Old Nicad Questions:

[donn_]

Buying older rechargeable Surefires has gained me a collection of older B90s and B65s, most of which were probably never maintained well.

I want to see if they are worth trying to use, and have some questions about them.

1. What is normal self-discharge on a Nicad pack? For example, I'm currently testing 10+ year old B65s which were never even out of the baggie. I charged one up this morning, and it took the charge, but has lost a quarter of a volt of charge in 6 hours (resting) since the charge. Is that normal, or too much? My hunch is it's too much, which leads to my second question:

2. Is there a way to restore any level of usefulness to older packs like this?

Thanks

 

[MarNav1]

Maybe SilverFox would know? I'm with you donn, if its dropping that much resting under load I'd bet it will fail quickly if it works at all.

 

[clintb]

Some past threads / recommendations by SilverFox:

Note: These address NiMh, but it's still applicable to do the 1/10C charge for 16 hours, then discharge, but since it's NiCd discharge to 0.8V per cell.

http://www.candlepowerforums.com/vb/showpost.php?p=2436470&postcount=3
http://www.candlepowerforums.com/vb/showpost.php?p=1277992&postcount=8
http://www.candlepowerforums.com/vb/showpost.php?p=2391945&postcount=5

 

[VidPro]

you will have to Wake them back up a bit first :sleepy: realign thier universe by removing the chaos of the earthen chemicals :tinfoil: By applying power the chemicals will be pushed into thier man designed purpose.

the voltage dropping doesnt much show you anything, unless it drops to like 1V as everything drops some when removed from the power that was going into it.

do the slow forming charge thing, then (on ni-cds especially) do about 3-8 normal to fast cycles of them, then test.

a capacity check would be better, because voltage doesnt tell you a lot, Although if you sit it around for 2 weeks, and its still sinking badly or has gone way low, that would still indiacate to high of self discharge.. you will improve these thing by some cycling, depending on how sick they are.

 

[donn_]

1/10C charge....forming charge...

Guys...I have the SF chargers for these cells. There isn't a lot of leeway in how the cells are charged. It's just plug them in and wait for the green light.

Apart from that, I have a couple of Tenergy hobby chargers which will provide anywhere from 2.4v to 12v charges for Nicad or NiMH cells.

 

[SilverFox]

Hello Donn,

If you are seeing self discharge issues in 6 hours, it probably means that your cells are out of balance. You are going to have to figure out a way to address the individual cells of the battery packs.

The SureFire chargers work very well for healthy packs, but they are not well suited to reviving abused or near dead packs.

As others have indicated, you need to start with a 16 hour 0.1C charge. Then you need to let the battery packs sit for awhile to check if all the cells are working. If they do not all respond, you need to progress to working with the individual cells in the pack and do some extra work on the dead ones.

Once you get all of the cells in the pack responding, then you will need to do several charge/discharge cycles to bring the cells back to "near" life. Your goal is to end up with over 80% of the packs initial capacity, and at this point you should be at least over 50%.

To get from 50% to over 80% involves several "tricks" depending on what the cells are doing. One trick is an over discharge at a very low current draw, but done with caution to minimize any damage. Another involves high rate charging for the initial 60% of the charge. Another involves extended trickle charging.

There eventually comes a time when you make a decision that your time is worth more than trying to revive the battery pack and you move on to the next one...

As far as self discharge rates go, the B90 packs should have about 80% of their initial capacity after 4 weeks.

Tom