The batteries for my DW907 are getting tired, so it's time to either try to wake them up or buy replacements. The batteries are DE9074, 12V, NiCd (I think).
- Has anyone successfully woken-up tired NiCds? What's the technique?
- Lots of places claim to sell batteries or cells but I don't know how to tell the good guys from the rogues; any recommendations?
Zapping can only be done to individual cells not complete batteries. It removed the dendrites that grow between the electrodes that result in shorted cells. Cells that might benefit from zapping will register zero volts across them even when the battery has been on charge. A battery pack that might benefit from some of its cells zapping will have an on-charge terminal voltage that is well below nominal rated voltage by multiples of 1.2-1.4 volts.
eg a 12v pack that only measures 10volts or so possibly has two shorted cells inside.
In my experience of tinkering with Nicads over the years, zapping can be successful to remove the short circuiting dendrites but once a battery pack that will come up to rated voltage on charge and yet goes flat sooner than expected is destined for the bin and can only be recovered by change ALL the cells in the pack.
Bob
Or for a high current device like a drill one cell which has lost electrolyte or started to gas so that its internal resistance is higher than it should be. The other cells then effectively destroy the weakest one by forcing current through it.
It is as well to wear eye protection when zapping cells. You do not want an eyeful of potentially hot caustic the electrolyte.
If you are into taking them apart then it is worth testing the cells individually for holding charge. Some are usually much better than others so you can make a useable lower voltage rechargable block out of them if you have a use for it. It is incidentally dangerous to do any of these tricks with Lithium rechargeable packs - they are inclined to self immolate at the slightest provocation and should have internal chips to disable charging if overheating or a malfunction is detected. This has not stopped certain makers laptops from catching fire.
Regards, Martin Brown
Do DwWalt not have recommended repair shops? FWIW I replaced the NiCADs in a B&D screwdriver and it was like new again so worth it if you like the tool.
But perhaps worth checking prices for similar tool first in case a new tool is almost as cheap as replacing the NiCADs.
Paul DS.
generally 100A plus in te reverse direction for a few ms.
Buy sanyo branded cells. In my days of using them for RC work there were none better.
Id assume they were sub-C's
Yes I'd agree, and the revitalisation does not seem to last more than a few months either. Shame but I think some harm is done when they are fully discharged like this hence the short life. Brian
Yes, this happened to a friends posh mp3 player, well not flames but too hot to touch and it had to be ceremoneously given a decent burial.
Brian
Not in the reverse direction.
I use a home-made 12V battery charger on individual cells. It will deliver well over 20A for a short time (it rattles the 20A meter violently on the endstop).
I 'splat' the cell for a second or two, and then check its voltage. If it is now around 1.2V, I change the meter to amps, and check that the battery delivers a short circuit current - typically a few amps. depending on the size of the cell, which rapidly decreases towards zero. [Note that, if the cell appears to be un-splattable (won't accept any significant zapping current - no sparks etc), it has dried out, and is no good.]
I again measure the voltage. If the dendrite whisker has been successfully zapped, the voltage will be slowly rising as the cell recovers from being shorted. If the voltage isn't rising, or is falling, the whisker is still there, so I try a re-zap.
If, after a few re-zaps, the cell refuses to play ball, I consign it to the pile for recycling.
If the zapping is eventually successful, I give the cell a normal full charge (and sometimes I'm feeling consciences, then give it a more-or-less full discharge and immediate re-charge). If I remember, I also mark the cell to remind me that it might be a bit suspect in the future, and to keep an eye on it.
As others have said, take appropriate precautions, just in case the cell should decide to explode.
Whatever he does, it has to be one cell at a time which means taking the battery pack to bits. At that time its often the best plan if you have more than one to check the cells and make a good unit out of the good cells in both then use the other to experiment on. Brian
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