Hi ppl!  I've been quiet for some time now on the list as I've had far too
much to do.
Now I'm back on the horse with a little question.

I am making a battery-charger/cycler and want to make the actual circuit as
simple as possible so that fellow hobbyists can make it without too much
hassle.

For battery-voltage I was thinking of using a simple voltage divider to get
signal within 0-5v for ADC.
From my understanding I would need to "see" a voltage drop over time of
something like 10 mV for NiCD in order to correctly terminate the
fast-charge.  For NiMH I should stop the charge when the voltage no longer
climbs within some set timeframe.  So, I would need a resolution of about 10
mV or better pr cell.  If I simply use the 10 bit ADC directly after scaling
voltage down to 0-5v I have would give 10.23 volts as the max cell-voltage.
This would not be enough.  I need charger to work with 8 cells, but it would
be cool to get it working with 1-12 cells.  A max cell-voltage of 2v should
be used I think as peak-voltage increases with charge-current.

Any ideas as to how I can adjust the scaling of battery-voltage based on
number of cells charging ?

I though of using a I2C capable digital potmeter, but they all seem to max
out at 0-5v.  I would need one where I could place the pL and pH points of
potmeter between the battery + and - poles on a 12 cell battery, preferably
even higher.  (18 volts or more!)

I was thinking of using a 0.01 Ohm shunt to sample the charge-current and a
opamp with 100x gain. That would give me a range of 0-5 amps at about 5mA
accuracy.

For the discharge current I was thinking of using a 0.01 Ohm shunt and
aopamp with only 20x gain.  That would give me a range of 0-25 amps at about
25 mA accuracy.

The last of the 4 ADC-channels could be used to monitor input-voltage as the
system will be ran from a 12v input.
I will need to include some sort of DC-DC step-up converter too, in order to
charge pack of more than 7 cells or fastcharge packs of more than 6 cells.

Some features I was thinking of:
- LCD display (1x16) that could display status etc and show how much mAh has
gone into the pack.
- Memory large enough to store 1 complete charge and discharge (or more)
- Serialport for remote control, or atleast data-logging of charge and
discharge-curves.
- Pack conditioner mode where the pack is cycled and discharge capacity
measured.  Cycle could be repeated N-times or untill capacity is no longer
improving.
- Cell-type specification (may also allow for Li-Ion/Poly charging.
- Cell-count specification

All ideas apprechiated :)

Kyrre Aalerud

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