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Originally Posted by gpsman1
. . .What am I looking at in post #1?
Did you take a hack saw and cut open one module to look inside?
Is the case just plastic?
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Correct. I had one module with a failed cell so the graph shows the voltage profile after adding water as an electrolyte replacement. But the dead cell never recovered and I used that module to find out what the internal structure looks like.
I clamped the module to a structure, put on safety goggles and protective clothing and decapitated it with a power saber saw. There were sparks and steam. The lower part, the cell assembly, is sitting in a large bucket full of water. I'll drain and refill until the KOH has been leached out of the electrodes.
Quote:
Originally Posted by gpsman1
In the Fords, we have 250 "D" cells. I am hoping if I ever find a defect, I can just swap out one ( or a few ) of the "D" cells.
But how would one, or a handful of new D cells behave with over 200 "old" cells? But I also suppose if I go to a junk-yard, I could find "aged cells" so they would be similar performance substitutes.
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The YahooGroup, Mk_1, is discussing this problem since they also have "D" cells. I've thought about the problem and suspect the same loss of H_{2}O reduces the capacity of their cells as it has in mine. But from the few sketches I've seen of "D" cells, a similar technique may work with them.
All of our batteries have a pressure relief valve so during periods of over-charging or excessive drain, some water in the electrolyte converts to O_{2} and H_{2} gas that escapes. The remaining water leads to a concentrated KOH solution that probably drives some of the KOH to form crystals. The difference between our batteries is the "D" cells have a steel case.
My current thinking is a small, shallow hole could be drilled in the cap with some risk of metal filings staying inside the cell. Then using a vacuum and valve setup, degassed, distilled water added to the cell. The small hole can then be sealed using the same 'spot welding' techniques used to affix the metal tabs.
Quote:
Originally Posted by gpsman1
. . . I read you had trouble with your drill holes not sealing.
May I suggest keeping the holes as small as possible ( 1mm ) and using a syringe to add electrolyte? Then maybe you would have more success sealing the hole. Maybe you could use a hot wire, or soldering iron to "melt" the tiny 1mm hole closed again?
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It remains a possibility and I bought some basketball, air filling needles for such an experiment. But I'm not ready to give up on the tee nut since this leaves a permanent, electrolyte refilling hole closed by a gas-tight nut. This would allow periodic servicing of the battery modules to replace the lost water.
I have data that strongly suggest 'new' batteries improve the performance of our Prius but we lose this capacity within 3-4 months. The first is the monthly mileage chart from a Dept. of Energy fleet study of the 2001 Prius. The second is a monthly mileage chart by Patrick Wong who had an NHW11 traction battery assembly replaced (under warranty.) But now I'm seeing a mechanism for this in my current battery refurbishment experiment:
You'll notice that the round-trip, efficiency increases as the battery recovers its capacity. This probably occurs as the internal resistance decreases.
I am now more convenced that a capacitor based, buffer for our battery packs makes a lot of sense. What I don't know, yet, is how much energy and what rates this capacitive buffer needs to handle. But it is entirely possible that this could significantly extend our battery life and let us use a smaller capacity battery pack.
Bob Wilson