Henrik HolmgŒrd wrote:
> 
> Hi all
> I have a small project I am working on and it is a, intelligent Pb acid
> battery charger for a system with 3 pcs of 12 volt Pb acid batteries
> connected in series each battery is a 100Ah type. I want to charge them with
> 10 A, and the charging have to stop when they are fully charged either
> controlled by the cell voltage, time or some thing else I haven't thought
> about. I want to use PWM and of cause this charger have to be controlled by
> a processor.
> I don't want to invent every thing again and there have been a lot of
> threads regarding charging batteries, so perhaps there have been one
> regarding a project like mine. If some one have a link to a similar project,
> or some other information I can use in my project I will be very pleased.

  Lead-Acid batteries charge off constant voltage, so charging "turns
itself off" basically; I'd think you could use LM117HV's, see the LM117
.PDF files, and applicable National Linear Briefs:

  LB-35 (Adjustable 3-Terminal Regulator for Low-Cost Battery Charging
        Systems)
  LB-47 (High Voltage Adjustable Power Supplies)
  LB-51 (Paralleling 3-terminal regulators)

  Try http://www.national.com/search/search.cgi/main?keywords=lm117 for
these <G>

  Something like 2 regulators, use their self-regulating to give you 10A
maximum, and have the PIC (or other micro) select various voltages by
swapping in parallel resistances with the resistors off the Voltage
Adjustment terminal of the LM117HV's.  (Probably can common these - I
think?  It's been a while, see LB-51 <G>)

  For power savings, if you use an FET to turn off the current through
the voltage divider, you won't drain current through that when not
charging (i.e. if you have AC power only sometimes, you may want to do
this.)  If it's only 20mA, you may not care (Sounds like this is pretty
low compared to the rest of your load.)  If this were a space probe,
you'd do that, though <G>

  Mark