20090109
Video: Repair Dead Power Tool Batteries
There is a great instructable video on how to zap Ni-Cd batteries with a welder and bring them back to life. Unfortunately, that video does not cover memory issues with Ni-CD batteries, welder settings, which direction your welder ground vs positive is, and how many times is appropriate for zapping. This video helps with those issues. Be sure to only try and zap cordless power tools that are Ni-Cd based. The newer tools are Ni-MH and Lithium based. Don't zap those.
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5 comments:
Hi, I posted a comment already at the two instructables that mentioned this techniques, so I will just repost it here - hopefully that is OK. I'm curious if you tried just fully discharging the cells with a resistor instead? This is what most nicd reconditioners do. Here's the instructable post:
"I'm cross posting this comment here too: http://www.instructables.com/id/Revive-Nicad-Batteries-by-Zapping-with-a-Welder/
I've seen the zapping approach mentioned before, but I wonder if anyone has compared this with the simpler method used by most NiCd battery reconditioners: for more severe crystalline formation, discharging to 0.4V/cell at a 0.2C rate, or applying a periodic exercise cycle to the cells every <3 months to minimize new crystalline formation
More information can be found here:
http://www.buchmann.ca/Chap10-page2.asp
The US an Dutch military (among other groups) have studied this quite a bit:
http://www.buchmann.ca/Chap10-page3.asp
Pictures of the crystals can be seen here:
http://www.buchmann.ca/chap10-page1.asp
I have seen 'zapping' used for slightly increasing performance (voltage rise) of cells used in RC racing communities, but am not aware of any quantitative evidence. The zapping is likely breaking up some of the crystals, but I wonder if it does as thorough a job as a deep discharge (?). New batteries have ~1 micron crystals, a battery in need of conditioning has crystals of ~10+ microns, an a deep discharge 0.4V/cell can break crystals down to ~3-5 microns - but I'm not sure what the high voltage pulse methods are providing (?)
more information on zapping here: http://www.buchmann.ca/Chap10-page4.asp
Zapping with a welder or a flash unit certainly sounds cooler than deep discharge with a load, but may be more trouble an less effective."
Ian,
Thanks for sharing the buchmann.ca resource. They have collected some excellent data.
My own findings agree to some degree with you and the buchmann links. You must discharge the Ni-Cds before charging them up.
I've found that most Ni-CD power tool chargers do not have the appropriate discharge option to remove the memory effects. Thus I use a welder in reverse to lower the battery charge. A resistor setup to bleed the battery also seems reasonable.
Simply lowering the voltage of a Ni-Cd pack to 1V and charging again has not been nearly as effective for me as zapping it reverse with a welder than zapping it again with correct polarity to bring the pack back. I find the stock Ni-Cd chargers struggle to charge a Ni-Cd pack that has low voltage. I suspect that powertool chargers sometimes have a low voltage cut off to avoid overcharging a pack with one dead cell.
>Thanks for sharing the buchmann.ca resource.
It is a good book an since their specialty was initially NiCd reconditioning, they have good data for this chemistry. Their Cadex battery conditioners are widely used. I used this resource primarily because it is available on the web. However, to develop a better understanding of battery chemistries, I've found this book to be much more thorough (although expensive):
http://www.amazon.com/Handbook-Batteries-David-Linden/dp/0071359788
>My own findings agree to some degree with you and the buchmann links. You must discharge the Ni-Cds before charging them up.
Monthly exercise cycles are very important for maintaining NiCd performance.
>I've found that most Ni-CD power tool chargers do not have the appropriate discharge option to remove the memory effects.
Most chargers for differnt battery chemistries suck (in my estimation). NiCd in particular, needs to be maintained according to a recoditioning program.
>Simply lowering the voltage of a Ni-Cd pack to 1V and charging again has not been nearly as effective
You'll want to drag the volatage down to at least 0.4V/cell for a pack that is in bad shape.
>I find the stock Ni-Cd chargers struggle to charge a Ni-Cd pack that has low voltage. I suspect that powertool chargers sometimes have a low voltage cut off to avoid overcharging a pack with one dead cell.
You're probably correct, my stock power tool chargers suck - they like to cook the cells too (not good). This is why I mentioned (in a previous blog post) the concept of an open source batery charger that is tolerant of different chemistries. I will likely proceed along this vector, as time allows. Most of it seems relatively simple, but I'm less certain of how to design the constant voltage/current source - FET's, yes, but I've not found a good existing circuit to work from yet.
Ian,
I appreciate you sharing these reference materials. I've ordered both books from amazon.
"Handbook of Batteries"
"Batteries in a Portable World"
The "Handbook of Batteries" is a expensive book at about $140. If you look closely below the used book section there are links for it for as little as $20.
No problem - $20 is a great price for "Handbook of Batteries", an well worth it.
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