Replacement for Hitachi LR135-31 alternator?
 

"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?

I think it may be 35A but that is likely the standard alternator Yanmar used
on even the 2-cyl engines.

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.

Yanmar had an optional 55A Hitachi for my engine that with slight
modification of the mounting bolt fits. This is what I have on our 2 cyl
Yanmar and it seems to work fine with our 200AH bank plus starting battery.
We don't have any fancy alternator regulator, but do have a Blue Seas ACR
battery combiner so as to use the maximum output voltage (as opposed to a
diode splitter).

Don't oversize your alternator - That engine may be rated at 12HP, but I
suspect at normal rpm, it would have a hard time making 10HP (BTW- I used to
have that engine on an earlier boat). Check the engine power curve. The
alternator may use up another ~2HP if the batteries are down leaving just
~8HP or less to drive the boat. For our 15 HP 2-cyl Yanmar, Yanmar recommend
no more than 80A but I do know some who have installed 100A units - this can
cause belt problems if the pulleys/belts are not rated for the power
required.

God Luck

GBM