Recovering Rechargeable NiCad Batteries

Did they tell you what voltage the capacitor should be charged to before connecting it to the battery?

Sorry, they say to charge it to 300v. They also say it can be done with a welder.

Get "them" to show how to do it first. How about uploading it to YouTube (other websites are available)?

Here is the link to the site I found. It makes sense, but he says the cause is sulphur crystals. I don't think that's possible in a NiCad battery, however I am not a battery expert. What do you think? http://www.instructables.com/id/Bring-Dead-Ni-Cad-Batteries-Back-To-Life/

Open circuit welder voltage appx. 80 volts max

I have done this before. You have to get inside so that you can measure across each cell. Fully charged, each cell should be about 1.25 volts. When discharged, there should be at least some voltage. If a cell reads exactly 0 volts, what has happened is that a whisker has caused an internal short. I used to charge an electrolytic capacitor of about 20000 uf and zap it through the shorted cell with the polarity to charge it in the correct direction. If you see some voltage on the cell after zapping it, you are successful.

There is plenty of info on the web about 'reconditioning' nicads. Typically they are ones used as backup which have been subject to a long boring life of trickle charging.
Some cycles of maximum current charge discharge can sometimes invigorate them.
Many many years ago we had a craze for radio controlled cars and we got loads of old burglar alarm backup batteries for free, these would yield some good cells for the heavy duty condition of RC cars.... oh happy days, when the sun always shone!
Del

Ah, the good old days....

http://articles.orlandosentinel.com/1985-12-28/news/0340900029_1_asphalt-track-auto-racing

Team Losi, Team Associated, Bo-Link, man that was so much fun.

I can tell you one thing about NiCads, they will take far more abuse than anyone would ever imagine. Used to break up old Makita battery paks as they used 1700ma cell as opposed the usual 1500ma cells found in most everything else.

I have come across nicads that have failed this way myself several times. When you put a multimeter across them you get low ohms. I have never tried the repair method of shocking them but rather just bought new nicads.

It is probably off-topic, but out of curiosity, how do you measure ohms of a battery with a multimeter.

Thanks for that Energyconversion.

I was hoping no6 Tank would reply.

I had visions of the meter set to 'ohms' and poking the probes on the battery terminals.

Hence the question.

Its better to look for low voltage/no voltage as some Ohmmeters do not like having voltage across the prods.....

The replacement is $55+ tax and shipping. After the problem I had with my Bosch charger/battery overheating, I don't want to go aftermarket. I was hoping to rejuvenate the battery. I had two of them, but when the first on died, I gave it to Home Depot for recycling. Now that I'm down to one, I can either buy a new one or try to zap this one back to life.

So give it a try. What is the worst that can happen, the battery is already dead.

Then again...

Back in 2007, June 21st to be exact, our house caught on fire from the Bosch charger/battery. The fire dept couldn't figure out where the fire started, so they blamed the water heater - which was at least 5 feet from my workbench. The most damage occurred at the work bench, but I didn't want to argue, so officially, it was caused by the water heater.

In the summer of 2001, I was working at our new store (getting it ready to open) and I heard a crackling noise and a burning smell. I saw the Bosch charger/battery sparking and the plastic had melted. I pulled the plug and grabbed the battery to remove it from the charger. I didn't think about the heat and I did get a mild burn. I contacted Bosch, who was very helpful and they sent me a new charger and battery. I asked if this has happened before and of course they said no.

I no longer let my Bosch charger run unattended and when the charge light shows complete, I pull the plug. I've heard some odd noises (clicking and such) when I charge batteries and if I leave it in the charger after the charge light turns green, the battery starts to get hot. I believe there is a design flaw in this unit, but I can live with the inconvenience of watching the charger. The drill is excellent and even though it isn't as powerful at my Milwaukee, it has been through a lot and I think it's around 18 years old. Pretty good for a cordless drill.

Yup. I had an apartment fire caused by a dustbuster charging station a couple of decades back. Luckily it was a sunny day and the firefighters at the station across the street heard the smoke detector and started walking the neighbourhood to find the source of the detectors alarm. When the tenant called me, it was after she returned from work. All she wanted from me was to hurry up with the repairs. That was how I found out.

Anyhow she told me that the charging station was running 'hot' and she thought that this was normal!

Ah yes, reanimating the dead via high voltage arc.....The Frank Enstonian method has been chronicled here many times...

http://cr4.globalspec.com/thread/85000

1000 MFD ???

1000 µF (micro Farad) i.e. 1 mF?

1000 mF (milli Farad) i.e. 1 Farad?

