ni-cad batteries

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Does anyone have any advice on how to revive ni-cad drill batteries? I hate to keep spending money on new batteries. I try to take cre of them, but they seem to only last a year or so. Any suggestions would be appreciated. Thank you.
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1ko wrote:

Over the years I've heard all kinds of stories that are somewhat akin to witchcraft.
Ni-Cad is old technology and if you are following the manufacturer's recommendation you're likely going to get the best performance/longevity (such as it is) and that't that.
Don't leave it in the charger beyond the standard charge time. Use it to depletion each time before recharging and hope that the manufacturer of your drill introduces a Li-Ion or Ni-MH replacement<g>
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regards to the number of charging cycles that they will endure) Nimh have a cycle rate of about 1/2-2/3 of what nicads will take, lion- a lot less than the nimh. Yeah, the nimh are cheaper now and the lion are even less (or close to it) but I've yet to hear of a lion that lasts for more than 3 yrs. I just recycled the last of my aa nicads from circa 1974. If the guy has that kind of problem, he should have cracked the battery case (if it was a tool battery that he was mentioning) and looked at the voltage of the individual cells. Me thinks he's using a dumb charger ....a shot in the dark with virtually zero info to go on...
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On Mon, 14 Mar 2005 13:39:05 GMT, the inscrutable Unquestionably

Uptime lowdown on my nicad revival: It's not worth it after all.
While I got one usable battery out of the two dead batteries, the capacity is no longer there and it goes dead in 2-3 days, with or without use. Cell discharge rates DO have to be matched after all.
Bottom line: Find replacements or inexpensive rebuilders.
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1ko wrote:

If you have a car battery charger, you can revive ni-cad batteries.
I TAKE NO RESPONSIBILITY FOR ANY INJURY YOU MAY RECEIVE BY DOING THIS
What happens with ni-cad is that the "memory" they develop is because of crystals that grow on the electrodes (internally, of course). As the crystals grow, the space bewteen the two electrodes gets shorter and shorter, and this is why the battery lasts for less time.
I've taken 1.5v batteries, and held a 12V charge on them for a second or two at a time (The battery will get warm). From what I understand, this will "burn" away the crystal inside, and will erase the "memory" they've developed.
It sure seems to work, but don't hold the charge on there for a long time or that battery could leak or explode.
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I do something similar, but use a variable power supply with an internal current overload protection of 6 amps. I put it at 14V, and hold the terminals on the battery for about 10 seconds.
You will need to take apart your drill battery to access the individual cells -- don't try this on the entire battery pack, as it won't work.
It seems to revive the batteries so that they last for another 6 months or so.
It may be easier to just go to a battery rebuild place -- the last time I tried this on one of my newer Maktia 9.6V NiCads, I had a heck of a time cutting open the battery case....
Regards,
-Steve in Banks, OR http://woodworking.bigelowsite.com
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OK a couple of comments on Nicad Batteries. I used to work in the handheld medical device world, real big on battery technology. So here goes: NICAD - High current low impedance technology capable of delivering large amounts of both burst and continuous energy. They are capable of delivering extremely large continuous current draw hence there popularity in the RC world (for example a sub-c sized cell (common in tools and RC) are capable of delivering 40-80 Amps this drives the current limitation to the wiring and motor rather than the battery, A comparably sized LI ION can probably provide no more than 10 Amps). Nicad is the lowest charge density (mAH per unit weight) chemistry readily available on the market today. Nicad is designed to be a complete discharge type of cell, meaning that it must be completely discharged between every charge cycle. Failing to do this causes passivation (accurately mentioned above as the creation of a crystaline struction in the cell). Passivation causes two primary problems first it decreases the total capacity of the cell, making it difficult for the batteries to completely discharge. Second, it causes a significant increase in the impedance of the cell. The effect of increased impedance is decreased voltage stability. In the case of fixed voltage batteries the ability to deliver a constant voltage with the drawn current is what controls the total output power of the battery. Last, Nicad cells are also very sensitive to over-charging. Over-charging causes the maximum capacity of the batteries to be radically reduced. This can be caused by the use of poor quality chargers or negligence with a decent charger. Good chargers have a shutdown that allows currrent flow to drop to zero once the battery has achieved its full voltage state. Passivation while very frustrating, is not a serious problem as is it not irreversible. There are at least two ways to deal with passivation. One as mentioned above is to shock the battery with a large amount of current. This is a dangerous and very tricky way to address the problem. The much easier and safer method is to completely discharge the batteries. Passivation can be almost completely eliminated by "fully" depleting the cells. I try to do this about once a year on all my Nicad packs. This can be done using the tools themselves. but you have to follow a few steps. Notably for badly passivated batteries you may have to repeat the process several times by recharging after the depletion process and doing it again. First, using the tool run the battery until they seem to be dead. It is best to use a drill or saw as they don't burn out like the flashlights.
Then let the battery sit for a while (1/2 hour to a few hours usually does it). During this time the battery will regain some available energy, this is caused by the breakdown of the passivated material chemistry Repeat the first two steps until you get nothing after several hours of resting. Another additional step that you can take is to place a shorting wire across the two power terminals on the depleted battery. (NOTE!!! NEVER DO THIS WITH A FULLY CHARGED PACK. NICAD CAN PRODUCE ENOUGH CURRENT TO ACT AS AN ARC WELDER AND FIX THE WIRE TO THE PACK WHICH MAY RESULT IN AN EXPLOSION) . Done properly this method will result in completely depleting the cells and a large reduction in passivation. NiCad batteries should have a long and productive life. If you feel like you haven't used your pack that much and you have not over charged it you probably can fix it following this process. I guess I should have said a bunch of comments on Batteries. Hope it helps.
W
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hikinandbikin wrote:

