Ni Cd charging

[avz]

Hi
I have a cordless drill that operates on 9.6V Ni Cd battery. unfotuately I lost its charger and I would like to ask if its possible to charge it from a bench power supply that I have - to set it to the proper ~9.6V and connect the battery terminals to it. the power supply can deliver 1A and it is current limited.
Thanks.

 

[MikeMl]

The correct way to charge NiCads is by time; not by final voltage. Nicads are usually charged constant-current at the 0.1C rate for 14 hours. The C is the capacity in AH, so for a 4AH battery, the 0.1C rate is 4/10 = 0.4A = 400mA. You have to put 140% of the charge in to get 100% out on the next cycle, so 14 hours at the 0.1C rate is the recommended full charge.

Set the supply to 1V open circuit; then short the leads and set the supply current limit to 400mA; then un-short the leads again and set the open-circuit supply voltage to something over 12V.

Now connect the battery and note the time. Disconnect the battery in 10 to 15 hours, or if it feels warm.

Once fully charged, NiCads will convert over-charge to heat, so if you do not know that the batteries were fully-discharged, then feel them and stop charging if they get warm to hot; other wise 14 hours.