> > As far as current regulation goes, I was going to use an opamp with a
> > push-pull driver stage to do both charging and discharging. A DAC will
> > be used to produce a +/- 2.048V signal that'll be fed to the opamp to
> > select the charge/discharge voltage.
>
> Charging should be current, not voltage, controlled.  I did mine with two
> separate circuits.  The discharge was a resistor to ground via a NPN
> transistor.  You don't need anything too fancy to discharge the
> cells.  The
> charge circuit was a voltage controlled current source.  PWM signals from
> the PIC were filtered to produce the control voltages.  This was all
> software PWM, but nothing needs to be done very quickly so it could be
> heavily filtered to allow good resolution.


I've done this as well, using an AVR to PWM a buck regulator at 500 kHz for
constant current, but I did get some indication from an electrochemist that
does battery chargers for a living, that NIMH can be charged by a regulated
source at 1.5V/Cell, more in a manner like you would a Gel-Cell.

NIMH is pretty interesting to charge, if you try to implement all the rules
that you'll find in the good data sheets from Panasonic and Sanyo.
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