Howdy,


Ok, the minimum you'd need to charge these is a voltage and
current regulated supply limited to less than 10A and 13.62
for AGM or 13.50 for gell (check the manufacturer's stated
the float voltage). No more than 14.1V in any case.

The vehicle voltage is not much higer than this with the
engine is running. It's possible to build a low drop linear
regulator to serve this function. Linear Technology or Micrel
should have an app note you can work from. This is the one
device solution. You'll get a couple of hundred milliamps
to an amp at 13.6V from as low as 14V maybe a bit less.
Good for keeping the auxilliary battery topped off but not
so good for recharging.

If you want faster recharge (which still won't be very fast
since 120%-140% of 100Ahr is is going to take 12H-14Hr at 10A)
I suggest a SMPS running off the vehicle battery it can charge
the gell cell even when the engine isn't running.

Try National Semiconductor's Web Bench power design tool and
roll your own with their parts.
http://www.national.com/appinfo/power/webench.html

For minimum recharge time a bigger SMPS (maybe a nice push-pull)
is required. I might try a simple switcher boost converter or
switched capacitor converter and raise the vehicle supplied
voltage to about 24V at a few milliamps to bias a series pass
MOSFET linear regulator. The output current and drop-out
voltage are then only limited by the mosfet pass device(s)
.... virtually unlimited! Though not as efficient as the
switcher. Maybe a good idea to throttle back the current
limit from 10A when the engine is running to a few hundred
milliamps when it is not. Though even that's too much if the
vehicle sits unused for too long.

Which causes me to ponder... you'll drain the vehicle battery
unless the engine is running. Even at 10A charge current a
full recharge requires a fair amout of driving! Perhaps it's
better to plan on recharging the battery from "dock side" power
and only trickle charge the battery from the vehicle to keep
it topped off. One of the low drop regulator IC's set to 13.6V
or a simple switcher(tm) would be all you need for that.



73,
Grumpy




JIMMIE wrote in news:0309608e-8c61-4bac-a667-
:

Im not sure but they are sealed 100Ahr batteries and the max recharge
rate is 10amps so definitly not FLOOD.
I have recharged them from my aux power connector in my truck bed but
this took a lot more care and effort than I wanted to give. Wife and
kid thought I was paying more attention to the batteries than them.. I
thought about feeding them from a constant current source. In this
case it would act more like a current limiter.

Jimmie