On Sat, 11 Mar 2006 17:20:55 GMT, in message

"Roger Long" wrote:

BTW my AGM's are working great the way I am using them, short motoring
periods and an overnight plug in about once a week to top them up.
With a 20 HP engine and very minimal hotel loads, they don't work hard
anyway. I'm just wondering how they would like being driven by the
low tech Hitachi alternator with its tiny built in regulator if I had
occasion to motor for 12 - 25 hours straight to move the boat
somewhere.

If your concern is over-charging from extended motoring, how about
adding a high current draw accessory that you can turn on whenever you
don't want those amps flowing into your batteries? Just a thought...
I'm sure I can find a way to burn plenty of amps, at least in terms of
the output of a cheap little alternator.

Or read the manufacturer's specs on the AGMs to find out what their
acceptable max continuous charging voltage is and make sure your
regulator doesn't exceed that.

The "Model T" alternator I used to have on my engine (A4) was
regulated to a voltage low enough that it never really fully charged
the batteries, so I could run the engine forever... Sort of the
opposite problem to what you are imagining. I only got full charge
when I got the chance to plug in overnight. You may be in the same
situation.

I would suggest that you partially discharge the batteries, start the
engine, then go for an extended motor cruise. Monitor the voltage
across the batteries and see where it stabilizes. Then make the
assessment about whether or not extended motoring will hurt your
batteries.

Ryk