Hi folks,
There are still a lot of puzzles to figure out before we go too far on this. Also, my guide has been a number of patents that need to be acknowledged and terms worked out. But these preliminary experiments are promising.
Some of the challenges that remain:
- best material for the service plug - it needs to be impervious to 6 M KOH solution yet support easy service by simple tools.
- how to install - a type of 'heat welding,' the service plug needs to be able to handle the maximum pressure of the existing safety value
- refurbishment procedure - I'd like to use a single service plug instead of the two in the current approach. The challenge is to normalize the replacement water across all cells and this is not trivial. But I think I have trick that will work.
- accelerate normalization or 'in car' process - I'm normalizing the cells with a 'discharge-charge' using an RC model battery system. This may not be the best approach. One other patent references using an elevated temperature and there is another charge-discharge pattern that might also help. We are essentially 'activating' the electrodes and this is not a trivial problem.
- proof testing - any refurbished module needs to be proof tested to make sure it won't fail in abusive conditions under cold or heat stress. This is not trivial since the failure mechanism can look like an electrolyte grenade or run-away hose spewing a stream of concentrated electrolyte. . . potentially very dangerous!
- investigate electrode leaks - it may be possible to decrease the maximum module pressure with a less strict valve and avoid electrolyte leakage around the terminal plugs. This would require more frequent water service but now we have a service plug!
There are lots of problems and issues to figure out. However, sharing what we've already learned will maybe encourage others, those who have some skills in this area, to collaborate. Then maybe we can come up with a kit that would allow folks to refurbish their own battery packs safely with a reasonable expectation of success.
FYI, the "plug-in lite" works on the principle that there is a maximum charge that would cause the control computer to see the traction battery as "at 80%." This means the control laws would try to use that extra charge to bring the battery closer to 60% and hopefully, do this by doing more EV and less ICE assisted warm-up. The nice thing is we are simply using the reserve capacity already in the battery so we start off each day with a peak charge.
Done correctly, the "plug-in lite" charger also monitors the health and status of each module during the 'top off' charge. It might also do some battery temperature management to try and keep the battery pack "not too cold" and "not too hot."
Interesting stuff.
Bob Wilson