Revive/restore dead Ni-Cd batteries - shocking or reverse charging - does it work?

Thread Starter

RogueRose

Joined Oct 10, 2014
375
I was reading and watching some videos on how some people "revive" dead nickel based batteries, mainly nicd batteries. Some people have said that putting a higher voltage on dead batteries does the trick while others stated that reverse charging is what does it. I've watched a number of videos on Yt (extremely painful - the posters move in slow motion and seem to have no electronics knowledge...). Some say "sufate" crystals build up between the plates preventing electron flow - but I don't see how that is possible with nickel batteries as sulfates arean't used to my knowledge - maybe they are confused with lead acid which does build up lead sulfate crystals.

Can anyone say if they have verifiable results with with reviving these types of batteries and if so, how do you do it? I am absolutely AMAZED at the number of videos showing people how to do this and the are almost all done by extreme amatures who don't even seem to grasp how batteries charge. Millions of views and generally positive reviews (SMH..) how is that possible..
 
I've done it, but it doesn't seem to be worth my time anymore. Nimh generally can replace a NiCd without doing anything special.

There are "plans" for some devices that will do it.

I just took a capacitor about 1000 uf or bigger and charged it to 40 VDC and discharged it into a 1.2 v NiCd.
Then I would monitor the resulting voltage and quit when there wasn't any more change. Then charge.
 

DickCappels

Joined Aug 21, 2008
6,374
When Ni-Cd cells discharge they tend to grow tiny whiskers between the electrodes which cause a short. This can be verified with a DVM, is should show zero volts across the cell and the cell should measure as a dead short.

To bring back the cell, at least until the whisker grows back, you need to dump enough current into the cell to blow the fuse but not hurt you while doing it.

As per KeepItSimpleStupid mentioned in post #2, this is often done by charging a really big capacitor and discharging it into the cell. This is can be done with a car battery or a large power supply but that is a very dangerous way to go because the amount of energy available from sources like that are for practical purposes unlimited and the chance of doing damage to the cell, the equipment, or yourself is very real.

You only need enough voltage to assure that adequate current is delivered to the short for a sufficient amount of time. 2% should be plenty.
 

Thread Starter

RogueRose

Joined Oct 10, 2014
375
I've done it, but it doesn't seem to be worth my time anymore. Nimh generally can replace a NiCd without doing anything special.

There are "plans" for some devices that will do it.

I just took a capacitor about 1000 uf or bigger and charged it to 40 VDC and discharged it into a 1.2 v NiCd.
Then I would monitor the resulting voltage and quit when there wasn't any more change. Then charge.
So was this for a battery pack or individual cell? if a pack, what voltage?
 

Thread Starter

RogueRose

Joined Oct 10, 2014
375
When Ni-Cd cells discharge they tend to grow tiny whiskers between the electrodes which cause a short. This can be verified with a DVM, is should show zero volts across the cell and the cell should measure as a dead short.

To bring back the cell, at least until the whisker grows back, you need to dump enough current into the cell to blow the fuse but not hurt you while doing it.

As per KeepItSimpleStupid mentioned in post #2, this is often done by charging a really big capacitor and discharging it into the cell. This is can be done with a car battery or a large power supply but that is a very dangerous way to go because the amount of energy available from sources like that are for practical purposes unlimited and the chance of doing damage to the cell, the equipment, or yourself is very real.

You only need enough voltage to assure that adequate current is delivered to the short for a sufficient amount of time. 2% should be plenty.
So is the polarity the same for this, and just using a higher voltage, or is the voltage revered like I had read in some other pages.
 

DickCappels

Joined Aug 21, 2008
6,374
Same polarity so that when the short is cleared the remaining energy in the capacitor does not charge the cell in reverse. I have only tried this on individual cells. In batteries I locate the shorted cell and only blast that one.

Before you go blasting away, check to see whether you have a shorted cell by applying current to it and observing the voltage.

It is important to charge the cell right after clearing the short. The Conditioning Mode described on page 9 of the document Bertus mentions in post 8 should be very good for this.

It is not a critical procedure, but you might find that you need tens of thousands of uf. The best way to find out is to try it yourself.
 

tcmtech

Joined Nov 4, 2013
2,867
I've tried every method I have ever found regarding trying to reviving dead worn out rechargeable batteries and I have to say in the end its was all just a waste of time effort and money for the tiny extension of their service life. Increasingly temporary fixes to permanent problems was all it ever added up to.

Contrary to what so many think batteries are a consumable item that ultimately wear out. The fact is even with the best possible charging methods and such Vs normal basic charging there is very little long term gains to justify it in the vast majority of applications day to day applications.

