Recently I have been working on a NiMH battery pack (7.2V / 2100mAh) charging circuit powered by a 12V solar panel. With some research I found charging NiMH takes different forms by measuring change in voltage, change in temperature, voltage across the battery.
I have used a LM317 to give output of 8V in its output which will be used to charge the battery. Also I have used a comparator LM311 to activate charging and discharging through MOSFET IRF510. And limited the current to 210mA to charge the battery at the rate of C/10.
I have set the hysteresis of comparator at VL at 7.3 and VH at 7.8 so when battery across battery crosses 7.8V it stops charging and it starts charging once the battery voltage drops below 7.3V.
Now my questions are:
- What diode should I choose to connect in series with solar panel to prevent reverse current when Solar panel produces no current? I prefer not to go with traditional silicon diodes since the voltage drop is high and cannot afford any voltage drop.
- Is there any design considerations I have missed in the circuit which I should be looking into keeping the circuit as simple as possible?
- I intend to use a load which will draw about 250mA from the battery, is it safe to use such load provided it will be ON simultaneously when the battery gets charged using solar panel?