Acceptable cell imbalance range?

[AAKEE]

Still 33mV imbalance.

Did you get it to sleep and let it balance the battery?
If the car balances the battery after tge charge, the SOC will go down as it burns of voltage from the high cells.

The highest cells is 4.1V
I do not know what is set as 100% in your model. For the cells themself, 4.20V is 100%. Someone else here would know I guess.


If the car was left to sleep and if there was any balancing done, just drive 5% of and charge to 100% again.

 

[islandbayy]

As AAKEE said, still a 33mV imbalance. I'd charge it to 100% a few days/times in a row. Also calibration could be off. A low SOC to 100% can help correct that.

 

[ran349]

Okay so I charged to 100% and let it be, but it doesn’t get above 97% and says it’s finished charging.



When I check scanmytesla:

View attachment 1008552


Cell information:

View attachment 1008554

Why is your HV battery showing 2.68 kW? That seems like a lot if your car is just sitting there.
Your DC-DC input power is much lower at 320 W.

 

[AAKEE]

Why is your HV battery showing 2.68 kW? That seems like a lot if your car is just sitting there.
Your DC-DC input power is much lower at 320 W.

Stepping inside the car starts the climate system, and a older non heatpump would probably use that for a while to heat the cabin to the set numbers.
(Of course the heating system can be turned off)

 

[nicog]

Hello,
I'm monitoring my HV pack continuously after my last post here and what I found out is that sometimes, somehow, something triggers the module 4th brick 6 voltage to go down:

for example:
1.
SOC 64.6% - brick imbalance in the module: 36mv, whole HV battery pack imbalance: 38mv. - data got 2 mins after driving.
SOC 62.1% - brick imbalance in the module 49mv, whole HV battery pack imbalance: 51mv. - data got 17 hour after resting over night (was always online)
SOC 55% - brick imbalance in the module: 28mv, whole HV battery pack imbalance: 29mv. - data got 2 mins after driving.

2.
SOC 93.2% - brick imbalance in the module: 29mv, whole HV battery pack imbalance: 31mv. - data got after charging to 100% and resting over 13 hours.
SOC 62.4% - brick imbalance in the module 48mv, whole HV battery pack imbalance: 52mv. - data got 2 mins after driving.
SOC 58.3% - brick imbalance in the module 47mv, whole HV battery pack imbalance: 49mv. - data got 19 hour after resting over night (13h online, 6h offline)
SOC 50.5% - brick imbalance in the module 30mv, whole HV battery pack imbalance: 34mv. - data got 5 mins after driving.

these stats are collected one after another
As you can see increase of imbalance is not related to resting or driving - I mean in the first example the imbalance was increased while parking from 36mv to 49mv for the problematic brick. In the second example the imbalance was increased from 29mv to 48mv while driving and it stayed at the same level while parking.

But one thing is clear: after sudden rising of the imbalance, it goes down again while next driving.

I saw this increase and decrease already 4 times. I think, because of this, I can not balance the pack to the old 0.04 - 0.06mv imbalance range.
Had anyone such kind of situation or can anyone guess, what it could be and how can I fight against it?

 

[Quickst]

The highest cells is 4.1V

Is the 0.1V between 4.1 and 4.2 the hidden capacity that Elon made available (unlocked with an OTA software upgrade) for Teslas during Hurricane Irma back in 2017?

 

[khorton]

Is the 0.1V between 4.1 and 4.2 the hidden capacity that Elon made available (unlocked with an OTA software upgrade) for Teslas during Hurricane Irma back in 2017?

No - the situation was that Tesla sold cars with different advertised battery capacity, but these models all actually had the large capacity battery. The usable capacity was SW locked to whatever capacity the customer had purchased. I.e. cars advertised with 60 and 75 kW-hr batteries. In fact both models have the larger battery. When the hurricane was approaching Tesla allowed the 60 kW-hr cars to use 75 kW-hr capacity for a few weeks.

More Info

 

[nicog]

My measurements have shown interesting picture:
In the rage of 62% - 63% SOC the imbalance increases with approx. 20 - 25 mv (for ex. from 27mv to 52mv).
I don't know exactly when it begins decreasing, but at 55% SOC the imbalance was 28mv.
What could it be to trigger the imbalance increase in such of SOC range?

 

[AAKEE]

My measurements have shown interesting picture:
In the rage of 62% - 63% SOC the imbalance increases with approx. 20 - 25 mv (for ex. from 27mv to 52mv).
I don't know exactly when it begins decreasing, but at 55% SOC the imbalance was 28mv.
What could it be to trigger the imbalance increase in such of SOC range?

