Strange battery temperature sensor readings

[Danijel]

Dear All,

I we been playing around with OBD dongle and Car Scanner in my ID.3 yesterday and I noticed a bit strange temperature reading:

At short: All other BMS readings were at the similar level, except HV battery temp point 4, which is always 10C below the others. As it can be seen in the picture, I did 2 scans yesterday and both show 10C difference.
When entering dashboard, HV battery temp point 4 is represented as lowest temperature of the battery.
The car seems to perform normally, no degradation is noticed. Unfortunately I bought a used one about 2 months ago, so it is a bit difficult to compare. I also didn't do much fast charging to see if the temp reading has any affect on the charging speed.

Questions / thoughts:

Has anybody experienced this already? I we been googling about this topic but no relevant data available.
Do you think this is an actual car problem, or it might just comm/app glitch?
General car warranty is over...can this fault (if exists) be treated under battery warranty?

Thank you very much!

[Midgex]

I would suspect that sensor of being wrong.
Two other modules will be adjacent, if their temperature readings are the same, and the same as the distant modules, it is probably just something to note, rather than to take the pack apart to correct.

I'm no expert on that, but have some practice in looking at a collection of measurements to make decisions.

[sidehaas]

I agree with Midgex that it's probably a sensor fault (or alternatively a software glitch) as it wouldn't be possible for one cell to have such a significant temperature delta either side of it in the middle of the pack. The question though is whether the BMS acts on that faulty reading and behaves wrongly as a result. You could rule out a carscanner glitch by trying a different app like EV Notify.
I think the best way to test it is probably a rapid charge. If you arrive somehere on low SoC with a min temperature of over 15C in the pack, it should charge at around 70-80kw ish. Over 20C and you should see 100kw+. If it's a lot below that (like 40-50kw or something) that would suggest to me that it's using the low temperature reading and limiting your charge rate.

I haven't seen anyone else report this and have no idea about the warranty situation, sorry. I think it would probably be difficult to prove to a dealer that you had a fault given that these readings aren't normally visible to the driver.

[Danijel]

Thank you both!

I did a test today in following conditions:
- 350 kW fast charger
- Tamb 19 C (66F)
- Tbat 15 C (59F)
- Initial SOC 12%

Peak charging power should be 125kW (2021, PRO, ID software 3.2)

The result was mind-blowing 42kW.

According to what you said this indicates a potential problem with DC charger / Battery itself.
Situation with temperature measurement remains the same, I also got confirmation from author of Car Scanner that there should not be any problems with the app.

Call for action I guess...

[sidehaas]

Thank you both!

I did a test today in following conditions:
- 350 kW fast charger
- Tamb 19 C (66F)
- Tbat 15 C (59F)
- Initial SOC 12%

Peak charging power should be 125kW (2021, PRO, ID software 3.2)

The result was mind-blowing 42kW.

According to what you said this indicates a potential problem with DC charger / Battery itself.
Situation with temperature measurement remains the same, I also got confirmation from author of Car Scanner that there should not be any problems with the app.

Call for action I guess...

If the true minimum battery temperature is around 15C, you'll never get 125kw, but you should get 70 or a little more.

[Danijel]

Thanx for info.

Are there some charts available, where charging power dependency from temperature at certain SOC is visible?

[sidehaas]

Thanx for info.

Are there some charts available, where charging power dependency from temperature at certain SOC is visible?

Not really. There must obviously be a complex algorithm within the BMS but it isn't public. You can find curves like this one which are valid if you have plugged in below 5% and the battery is in a good temperature range (min battery temp above 25, max below about 45-50C). If you have plugged in at higher SoC or the battery is cooler, you will not get the charging rates shown in this chart as a function of SoC. You just have to learn it really.
Very roughly, I find that if I plug in below 10-15%, with the battery above 15C I'll get a peak of 70-80kw, above 20C I'll get 90-110kw, above 25C anything up to 134kw (which I've seen 4 or 5 times).

[Danijel]

HI,
Thank you for all valuable information
I have arranged with the dealer next week and let's see what their findings will be.

[Danijel]

Dear all

After some ping pong with VW and after several discussions with Service personnel the car was finally accepted to the garage. The result: 2 modules were replaced under battery warranty. It was quite a relief that VW absorbed this cost of 3000€. The temperature readings are now fine, will do the charging test in following weeks.
My learning from the story was, that everybody tried to convince me that it is a charger problem. Luckily I had this faulty temp reading, which helped me with the convincing the service personnel.

[sidehaas]

Sounds like a great result, let us know if it now charges as expected!

[Danijel]

Hi,

I tried yesterday and it works like a charm...100 KW @30%