I've been thinking about the NIMH dendrite/whisker issue and the high level of self discharge it may cause. I thought we should start this thread to discuss it in bit more depth and perhaps outline our thoughts for a safe unit to accomplish this zapping.
Are we talking about zapping a whole subpack at once or are we talking about removing the orange sleeving and finding and zapping only the affected cell in the stick?
Why am I asking, well another UK owner has just approached me with dead dying battery issues so I may want to explore this further to help him.
I have been using the capacitor zapping technique for 20 years, with many great recoveries, and a few failures. Since the idea is to pulse the bad cell with as high a peak current as possible, the quality of the connection, and any series resistance will drastically effect how well it works. Trying to zap the whole pack would need a capacitor bank, charged to 500-1000V, and with all of the series resistance, would still limit the peak current.
I suggest removing the sleeve and zapping the individual cells.
A camera flash capacitor has enough stored energy for a single cell, the trick is to get the energy into the cell without burning a hole in the side of the case where the discharge happens, thus my earlier suggestion of welding clamps.
Ron Hanson left me a couple of subpacks with some cells that had high self discharge, which I will quantify and try to repair.
I've been thinking about the NIMH dendrite/whisker issue and the high level of self discharge it may cause. I thought we should start this thread to discuss it in bit more depth and perhaps outline our thoughts for a safe unit to accomplish this zapping.
Are we talking about zapping a whole subpack at once or are we talking about removing the orange sleeving and finding and zapping only the affected cell in the stick?
I don't think it's feasible to dismantle a stick down to its' 6 cells. I think zapping an entire subpack at once is the only way to do it. If it works, great, if not, toss the stick in the garbage.
One thing you have to keep in mind is that testing will take time. I would zap the bad stick and charge up it and another known good stick. Then compare the voltages. I don't think you'll see a drop for at least three days. Safer to wait a week.
I don't plan on trying to repair fast-discharging sticks unless Mike has great success. I'm warrantying my rebuilt batteries, so I can't afford to risk it at this point.
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2000 MT #4227 175K miles - Citrus Yellow, BetterBattery
I don't think it's feasible to dismantle a stick down to its' 6 cells. I think zapping an entire subpack at once is the only way to do it. If it works, great, if not, toss the stick in the garbage.
However if you slit the shrink cover off the known bad stick can you not measure the voltage of the individual cells as the positive centre pip of each cell is welded to the case of the one in front of it?
So by zapping through the case of two adjacent cells you only zap the one cell. I haven't actually looked at a subpack to confirm this theory, but is that correct? A couple of giant croc clips should sort the zapper.
Just need a double switch method to fire it, so that both hands have to be on seperate switches to fire the zapper system.
In all the nimh cells I have seen before the case is the negative terminal.
If the heat shrink is removed from the subpack, each cell can be accessed just as Peter suggest.
Big battery terminal alligator clips are what I will use, and will discharge the cap into the other end of the leads.
When I get around to playing with the subpacks that Ron gave me, I will document the process.
If the big clamp does not get a good enough purchase... another option would be to use a round sleeve ... like those round metal tightening rings... I forget what they are called ... but you turn the screw and the metal loop gets smaller for home improvement stuff ... a variation of that would allow you to connect to a much larger surface are on the outside of the cell... this would distribute the charge over a larger area.
I would be interested to see some data when people start doing this...
Maybe If I find a high Self Discharging cell I will try it myself... but no such animal yet.
If the heat shrink is removed from the subpack, each cell can be accessed just as Peter suggest.
Big battery terminal alligator clips are what I will use, and will discharge the cap into the other end of the leads.
When I get around to playing with the subpacks that Ron gave me, I will document the process.
Yeah, well you can manufacture your own tools. I on the otherhand have to rely on what is available.
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2000 MT #4227 175K miles - Citrus Yellow, BetterBattery
Ian,
I think you are speaking of a stainless steel hose clamp?
Yes that would work,you could clamp the bare end of some wire under the hose two clamps, and just touch them to the capacitor terminals, and let the arc happen there.
Ian,
I think you are speaking of a stainless steel hose clamp?
Yes that would work,you could clamp the bare end of some wire under the hose two clamps, and just touch them to the capacitor terminals, and let the arc happen there.
YES!!! that's it.... I was about to make a trip to lowes just to figure it out.
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Subpack Zapper!
... but you turn the screw and the metal loop gets smaller for home improvement stuff ... a variation of that would allow you to connect to a much larger surface are on the outside of the cell... this would distribute the charge over a larger area.
I on the otherhand have to rely on what is available.
