garygid said:
I am aware that many things CAN be done, and MIGHT be done.
However, I am more interested in what IS DONE by the systems IN the LEAF.
If current-counting is done to estimate SOC, then one cell with (for example) a high self-discharge would get to the low-voltage limit first, and (perhaps rather unexpectedly) stop the car, even when the car's SOC "calculation" was estimating sufficient remaining charge to go another 10 or 20 miles (under the present driving conditions).
Ok. Thanks for the help here.
If I understand your proposed scenario correctly, you're suggesting that if the car only uses current counting to estimate state of charge (SOC) that it could miss a significantly failed cell which in turn could result in an erroneous range display and potentially leave a driver stranded on the side of the road?
A number of members have talked about current counting, cross checking with cell voltage, pack models, and sloped discharge curves. It's pretty clear that the car does not rely on 'ONLY' current counting. That appears to stop your chain of events before it starts. Moving on, though...
We know from the tech info direct from Nissan that the car directly measures cell voltage. We know it can do that 24/7 in all driving, parking, or charging conditions. We also know that the car does a diagnostic to measure cell internal resistance - which it stores in the battery controller in the pack. We also know that data from the battery controller travels via CAN bus to the main vehicle controller - and that the vehicle controller splats data on the driver's displays and also decides if it can honor a driver's request to go or stop or charge.
So far so good.
We also know that the car uses the cell voltages to decide if the battery is in trouble. If any cell (parallel group - two per module) rises above or falls below the safe zone (not the absolute cell limit - but the operator safe zone!), it triggers a "no charge/no drive" hard fault and the car will not move.
(Important points here - the car will
not allow one to over charge or over discharge any cell. It
could happen but it would take a controller failure - and the controllers are monitored as well - and a controller failure stops the car - which should also prevent over discharge or over charge. Belt and suspenders. Redundancy. Good Things.)
Your proposed chain of events breaks a second time because a 'high self discharge' is a direct indication of a failed cell. A cell with a high self discharge has an internal short or some other significant damage - and its internal resistance and thus cell degradation value will change significantly. This doesn't happen quickly or instantly or catastrophically unless someone shoots the battery box, so we'll ignore that situation for the moment.
The car tracks internal resistance at the cell level. Well before a cell gets bad enough to leave a driver stranded, the computer will set error codes and alert the driver of the battery failure.
Therefore no - it's my opinion that the chain you propose cannot happen in the real world.