Hi,
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Originally Posted by steve8pi
Really interesting pictures, Bob. I don't ever intend to do that, but fun to see pictures and data of your experiments. Please be very, very careful!
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Indeed, it has to be done carefully with safety first. Concentrated KOH is ever bit as hazardous as sulfuric acid.
Quote:
Originally Posted by steve8pi
It'll be interesting to see if you get to the point of resurrecting a dead cell. We'll have to start calling you Dr Frankenstein.
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I'm curious about failed cells but am really concentrating on recovering the capacity of failed modules. To really analyze a failed cell, I would need to carefully dissect one in a safety cell with optics, fine probes and a set of reagents. It would be fascinating but a poor use of time:
- 38 modules - NHW11 traction battery pack
- 228 cells - NHW11 traction battery cells
Every module returned to service with significant return of capacity is another replacement for a full-up, traction battery with one or two failed modules. The other 36-35 modules continue to provide service until the next weak module failure. If we are talking about 2-4 years that is a good return on investment.
Quote:
Originally Posted by steve8pi
I see the charge cycle is labeled as 0.2C, and the discharge is 6A. What is the C rating of this cell/module? (I'm curious what the discharge rate is in C units)
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Fresh, these modules are rated at 6.5 Ahr, which is what I'm using for the upper rating. However, the modules from the failed pack that don't have failed cells are measuring 2.2, 2.0, 2.2, 2.2, 2.0, 2.3, 2.2, and 2.3. So what I'm using is:
6 A - discharge rate, ~1C
1.2 A - charge rate, ~.2C
Right now, I have two under test. One had an early tee nut failure to seal and showed out gassing. I'll have to rework that tee nut installation. Later, I need to stress test these tee nut modified modules under high current source and sink loads, ~75 A, and temperature extremes, <0C and ~50C. I'm not reworking these modules to have them fail in the winter or the first hot summer day. But how we access the cell for electrolyte replacement doesn't matter if the AHr rating isn't high enough.
The second module is showing signs of increased capacity. The initial 2.2 Ahr appears to have reached 3.2 and continues to increase. This slow increase in capacity makes sense as the KOH ions migrate into the areas recently wetted by distilled water. Using a KOH solution instead of distilled water would more rapidly return the cells to a higher capacity but I'm not ready to take that step, yet.
There remain questions about how the pressure relief valve works. We don't know the pressure threshold and this needs to be measured. I also need to learn more about KOH mechanical properties since there is evidence of electrolyte leakage around the "+" terminals, the ones treated in the resealing TIS. The NHW20 modules are substantially stronger and this and the condition of well worn, NHW11 modules suggests it was needed.
Bob Wilson