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Old 11-09-2007, 16:50   #1
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Yanmar 2GM alternator & regulator replacements

I have a Yanmar 2-cyl fresh-water cooled diesel. The Hitachi MES3163M alternator, rebuilt twice this summer, once to upgrade output, once for blown diodes (idiot tech #1 didn't connect field interupt). Last weekend, with 3-hours easy running, it overheated and seems toast (substantial burnt smell). I suspect my Balmar Maxcharge MC-612 voltage regulator was not set properly (tech #2). I have two 6v deep-cycle and one 12 start batts. I'm rather frustrated with unreliable equipment and shady service. Any suggestions for something bulletproof?

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Old 11-09-2007, 19:32   #2
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Any suggestions for something bulletproof?
Without a proper installation you best stay at the dock. Nothing it really idiot proof. I set up a Balmer 612 last summer and they are nice but in the hands of an idiot you can trash all the batteries too. Invest in a good digital multi meter and do some reading (lots here). You may need to just go ahead and turn yourself into someone that knows what they are doing instead of rolling the dice all the time.

With batteries and charging it's the whole picture or you are going to get screwed up some how.

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37 15.7 N 76 28.9 W
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Old 11-09-2007, 22:41   #3
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It seems strange that the alt has fried and not the batts. Do you know what/how it wasn't set properly? More details may help us.

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Old 12-09-2007, 10:14   #4
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I've never heard of increasing output by rebuilding. Could that be associated with the "running hot"?
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Old 12-09-2007, 14:18   #5
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Keeping the alternator alive

Do not rely on field disconnects in battery selector switches to prevent burning out the alternator diodes when your system is wired such that the alternator can be disconnected from all batteries.

Do not place any fuse or disconnect switch between an alternator and at least one battery. That one battery must be the one that the regulator is voltage sensing. If one MUST follow the letter of ABYC wiring recommendations by fusing the wire between the alternator and battery AT THE BATTERY END of the wire ONLY then wire in a diode in parallel with the fuse with the cathode connected to the battery end of the fuse. The diode must be rated to carry the maximum alternator current. The wire also must be rated to carry the maximum alternator current.

ALL alternators are by their nature current limited into a short circuit and, therefore, no fuse is needed at the alternator end of the wire. Should the wire be shorted at the alternator end the fuse will blow and if the short is removed then the alternator will still "see" the battery through the diode and not blow its own diodes due to the fuse being open.

I agree that you should learn to "program" the Balmar regulator yourself and verify that it is wired correctly. If you have the optional alternator temperature sensor and follow the aforementioned recommendations you will have a fairly robust system, assuming that you do a good wiring installation with strain-reliefs etc.

If you find an 80A Hitachi it shoud be a drop-in replacement and most of those are capable of generating over 90A, the safe reliable limit for the belt on your engine.
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Old 12-09-2007, 14:58   #6
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Rick, very interesting info wish I had seen that solution before I blew my diodes from a breaker opening. Where does one get a diode like that?

Is a Zantrex ZapStop of any value here? Or does it just handle brief spikes in voltage?

Do you know if a Prestolite 8MR2069TA 90Amp alternator is as robust as the Hitachi one you mention? I need a 2" spool mount and the unit I mention seems to be a direct fit replacement for my 51 amp unit and they are easily converted to external regulation.
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Old 12-09-2007, 17:14   #7
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The Prestolyte should be a good unit as long as it mounts properly for you.

The Xantrex Zap-Stops are made using Motorola transient protection diodes designed specifically for the automotive application of "load dump" absorption. Yes, they are only for transients and will not protect against sustained excess voltage caused by open-circuiting the alternator from a load for more than several hundred milli-seconds or so.

It is a good idea to use one Zap-Stop for every 100A of alternator output rating.

There are many diodes available that will do the job. It is not necessary to use Schottky diodes yet here is one package that will work:
MBRP60CT which is an ON-Semiconductor (formerly Motorola) dual diode with integral heat sink that can be mounted on another piece of metal for greater heat dissipation. Stand-alone with no additional heat sink it will easily handle a 100A alternator if you parallel the two diodes. It costs about 20 bucks and should be easy to mount and wire up. Digikey is one source..there are many others.
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Old 17-06-2011, 11:13   #8
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Re: Yanmar 2GM alternator & regulator replacements

This thread is s few years old.....Does have some info that may help me resolve the "smell" that my Yanmar 2gm alternator is omitting. The motor (and alternator) has 25 hours on it when i purchased the vessel. Occasionally the alternator omits the burning smell......! I thought it was when i hoisted the sails taking the load off the motor the smell came, i guess that is inconsequiencial.

Where to start with the troubleshoot? I am guessing it has something to do with the voltage regulator, however this green horn cant even find it! I have no history on who has installed what previously, so i will have to start from scratch and hope no damage has been done.

Any advice get this job started.

all the best


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2gm, alternator, regulator, replacements, yanmar

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