I observed a specific behavior related to battery monitoring, which sounds a bit weird in my eyes.
BYD batteries provide only the min and the max cell temperatures. On Victron the min and max temperatures are display on detail section, where main section and VRM show a “common” temperature.
This “common” temperature is chosen as min temperature as long as max cell temperature is ≤ 30°C.
As soon as max temperature exceeds 30°C the “common” temperature switches from min to max cell temperature (analogue on temperature reduction). This circumstance is not really helpful for battery monitoring (see example below).
Personally I would prefer a stable/constant application logic for common temperature representation (could be also an averaged min/max).
Is there an actual intend to apply that logic or is that an actual bug?
Generally speaking, there should be 3 temperatures available for the user.
One temperature for the BMS electronics and the other two for the cells.
The one for the BMS is read on the 0x356 CAN ID, the ones for the cells are read on the 0x373 CAN ID.
It may be only an impression that only the cell temperatures are available, it may very well send the BMS temperature but it’s not so obvious.
In your case, and on many other batteries, the end of the charging is characterized by a steep increase of the BMS temperature, especially on the balancing period, when the electronics from the BMS are working hard for balancing.
Maybe it’s just a coincidence that the BMS temperature is the same as the maximum cell temperature.
Thanks for your detailed reply, Alex!
Since I have no access to the bms code, for me the retrieval was not clear so far.
Concluding the additional details the the issue might be directly located in BYD BMS.
The potential coincidence that you mention, I would exclude. When you look to the VRM graph, the temperature falls immediately by 5°C, when the max cell decreased by 1°C. I would exclude that range for a common temperature, expecially, when max temperatures also increased only very slowly.
Good point! I also observe with pylontech that min and max temperature displays only cell temperature. Near 100% BMS electronic temperature is quite different and often much higher. From security point it is not so important, but for me it is an indicator that balancing is working and how long it is working. I observe it often with battery view, but to get it in the details of battery would be helpfully.
Indeed, because the /DC/0/Temperature is a key generally assigned to the temperature of any device that can communicate its internal temperature or the temperature of a sensor assigned to it.
In the case of Pylontechs is generic assigned by the Venus OS to the unit’s temperature, but internally is consistent with the BMS temperature, which, depending on the battery status, can be very different than the cells’ temperature.
You can log into battery console and see.
An example below:
