Ni Cad Batteries

[dr18931]

I salvaged some Ni Cad batteries from a crane magnet fail safe system.

The batteries are 30 ah 1.2volt cells, they are strapped and bussed 5 together

which makes 6 volts. I tried to charge the batteries and they do not seem to take a charge.Does any one know how to determine if they are serviceable or scrap. My goal is to use them as additional storage in a cycle charge system that I presently operate at a remote cabin.

Thanks for any response Doug

[thunderhead]

Some things worth checking are:-

1. do they have enough electrolyte?  Some NiCd batteries need to be topped up with distilled water from time to time
   
2. are you charging them to a high enough voltage?  NiCds typically discharge to 1.0v per cell and charge to 1.7v per cell  (see http://www.azsolarcenter.com/technology/batteries/pdfs/ch4.pdf for some charge/discharge curves).  So your bank of 5 will need to be charged to 8.5v.
   
3. you may need to replace the electrolyte, since it absorbs CO2 from the air over time.  I believe you can buy the electrolyte from caving shops: it's mostly potassium hydroxide (caustic potash) which is corrosive and may cause chemical burns.  Dispose of the old electrolyte with care, as it will contain cadmium, which is very, very toxic.
   
   

From what I've read in the EV community, wet NiCd cells often make a good recovery after a few charge/discharge cycles.  But if this doesn't work out for you, please dispose of them carefully, as cadmium is very very toxic.

Hope this works out for you.

[nickelbender]

I just stumbled across this....

Are you aware of any method to freshen up old weak NiCd flooded wet cells?

We send out our old trays of batteries to a company that desulfates our lead acid batteries and they come back ok. But know one seems to know what they do to the NiCds

[thunderhead]

I'm not sure what the mechanism is that is making your NiCd cells weak.  If the electrolyte is good, though, cycling the cells should build up the nickel and cadmium hydroxides that store the charge from the metal electrodes.

If the electrolyte is replaced, be careful of how you dispose of the old electrolyte, as it will be contaminated with cadmium.