18v rechargeable battery resurrection

[Potszer]

I recentely came on to an add on e-bay telling about a product on how to restore nickel cadium rechargeable batteries that had lost there abillity to hold a charge ,the add stated that the procedure used was to zap these batteries with a surge from a car battery or other source and this would eliminate the what it refered to as "crystal denidrite growth" that had built up in the cells and caused the failure of the battery to hold its charge.. The product the add was selling was "Battery Resurrection,Pro Version" I would appreciate any info you can give me on this subject and thank you

 

[(*steve*)]

Yeah, it's true (at least to some extent).

The end of life of a NiCad is usually marked by it, having been left discharged for a long time, ending up as a shorted cell.

You can't recharge it, because there is a dead short.

I found (as I suspect many, many, many others did) that a high current pulse will restore them to a state where you can charge them. Indeed their capacity seems quite good after you do this.

I did this as a party trick, I am sure that they will not last very long. Yeah, I have really fun parties.

My technique used a charged capacitor because it was very easy to deliver a small charge very quickly which did not risk dangerous overheating and possible battery rupture. I would not contemplate using a car battery because it just sounds too dangerous.

edit: a capacitor is a far cheaper option.

Best to buy new batteries anyway because there's going to be different capacity and that's not good for them (it may have caused the battery to die in the first place).

 

[55pilot]

To add to what Steve has said, the basic concept is real and has been known since the 80's or possibly earlier. But I can not vouch for the particular product. I do not know if that is what they do and how well they do it and how much safety precautions are built into the product. Doing it wrong can cause a battery failure, fire, death and all sorts of other bad things.

---55p

 

[Potszer]

Thank you Steve for your quick reply: could you tell me what type of capacitor you used? and would a 12 v battery charger for auto batteries work if set to the start position in order to deliver 55amps?

 

[55pilot]

would a 12 v battery charger for auto batteries work if set to the start position in order to deliver 55amps?

As I posted above, doing this can be dangerous. I can not say if the product you originally asked about is safe or not, but connecting any NiCad battery to a lead acid battery charger is definitely extremely dangerous. DO NOT DO IT.

---55p

 

[(*steve*)]

Remember -- this only works on NiCad's

I would recommend you get a 100uF capacitor (I used a capacitor from a disposable camera).

Charge it up to about 20 to 50 volts.

Discharge it across the shorted cell with the positive end of the capacitor to the positive end of the cell. (It's better to do this to the affected cell rather than across the entire battery)

See if the battery begins to charge when placed in a charger.

WARNING: The capacitor will make quite a bang when you discharge it across the cell. Also the capacitor itself is quite dangerous when charged (obviously more-so at higher voltages) so keep your fingers away. For your own safety it's best to arrange things so the charge and discharge can be done with one hand in your pocket. Whilst the voltages I've suggested are not likely to be deadly, it's good practice to avoid the possibility of a shock across your arms -- and therefore your chest.

The device I used was the complete innards of the flash from a disposable camera with the flash tube removed and a pair of long (and well insulated wires added. A voltmeter was placed across the leads so I could terminate the charge at whatever voltage I wanted (be aware that some of these cameras won't allow you to do that).

Those disposable flash units are powered by a single 1.5V AA cell, and can deliver up to 7 joules of energy via the capacitor into a load. This is certainly in the range that can kill you if you manage to apply it to yourself "correctly". So BE CAREFUL.

If you resurrect a cell in a battery, be aware that it will be 100% discharged and the other cells may not be. This WILL cause problems if the battery is charged as a whole. If you can't charge the cells separately, the next best option is to carefully discharge each cell to 0V and charge the battery from there.