been reading this off and on while working and waiting for things. just a few points i’d like to make based on experience.
- if one pgroup drops below the good zone LVC in the ESC wont know or care
- If one pgroup drops below the good zone the BMS will know and shut it down.
- if you can catch the lower capacity pgroup before all the cells in it drop below the good, check for broken welds and fix them, if that was the issue the group will rebalance itself out and then you can use a balance charger to get it back in line with the other groups.
- if one pgroup drops below the good zone it must be removed regardless of cause or cost or inconvenience
- if the cycle life of the entire pack is less than say 10 charges you can drop new cells in there and replace the pgroup with little or no consequence.
- If the cycle life of the entire pack is higher than that I wouldn’t do it unless you have an external balance charger, you’ll be fighting drift forever because
- most BMSs suck at re-balancing and one groups in your pack now has a slightly different capacity
- most BMSs suck at handling regen voltage spikes in a way that’s freindy to the rider
- a BMS won’t prevent cell death within a pgroup, just keep you from using the pack while it dies slower
- discharge protection events while riding can be lethal
- over charge protection events while braking can be lethal
So, to sum up, in my opinion, fuck BMS protections on the charge/discharge path between the cells and ESC and if you have a dead pgroup in most cases you should rebuild your whole pack with new cells unless you lucked out and just had broken welds on otherwise good cells.