Too late to edit my post?( 1hr limit?)
6mV balance all the way up to last check point 73% SOC.
I saw 4mV at 87% SOC.
I sat in the car for the last 10 minutes of the charge and SMT showed alternating 4 and 6 mV during that time. When it stopped charging, It said 4mV.
Now the car will stand for a few hours, to see the actual imbalance after this.
Charging just finished at 90% SOC.From my experience with lithium batterys in other applications the balancing always is done on top of the SOC, thats also the aim of the balancing, to have similar SOC and voltage( = performance) from all cells.
If you dont go to the absolute zero SOC, of close to it, the only real gain is to balamce it on the top of the range, to reach as close as 100% on all cells. Charging must be stopped when the highest cell reach 4.20V. If The imbalance causes the average Voltage to be 0.1V below the sibgle highest cell at 4.20V, we loose more than 10% capacity.
For cycles between below some 90% and below there might be less advantage of balancing the cells, a balancing session at low SOC might even cause more imbalance at higher SOC’s, because of different cell characteristics.
Well, knowing this, I arrived from a two day trip, about 600km.
My battery has shown 4.00mv imbalance for more than two months with quite shallow charged. I never have seen less than 4mv, so I leaning to the guess that 4 mv is the target when the BMS stop balancing.
When I arrived at home yesterday, I had 20% SOC, 3.47v / cell 6mV imbalance and 16.75C batt temp. I put the car in the garage and waited 5hours.
Still 20% SOC, 3.48v/cell and still 6mV. Cell temp 15.75C.
No balancing seem to have taken place during these 5 hours.
I put the car on charge to 62% with the WC at 5.5kW and by calculation from both charge time remaining and also the Kwh needed/ charging power I did get a time early this morning, I added 5hrs and that time just passed so I checked the imbalance. Still 6mV.
As it looks, no cell balancing seem to have been occuring during the charging session or after during these 5 hours.
So, the car is now on charge for a 90% SOC, I will check the imbalance when the charge is complete and also leave it for 5 hours and check.
Cell imbalance should not be a BMS estimate but actual values, so I think we can rely on these voltages as ’true’.
6mV balance all the way up to last check point 73% SOC.
I saw 4mV at 87% SOC.
I sat in the car for the last 10 minutes of the charge and SMT showed alternating 4 and 6 mV during that time. When it stopped charging, It said 4mV.
Now the car will stand for a few hours, to see the actual imbalance after this.