A bit strange if the imbalance increases at a specifik SOC like that.

Charge from low to high SOC in a single chsrge and tsne readings omce/hour?
SOC - voltsge -imbalance.
Also check which cells that does what - screen dumps of the BMS page with all voltages?

 

[islandbayy]

A bit strange if the imbalance increases at a specifik SOC like that.

Charge from low to high SOC in a single chsrge and tsne readings omce/hour?
SOC - voltsge -imbalance.
Also check which cells that does what - screen dumps of the BMS page with all voltages?

Agreed. I've never seen the imbalance get better the lower the SOC, it should be the exact opposite.

 

[islandbayy]

My measurements have shown interesting picture:
In the rage of 62% - 63% SOC the imbalance increases with approx. 20 - 25 mv (for ex. from 27mv to 52mv).
I don't know exactly when it begins decreasing, but at 55% SOC the imbalance was 28mv.
What could it be to trigger the imbalance increase in such of SOC range?

A few thoughts, and I'm taking a shot in the dark here.
There were reports of BMS Boards incorrectly sensing voltage, and the BMS trying to compensate for that after a firmware update. It's been a while since I read those reports/posts. I believe it was due to cold solder on the BMS boards causing poor connection for that sensor.
That is about the only thing I can think of right now. A fault in the BMS.

 

[nicog]

Hi all,
I'm back now with new data in my balancing process.
As I already mentioned above, in the specific SOC range the Imbalance of brick 6 of the module 4 increases. this SOC range is 61-66% where the imbalance begins to increase and decrease. It is not depending on charging or discharging process - the imbalance increases always from 66 to 61 % SOC down (discharge) or from 61 to 66% SOC up (charge).
Because the increase of imbalance in this SOC range is to high, the BMS can not compensate it afterwards and the imbalance decreases when the SOC is above 66% or under 61% SOC, but it stays always increased as it was before.
In my experiment, I tried to stay above 66%. I charged 4 times during last week. the start SOC was always above 70% and end SOC was first time 95%, than - 99%, than - 90% and than 91%.
I can write here, that my imbalance is now down from about 40-45mv to 15mv.
I have to say here, that the battery is balancing while the car is resting but online, and while the car is slipping. It is balancing the Pack while the SOC is 99% and while the soc is 83%. What I'm trying to write here, is that the MBS is trying always to balance the pack.

But now I have one question here:
How can I keep the pack balanced based on the problematic imbalance SOC range from 61% to 66%?

A few thoughts, and I'm taking a shot in the dark here.
There were reports of BMS Boards incorrectly sensing voltage, and the BMS trying to compensate for that after a firmware update. It's been a while since I read those reports/posts. I believe it was due to cold solder on the BMS boards causing poor connection for that sensor.
That is about the only thing I can think of right now. A fault in the BMS.

I think you are right because of incorrectly sensing voltage. But do you think, the software can handle this problem and after some charge-discharge cycles, the BMS will correct it by itself?
If not, what do you think, what can I do in this case to solve my problem?

Thank you all for your great help and support!

 

[islandbayy]

Hi all,
I'm back now with new data in my balancing process.
As I already mentioned above, in the specific SOC range the Imbalance of brick 6 of the module 4 increases. this SOC range is 61-66% where the imbalance begins to increase and decrease. It is not depending on charging or discharging process - the imbalance increases always from 66 to 61 % SOC down (discharge) or from 61 to 66% SOC up (charge).
Because the increase of imbalance in this SOC range is to high, the BMS can not compensate it afterwards and the imbalance decreases when the SOC is above 66% or under 61% SOC, but it stays always increased as it was before.
In my experiment, I tried to stay above 66%. I charged 4 times during last week. the start SOC was always above 70% and end SOC was first time 95%, than - 99%, than - 90% and than 91%.
I can write here, that my imbalance is now down from about 40-45mv to 15mv.
I have to say here, that the battery is balancing while the car is resting but online, and while the car is slipping. It is balancing the Pack while the SOC is 99% and while the soc is 83%. What I'm trying to write here, is that the MBS is trying always to balance the pack.

But now I have one question here:
How can I keep the pack balanced based on the problematic imbalance SOC range from 61% to 66%?


I think you are right because of incorrectly sensing voltage. But do you think, the software can handle this problem and after some charge-discharge cycles, the BMS will correct it by itself?
If not, what do you think, what can I do in this case to solve my problem?

Thank you all for your great help and support!

Thanks for coming back with an update.

