Hi All.
I saw this add on flea-bay that suggested rechargable battery packs for drills etc could be rejuventaed if their voltage had dropped... :-\
I did a  little (very little) bit of research showed you would need a 36v battery to "fix" a 18v battery.
Is this just a scam???
does it have any merits.
I have 3 ryobi 18v nicad batteries that are starting to get very lame in performance.....
Any ideas anyone.....
thanks

I found this on another forum;

NiCads that won't hold a charge may return to near new condition using
this procedure. It is worth a try and maybe save $50 or more. If it fails for you, it doesn't cost much.

Discharge the battery as much as possible.
Put in freezer for 12 hours.
Remove and let thaw to room temperature.
Put in charger and let charge normally.

Two men reported this as a solution to Woodworkers Journal's e-zine.

Be very careful if you try it to thaw the battery thoroughly before charging as nicads can explode if charged below 5 Centigrade.

I was also told years ago that nicads could be revived by "flashing" 240V across them.

I have never tried either, but if you have a buggered battery, what the heck?

Here's something else;

http://www.instructables.com/id/Revive-Nicad-Batteries-by-Zapping-with-a-Welder/

From my 10 minute Google there seems to be a lot of info out there for free, so don't bother buying anything off ebay because it will only be the same info.

I might try this my self on a totally dead Bosch 24V battery I have. I'll let you know if it works if I have any hands left!

Ship-badger said:

I was also told years ago that nicads could be revived by "flashing" 240V across them.
I have never tried either, but if you have a buggered battery, what the heck?

Click to expand...

That catogorically applies to lead acid batteries and not nicads. and 240 volts is way excessive.

the lead plates in leadacid batteries suffer from a build up of salts over the years (bit like rusting). These salts can be 'shocked' off the plates by passing a high voltage across them - just giving the lead plates a new lease of life. Mainly used for rejuvingting oldham lead acids. Hence 24 or 36 volts across a 4v oldham should be enough.
Think this has been covered before on the forums.

I may be wrong about nicads - but I wouldnt try this on them.

The high current/voltage across the battery technique used to be a favourite for sorting out memory effect on NiCads. All major manufacturers of NiCads claim their cells no longer suffer from this effect.

I'm not going to comment on the effectiveness of some of the snake oil on offer on the internet, save to say that I don't bother with any of it myself. When my batteries go dead, I go and buy new ones from a reputable source.

What I will say (and I apologise to those whom I am teaching to suck eggs) is do not under-estimate how 'exciting' it could be to try connecting any rechargeable battery, in any state, across a live 230V mains supply.

I cannot over-emphasise that this is not a technique which should be attempted by anyone who does not have the equipment to properly control the current through the battery and fully understands how to use it. You would also need a safe place to do the experiment. I'd consider doing it in my (largely empty) 3000 sq ft barn, but nowhere smaller! I'd also have a fire extinguisher to hand, and make sure I was on the other side of something capable of deflecting the bits if the battery explodes when the current is turned on.

OK, so you might get away with it, but if you don't, it's going to be ugly. Think flash and bang. Think flying bits of battery case and metal. Think lethal voltages connected to said flying bits of metal. Think bits of flying plastic on fire. Think flying battery acid or other electrolyte. Think of something better to do with your time!

Nick.

I agree with Nick....

I know the "shock" technique works with car batteries, using a 24v truck battery on a 12 volt car battery, but 240 volts on  NiCad.... the results would be ...erhm....."unpredictable"

If I was going to do it, id have an fuse is series, to effectively limit the duratio of the pulse to however long the fuse took to blow....but flying molten metal sounds  a distinct possibility.

I wouldn't do it at all - consider the phrases "digitally challenged" & "facial reconstruction"!
The only safe advise I can give is to discharge the batteries to near flat and then recharge - repeat til bored. This will eliminate the ni-cad memory effect, if this doesn't work do as Nick suggests - get new 'uns!

There is some merit in passing a high current through a NiCd. Over time, metallic crystals grow inside the cell, and eventually short the cell out. By passing a high current (I just used a 12V car battery) through, you can destroy the short, and restore some kind of functionality.

I did this successfully, but realised that by the time the battery is doing this, you might as well sling it out and buy a new one.

I wouldn't use mains BTW! Too much energy.

Chris.

ChrisJC said:

There is some merit in passing a high current through a NiCd. Over time, metallic crystals grow inside the cell, and eventually short the cell out. By passing a high current (I just used a 12V car battery) through, you can destroy the short, and restore some kind of functionality.

I did this successfully, but realised that by the time the battery is doing this, you might as well sling it out and buy a new one.

I wouldn't use mains BTW! Too much energy.

Chris.

Click to expand...

As you say, "some sort". But who wants to use a Nicad knowing that somewhere in its innards there was once a short circuit which is now a burned-out mess with goodness knows what collateral damage and liable to form again at any time?

I once used a few paperclips to wire a battery up to 240v direct. I was lucky to only get shocked down a flight of stairs, i was only about 5 but looking back on it things could have been a lot worse.

The freezing method can work, but again can be risky, the concept (as far as i understand) is using freezing as a methos of breaking the performance reducing crystals that form in nicads through the charge discharge process.

The freezing process can cause the structural integrity of the cell to fail, as can the knocking you have to give the cell whilst it is frozen.

I have used this technique on stand alone cells and fx2 cells to varying degrees of sauces, some good, others bad.

First of all thanks everyone for the advice hints and tips....
I passed this info onto my Dad who informed me he had the same problem with some of his nicad drill batteries.
He has a 240v power pack that converts to 30v dc or something like that...
Any how we zapped 5 18v packs.
The first (and the guinea pig) was a real old one that produced nothing even after a charge...
The initial voltage across the ends unloaded was something like 1.3v.
After a 30v zap it went up to 20v..
2 others started at 16v across the ends and ended up 19.4 after the zap.
The other 2 started at 18v and also went upto 19.4 after the zap.......

All 4 apart from the real old guinea pig held their charge at those figures....
The old one dropped its voltage over the hour so we guessed a cell was duff in the pack....
I havent done a full charge and discharge on them yet and wont be able to (sadly) report on any improvement or not because my circular saw motor died....have now replaced the motor (good old ryobi) but the newer motor will give different performance so sadly I cannot report fairly on any subsequent improvement or not.....
Anyway I will report on any significant changes if they occur from the voltage across the ends in the meantime....
One again Thanks all for your advice-tips...
Carm