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Old 21-10-2015, 19:58   #1
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3HM Alternator

Hello all,

I had some starting trouble on my way south, thought it was starter, then electrical, ended up being the battery. I got a new battery and now thinking it might be the alternator which is not even charging the battery. I brought the alternator to a car shop, they tested it and said it failed only putting out 11.6 volts.

So, some facts, its the new alternator type (picture below).
The previous owner did not have all the wires hocked up, some just attached to the alternator and dangling. Reading on the manual does not explain much about the R and L slots on the back, nor the wire on the side and if they have an importance.

So I wonder if the alternator is actually faulty, or if maybe just not hooked up properly. Is there a way I can test the alternator while engine is running myself on the boat?

Also anyone know which wires need to be hooked up etc to charge battery. I was told one of the slot like attachments needs to be hooked up to get the current to start moving and charge the battery.

Also if not working, anyone know a good place to get a working alternator for a decent price? The shop which tested it quoted me 450$ and said go else where for they are way too expensive, but I know yanmar parts are all expensive so who knows.

Thanks all!


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Old 21-10-2015, 20:28   #2
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Re: 3HM Alternator

The auto electric shop would have wired it correctly for the bench test. If you have a competent shop they can be fixed/rebuilt and they should be able to tell you what wire goes where. A new one should have a diagram for installation.

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Old 21-10-2015, 20:33   #3
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Re: 3HM Alternator

I do think they tested it correctly true. But he also had no idea about where the wires go and such, and why there were so many connections on mine etc.
I would ideally not like to buy a new one, but I guess if I get it rebuilt they should know what goes where.

Anyone know any good alternator rebuild places in San Diego?
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Old 22-10-2015, 03:08   #4
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Re: 3HM Alternator

See pages 152 - 159
Gord May
"If you didn't have the time or money to do it right in the first place, when will you get the time/$ to fix it?"

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Old 22-10-2015, 03:23   #5
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Re: 3HM Alternator

There are threads about testing alternators, and also threads about replacement alternators, just try the search and you should be ok.
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Old 30-10-2015, 16:38   #6
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Re: 3HM Alternator


Thank for all for the help. I ended up getting a new one for 15$ more then rebuilding the old one and gave them the old one.

Now the problem is the wiring setup. The previous owner who set it up was missing a lot and had somethings poorly jurry rigged. That PDF is amazing! But it does not have my exact alternator, I can use the closest one, but even then I am not knowledgeable enough to know what "excite" and "aux" mean, and where those wires could go. Any help would be great.

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Old 30-10-2015, 17:06   #7
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Re: 3HM Alternator

Boatinfo - Yanmar Service Manual for 1GM10, 2GM20, 3GM30, 3HM35

See page 12-20 (page 352 in the pdf or whatever is is). It is a drawing of the internal and external wiring of the alternator.


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