1000 MF (Mega Farads) i. e. non existent?

Apart from that Good Answer.

MFD is common in USA to denote ufd,(microfarad),although it may be somewhat dated, it is still used on motor start capacitors. MMFD (micro-micro farad) was used for picofarad.Vacuum tubes were called valves in England.

Just different colloquial names for same thing.

Once a cell has a whisker, it generally simply grows back over the tiny gap made by the discharge. Sadly.

The rest of the cells will also probably soon start as well.....

But never, ever discharge ANY, of any chemistry Battery in this manner as you will weaken some if not all of the cells. Lifespan severely reduced.

Once any single cell is down to (usually) around 1 volt, the battery should be recharged.

Not overcharged. Never left on ANY charger for longer than needed to get to 100% of charge, or even slightly less....

Read the earlier post about weak cells being reverse polarized if over discharged, and made weaker.....

A lead acid leisure/deep discharge battery will probably handle it, but it still will not improve the battery.....a waste of time!

Guess I must have been lucky.I have been using 2 battery packs in my drill for over 10 years.I used the procedure I gave to zap them back and then followed with a full charge/discharge cycle. The battery sees heavy usage.

I have had to replace one single cell in one pack and it takes practice to solder the tab without overheating the battery in the process.I use a production-line method,with the soldering tip very hot,and pre tin the tab,so it only takes about 1 or 2 seconds to make a good solder joint.Not as good as the factory spot-weld, but good enough for my purposes.Haven't had a joint failure yet.

The tin whiskers do not apply to the nicad batteries, it is hydrogen bubbles that create an insulating layer around the electrodes,at least that is what I read around 25 years ago.Of course, old knowledge is being replaced as chemistry advances, so that theory may now be all wrong.

I guess ignorance is bliss,because my system works for me.

YMMV.

You have been very lucky then!

I did a little research and found several sites saying the same thing like here:-

http://www.hardwaresecrets.com/article/The-Truth-About-NiCd-Batteries/292/2

I read on page 2 (and 4) that fully discharging to under 1 volt per cell damages them.....

On page 3 it mentions the Dendrites (the whisker!).

Page 4 is also very interesting.......

None of which appears to support your methods.....

Ditch the NiCds. I've heard of restoring Pb and NiCd batteries, been there done that, waste of time and doesn't last long if it works.

Get some LiIon batteries (3.7V each), open the existing battery pack and replace. You can exceed the voltage of the original pack if it is a good quality drill like Bosch, AND you don't use it continuously for LONG periods, but don't overdo it. Chances are the new batteries will occupy a much smaller volume than the old ones.

Buy a LiIon balanced charger and matching PSU. Don't try charging with a mickey mouse setup. Kills LiIon fast and is a health hazard (see picture another reply).

The total cost will be a bit more than a new set of NiCds, but will run a lot longer and stronger on a charge.

You have to do this on a "per cell" basis and not a pack basis. That might be difficult with a drill battery pack. Sometimes it works and sometimes it doesn't. If the voltage across the battery is zero, it probably wont work. As you zap, the open circuit voltage increases.

I've used what i had available, a few hundred uF and 40 V. Charge and discharge into a single cell and monitor progress with a voltmeter after the discharge.

The method vaporizes the whiskers that form.

Remember, that the care and feeding of NiCds require that you drain them significantly before charging.

So, once the voltage does come up and you get at least a charge cycle, discharge the battery with a resistor and charge again. Again, you have to do this on a cell by cell basis.

NiCd's can actually reverse their polarity with neighboring cells.

Andy:

Restore discharge 0.4 V/cell. From experience: When they are dead, the voltage can be in mV before pulsing.

Included photomicrographs.

http://batteryuniversity.com/learn/article/how_to_restore_nickel_based_batteries

Ni Cads develop internal shorts and that is why the 'zap' method will sometimes remove the short but it will not be full capacity and are limited in how many few hundred or so charges it will take. I have replaced them in the past with new ones with the same capacity or Amp/hours like 500ma A/H. This is the best way to do it. Just make sure to buy the same size and capacity and they are not very expensive. You can find them with leads welded on the +/- terminals at electronic suppliers like Jameco, Mouser, etc on line. Also dropping Ni Cad batteries, due to the shock, will sometimes cause these internal shorts to develop. After replacing them, check that during charging they do not get real Hot a bad sign you are overcharging the wrong replacement but it is OK for them to be warm, that is normal.

Good to know. I've dropped this drill many times, though it is pretty old and the battery has been through many cycles.

Thanks for the info.

here they don't promote the hot science