Geek question: What method (or methods) do I have to read individual cell voltages?

[j.w.s]

I would like to read and record individual cell voltages. Basically I'm curious to see how the Taycan does pack balancing, among other things.

What methods are available to read the voltage of individual battery cells or, barring that, measure the delta between the higest and lowest cell voltages? API? OBD? Other?

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[lcarron]

I would like to read and record individual cell voltages. Basically I'm curious to see how the Taycan does pack balancing, among other things.

What methods are available to read the voltage of individual battery cells or, barring that, measure the delta between the higest and lowest cell voltages? API? OBD? Other?

You can use car scanner app on the obdII and read each cell individually.
Here is the balancing process description from the Audi gt documentation. Btw you can find it somewhere on this forum.


Cell balancing
In this example, a cell is 100% charged and the charging procedure is complete. However, the high-voltage battery charge level is only 92.5 %. Balancing means that this cell is now discharged via a resistor and can thereby continue to be charged until all cells have reached the same charge level. This allows the high-voltage battery to achieve its maximum capacitance.
To do this, the battery regulation control unit J840 compares the voltages of the cell groups. If cell groups have a high cell voltage, the battery modules control unit responsible receives the balancing information. After the ignition is switched off, the battery reg ulation control unit J840 checks whether balancing is necessary and initiates the process as appropriate. Only the control units on the sub-CAN are active when this is done. Balancing is performed at charge levels greater than 30%.
Cell balancing takes place passively, meaning that the energy is dissipated as heat via resistors. The high-voltage battery control unit controls and monitors cell balancing. Cell balancing takes place only by discharging individual cells. Cell balancing starts every 60 minutes after the vehicle is switched off, once the difference in capacity between the cells reaches approximately 2% (120 mAh) and the charge level of the high-voltage battery is more than 30%.

 

[j.w.s]

OK so the software recommendation is: Car scanner ELM from https://www.carscanner.info/

Recommendation for a BLE ODB dongle? Vgate vLinker C+ looks good, but several folks report having problems with it on the Taycan. OBDLink MX+ seems well regarded but is more expensive than most, and does not list car scanner ELM in its compatibility list.

I mention the above to show that I have done a bit of research, but would prefer to defer to someone who has a "known good" combination of hardware and software to share. Your experience and recommendations for the Taycan?

 

[800v]

Concretely, the Vgate vLinker MC+ Bluetooth OBD2 adapter (iOS and Android) and the Car Scanner app worked for me (on Android). (You get a high voltage battery active warning when you insert it but that seems standard with any ODB2 plug. Also, I needed to wait a bit before I could connect the bluetooth (and the password is in the documentation booklet)).

Here is a post of mine where you can see the individual cell voltages.

 

[j.w.s]

Thank you for the advice Icarron and 800v. Just a quick note to say that this combination works:

OBD2 Dongle: OBDLink MX+
device: iPhone
Software: Car Scanner ELM OBD2

Connecting works as you'd expect and is extremely easy, and there is an abundance of interesting information available, including the battery and BMS details that I was looking for. There is one odd quirk metioned by several people: When you connect your phone to the dongle, you get a giant "high voltage battery active" error that does not want to go away. I want to read static data, not data while driving, so this does not bother me.

 

[Gubab]

Just go into Drive mode and the warning will disappear.

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