willmhull wrote: ↑
Sun May 02, 2021 2:57 pm
Is the friction brake engaged only when the entire pack is full or with each individual full cell in the battery?
The battery management system attempts to keep the charge levels of all cells close to equal at the high charge level end, so a full pack would also imply each cell being full. However, according to some British i3 owners who attended a briefing by BMW engineers early on, cell balancing doesn't occur when the displayed charge level is less than ~80%, or maybe it occurs only very slowly, and occurs only when no current is flowing in or out of the battery pack; i.e., when the battery pack is idle. So if you haven't allowed the battery pack to rest very long above an 80% charge level, some cell imbalance could exist.
When charging, the charging power tapers off as the charge level approaches full. I assume that regen braking power would also taper off to avoid damage to the battery pack. So at higher charge levels, an i3 might be mimicking pure regen braking power at lower charge levels by blending lower regen braking power with friction brakes. The brake rotors on our i3 have rusty surfaces which allows me to hear when the friction brakes are being used. However, I don't typically charge above 90%, so I probably haven't experienced much regen braking mimicking.