Lithium Cell Inductive response

[agganitk]

Hello ,
I am working on BMS. I am working on timing of discharge mosfet switching off. If Switching off too fast, then mosfet might get damaged due to inductive response of cell.
Does any one have data or guideline  for L of  NMC or LFP battery so I can calculate V  from L dI/dt before I jump into real experiments.

Thanks

[Siwastaja]

Cells internally are well sandwiched "capacitors" with little inductance, most comes from the fact how external connections are placed; side by side, or from opposite ends? Then wiring between the cells, and finally the wiring exiting the pack to your circuit. Remember to use worst-case wiring if there is a possibility someone uses loose 5-meter cables all over the place instead of the 10cm nicely parallel stub you though everyone would use.

You get close by simply modelling the battery pack and wiring as a wire loop of the actual pack geometry, assuming the inductance between + and - terminal is just caused by the distance of the terminals. Once you have the geometrical drawing, you'll find inductance calculators online.

[mzzj]

Fairly easy task IF you don’t plan to implement short-circuit protection.

[Siwastaja]

I didn't struggle with short-circuit protection. But it requires quite large MOSFETs and understanding of the SOA curves. And some capacitance and large TVS diodes because the avalanche ratings of even large MOSFETs are not that great.