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flat5 · 07-26-2005, 08:01 AM

basmoq, I said one way they fail. Zapping will not fix the battery when it fails this way.

When there is internal leakage caused by corrosion and a build up of crystals, zapping does work. The battery will still produce these crystals that touch adjacent plates (and bleed the charge away) so the battery has to be zapped again. and again.

ok. I found someone who can explain it better.
http://www.batterieswholesale.com/faq_nicad.htm#14

There are two main reasons cells fail, other than abuse. One is separator failure, and the other is degradation of the active material. The first is far more common, and the result is a shorted cell. Every time a cell is charged, the active material is redeposited on the plates. Ideally, this occurs uniformly across the surface of the plate. However, in reality, there will be bumps and valleys. When there are bumps on both the positive and negative plates are adjacent, separated only by the separator, the resistance between those two points is slightly less than in other regions of the cell. So, the current density there rises. This means that more material is deposited there, contributing to even more "bumpiness". In reality, needles called dendrites form, and given time, they can force themselves through the separator to short the cell. A cell that appears to self-discharge in a couple of days has dendrite problems, and will soon completely short out. Plan to replace the cell. Degradation of the active plate material is just a normal aging process of cycling. Both of these mechanisms are very good reasons to avoid cycling the cells after each use. Cells should live to about 1000 cycles if treated properly. Anything over that is gravy.

Q: I've seen people talk about zapping cells to revive them

A: Yup -- a quick fix it. When cells short due to dendrites, the piece of material that is actually shorting the cell is very thin. So, by forcing a huge impulse of current into the cell, one can vaporize the dendrite -- sort of blowing a fuse. This works, and can revive an otherwise shorted cell. However, it is a stopgap measure at best. First, the fact that one dendrite has formed means that another is not too far behind. Second, the material that was vaporized has now permeated the separator material, forming a resistor that shorts the plates. The cell may no longer be shorted, but will still have a poor charge retention. Besides, unless done properly, this can be dangerous as large currents are necessary.

07-26-2005, 08:01 AM	#15 (permalink)
flat5 Very Insignificant Pawn Location: Amsterdam, NL	basmoq, I said one way they fail. Zapping will not fix the battery when it fails this way. When there is internal leakage caused by corrosion and a build up of crystals, zapping does work. The battery will still produce these crystals that touch adjacent plates (and bleed the charge away) so the battery has to be zapped again. and again. ok. I found someone who can explain it better. http://www.batterieswholesale.com/faq_nicad.htm#14 There are two main reasons cells fail, other than abuse. One is separator failure, and the other is degradation of the active material. The first is far more common, and the result is a shorted cell. Every time a cell is charged, the active material is redeposited on the plates. Ideally, this occurs uniformly across the surface of the plate. However, in reality, there will be bumps and valleys. When there are bumps on both the positive and negative plates are adjacent, separated only by the separator, the resistance between those two points is slightly less than in other regions of the cell. So, the current density there rises. This means that more material is deposited there, contributing to even more "bumpiness". In reality, needles called dendrites form, and given time, they can force themselves through the separator to short the cell. A cell that appears to self-discharge in a couple of days has dendrite problems, and will soon completely short out. Plan to replace the cell. Degradation of the active plate material is just a normal aging process of cycling. Both of these mechanisms are very good reasons to avoid cycling the cells after each use. Cells should live to about 1000 cycles if treated properly. Anything over that is gravy. Q: I've seen people talk about zapping cells to revive them A: Yup -- a quick fix it. When cells short due to dendrites, the piece of material that is actually shorting the cell is very thin. So, by forcing a huge impulse of current into the cell, one can vaporize the dendrite -- sort of blowing a fuse. This works, and can revive an otherwise shorted cell. However, it is a stopgap measure at best. First, the fact that one dendrite has formed means that another is not too far behind. Second, the material that was vaporized has now permeated the separator material, forming a resistor that shorts the plates. The cell may no longer be shorted, but will still have a poor charge retention. Besides, unless done properly, this can be dangerous as large currents are necessary. Last edited by flat5; 07-26-2005 at 08:09 AM..