ray lunder wrote:

Ahoy, I could only find one technical reference for this which claims
it's a 30 amp alternator. Could this be correct?

Yes, that is correct for the alternator for a Yanmar YSM12 which it
sounds like you have.

I measured about 13.2v output at
idle and I had to rev the engine to over half throttle to get 14.4v
out of it. (my batteries were topped up at the time if that makes a
difference).

Sounds about right.

It's on a 12hp Yanmar one cylinder diesel and I'd like to charge my
house batteries (220AH) and a 12v starting battery.

Take a look at Leece-Neville which is now part of Prestolite.

You want a unit that is rated about 60-80 amps, but will have at least
a 50 amp output at engine idle.

Talk to their application people in distributor sales.

I've been away from that business too long to have current knowledge.

Lew





If I'm beginning
to understand these things I'm to look for an alternator which will
produce 30% of my amp hour capacity. Since I'll probably charge the
two systems separately I guess that's around 70 - 80 amps. My crank
pulley is about 4" diameter, O.D. to O.D.. I need a 3" foot model to
fit my engine. Any similar experiences, recommendations, empowering
observations? Ok, the spell chek is complete, I had eleven errors.
Thanks again.