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Old 31-01-2015, 18:18   #1
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YANMAR 3GM30F alternator

A friend fried his alternator. Not quite sure, but I think he managed to switch his pos/neg battery cables...

Anyone rebuilt one of these? Are internal parts available? Hate to just pitch it on the junkpile if it is salvageable.
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Old 01-02-2015, 14:57   #2
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Re: YANMAR 3GM30F alternator

I had a faulty alternator on my 3gm30 when I bought the boat. Looked at a replacement from Yanmar or an equivalent and they wanted 100s of pounds. Went to the local breakers yard and he had a shed with hundreds of them in, one from an old ford fiesta cost me 10 quid and its worked for 2 years. For that money I don't care if it rusts to pieces on the boat I'll just buy another one.
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Old 01-02-2015, 15:05   #3
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Re: YANMAR 3GM30F alternator

Yanmar alternators are made byHatichi and found in pretty much all Japanese cars. Very common everywhere. A auto parts store should have brushes and rectifier for it. Also ebay and amazon.
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Old 01-02-2015, 15:17   #4
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Re: YANMAR 3GM30F alternator

1. It's always good to have a reputable alternator shop known locally. Find one in your neighborhood, it's worth its weight in gold. You can save bundles of $$, since it's the guts that go, and the cases can be replaced, too, without spending the $$ on something new.
2. Hitachi/Yanmar Alternators: (by Maine Sail)

Some alternators though, such as those made by Hitachi and found on Yanmar diesels, are dumber than a pound of beetle poop. Actually, to the alternator, they are pretty smart but to your batteries and the speed of charging they are flat out stupid. Why?

Hitachi alts with dumb regulators, and some others, limit voltage but also reduce voltage based on alternator temperature. This is a self protective feature installed in the internal dumb regulator to prevent the alternator from cooking itself. Remember voltage is the pressure that allows more current to flow. So, if we reduce the absorbtion voltage, then we also reduce the current the alternator is supplying.. The battery simply will not accept the same current at 13.4V that it did at 14.4V and as a result the alternator will run cooler. What do you suppose this does to your batteries over time.......?

The problem is that when cold you will get 14.3V to 14.4V out of the Hitachi but as the alternator heats up the dumb regulator begins to reduce the CV/voltage limit based on the alternators internal temperature. It is not uncommon to find a Hitachi alternator at 13.4V when hot. This is REALLY, REALLY DUMB....

If you have a dumb regulator, and notice the voltage dropping, it is likely a temp compensated dumb regulator. Get rid of it or plan to buy new batteries more often.

If you have a temp compensated alternator or a Hitachi alternator on a Yanmar you really are in dire need of external regulation if deep cycling a larger battery bank.

This is from:

Musings Regarding External Regulation - SailboatOwners.com

and this, too:

Hitachi Alternator and Smart Regulator Instal Question
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Old 01-02-2015, 17:14   #5
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Re: YANMAR 3GM30F alternator

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Originally Posted by sanibel sailor View Post
Anyone rebuilt one of these? Are internal parts available? Hate to just pitch it on the junkpile if it is salvageable.
I've had two rebuilt. Yes, internal parts are readily available. I've bought brushes at a Yanmar dealer and they were about $15 as I remember.

If you can bring it into Savannah GA, DC Electric will rebuild it for you for about $115. (I have no connection, they rebuilt mine).
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Old 01-02-2015, 17:24   #6
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Re: YANMAR 3GM30F alternator

Not much to rebuilding an alternator. Google "rebuild an Hitachi alternator".
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Old 01-02-2015, 17:50   #7
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Re: YANMAR 3GM30F alternator

My alternator seems to peak at about 13.8V. Sometime I'm going to add a diode to the sense wire to fool the alternator in thinking the voltage is 0.6V low. I'll put it on a switch to bypass the normal sense voltage when I want to take the voltage up to 14.4.

Sort of a poor girls external alternator.
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Old 01-02-2015, 18:55   #8
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Re: YANMAR 3GM30F alternator

SC, a diode, or a resistor?


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Old 01-02-2015, 19:05   #9
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Re: YANMAR 3GM30F alternator

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SC, a diode, or a resistor?

Diode as it has a fixed forward voltage drop across it. you could do it with resistors too, but the circuit would require two, with reference between ground and 12v, I think and you get +/-10% based on resistor temp.

A diode is simply installed in series with the sense wire. Add a DPST switch to toggle between diode and bare sense wire.
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