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Battery imbalance cell reading changes

5JWX

Member
Oct 31, 2022
8
0
UK
I have a 2014 Model S with a refurbished 2020 85 battery pack. Car won’t drive or charge, shows numerous errors
Using scan my Tesla I have a big imbalance issue, ranges in seconds from 1000 to 2245mV
The bit I don’t understand is the voltage in modules 8 & 10 fluctuate between 3.6v to 1.6. Guessing I have a coolant leak to have effected 2 modules?
Can anyone confirm the module numbering system?
Anyone had this before, everything I’ve read online has more or less static low voltage not fluctuating like mine.
Thanks
 

Attachments

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5JWX

Member
Oct 31, 2022
8
0
UK
Update
I have a cell difference 2.5v but the reading are very erratic & does this on modules 8 & 10. It will show all cells approx 3.6v then 2 cells from module 8 & 2 from 10 will suddenly drop to 1.6v then back up to 3.6v the faulty cells are in the same position on scan my Tesla; 1st row top right & 2nd row bottom left. They change at t tree exact same time.
Car is a 2014 model S with reconditioned pack fitted 2.5 years ago by Tesla.
I’ve stripped down the pack expecting to find water/ coolant but cannot visually see anything.
I have isolated each module & checked the voltages. From memory 12 are all 22.76, the lowest reading was 22.74, some 22.75. Which were all much closer than I had expected. My knowledge suggests all my modules are good?

I now assume I have a fault with the BMS circuit boards but how can 2 go down at the same time? Or could it be a BMS wiring fault within the pack, or fault the pack circuit board situated at the rear of the pack?
Has anyone come across this?

If I don’t get any response my next plan is to move the modules around in the pack, & the BMS circuit boards, refit the pack to the car & see if the fault has moved.
Unless someone has a better idea.
All input welcome

Thanks
 
Okay 5J,
It sounds like you're moving in the right direction.
Pull modules 9 and 11 out of the pack.
Measure voltage on 6 individual bricks on each module.
Do some bricks measure 1 or 2 volts?
Yes? Module requires replacement.
No? 3 volts or more? Lucky you. Most likely BMS board on the module failure, requires board replacement.
 

5JWX

Member
Oct 31, 2022
8
0
UK
Okay 5J,
It sounds like you're moving in the right direction.
Pull modules 9 and 11 out of the pack.
Measure voltage on 6 individual bricks on each module.
Do some bricks measure 1 or 2 volts?
Yes? Module requires replacement.
No? 3 volts or more? Lucky you. Most likely BMS board on the module failure, requires board replacement.
Thanks.
Does the fact the whole module voltage is a consistent 22.76v not mean the module is ok then?
Okay 5J,
It sounds like you're moving in the right direction.
Pull modules 9 and 11 out of the pack.
Measure voltage on 6 individual bricks on each module.
Do some bricks measure 1 or 2 volts?
Yes? Module requires replacement.
No? 3 volts or more? Lucky you. Most likely BMS board on the module failure, requires board replacement.
Thanks for the info, I assumed if the module are all equal the batteries were ok but your right if one or two cells are out it wouldn’t show across the entire pack.
I’ll check the individual cells over the next few days.

Scan my Tesla shows issues with 8 & 10, you say check modules 9 & 11, is that correct, if so I didn’t realise that, I’m working on the modules being numbered as per attachment but not 100% sure it’s correct.
Thanks
 

Attachments

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I was trying to make out the numbering on your somewhat fuzzy scan my Tesla attachment photo. You are probably correct with modules 8 and 10. The important thing is that you get what I'm driving at.
And the layout attachment above shows correctly. You know what you're doing. You'll be fine.
Let us know what you find, battery trouble or circuit card trouble.
 
Thanks.
Does the fact the whole module voltage is a consistent 22.76v not mean the module is ok then?

Thanks for the info, I assumed if the module are all equal the batteries were ok but your right if one or two cells are out it wouldn’t show across the entire pack.
I’ll check the individual cells over the next few days.

Scan my Tesla shows issues with 8 & 10, you say check modules 9 & 11, is that correct, if so I didn’t realise that, I’m working on the modules being numbered as per attachment but not 100% sure it’s correct.
Thanks
If you still have the issue, I think you should ask for a low cost Tesla repair option. I understand that they are offering at least a 4-year warranty with pack refurbishments / replacements. These third-party companies can help also with main battery repairs:

www.057tech.com (Offers a main battery warranty)

www.recell-ev.com
 

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