Shocking NiCads back to life

[Ferg]

Has anyone tried this?

My cordless drill has two dud batteries. If I were to replace them I would do as well to buy a new device money wise. I've seen you tube videos showing the process of shocking NiCads by using double the voltage to recover they're charging capability. I wondered if anyone had done it and could share their experience with this.

[robin]

I know that they are dangerous and on that basis alone I think applying much more than the recommended charging voltage is a really good idea

It won't fix it though - it vapourises the dendrites but they grow back ...

Cheers,
Robin

[tut]

Did you mean a good idea Robin, or the opposite?

tut

[robin]

I mean it's a good way to create a big bang and a fire, otherwise it's a bad idea

Cheers,
Robin

[tut]

Ah so, a bit like my three phase wiring set up for 20 halogen electric fires around the house.

tut

[robin]

Quite. That's truly special wiring

[tut]

Actually the fuse box did catch fire a few years ago, but that was because it was one of the old type massive cast iron ones with big bakelite fuses.

As it kept blowing, I doubled up the 30amp fuse wire which seemed to do the trick, but it was obviously obsolete. The insurance company agreed, so it was all replaced with new equipment and no problems since apart for the master ECB occasionally tripping.

Quite proud considering my "A" Level Physics results.

tut

[Ferg]

I know that they are dangerous and on that basis alone I think applying much more than the recommended charging voltage is a really good idea

It won't fix it though - it vapourises the dendrites but they grow back ...

Cheers,
Robin

I'd tend to agree. I suppose the question is, do the dendrites grow back at the same rate as before? Will look further.

[robin]

The dendrites puncture the insulating layers inside the battery; I don't know much about the chemistry but I suspect that once the insulating layer is punctured you reduce the charge capacity of the battery dramatically. You also need to be very careful of heavily depleted multi-cell packs. The chances are you will have wrecked the capacity of each cell differently. Now when you charge the cell pack up the more wrecked cells will reach full charge much earlier than the less wrecked ones and will overcharge - thus further damaging them; when you then discharge the pack the same cells will become flat first and thus overdischarge (reverse charging from the other batteries) and you'll wreck them more.

Basically it's a fools errand - take them to the local tip for battery recycling and buy some new packs or tools as required (I don't buy cordless things any more because I'm pissed off with battery packs dying - then again, I don't actually do any DIY ).

Cheers,
Robin

[Rich H]

Tut, the solution to your fuse problem:

[robin]

The one on the right doubles as a crank shaft pulley bolt if required

[Ferg]

lol

I think I was just kidding myself I wasn't going to have to buy a replacement. Thanks for the voice of reason...

[Ferg]

Should have wiki'd it in the first place....

Dendritic shorting

When not used regularly, dendrites tend to develop. Dendrites are thin, conductive crystals that may penetrate the separator membrane between electrodes. This leads to internal short circuits and premature failure, long before the 800–1,000 charge/discharge cycle life claimed by most vendors. Sometimes, applying a brief, high-current charging pulse to individual cells can clear these dendrites, but they will typically reform within a few days or even hours. Cells in this state have reached the end of their useful life and should be replaced. Many battery guides, circulating on the Internet and online auctions, promise to restore dead cells using the above principle, but achieve very short-term results at best.

[thinfourth]

1 Are they NiCads?

2 Have you considered gutting them as a lot of them are standard cell size inside

[Ferg]

Yep, definitely Ni-Cd. Hadn't thought about inserting new cells.

Found a similar replacement device inc battery for £49 compared to just a battery for £32. Bizarre.