a quick, but important clarification
BMS_029 is not triggered by a cell imbalance, but rather a pathological reduction in brick capacity - for example, a battery pack might have 2-3 bricks with a max capacity in the 213 Ah range and 3-4 bricks with a min capacity in the 210 Ah range, with an average of all bricks in the pack in the 211-212 range. Everything is chugging along fine, then at some point one of the cells fails (usually, but not always, in one of the lower capacity bricks), dropping the capacity of the failing brick to around 206-208 Ah and eventually triggering a BMS_u029 weak short error. (note: the BMS_u29 isn’t triggered by a specific capacity delta per se, but rather an abnormal/unexpected decline in a brick’s capacity that may be the result of something more concerning… such as dendrite growth, etc.)
on the otherhand, a BMS_u018 is triggered by a SoC imbalance - typically a delta of 10-15% or more <digs up notes on SoC spec> - where no one brick has necessarily failed, but the pack overall is out of balance. interestingly, it’s possible for a BMS_u029 to ultimately result in a BMS_u018 as the capacity in the failed brick continues to degrade to the point that an overall imbalance error (BMS_u018) is eventually triggered, but the two are a distinctly different failure modes.
it’s important to be clear here that these BMS_u029 errors aren’t the result of some random OTA update, but the result of an underlying brick failure.
as
@wk057 and
@Recell have pointed out here and elsewhere, the fact that these errors might arise sometime after an OTA is otherwise complete happenstance - a brick failure has occurred, and has likely been headed that direction for some time. the data (vs. anecdotes) do not support the hypothesis that OTA updates are the source/root cause of these issues.
doubtless,
@wk057 can add additional color to the above
(additional note: detection of brick failures by the BMS has of course improved over time, by way of OTA updates, but better detection and handling of these brick failures and improved safety is a good thing, right?)
