Yanmar 35amp to 55amp

[OldManMirage]

My Yanmar 2QM20 has the standard 35 amp alternator.

I see the standard for 2GM20 models is a 55 amp.

I would like to replace my current 35 amp alternator with a 55 amp, and keep my old one as a spare.

Given that the footprint is the same, and electrical connections the same, does anyone see a problem with this ?

I guess I need to check pulley size also to make sure the belt would fit.

But I can't see that this would cause any issues.

I know it's not a huge difference but I thought if I'm buying a new one I may as well get a few more amps out of it.

[TheOffice]

No reason to worry

[hlev00]

Double check your wiring to be sure the sizes leading to and from the alternator are still sized adequately. Given the seemingly small increase and that stock alternators fall pretty short of putting out their full capacity, you shouldn't have a problem. But still worth the exercise as you will probably get twice the current with the larger alternator.

[OldManMirage]

That sounds like what I was thinking too. Thanks !

[partingclouds]

My 2QM20 came with a 55 Amp Hitachi.

[Stu Jackson]

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 absorption voltage, then we also reduce the current the alternator is supplying.. Any battery at any state of charge 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:

http://forums.sbo.sailboatowners.com...d.php?t=125392

and these, too:

http://www.cruisersforum.com/forums/...on-125843.html


http://www.cruisersforum.com/forums/...or-142083.html

[cr180]

If you plan to cruise and use your engine at idle for battery charging while at anchor, give balmar a look. Not only have smart regulated output but have near rated output at low engine rpms. The stock alternators require high engine rpms to achieve rated output.

[Moosemiester]

What CR180 said. Ballmar is the gold standard, you will not regret this expense, especially if you have refrigeration, chartplotter, radar, etc

[OldManMirage]

Thanks for more information.

I don't plan to use the engine for charging. I have a pretty good solar setup which seems to supply adequate power so far.

My thought was - I want a spare alternator when I go cruising, so if I'm going to buy one may as well move up one notch and keep the old one as the spare.

And I'm also on a pretty strict budget and trying to keep things as simple and inexpensive as I can. So things like Balmar's are definitely out of budget.