For me when a battery starts going bad it gets replaced with a new one shortly after and of preferably higher quality and capacity which pretty much is a 100+% guaranteed fix to a problem that's just going to get worse.
 

ian field

Joined Oct 27, 2012
6,539
I've done it, but it doesn't seem to be worth my time anymore. Nimh generally can replace a NiCd without doing anything special.

There are "plans" for some devices that will do it.

I just took a capacitor about 1000 uf or bigger and charged it to 40 VDC and discharged it into a 1.2 v NiCd.
Then I would monitor the resulting voltage and quit when there wasn't any more change. Then charge.
Ni-Mh cells have higher internal resistance. When I used them in a shaver - 2300mAh AA cells (brand new) gave shorter running time than the knackered 500mAh cells I took out. The Ni-Mh cells got fairly warm, so I guess that's where the missing energy went.

Generally speaking; recovered Ni-Cd cells are never quite the same.

Pulse charging is worth a try on Ni-CD cells - but can ruin Ni-Mh. One of my more successful experiments was a pulse charger built around an old AT PSU. A dummy load resistor on the 5V rail got the PSU to run, a capacitor coupled charge pump voltage doubler from a 12V secondary charged the battery. In the voltage doubler; the shunt diode was Shootky barrier to minimise the reverse voltage excursion and the feed diode was fast silicon, the reverse recovery characteristic produced negative spikes in the charging current.

Temperature sensing can allow brutal charging current, as the cells near full charge the temperature crosses the switch off threshold more rapidly - so it ends up cycling at a fairly quick rate, that's a kind of pulse charging.

Both charger types gave me good performance from cells that were rescued from a skip.
 

tcmtech

Joined Nov 4, 2013
2,867
Ni-Mh cells have higher internal resistance. When I used them in a shaver - 2300mAh AA cells (brand new) gave shorter running time than the knackered 500mAh cells I took out. The Ni-Mh cells got fairly warm, so I guess that's where the missing energy went.
I would be far more inclined to suspect you got some grossly over rated very poorly made ones that were nowhere close to being an actual 2300 mAh cell.

I use Tenergy high capacity 2200 - 3000+ mAh sub C NiMh cells from here, http://www.all-battery.com/index.aspx, for all my cordless tool battery pack rebuilds now and they run circles around even the good near new NiCad battery packs that havent given me problems yet. Far more power for far longer and they don't heat up as much either.

Now however on the first few battery packs I tried rebuilding with off brand cheapo cells I got elsewhere that were suposedly 3200 - 3600 mAh they proved to be far more like what you experienced. Way less power and run time than what they replaced and got dangerously hot the first time they were ran hard on top of it. My guess is they were likely 1000 - 1200 mAh low drain rate types falsely badged and marketed as high capacity cordless tool cells. :mad:
 

Thread Starter

RogueRose

Joined Oct 10, 2014
375
I would be far more inclined to suspect you got some grossly over rated very poorly made ones that were nowhere close to being an actual 2300 mAh cell.

I use Tenergy high capacity 2200 - 3000+ mAh sub C NiMh cells from here, http://www.all-battery.com/index.aspx, for all my cordless tool battery pack rebuilds now and they run circles around even the good near new NiCad battery packs that havent given me problems yet. Far more power for far longer and they don't heat up as much either.

Now however on the first few battery packs I tried rebuilding with off brand cheapo cells I got elsewhere that were suposedly 3200 - 3600 mAh they proved to be far more like what you experienced. Way less power and run time than what they replaced and got dangerously hot the first time they were ran hard on top of it. My guess is they were likely 1000 - 1200 mAh low drain rate types falsely badged and marketed as high capacity cordless tool cells. :mad:
I'm looking at doing some rebuilds and was wondering what you use for connecting tabs or if you use batteries with tabs/wires already connected/ Is there any benefit to using a CD spot welder to attach tabs vs using wire?
 

tcmtech

Joined Nov 4, 2013
2,867
I'm looking at doing some rebuilds and was wondering what you use for connecting tabs or if you use batteries with tabs/wires already connected/ Is there any benefit to using a CD spot welder to attach tabs vs using wire?
I typically get the cells with tabs on them but when I don't I just prep the metal surfaces with the Dremel and a grinding stone then solder them on with the big 150 watt buzz gun being if the tip is tinned and hot it will lay down a good solid solder bead that will bond to the metal fast enough to not cause any considerable amount of heat transfer into the actual inner cell components.

Grinding the surface clean is the key to getting the solder to bond fast and at minimum temperature though.

As for bonding straps I like to use 14 ga solid copper wire that's been flattened out with a hammer to make it into a ribbon.
 
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