Tamaroak wrote:
I have a 1997 Monk 36 with the Cummins 6BT5.9M 220 engine. I'm switching
to six golf cart batteries for the house bank and wonder if the stock
alternator is big enough for this application.

Does anyone out there know how many amps that alternator is likely to
crank out?

Capt Jeff
"Adirondack"

Cummins might have rigged that engine with any of several alternators
when it was installed.

You will need to check the info plate on the alternator.

The basic premise for calculating alternator size is 4:1. Your
alternator output in amps should be at least 1/4 the amp hour capacity
of the battery bank it is being asked to charge.

There are two good reasons why you don't just run out and slap on the
biggest alternator that will fit on your engine's bracket. First is the
drive belt capacity; a very high output alternator will snap drive
belts like cheap rubber bands. You can always go to a larger pulley for
the belt, but if you do that you run the risk of plowing headlong into
the second good reason for not simply slapping on the highest output
alternator you can lay hands on:
waterpump side load. Engines with a coolant circulation pump driven by
a belt shared in common with the alternator can experience too much
side load on the pulley when the larger belt is tightened up (and that
can lead to premature failure of the waterpump).

Should you decide to go for a monster alternator, one of the better
approaches is to add an additional crankshaft pulley of sufficient size
and drive the alternatior with a dedicated belt.
Some of the boaters who go this route will actually mount the
alternator on a custom bracket near the engine rather than on the
original bracket.