Simply ENVY.
I'm at 76 kWh NFP.
It seems that even if you leave your normal way to charge (AC to 55-58%) to a more stressful way (DC SuC) , you always have the better NFP ever.
I still continue to experience drops when i let the car (due to force majeure ) under 20% SOC.
Then it recovers some but not all what lost in the drop.
About balancing (going near 90% or to 100% and let it charge up to stop) I don't understand if it has something to do with IMBALANCE in SMT in mV.
I always have 4 mV imbalance ( rarely 6.00).
This means that the BMS is perfect calibrated? What the relation between the Imbalance shown and the BMS being not accurate/calibrated?
And the BMS (Battery Management System) is Calibrated or Balanced? OR are the cells to be Balanced?
If at 4.00 mV this means that theere is no room for improvement?
Curiously... just after a 100% prolonged charge (up to complete Stop) the imbalance on SMT is Higher in my car
@Candleflame already answered but I’ll fill in a little.
4mV seems to be the normal imbalance in the middle of the SOC range, when the battery is at rest Or carefully driven.
I Always see 4mV when I check. 4mV is not much, so that for sure cool.
I can see 6mV when parking my car in the garage at about 30% after a 50km drive from work, that settles to 4mV quite fast after the parking).
Balancing the battery is only needed to either get it 100% properly filled with energy. ( some EV manufacturer may balance in the bottom instead).
If the battery is normally balanced and is at 4mV in the normal SOC range, the imbalance will increase when charged to 100%. This is due to the small differences in the cells, a cell with smaller capacity will hit 4.20V(the limit for a li ion cell of the NCA type). Typical imbalance when reacing 100%/4.20V is about 10-20mV if the battery shows 4mV in the medium SOC range.
If no balancing is done, some of the cells will not reach full capacity and the charge will not give the maximum energy. Normally there isnt that much difference in energy from the first cell reaches the ”full” value.
(My battery had 8mV when it reached 100% on the yesterday charge. For a brief moment the imbalance alternated between 8 and 10mV so it maybe topped somewhere between 8 and 10, when the charge was finished it was at 8mV, and soon after driving commenced so no long time to balance it. I also had a full charge until stop 6 days before this one, thats probably the reason for being quite low on the imbalance this time).
Balancing is only needed at higher SOC to make sure all cells can get close to full, thats the reason for balancing not be done below 90%.
Also, balancing is done by burning of the energy in the highest cells so if it alway was done, it would cost energy unnecessarily.
As
@Candleflame wrote, BMS ”Calibration” is about the BMS having the correct estimation about the batterys actual capacity.
I see daily in a swedish facebook teslagroup that these two(balancing battery and BMS calibration). is mixed up and misunderstood.
They are not connected, so you could have a very unbalanced battery with for example 30mV imbalance, but if the BMS has a correct estimated battery capacity, the BMS is spot on( ”well calibrated”).
The BMS calibration is about getting the car to sleep(contactors in the battery open and the battery gets to rest which let the cell voltage come to the resting voltage(Open circuit voltage, OCV). That voltage tell the BMS what the true SOC is. For example, a 100% SOC fresch cell holds 4.20V, or very close but with the Car not sleeping, lights on and maybe the AC/heater the load causes the voltage to drop to perhaps 4.19V or so.
The BMS would need to get one reading of the OCV at high SOC and one reading at low SOC. As the BMS knows the energy that goes in and out, it can calculate for example that it was 60 kWh between 15 % and 90% SOC, that give 75%= 60kWh —> 100% = 80kWh.
Maybe the BMS needs more than two readings to get a proper result, I havent done any ”calibration” by purpose.
