On 20 May 2006 14:47:33 -0700, in message
.com
"Tim" wrote:


Ryk wrote:
On 15 May 2006 07:50:23 -0700, in message
. com
" wrote:

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.

I have read this in all sorts of places but haven't seen a good
explanation for the why of it, other than the common sense notion that
it would be nice to get from 50% to 75% in not too much more than an
hour. I agree that it seems like a sensibly balanced rule of thumb.
I'm not sure I see why charging a 400 AH bank at 50 A would be a bad
idea. Maybe something about not running the alternator full out for
hours on end?

65 A into 200 AH seems to be working for me....


The thing is, you're not throwing a constant 65a into a 200AH battery.
When the typical integral regulated alternator kicks in, the voltage
setting is usually in the 13.8-14.2 amp. range. Higher on modern
vehicles. The Alt. is forced to throw a full amp load in the Battery,
but as it charges, the voltage will remain the same on the alt. output,
however the amperage will decrease down to say 7-10 amps. The more
fully charged the battery, the less amps it takes to maintain it at the
set voltage.

Yes, the alternator never drives all that current into the batteries.
The highest I have seen is around 45 A at high voltage as controlled
by the Balmar smart regulator, tapering off as the batteries approach
a full charge.

I'm more wondering whether there are reasons not to increase the
battery bank capacity without increasing the charging capacity.

Ryk

"Tim" wrote in news:1148166699.442538.194970
@g10g2000cwb.googlegroups.com:

And a 105 A alternator, w/ a 90 A consistant load will burn the Stator
and/or recitifiers out in a short amount of time...



Precisely why the ones on the big diesels are OIL COOLED as well as gear
driven...