NiCad Battery Charger Circuit

This array charger ambit is advised for recharging NiCad batteries based on an AC-powered accepted antecedent method. It can crank out as abundant as 1 amp and can be adapted to go alike college by allotment altered accessories for Q1. Since this ambit uses AC band voltages and currents, amuse exercise acute attention during assembly, turn-on,

and test. NiCAD batteries accept a accommodation blueprint alleged milliamp-hours. This amount alleged “C” is a admeasurement of how abundant absolute accepted they can accommodate in one hour. Milliamp-hours is addition way to accurate the activity independent in the battery. To recharge a NiCAD array conservatively, it is accepted convenance to pump a accepted of 0.1 C into the anode or absolute terminal for about 12 hours. Therefore, if you had a D-size NiCAD with a accommodation of 4000mAh, you would appetite to allegation it at 400mA for about 12 hours. Addition advantage of this charging address is that it is affable on batteries and doesn’t account them to lose accommodation as bound as the fast allegation techniques.

The achievement accepted of this array charger ambit is controlled by the accretion of the bandgap advertence diode and the base-emitter alliance of the PNP transistor. The PNP transistor provides abrogating acknowledgment to the aboideau of the MOSFET. As acclaimed in the schematic, the batteries actuality answerable can accept a absolute of 12V which is agnate to about 8 NiCAD’s in series. The achievement accepted is bent by the amount of R1 which is bent by:

R1=3.2Volts/Iout
The ability amusement of R1 will equal:
Pr1=3.2Volts*Iout
Be abiding to accommodate pleanty of heatsink for Q1 and accept an appropriately sized resistor for R1. The afterward table summarizes some of the resistor accepted combinations that are possible:
Iout Resistor Amount Resistor Power
100mA 33 ohms 1 watt
500mA 6.2 ohms 2 watt
1Amp 3.3 ohms 5 watt