Substitute for NiCd

[veedub565]

Hi,

Possibly this belongs in the renewable energy forum. ANyway, I have a new old stock backup battery:

NiCd
12v
1000mAh
50mm dia
95mm long

It is still in the original packaging and never been used...... but, get this, date of manufacture is 1991


Now I know that NiCd batteries are great for long term storage, but 25 years may be pushing it. And you are still supposed to give them a charge once a year or so. This one has never been charged! At this point it is likely that there are Cadmium deposits or whatever shorting out the cells.

So, any idea's what I can replace it with? since NiCd batteries aren't really sold anymore, except for specific circumstances. It is a backup battery in a piece of old telephone equipment which I am working on. It receives a constant trickle charge the whole time so NiMh are out.

[Kleinstein]

I would give it a try first. Some cells are really robust. For a low demand purpose I still have an old 500 mA AA Cell running - it should be from about 1980 and was not used for quite some time (e.g. 1995 to 2010).

[peter.mitchell]

whats the trickle charge current like? you could add a series diode and resistor parallel to limit the trickle charge more so the catalyst can deal with itand the diode lets the cell deliver full current the other way with a nimh

[johansen]

nicd's are not like lithium ion where once they are dead, they aren't really dead yet.

once they are fully discharged there are no further reactions that can take place.
a 25 year old, never charged cell may still be good. however the seals could have dried out and you may need to add water, usually impossible to do.

[amspire]

I have a pair of Radioshack Walkie Talkies from 1989 and they had 10 Japanese made NiCd AA cells in each. Of the 20 cells, 15 are still working brilliantly. The five I chucked out were working but were showing signs of leakage.

So it is definitely worth giving the 25 year old batteries a go.

Usually, to replace NiCds with other batteries, you have to design a new charger circuit.

You can still get NiCd on eBay, Aliexpress, etc. If the existing batteries no longer work, you may be able to break open the 12V battery case, and replace the internal cells with new tabbed NiCd. Twelve 2/3 AA tabbed NiCds are on ebay for A$9.42 and they should easily fill in the old battery case with room to spare. Full size AA tabbed batteries are probably too long.

[veedub565]

Having a go at charging it from a PSU. It's taking some current so here's hoping it may be ok.

Not sure what the trickle charge current is in the equipment it's installed in.

[veedub565]

It's suckin about 350mA at 15v (12v battery)

[amspire]

It's suckin about 350mA at 15v (12v battery)

That is a bit much. You probably shouldn't charge at any more then 100mA. Batteries of this vintage did need 16 hours to charge. Give it a few hours at 100mA and then check the voltage. If it is something below 12V such as 10V or 8V, then you almost certainly have shorted cells.

[macboy]

It's suckin about 350mA at 15v (12v battery)

That is a bit much. You probably shouldn't charge at any more then 100mA. Batteries of this vintage did need 16 hours to charge. Give it a few hours at 100mA and then check the voltage. If it is something below 12V such as 10V or 8V, then you almost certainly have shorted cells.

Nonsense. I used to play with R/C buggies 25 years ago and we charged our NiCd packs in 15 minutes at about 5 A. These were made of sub-C cells, still very common. I still have some of those packs, and they still work today, after being stored for 20 years discharged.

However, the advice to charge at 1/10 C (100 mA for a 1000 mAh pack) for 16 hours is appropriate. This slow (over)charge is important especially when reconditioning old cells that haven't been charged in a while.

[veedub565]

I didn't leave it at high current for very long, wound it down a bit to more of a trickle charge. Left it disconnected overnight, rechecked this morning and it's holding about 13v

It's currently taking 50mA at 13v

What sort of voltage should the charger be set to on a 12v NiCd ? 

[hayatepilot]

Just use a constant current source. The voltage doesn't matter.
Fully charged a NiCd Cell can reach 1.6V (depending on charge current)

[macboy]

I didn't leave it at high current for very long, wound it down a bit to more of a trickle charge. Left it disconnected overnight, rechecked this morning and it's holding about 13v

It's currently taking 50mA at 13v

What sort of voltage should the charger be set to on a 12v NiCd ?

You need a current regulated supply. The voltage can be set much higher than necessary; the power supply will be in constant current mode and its output voltage will end up being the voltage of the battery, which depends on the set current and the state of charge. For a 12V pack I would set it to 20 V. For a 1000 mAh pack, I would set it to 100 mA or less (less for small, more delicate cells, not durable AA or sub-C types). At charge current of 1/10 capacity, charge 16 hours (not less), and for lower charge current, scale up the time to deliver 1.6x the capacity (e.g. for 1000 mAh cells at 50 mA charge, you need 32 hours at 50 mA to deliver 1600 mAh). This slow overcharge does not damage the cells since the gases produced are able to recombine into water. Overcharging at a high rate is another story... don't do that. Also, the overcharge is necessary since the surface area of the NiCd cell is very high, and parts of that might become fully charged before other parts. The overcharge allows the entire cell to fully charge, and the gassing/recombination that occurs within also help evenly redistribute water throughout the cell.

[CJay]

It's suckin about 350mA at 15v (12v battery)

That is a bit much. You probably shouldn't charge at any more then 100mA. Batteries of this vintage did need 16 hours to charge. Give it a few hours at 100mA and then check the voltage. If it is something below 12V such as 10V or 8V, then you almost certainly have shorted cells.

Bad person that I am I have dumped *lots* of current into shorted NiCd cells at voltages way in excess of ratings. It often works to remove the short and the cells then recover with a careful charge.

of course, I'm not recommending anyone else do this, danger....