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Old 21-08-2014, 06:54   #1
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Join Date: Oct 2013
Location: Kingston
Boat: Columbia, 8.3, 27.2 feet
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Yanmar 2QM15 Alternator/Generator

I started up my engine yesterday and let it run in neutral at the dock for approx 5 minutes max. Put my hand on the alternator and found it to be very warm, not hot but warmer than I would have thought. Stopped the engine and took off the belt and manually spun the pulley. No bearing noise and it turned freely. The battery it was charging was charged enough to start the engine easily so it wasn't discharged. I have had the engine for this season only and I guess I've never felt the generator before. Is this something I need to be worried about.
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Old 21-08-2014, 07:06   #2
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Location: Cowichan Bay, BC (Maple Bay Marina)
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Re: Yanmar 2QM15 Alternator/Generator

Nope, alternators get hot. But...

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 -

and this, too:

Hitachi Alternator and Smart Regulator Instal Question
Stu Jackson
Catalina 34 #224 (1986) C34IA Secretary
Cowichan Bay, BC, (Maple Bay Marina) SR/FK, M25, Rocna 10 (22#) (NZ model)
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2qm15, alternator, generator, yanmar

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