusible link right off the power side of the alternator. I installed an in line 50amp fuse (the big kind) in place of the fusible link, and BAM, problem solved.... so I thought.

The boat ran great all summer for countless hours. When I fired it up this year, same problem. This time however, not only was the fuse blown,but two diodes and the stator were smoked in the alternator too!!:mad-new: I had the alternator rebuilt again (by a very reputable professional), added a direct ground wire from the alternator to the battery, cleaned all the connections at the starter solenoid, replaced the solenoid. When I fired it up, it showed a normal slight charge at idle. When I brought it up to 1,500 rpm the charge increased as it should, then GONE. The fuse is fine, but I think it smoked the alternator again! Ideas would be of great help at this point. I think this was a problem before I owned it, and it's getting worse.

Thanks!

 

[bruceb58]

I am assuming you aren't using the alternator type that came with the boat that used an external regulator right?

I wouldn't bother with a fusible link or fuse from the alternator. If you do use one, you need a way bigger one than 50A as that is likely close to what your alternator puts out. Once that fuse blows, your alternator no longer has a load and that is why it fails.

 

[Chad Flaugher]

Bruce, the set-up is stock from what I gather. Prestolite alternator with a 3 wire external regulator. New findings today was the regulator is shot, as is the alternator. My hope is that the regulator is the cause of the problem, and the tech that has rebuilt the alternator feels that this is the cause as well. The guy working on the alternator (again, VERY well known in the area as THE BEST) suggested that the 50amp fuse is way to big. Therefore the alternator fails before the fuse. Kinda makes sense, as the alternator is blown and the fuse is not. Should have the parts by Tuesday, hoping for the best!

 

[bruceb58]

Ditch the external regulator alternator and buy a modern internal regulated alternator.