This now reminds me of a shunt regulator I did to equalize a series string
of lead acid batteries in an electric car. There I used a PIC to PWM a
transistor that switched a power resistor on and off. The PIC also drove
an opto isolated open collector bus with the battery voltage, battery
current (sensed the voltage across the negative lead going to the next
lower battery), temperature, bypass current, etc.

I suggest using power resistors as the load, as they are cheaper per watt
than power transistors. I also don't really like the variable resistance
of using an incandescent lamp as the lad. I did, however, use an
incandescent lamp as a current regulator to charge the batteries. The
charger consisted of three SCRs acting as switched rectifiers (to turn off
the charger at the end of charge) from a 3 phase wye service. These drove
the incandescent lamp to the positive side of the battery string. The
incandescent lamp was bright at the start of charge and dim at the end of
charge.

Good luck!

Harold




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