failure mode #1 Shorted Cell and the cell Zapper fix?
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Cell Zapper test #1
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In years past I have used a capacitor to zap shorted NI CAD batteries back to life.
I ran some test on the first stick from Ron's shorted cell pile of subpacks.
Cell #1 (most positive) was lower voltage than than the others an hour after the stick was taken off the overnight 350MA charge.
I put a 3 A charge across the low cell, and instead of raising in voltage, it dropped, as it began to short.
I dug out the stored energy demo from the hybrid car class. We use it to show why you need to turn off the switch and wait for the capacitors to discharge before touching anything. The 6100uF cap has copper buss bars, and a voltage doubler circuit to get 350VDC from the 120V AC line.
I charged the cap to ~100V and discharged it right on the heavy brass wingnuts.After A look at the voltage under charge, and still shorting. Another zap this time @ 250VDC and the short is gone, and then for good luck, I charged the cap to 350VDC and zapped the whole subpack.
You can see that each discharge generates a divot in the brass nut and capacitor buss bars. Wear ear and eye protection as it sounds like an M80 going off, and molten metal can spray out if you don't make the contact fast and hard. Lots of the capacitor energy is not making it to the cell, and is making explosive metal plasma.
After confirming that the cell voltage was rising at about the same rate as the other cells, I put the whole subpack on a 3A charge until the cells were at 90%, then finished with a 350MA for several hours. Final cell to cell voltage while under charge was within 0.05V
Will see what happens overnight and do more testing tomorrow.
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