Cell unbalancing

Highest cell is Cell 6 at 4.000V with estimated capacity of 2550mAh. Lowest cell is Cell 4 at 3.921V with estimated capacity of 2280mAh. It makes a difference of 79mV and 270mAh.

With a 50mA current to balance cells, this test will at least last 5h.

FSM logs

c++
1	"Entered state INIT"
1	"Log: 'Initializing environment...'"
1	"Log: 'Environment initialized !'"
1	"Log: 'Initializing battery IC...'"
1	"Log: 'Battery IC initialized !'"
2	"Log: 'Configuring battery IC...'"
2	"Log: 'Battery IC configured !'"
2	"Log: 'Initializing SoH...'"
2	"Log: 'SoH initialized !'"
2	"Log: 'Initializing SoC...'"
2	"Log: 'SoC initialized !'"
3	"Log: 'State fields initialized!'"
3	"Log: 'Battery initialization complete!'"
3	"Left state INIT"
3	"Entered state DISCHARGE"
3	"Log: 'transitioning from INIT to DISCHARGE'"
5	"Left state DISCHARGE"
5	"Entered state CHARGE"
5	"Log: 'Charge enters charge-and-balance mode'"
5	"Log: 'transitioning from DISCHARGE to CHARGE'"
2516	"Log: 'Charger has not enough current: -0.290000'"
2516	"Log: 'Charger has stopped giving current: -0.330000--0.290000'"
2516	"Log: 'Charge leaves charge-and-balance mode'"
2516	"Log: 'Charge enters final-balance mode'"

5-10_charge_40V_1_cell_above_80mV.dat

11005.8KB

Cell9	Time (s)	Tension (V)	Capacity (mAh)	Intensity (mA)
P1	4000	4.054	2697
P2	11500	4.041	2639
Delta	7500	0.007	58	27.84

The CV phase start really early as the battery was about 39.6V.

It slowly reduce current as expected then enters in Final Balance.

If we take a 2hour (7200s) range in Final Balance for example:

From 4300s at 4.052V (2694mAh) to 11500s at 4.042V (2642mAh), we get a voltage drop of 0.01V for a total of -52mAh in 2 hours. A balancing average of 26 mA.

Cell9	Time (s)	Tension (V)	Capacity (mAh)	Intensity (mA)
P1	5000	4.029	2609
P2	30000	3.986	2498
Delta	25000	0.043	111	15.984

💡

Graph show a balancing average of 26mA to 16mA with ours set to 50mA.

I continued the test until cells gets fully balanced. They do.

FSM logs

c++
1	"Entered state INIT"
1	"Log: 'Initializing environment...'"
1	"Log: 'Environment initialized !'"
1	"Log: 'Initializing battery IC...'"
1	"Log: 'Battery IC initialized !'"
2	"Log: 'Configuring battery IC...'"
2	"Log: 'Battery IC configured !'"
2	"Log: 'Initializing SoH...'"
2	"Log: 'SoH initialized !'"
2	"Log: 'Initializing SoC...'"
2	"Log: 'SoC initialized !'"
3	"Log: 'State fields initialized!'"
3	"Log: 'Battery initialization complete!'"
3	"Left state INIT"
3	"Entered state DISCHARGE"
3	"Log: 'transitioning from INIT to DISCHARGE'"
6	"Left state DISCHARGE"
6	"Entered state CHARGE"
6	"Log: 'Charge enters charge-and-balance mode'"
6	"Log: 'transitioning from DISCHARGE to CHARGE'"
613	"Log: 'Charger has not enough current: -0.290000'"
613	"Log: 'Charger has stopped giving current: -0.340000--0.290000'"
613	"Log: 'Charge leaves charge-and-balance mode'"
613	"Log: 'Charge enters final-balance mode'"
32690	"Log: 'Battery is balanced'"
32690	"Log: 'Last Charge FSM state: final-balance'"
32690	"Left state CHARGE"
32690	"Entered state DISCHARGE"
32690	"Log: 'transitioning from CHARGE to DISCHARGE'"

5-10_charge_40V_1_cell_above_80mV_2.dat

32390.7KB

40V Charger. 1 Cell above 80mV

Cell unbalancing