vreihen wrote: ↑
Mon Jun 10, 2019 10:01 am
I thought that I read somewhere about BMW software-limiting the top end of the battery pack for longevity reasons, where 100% full isn't really 100%? Am I confused and it was actually someone else doing it?
When I leave home every morning with a full charge, regen seems to work fine at the stop sign on end of my street. Don't know if it is the above leaving some battery buffer space or it is just a transparent use of the mechanical brakes, but it one-pedals the same AFAICT.....
The top of the pack is indeed limited at 94% of actual capacity for a healthy battery. In case of 60Ah it's about 4.09V cell voltage (actual 100% should be about 4.15-4.20V cell voltage, haven't seen a SOC / cell voltage curve for i3, let me know if you saw it). If you check your pack via ISTA+ software, you'll see that the upper buffer may exceed 6% in case of battery degradation. E.g., in my case the upper buffer is almost 16% of the gross pack (21.8 kWh). But that's on paper, in SOC % of the gross capacity. ISTA+ also reports cell voltage, and it's 4.09V for my car with over 10% of the battery degradation, the same as for any healthy pack out there. Judging by cell voltage alone, once your battery degrades, the bottom buffer (usually at 8%) is effectively increased, i.e. cell voltage is still quite high for very low SOC. I provided details with screenshots on this in this thread on cell balancing viewtopic.php?f=11&t=13535&p=56484#p56484
Now, regarding the regen, it's not effectively working at 100% SOC, which is expected. The car decelerates as usual, but you can hear the brake pads being applied if you turn the music off and there is no street noise. There's a quirk there as well, I tried to find out details asking the FB community on the subject here https://www.facebook.com/groups/BMWi3/p ... %22O%22%7D
. The thing is, even when you are leaving at 100% SOC and there's no actual regen (brake pads are applied instead), the car still reports regen in the trip computer data on the dashboard, just check my screenshot below with a whopping 11 miles/kWh efficiency at 100% shortly after I departed. I'm thinking the BMS just doesn't have a clue what's going on there with the batter, efficiency etc., the model that produces these estimates is very flawed.