Do I think the software can handle this problem? For the long run? No. My personal (and others) belief was that it was a stop-gap measure to get battery pack out of warranty period.
If it is indeed the issue, you COULD open the pack, and swap out a BMS board for that module. Unlike the cells, which need to be matched as perfectly as possible to the remaining modules of cells, BMS boards are replaceable with little issue. You Will need Tesla Toolbox software though to make the car accept the BMS board, I believe.

 

[nicog]

Thanks for coming back with an update.

Do I think the software can handle this problem? For the long run? No. My personal (and others) belief was that it was a stop-gap measure to get battery pack out of warranty period.
If it is indeed the issue, you COULD open the pack, and swap out a BMS board for that module. Unlike the cells, which need to be matched as perfectly as possible to the remaining modules of cells, BMS boards are replaceable with little issue. You Will need Tesla Toolbox software though to make the car accept the BMS board, I believe.

well. today I discharged the pack down to 66.2% and the imbalance was stable 13-14mv. I'm so happy to see such kind of low imbalance. No i'm charging to 90%. I'd like to get back my 4-8 mv imbalance

I have one thing to try: I think I did not disconnected the 12v battery and Hi voltage battery pack until now. I'd like to give a try to disconnect and live them 12 hours disconnected. Maybe it will be reset and will functioning correctly again.

If not than only one thing I can do, it to replace the BMB of the problematic module!

Thank you @islandbayy for your quick answer.
I will come back as soon as I have new update.

 

[islandbayy]

well. today I discharged the pack down to 66.2% and the imbalance was stable 13-14mv. I'm so happy to see such kind of low imbalance. No i'm charging to 90%. I'd like to get back my 4-8 mv imbalance

I have one thing to try: I think I did not disconnected the 12v battery and Hi voltage battery pack until now. I'd like to give a try to disconnect and live them 12 hours disconnected. Maybe it will be reset and will functioning correctly again.

If not than only one thing I can do, it to replace the BMB of the problematic module!

Thank you @islandbayy for your quick answer.
I will come back as soon as I have new update.

No need to disconnect the 12v battery, that will not reset the BMS.
In the service menu, there should be an option for "reset bms". I know the option is present on MCU2 (even MCU1 upgraded to MCU2 vehicles) though I do not know what the menus look like on MCU1. Look there first. I believe you select the option, pull the fire loop under the hood to disconnect the main contactor, then run the BMS reset. It takes about 1 minute or so to do the reset. Range may be off the first drives & recharges after that. Run it low and then up to 100% to let it recalculate the pack capacity.

 

[nicog]

No need to disconnect the 12v battery, that will not reset the BMS.
In the service menu, there should be an option for "reset bms". I know the option is present on MCU2 (even MCU1 upgraded to MCU2 vehicles) though I do not know what the menus look like on MCU1. Look there first. I believe you select the option, pull the fire loop under the hood to disconnect the main contactor, then run the BMS reset. It takes about 1 minute or so to do the reset. Range may be off the first drives & recharges after that. Run it low and then up to 100% to let it recalculate the pack capacity.

In MCU1 there is no BMS reset function. I looked already in the service menu.

 

[nicog]

I discharged the pack not lower than 68% and always charged not lower than 90%. I did it 5 times and at the end I balanced my HV battery pack to 4-5 mv.
After that I charged it to 90% and discharged it to 35% but my imbalance was 5-6 mv after 3 hours resting time.
Today I discharged it from 90% to 51% using the whole time the heating, but the imbalance is the same - 4-5mv !
I don't know what's exactly was going on, but I'm so happy that the pack is working as it was.
And the range is back from 335km to 353km as it was before.

 

[AAKEE]

I discharged the pack not lower than 68% and always charged not lower than 90%. I did it 5 times and at the end I balanced my HV battery pack to 4-5 mv.
After that I charged it to 90% and discharged it to 35% but my imbalance was 5-6 mv after 3 hours resting time.
Today I discharged it from 90% to 51% using the whole time the heating, but the imbalance is the same - 4-5mv !
I don't know what's exactly was going on, but I'm so happy that the pack is working as it was.
And the range is back from 335km to 353km as it was before.

As the bricks will have slightly different capacity you will have more imbalance outside the point (SOC-level) where the battery was balanced.

Well, seems like everything is ok

 

[nicog]

As the bricks will have slightly different capacity you will have more imbalance outside the point (SOC-level) where the battery was balanced.

from 90% to 35% there was no different imbalance at all. only first time, when I discharged the car from under 66% I got slightly higher imbalance in the range from 63% to 61%. it was about 10mv, but after it decreased to the 4-5mv.
I will write here when I will go down to 10% SOC and check the imbalance.

Thank you @AAKEE, @islandbayy and all others for your help and support!

P.S. the image is from SMT at 51% of SOC