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Ni Cd battery charging

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manishanand14

manishanand14

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Hello Everyone!

I have a constant current charger built around LM317 set at 200mA to charge a Ni Cd Battery rated 4.8V/1000mAh (series connection of 4 AA cells).

Do I need to charge it for 5 Hrs to completely charge it.

The manual says standard charge @100mA for 14 Hrs

I don't want to use a complicated circuit.

Also tell me at other charging current setting how do I calculate the charging time.
 

5 hrs is the theoretical time, its better to allow a little more , say 5.5 Hrs.
In order to keep the batteries cool, most are designed to charge over 10 Hours. "fast" chargers actually monitor the batteries temperature as they charge to keep it within the manufacturers limits.
I would modify the circuit to switch in a different current sensing resistor to drop the current to 100 mA. There will be a series resistor of (I think) of about 6 ohms, wire in another resistor of this value IN SERIES with the original, so by throwing the switch you can short out the new resistor and go back to 200mA.
Frank
 

Please tell me what is the procedure to correctly tell that the battery is fully charged.

Does 5.6V (1.4V per cell) open circuit voltage tells that the battery is fully charged.
 

No, measuring the voltage as you are charging it is not a reliable way to detect fully charged. If you really want to know you need to measure temperature rise in the battery too. There is no simple circuit to do this right. About the best you can do with a simple circuit is use a very low current and let the battery continue to trickle charge. Or get a more complicated circuit and do it right.
 
Why don't you read about charging old-fashioned Ni-Cad batteries at the website of a battery manufacturer like www.energizer.com ? Click on technical Info at the bottom of the home page and search for Ni-Cad. They have a Ni-Cad Applications Manual among their datasheets. www.batteryuniversity.com also tells you all about charging a Ni-Cad battery.

Here in the West, we use a battery charger IC to properly charge a battery. It does everything correctly.
Here, modern Ni-MH cells have replaced toxic Ni-Cads and the Ni-MH cells are a big improvement. But old-fashioned Ni-Cads are still used in cheap Chinese solar garden lights.
 

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