Ray,

You got a couple of good answers so far, but I can not resist muddying
the water just a little more. The rating published is often optomistic
as referenced to sailboat applications as they seldom run at rated speed
and are often charging at the top of the recharge curve so they won't be
near the published capability.

There is an available 90amp unit that is a bolt-in kit. It will just
take some looking as I do not have the part number available. I know of
two of these installations that were done by owners. A Yanmar dealer
probably would (expect to be quoted at least 250$us). Some sets I have
installed were a 500$ alternator and separate regulator package and the
owner has always been delighted.

Be aware that 90amp machine will eat near 2hp. That may be critical and
if you currently often run at full rack (wide open), you may wish to
include a field shut off to get those 2 horses back pulling. It will
also destroy drive belts that were less than terrific. Always have at
least one spare on hand.

I do several of these upgrades in a typical year. If you have any other
questions, I'm here a lot.

Fair Wind and Smooth Sea
Matt Colie

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? That's immeasurable,
that's minuscule- that's nothing. 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).
It's on a 12hp Yanmar one cylinder diesel and I'd like to charge my
house batteries (220AH) and a 12v starting battery. 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.