Cell voltage difference a function of SOC, explanations?

[JodyS21]

The Torque Pro app makes it look better though, where they're all the same at 4.2V.

That app uses a configuration file that you specify yourself doesn't it to get and display data? So there's probably a slight bug in what it's doing for that data entry causing it to show "4.2"

 

[Kithmo]

That app uses a configuration file that you specify yourself doesn't it to get and display data? So there's probably a slight bug in what it's doing for that data entry causing it to show "4.2"

I don't know about configuring it, I just clicked the Torque link in the ZS EV app and the PIDS were already there. I don't remember, I could have added them myself previously.

 

[Kithmo]

Most people's data I've seem do have around 20mV difference after a balance. So yours is a bit out of the normal range, not sure if it's really anything to worry about particularly though.
You could try looking to see if it is just a particular cell pack that has the larger than normal difference.

Just charged and balanced and checked again. Scrolling (live) through the add new PIDS on Torque, which shows the values to 3 decimal places, "MG BMS Unit 06 MinVolt" is showing as 4.182V, the rest are all above 4.2V and within 14mV of each other, so it looks like the 06 module contains the cell that's low.
FWIW, at 100% charged, SOC is 97% (on the old BMS), now showing 455.5V, previously was 456.25V on a warmer day. SOH still 100% though.

 

[JodyS21]

Just charged and balanced and checked again. Scrolling (live) through the add new PIDS on Torque, which shows the values to 3 decimal places, "MG BMS Unit 06 MinVolt" is showing as 4.182V, the rest are all above 4.2V and within 14mV of each other, so it looks like the 06 module contains the cell that's low.
FWIW, at 100% charged, SOC is 97% (on the old BMS), now showing 455.5V, previously was 456.25V on a warmer day. SOH still 100% though.

Hmm that's interesting, I wonder if after several more balances it'll sort that low cell out.
It's possible of course that the new BMS would balance it better, they were trying to sort out a balancing issue originally which is why they started releasing new BMSs way back before they broke it.

 

[Kithmo]

Hmm that's interesting, I wonder if after several more balances it'll sort that low cell out.
It's possible of course that the new BMS would balance it better, they were trying to sort out a balancing issue originally which is why they started releasing new BMSs way back before they broke it.

I think I've just got a low cell for some reason. I've probably full charged and balanced between 15 and 20 times since I installed the app and IIRC, the minimum value (on the app) has always been the same, 4.182V. Although it's not improving, thankfully it doesn't seem to be degrading either (fingers crossed).
Do you know if it's possible to get the Torque app to display more accurately, maybe to two or three decimal places ?

 

[rbpasapera]

I think I've just got a low cell for some reason. I've probably full charged and balanced between 15 and 20 times since I installed the app and IIRC, the minimum value (on the app) has always been the same, 4.182V. Although it's not improving, thankfully it doesn't seem to be degrading either (fingers crossed).
Do you know if it's possible to get the Torque app to display more accurately, maybe to two or three decimal places ?

Yes, you can change the decimal places.

Long press the display and select "display configuration", then select "number of decimal places". Enter the number of decimal places you wanna see on the display.

 

[Kithmo]

Yes, you can change the decimal places.

Long press the display and select "display configuration", then select "number of decimal places". Enter the number of decimal places you wanna see on the display.

Thanks for that, very useful to know.

 

[DuracellBunny]

I’m not being funny - but exactly why are you doing this? Aren’t you causing yourself undue stress over something that you can’t do very much about?

I was wondering what impact on battery capacity fast charging has and if I can get away with it if I slow charge it to do load balancing. Sharing charging patterns and data gathered with an OBD gadget helps to protect battery capacity.

 

[Peter WA]

Just a quick update: since I started this thread in early September I have not balanced my battery. The voltage difference between highest and lowest cell has remained virtually the same, 17mV or at most 18mV whenever charge levels are above 70%.

Initially I was regularly charging to about 90% or slightly above (to get to an actual 90% of capacity). I have since found a 'battery stress chart' that makes a raw SOC of 80% (about 84% in the car display) a safer cut-off for charging with longevity of the battery in mind. I mostly charge to that level now, and only go higher if I have a very long trip planned that needs more.

I don't plan to do another balance charge until either the cell difference increases significantly (close to 25mV) or I feel that my battery capacity is diminished.

SOH is still shown as 100% at an odometer reading of 14464 km.