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Old 06-17-2021, 09:19 AM   #1
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alternator 110 degrees engine stone cold

Crawling over the top of FL108 and felt the heat coming off the alternator. The engine hadn't been run for 2 days. The alternator was replaced with a remanufactured unit 6 months ago. Turned off battery charger and checked 12 hrs later 105 degrees. Any ideas on a fix other than remove/replace?
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Old 06-17-2021, 09:55 AM   #2
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Try a rebuild job. My guess is that one or more of the diodes has shorted. Usually they fail open. But in this case if shorted it lets current from the battery back into the alternator and heats it up.

A rebuild job is usually new diodes, bearings and a general clean up which sounds like all you need.

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Old 06-17-2021, 12:07 PM   #3
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Another potential cause: The field should be wired via the ignition switch and not directly to 12V otherwise it will continue to drain the battery. Check for 12V on the field terminal when engine is off to eliminate that cause.
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Old 06-17-2021, 12:46 PM   #4
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Probably a failed diode. You can buy replacement parts and there's trouble shooting guides online.

It's easy to rebuild an alternator. It takes about 30 minutes to take apart and reassemble. It's not rocket science. Some places for rebuild kits and parts:
https://alternatorparts.com/
https://www.dbelectrical.com/alternator-parts/
https://www.aspwholesale.com/
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Old 06-17-2021, 04:22 PM   #5
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When port engine, with warm alternator, runs, it's amp gauge reads 0. When the starboard engine runs, it's amp gauge reads 30. Good reason to remove port alternator. New issue is that the battery selector switch doesn't turn power off. My bro recommends disconnecting the negative terminal of each of the 3 batteries. Then remove the power wire from the alt and tape it off. Then reconnect terminals for 12V power for, lights and fresh water pump. The battery selector switch has 4 positions - OFF 1 ALL 2. It has always been set on ALL. I have 3 batteries connected to a Charles 30 amp charger. Engines start in all 4 positions. 12V power does not work in OFF.
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Old 06-17-2021, 05:18 PM   #6
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I did a lot of rewiring on my GB42 when I had one, primarily after I added two sets of golf cart batteries behind the two main engines to make a "house" bank. Yours sounds like how I inherited mine; three batteries with one for the generator while the other two had an automatic paralleling relay to send their combined power to which ever engine was being started. The poor thing about this was the fact that at anchor, I was using starting batteries to power the house loads hoping that they would not be depleted when it came time to restart the engines/generator, assuming you don't use the genny overnight. I would guess that your third battery (generator?) has no interface with the 1-2-both-off switch, and that it is just the two main engine starting batteries which got to the 1 and 2 posts on that switch. Unless you have a reliable drawing, you will have to trace the cables. The battery switch you describe, if it was like mine, is just for house loads and does NOT interrupt the circuit between the alternator and the batteries; so, despite the fact that it has a warning on it not to shut it off while the engines are running (in order to not blow the alternator diodes), you probably can, but test the circuit first with the engines off. The big battery disconnects which you should find in the engine room very well could interrupt that circuit - again, test it.

Leaving the battery switch on ALL offers the opportunity for a dead cell in a battery to drag the other two batteries down with it. Since the starters are independent of this switch, you don't need it in other than 1 or 2 most times which lets them remain separate. I added a second battery switch which allowed me to select the third battery into the mix for house loads should the loads demand.

If you ever want a look at my final design, send along a private message with an email address, and I'll send along a .pdf file.
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Old 06-19-2021, 02:12 PM   #7
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what changed?

Alternator was checked out by the shop and it'd make amps. So it's was opened up and there 2 wires that had worn through insulation and could touch and possibily create a terminal problem. Not an immediate priority but taken care of. Reinstalled and it works! But it also gets hot when not running. Disconnected the small gauge jumper wire and it cools down. Wire is connected to power lug and small post on upper back of case. Stbd engine alternator has a Leece Neville 200 amp that's corresponding wire is Negative. So Port may have had a heating issue from the 1st installation Jan 4 2021. When I have jumper wire alligator connected and I get amps and then with engine off heat that continues 117 degrees. Removing alligator for now
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Old 06-19-2021, 02:54 PM   #8
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Have same issue with a new 3 month old large frame alt on ours.
Same thing, noticed it warm after 2 days and a screwdriver sticks to the front indicating blown diodes.

Took it off and boxed it up
Will be another couple of months before I can get it replaced or repaired under warranty

Engine and systems can run without it but it was nice having 70amps @ 24v smashing in on night passages.
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Old 06-19-2021, 09:25 PM   #9
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Suspect the exciter circuit is constantly energized. I use a similar alt on my Cummins, the exciter is energized through an oil pressure switch. That keeps exciter off unless engine is running.
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Old 06-20-2021, 09:35 AM   #10
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Old 06-20-2021, 11:20 AM   #11
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Sounds like your exciter wire is hot wired to the batts or to a power source that is not powered through your ignition switch. That will cause your exciter to power up and help drain batts. I bet that is why those wires got a little to warm.
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Old 06-20-2021, 05:50 PM   #12
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Quote:
Originally Posted by Ski in NC View Post
Suspect the exciter circuit is constantly energized. I use a similar alt on my Cummins, the exciter is energized through an oil pressure switch. That keeps exciter off unless engine is running.
Maybe

Wired it identically to how the previous one was done, same alt, straight swap.

Only thing that has changed this time is the shroud has not been put back on (PITA to do) so now I can see and feel the alt.

But the alt does not seem to be charging leading me to think its got issues.
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Old 06-22-2021, 09:25 PM   #13
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The observation was made that the problem alternator was stator activated. The other engine's is a trio activated. So I exchanged for trio, installed it, not getting warm and produces amps when engine is running. I'll see if I can get pictures posted
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Old 06-24-2021, 10:22 AM   #14
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Alternators

[IMG]20210617_130918.jpg[/IMG210621_114327
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