How to restore NiCd battery capacity to full???

[amiklic1]

I got 10 cells of NiCd batteries, each 1.2 volts / 240 Ah, connected in series, so the 12 volt system is present. Every cell can have 13.7 to 14.0 volts vhen full.

It is strange that my wind generator ( 125 watts Piggot's design) charges them very fast. So, with the wind of about 18 kmh ( 5 m/s) , they come from 9 volts to 13 volts for about an hour.

Also, what's been charged fast, drains fast, so when I connect two H4 lamps, every of 60 watts, I can see my voltmeter is going down.

I think that those batteries haven't seen the charger for a while before I got them, so capacity fall down...

What can I do to restore battery capacity???

I read somewhere to discharge them to minimum, then to charge them with very high amps, and do about three such cicluses, and then to charge them with nominal voltage ans manufacturer's suggested amperage..

I am a bit afraid that MY BATTS ARE DEAD!!

[Flux]

How far do the volts fall?. I think 10 cells will fall to 11v fairly quickly on load.

If they fall to 10v quickly you have a problem. I don't think repeated charge and discharge will help much, they don't have the memory problem of sealed NiCd.

The only hope is to check the specific gravity of the electrolyte and change it if it is very low. They absorb CO2 from the air over the years.

Do you know how old they are? Some people seem to keep them going for a very long time, but the ones we had at work weren't much use after 20 years.

If SG is below 1.16 it may be worth trying one cell with new electrolyte to see if it improves. The manufacturers used different electrolyte for different types of cell, but it was never disclosed what it consisted of. I think your only chance is to start with 30% solution of KOH and dilute until SG is 1.2.

Flux

[pwr]

Ni-cads take 1.75 volts be cell to get fully charged.

[ruddycrazy]

I have a bank of Nicad's that I got from a military installation and my mate who uses the same batteries at work suggested to drain out the electrolyte and wash them out with distilled water then replace with new elecrolyte. He says they do that every year and they get upto 20 years from them but replace them after 15 years to be on the safe side.

Hope this helps Ruddy Crazy

[Chagrin]

The theory behind the high-amperage burst charge is to burn away "whiskers" that have formed between the positive and negative elements. Google for "NiCD whiskers" and you'll find the information you're looking for.

[Flux]

Yes they do need above 14v to be fully charged, forget your shunt regulator at the moment to be sure they are fully charged. 14V is more or less a float charge and they need to go above this if they have been low.

American manufacturers may have different ideas about changing electrolyte, but Britannia Batteries advised to discharge below 0.8 v per cell, tip out the electrolyte, allow to drain for not more than 30 minutes and refill. They advise against a rinse with distilled water.

Rudy Crazy, that life is similar to what we obtained, others seem to claim 30 or more years, probably they have limited capacity at that age.

Flux

[twidget]

Ive been running some old used nicads for about 6 years now. If your voltage only got to 13.8, you probably had nowhere near a full charge. Under charge the voltage will go hi early. For me to get a full charge I charge until my voltage is about 16.2v. Even this is not really a good indicator of charge state. Its recommended that an amp hour meter be used to monitor charge state. But for me the voltage topping at 16.2 is good enough.  HomePower magazine had some articles in its early days about nicad restoring. I forget where they were but I did run accross them in an archive on hte net for free. Each issue was a zip file

Just my two cents

Twidget

[twidget]

one thing I forgot to mention in my post.  125w genny at 12 volt is roughly 10 amps if your batteries are drained it would take a 24 hour charge + to fully charge the bank with the genny at max output. I charge with 400 w solar but find in the winter I need to dump in about 4KW HR a week to keep my charge levels up.

It would be nice to hear from anyone else running flooded NICADs and their thoughts..

As always, just my two cents

Twidget

[boB]

>>burst charge is to burn away "whiskers" that have formed between the positive and negative element

Another word you may want to try in this search is dentrites.

boB

[Nando]

each cell charges to 1.37 volts NOT 13.7 volts.

Check the fluid, it seems that is very low, add DISTILLED WATER ONLY, NOT filtered water, you need water with PH=7.00 NO alcaloid of any type, no Calcium etc.

You do not need to discharge them right now,

Nando