BMS failure mode.

[Mattb4]

What is the most likely failure mode of a standard BMS? Does it block all current or does it simply stop performing any safety cutoff functions? If it just becomes a non performing lump, with current flow, I wonder how you would know it was no longer functioning if your charge controller was operating within normal specs and you did not overly discharge the battery.

Certainly for the whizbang communication type BMS it would be more apparent but many liFePO4 batteries do not include that stuff.

 

[HighDesertOffgrid]

Good question.

 

[400bird]

With a BMS that flows current through it (not through an external shunt and contactor/breaker, my research says they almost all use mosfets. The most common failure mode for a mosfets is shorted. As in, the BMS can't stop current flow.

You can also have cascading failed open under load, where the first one fails open, increasing the load on the remaining parallel mosfets, which then are even further loaded, and the process continues until they're all out of magic smoke. This failure mode is more like when your running at the very upper limit of the mosfets' rating, at least in other applications.