i3 Battery charging - Degradation real life experience

[Clanduncan]

!20Ah. This is my readings. Built FEB ‘22

Cell voltage deviation seems to be the key value?

This was at 92% which might be the reason for the slightly lower level than the 100% numbers @Clanduncan has seen

Hiya, Mine was produced via 'Electrified', but what app do you use to produce those figures?

 

[alohart]

Cell voltage deviation seems to be the key value?

Correct. Voltage is actually measurable whereas charge level and capacity are calculated values that aren't as accurate. Voltage is what the cell charge level balancing algorithm uses assuming a correlation between voltage and charge level, usually good but not exact.

 

[alohart]

I will post again in a few months after leaving the car plugged in and charging for as long as possible.

I will be surprised to see an increase in usable capacity no matter how long you leave an EVSE plugged in because the maximum cell voltage difference is only 0.004V, assuming that the voltage can be measured with such precision. That suggests excellent cell charge level balance already. The Electrified app displays a precision of only 0.01V, so the Electrified app would show perfect cell charge level balance in your battery pack.

 

[alohart]

Hiya, Mine was produced via 'Electrified', but what app do you use to produce those figures?

That looks like the relatively new eFlow app. Its license fee is more than I'm willing to pay when free apps like mi3 (iOS) and Electrified (Android) display the same data.

 

[i3m3fan]

!20Ah. This is my readings. Built FEB ‘22

Cell voltage deviation seems to be the key value?

This was at 92% which might be the reason for the slightly lower level than the 100% numbers @Clanduncan has seen

Oh that's flow or mi3 ??

 

[Gonville]

Hiya, Mine was produced via 'Electrified', but what app do you use to produce those figures?

The Bimmercode folks. They called it initially Bimmerflow but have changed the name to ‘eFlow’.

 

[Gonville]

Oh that's flow or mi3 ??

eFlow

 

[Gonville]

That looks like the relatively new eFlow app. Its license fee is more than I'm willing to pay when free apps like mi3 (iOS) and Electrified (Android) display the same data.

That’s true but it’s bundled for us and it was a one off. I appreciate supporting these app developers as many nice ‘free’ apps I have had in the past have a tendency to fail to be updated as the operating system moves on. I did it mainly to try and gain knowledge to support the charge to full mantra.

 

[Gonville]

I will be surprised to see an increase in usable capacity no matter how long you leave an EVSE plugged in because the maximum cell voltage difference is only 0.004V, assuming that the voltage can be measured with such precision. That suggests excellent cell charge level balance already. The Electrified app displays a precision of only 0.01V, so the Electrified app would show perfect cell charge level balance in your battery pack.

eFlow is giving that 0.4mV variation on mine as well so 3 decimal places so I am assuming that’s the data in the BMS?

 

[jfk68]

I will be surprised to see an increase in usable capacity no matter how long you leave an EVSE plugged in because the maximum cell voltage difference is only 0.004V, assuming that the voltage can be measured with such precision. That suggests excellent cell charge level balance already. The Electrified app displays a precision of only 0.01V, so the Electrified app would show perfect cell charge level balance in your battery pack.

So, which element could explain the difference in capacity between the cells ?

 

[alohart]

So, which element could explain the difference in capacity between the cells ?

Cell charge level balancing occurs at a high charge level ("top balancing") which would try to equalize the voltages of all 96 cells despite any capacity differences. Your battery cells' charge levels look to be very well balanced at a high charge level. However, were you to display these data at a low charge level, the minimum and maximum cell voltages would likely vary more with the lowest capacity cell having a considerably lower voltage than the highest capacity cell. This would be worth doing.

The capacity difference could be due to several reasons. Maybe the internal resistance of the low-capacity cell is higher than other cells such that some of the energy added to the cell during charging would be converted to heat rather than increasing the charge level thus reducing its capacity relative to other cells with lower internal resistances. Or maybe an internal irreversible chemical reaction is consuming some of the cell's energy thus reducing its usable capacity. There are probably other things that could explain the reduced capacity. However, the reduced capacity is probably permanent with nothing that could be done to increase the capacity. A series-connected battery pack like that in all i3's is only as good as its weakest cell. When the voltage of the weakest cell decreases below a certain level, the BMS would prevent further discharge to protect this cell from further damage even though other cells could be discharged more. This effectively reduces the usable capacity of the entire battery pack.

 

[Darlouis]

Checked mine today, first time for a while. Not charged it for a few weeks (I don't cover many miles) and hasn't been charged to over about 80% for I think a few months. My smart charger slightly overcharges sometimes to 81%. Shame Electrified doesn't show three decimal places for voltage.

 

[alohart]

Not charged it for a few weeks (I don't cover many miles) and hasn't been charged to over about 80% for I think a few months. My smart charger slightly overcharges sometimes to 81%. Shame Electrified doesn't show three decimal places for voltage.

Looks good to me. A voltage difference of only 0.01V between the lowest and highest cell voltages seems good. I don't know whether the voltage measurement is accurate to 0.001V as displayed by the iOS mi3 app.

 

[Zwerius]

Checked mine today, first time for a while. Not charged it for a few weeks (I don't cover many miles) and hasn't been charged to over about 80% for I think a few months. My smart charger slightly overcharges sometimes to 81%. Shame Electrified doesn't show three decimal places for voltage.
View attachment 1772

may be a strange question, but how do you make this visible? Is it on the screen of the i3? Or do you have separate equipment?

 

[alohart]

may be a strange question, but how do you make this visible? Is it on the screen of the i3? Or do you have separate equipment?

Separate equipment. A smartphone app, mi3 for iOS, electrified for Android, or eFlow for either, plus an OBD to WiFi or Bluetooth adapter for a wireless connection between the i3's OBD port and a smartphone.