TECH TIPS

.Simple Ni-Cad Charger

The circuit is a constant current Ni-Cad charger using a 7805     5volt regulator.

You will notice that the regulator is not connected in the normal way. the centre leg is the sense leg, and generally detects the voltage between the output and ground, ie in this case a 7805 is 5volts.  In this circuit we are detecting the voltage drop across the resister Rs. the value of Rs is set for the batteries we wish to charge. If Rs is 82ohms (0.5watt) the circuit will charge at 60ma. In fact connect an amp meter (Set to mA)

short the output and the total current drawn would still be 60mA. You can charge 1 or more cells depending on the input voltage .  If you don't feel safe with mains voltage Don't make your own transformer power section.  You can however charge from a car battery or shack 12v PSU. Don't forget fuses.  Any question see me at the club.  Or e-mail me at the club.