Great explanation. Good to hear I'm not full of shit! (on this subject, anyway!).
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<snip>

<snip>
I have to try this with my PC drill NiCads. I have had some success by clamping the drill "on" and then re-charging - repeating many times for a week or so.
This new method sounds even more promising.
Lou
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On 14 Mar 2005 12:24:54 -0800, "hikinandbikin"
snip
Done properly this method will result in completely

What happens to a NiCad's performance after it is frozen?
Thunder
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On 14 Mar 2005 12:24:54 -0800, "hikinandbikin"

I have it from an absolutely unimpeachable source, i.e. the latest issue of "Handy", the magazine of the Handyman Club of America, that you are all wrong.
In response to a reader letter querying "The three manufacturers [of his cordless tools] all recommend completely discharging the batteries before recharging them. Which is the right way?", the HCOA responded to ignore the manufacturers' suggestions:
"It's quite possible that the practice of completely draining tool batteries before charging originated from the manufacturers of earlier-generation tools. Regardless, now we know better. Do not completely drain your batteries by holding down the trigger. As soon as you detect that the tool performance is diminished, it's time to recharge."
Luigi Who is wondering whether HCOA has some interest in getting people to buy more batteries and who suspects the competence of their "advise" is on par with the competence of their subscription department who keep on sending the magazine despite his not having paid for it. OK, in a momentary lapse of judgment 5 years ago, I did join and have the drill bit index to prove it.
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Surprisingly this is exactly what my 18 volt XRP DeWalt drill manual says.("As soon as you detect that the tool performance is diminished, it's time to recharge.")
Dave Hall Who thinks HCOA may have read a DeWalt manual before responding. However, they most assuredly borrowed it from someone else as they would never have a DeWalt tool for testing by a "member" since it costs more than a drill bit index.
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There is always some ambiguity in what "fully discharge" means. To some, that means wipe out any power the battery may have, to others, it's drain until it is not particularly useful. Draining the battery of all power will destroy it. Discharging it until it's not useful (as in "performance is diminished") won't damage it.
Mike
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Mike,
Draining a nicad battery will not destroy it. In fact, nicads have a memory effect, through which the battery thinks it is discharged, when it isn't. The best way to deal with that situation is to completely discharge the battery once in a while.
Nickel metal hydride batteries, on the other hand, do not have a memory and can be recharged after only a partial discharge.
Ken
Michael Daly wrote:

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that's a myth that has been history almost as long as the cells themselves (G)most people would have no way of completely discharging the cells anyway. and overdoing it will kill the cells pretty fast.
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Steve Knight wrote:

??? A piece of wire won't do it?

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The serious radio controlled car racers used to use NiCad batteries and discharged them nearly completely after using them and before charging them the next time. A wire has too little resistance, and could discharge the cells so fast as to cause heat damage, so resistors of the right value were used. Couldn't just use one resistor across the ends of the battery (battery = several cells in series), as some cells would discharge before others, and the one(s) that discharged first could be exposed to reverse charging from the rest; a bad thing. As a result, folks made fixtures that applied the correct resistance across each cell (if there were 6 cells in the battery, it took 6 resistors), requiring connections to the junction between each pair of cells. Don't know if this would be practical for the types of batteries used in power tools. Kerry (ex RC racer)
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On Sun, 20 Mar 2005 18:55:17 GMT, "KERRY MONTGOMERY"

Something like this: <http://www2.towerhobbies.com/cgi-bin/wti0001p?&I=LXGGJ0&P=M
You guys would be shocked (no pun intended) to find out just how advanced the r/c hobby is regarding batteries.
Barry
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The "memory effect" mentioned by many "experts" occurred exactly ONCE in a satellite system battery that had precisely controlled discharge and charge cycles. A simple overcharge or slightly deeper discharge removed any possibility of the "memory effect" The chemistry and construction of the cells were changed for consumer usage - memory effect is, for all practical purposes, close to impossible in these cells.
The effect of reduced NiCad capacity observed in the outside world is strictly speaking "capacity depression" and is absolutely nothing to do with partial discharge and topping up over multiple cycles. Overcharge the battery by a few % and it no longer occurs.
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