On Thu, 27 Mar 2008 12:08:40 -0700 (PDT), "
wrote:

On Mar 26, 5:46 pm, Larry wrote:
... A 100A alternator will NOT put out 100A! It will put out 100A for a FEW
MINUTES, then must be cut back to prevent its heat destruction....and I
didn't know that, myself. ...

I'm sure you're right. On the advise of a rather eccentric, but I
think very competent EE (Gary Pacey of Outback Marine) we installed
oversized alternators and then down-rated them. At least in theory
they are supposed to be able to run continuously around 100 amps. At
any rate, I've used them to charge my ~500ah bank of AGM's for years
and they've handled it well. Underway that means they run full out
for ~15 minutes a couple of times a day. At anchor the solar panels
do most of the work and I the alternators much less of a workout.

I seem to recall that for best battery life you should charge it at
the 20 hour rate. You have a 2000 AH starting battery? [Ten times the
size of the one on Cat's biggest bulldozer]. Charging a 25 AH battery
at the fifteen minute rate has to be a poor idea.

Casady

On Mar 27, 11:04 am, (Richard Casady)
wrote:
I seem to recall that for best battery life you should charge it at
the 20 hour rate. You have a 2000 AH starting battery? [Ten times the
size of the one on Cat's biggest bulldozer]. Charging a 25 AH battery
at the fifteen minute rate has to be a poor idea.

Sorry, I wasn't clear. The batteries absorption rate drops below the
alternators full output at about the 15 min mark if the batteries have
been deeply discharged. I dont' stop charging at that point, I just
stop asking as much from the alternators. These are AGMs and have
unusually high absorption rates. I do not use a separate starting and
house bank. I have a small reserve battery for emergency starting but
otherwise use a 2x8D Lifeline bank for all of my electrical needs.

-- Tom.

"Richard Casady" wrote:

I seem to recall that for best battery life you should charge it at
the 20 hour rate. You have a 2000 AH starting battery? [Ten times
the
size of the one on Cat's biggest bulldozer]. Charging a 25 AH
battery
at the fifteen minute rate has to be a poor idea.


Rule of thumb given to me by an old time Trojan application engineer:

Recharge rate = 15% of total connected AH rating of bank.

Based on 2000AH bank, it will accept a 300A recharge rate without
complaint.

Every 100AH consumed requires 125AH replacement.

Yes you can play games with the above, but it will come back to bite
you.

Wet cell battery technology hasn't changed much in the past 100 years,
it is a very mature product.

Lew