Hey guys,

The Elektor magazine had an article a long time ago on how to use a pwm
output to be used as a reference for a power supply. The circuit also used
the PIC micro to sense current.
This has variable voltage and current adjustments so i'm thinking that if
you had a decent device (or maybe 4066 on decent 10 bit a/d) you could do a
loop and pretty much configure the charger for 8 or so channels easily.
One would simply end up with a few LM324's, shunt and a decent fet per
channel.

I'm about to embark on a similar project as i'm also irritated with
adjusting 10x lm317T's in a multiple SLAcid/gel cell charger.

However, i'm going to try and use an ATMEL with C.
my first choice for reference will be the TL431 seeing as every supplier in
ZA has an issue with service ;)

On the accuracy of the charge voltage, I have somewhat of a large outlay to
protect ...
The batteries themselves are charged, and then discharged until about 11V or
so when "cutout" pic switches the output off and increments a register in
eeprom for stats. THe batteries are often left on 13.8 volt float charge.

There is a diode (A600 iirc ) in series with the chargers output and the
charger is set for 14.2 volts with fluke multimeter.

The important thing is to calibrate it while its heatsinks are not in a
frozen state. Being a charger, it tends to get a bit warm. This being said,
the unit has never varied more than about +- 0.2 volts and this is within
the range of the battery, which they quote as happily being from 13.7-14.2
If you are not floating the voltage, you can even charge up to 15V.

The nice one to have, would be the one where you have the option of a diode
network to sense the battery temperature too. This i know makes a big
difference as on a hot day, the charger current limits alot more than a cold
day.

My guess is that our chargers will be too expensive to make and we'd have
NASA worthy specs :)

I do however think that battery charging is an avenue not well known and
this thread is providing an even more usefull function. The information in
this thread alone was never before seen in anyones reference texts ;)
J



On 1/8/06, David VanHorn <dvanhorn@microbrix.com> wrote:
>
> >
> >
> > The PSU output should be temperature compensated too, as the
> > float voltage varies with temperature (13.6-ish - 13.8-ish)
>
>
> I would if the temperature varied much, but these are shirtsleves
> environments.
>
> I've done the TC routine with 317 based chargers though, it's not hard.
> --
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--
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Regards
John

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