[brian_]

I don't know what drove GM to this level of complication to avoid some wire length... perhaps isolation issues within the pack with their battery voltage of up to 800 V while charging?

 

[brian_]

Dumb question: How do these balance cells? Do the individual boards drain individually?

Presumably yes. Although more sophisticated systems are possible, it appears that BMS balancing is normally based on discharging individual cells through bypass resistors, so there's no need for current to flow between the cell and a central BMS device. It is common for modules to be equipped with "slave" BMS units which handle this themselves, only using their connections to the BMS master for coordinating communication; that makes a wireless network a straightforward (although unnecessary) variation on the usual wired network between BMS master and slaves.

 

[brian_]

With wireless bms? Ok, change a line in the BMS master configurator, you just stamp out Ultium modules like nuts and literally don't care where they end up in.

That part about the module is true whether the module's BMS slave is wired or wireless. Arguably wireless is worse for module complexity, because each module must be configured to a specific position in the system (by a configuration switch or setup process), rather than just plugged into a BMS master port which implies the position. But it's a minor detail either way.

 

[brian_]

It's interesting that the company that builds dozens of different models with a huge number of variations of each of them - often in equipment which communicates with the rest of the vehicle - hasn't resorted to wireless for anything else. Perhaps the issue in general is interference (that would certainly concern me), and having all of the BMS components inside the same metal box presented an opportunity.