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# Charging problem

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#### thebigbasicq

##### New Member
What will happen if I charge a 1.25V NiCd cell at 4V but supplying only the required amount of current?

if you apply 4V to it and you let it absorb the current it needs in a few seconds it will BLOW!!! and yo ucertainly dont want that. if you aply 4V to it and let it draw an amount if current required for a recharge, the voltage across it will drop at about 1.4V

Nicad batteries require charging at a constant rate of current.

This can be achieved by using a constant current source, irrespective of the voltage, although the voltage does need to be appropriate for the cell or battery pack being charged.

The charging current depends on the mAh rating of the cell, and is expressed as a C/n rate. Example a nicad cell has a capacity of 500mAh then the appropriate charge rate would be C/10 (the 10 rate is the preferred time period) or 50mA...If the cell is capable of being fast charged then the C/n rate could be C/1 or greater....2C or more....

I use nicd packs a power source for electric R/C and use special microprocessor based chargersfor fast charging my packs usually in under 30 mins....but these are special packs, not your average domestic nicad.......

HTH Chip

What is

the 'n' in the expression? Is it no. of hours?

Sure thing.........n= hours....C= batt capacity in mAh or Ah if its a big battery/cell...

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