Have you ever wondered why sometimes your Nicad Battery just seem to have died after being charged. Or maybe the batteries deliver the current in the wrong direction and
discharge quickly. Chances are you have placed the batteries in the wrong direction in the charger box. Charging Nicad batteries in the reversed polarity will cause no physical
damage to them that is why you cannot notice your error at once. To prevent this from happening let electronics do the protection for your Nicad batteries. Use the circuit featured here.
It is a Nicad charger with a built-in protector against reverse polarity charging.
This simple battery charger is designed to charge size AA Nicad batteries. It is a common knowledge that in charging batteries, the probability of interchanging the terminals'
polarity is very high. If this happens, the battery might be damaged. Since we are only humans and we tend to repeat our mistakes, we better let electronics do the protection job for us
and guard against this mistake.The error can never happen
when using the charger circuit featured here since its charging current flows only when the battery is connected in the right direction.
The charging current is around 50 mA. The entire circuit works as a constant current source. Polarity protection is done by T1, D1 and R1. When the battery is connected
correctly, transistor T1 conducts and
switches on the constant current source T2. The LED lights up when the circuit is charging. Otherwise, you know that you have made the mistake again. This time however, just
reverse the batteries to start charging.
Take note: this charger circuit can charge up to maximum of 4 Nicad batteries connected in series. Do not exceed this number of batteries if you do not want to destroy the charger
circuit and eventually your expensive Nicad batteries.
Parts Placement Layout
External Wiring Layout
Electronic Circuits volume 1.0 - Circuit Nr. 52
The complete data of the electronic circuit described above can be found in the following book and is available from Amazon.com.
Click on the image to view the book.