Battery Charging Regime For Slow Charge?, C/10 charging for NiCd battery

[treez]

Hello,

We are charging four series NiCd (SAFT VNT D U ) cells at C/10 (~450mA) .

Our charger is just a 450mA current source which can be turned on and off, it can't be reduced or increased.

Since our charge rate is so slow, does this mean that we can use a very simple charging regime, whereby we simply monitor the voltage across the cells, and when its got up to 5.6V, we simply stop charging it?

SAFT VNT D U cell
http://www.saftbatteries.com/doc/Doc...d6a0ff6b3f.pdf

[AwesomeMatt]

Not regime. Perhaps regimen is the word you're looking for.

And, hrm.

NiCads have a "feature" of their chemistry whereby they turn excess current (caused by excess voltage) into heat. And as long as you don't have too much heat for them to dissipate, they don't explode or get damaged.

C/10 isn't slow for NiCads though.
C/40 is perhaps slow.

NiCad chargers use one or a combo of 3 methods to determine shutoff:

1 - Temperature.
2 - Voltage dropping (after peaking, it starts to drop again as it heats up from overvoltage).
3 - Time.

But, if you don't want to juice them up to 100%, charging them to something less than their peak voltage, at a slow rate, and just leaving them there is probably fine. Probably not optimal, might be harder on your batteries, but, meh, probably functional.

http://batteryuniversity.com/

[treez]

C/40 sounds better....but this is an emergency light, and i dont know if the regulations will allow recharge in such a long time.

I have written off for a copy of the standards, but received nothing as yet.

[treez]

do yo uknow if while charging a stack of cells, does one have to do individual cell voltage monitoring?

...and if one does, does one have to do this with all cell chemistry types?....or is it just Lihium ion ones which need this individual cell voltage monitoring?

[Nothing40]

Individual cell monitoring/balancing is required for lithium chemistry types,but not so much for Nicd/Nimh types,in most applications. You can if you want to,but in this situation it's probably overkill.