Can you rule out the possibility of adaptive battery management by the BMS?RegGuheert wrote:Agreed, except I think a software problem is a very long shot here. I would expect software problems to arise in more than a couple cars and in more than just one climate.drees wrote:There's only two things that might cause one car to turtle at 350V and another to turtle at 290V.TonyWilliams wrote:turtle voltages had a SIXTY volt spread. I'll suggest that batteries at 350 volts could have gone much farther, maybe as far as my car went with 290 volts remaining. This reeks of a BMS problem; hardware of software, or both.
1. A software problem. No further explanation needed here.
2. At least one cell-pair with significantly lower capacity than the rest - one cell-pair hit the low-voltage limit and the BMS shut the party down. Should be easy to check with a Consult by taking this car down near turtle.
The BMS in the LEAF terminates both charging and discharging based on voltages at the cell and the pack level. Phil has told us that his LEAF's voltmeters appear to be accurate to within about 0.1% and that the low-voltage meters cross-check with the high-voltage meters and throw codes if there is a discrepancy. So, no, I do not think we are losing any range due to instrumentation issues.
The sixty-volt difference in discharge voltage is *precisely* what I would expect to see between a new pack and a severely degraded pack. The cells in the new pack should all have similar capacities, so none should go below the knee prematurely. But in a pack without a TMS driven in a very hot climate some cells will live in an even HOTTER environment than others. Those cells will deteriorate faster and will therefore have higher internal electrical resistance, possible greatly higher. As a result those cells will get even hotter and will quickly go downhill.
This condition is exactly what Nissan's CELL VOLTAGE LOSS INSPECTION test is designed to identify. If Scott's car is the one that terminated at 350V, then I find it irresponsible that Nissan has not reported the amount of variation found in the cells in his pack.
Again, I will say that I would find a histogram of cell capacities from a degraded LEAF to be quite informative right about now. I don't think we can expect to get that from Nissan. Anyone want to purchase a battery and give the old one to Phil to document?
IMO, Nissan must have designed the LEAF BMS with battery life, rather than convenience to owners, as the primary goal.
How successful Nissan was, is now the larger question.
But can you conclusively rule out variable battery warning levels, and shut down, as evidence of a the BMS functioning as designed, rather than a malfunction?
Would it not make a lot of sense for Nissan to include measures intended to protect of the battery from premature capacity loss (or, much worse from Nissan's point of view, a "failure" warranty claim) based on the prior conditions of use, into the BMS?
As one example, the BMS may have noticed a Nissan driver believes they can make daily 60 mile freeway commute in Phoenix temperatures on one charge, (or a 80 mile one, with a quickie at the local DC) in their LEAF and now, the BMS is trying to tell the Driver, that he or she cannot, and still expect to maintain (some unknown level of) capacity for (some unknown) period of time.