fafrd,
could you please say what exactly got burnt on your defective BMS?
Maybe make some pictures.
What mosfets are used, etc.?
Sorry, if you'd already answered this.
I did already answer somewhere or other, but here is is again;
Not exactly certain what smoked/burned but highly suspect is was one or more of the power transistors, likely the outermost one (nearest non sense-connector end).
The main P- metal busbar-contact that I chose to bolt my P- wire to proved to be defective - it was unsoldered over most of it’s length and only soldered to the main board at the very ends.
So rather than fanning out to the full array of power transistors over it’s entire length so that they could share the load / current equally, all of the 80A current was steered to the ends of the bus / contact bar before going into the main board close to the location of the first and last power transistors.
This is the theory, anyway (that one or more power transistors overheated because they were shutting more than their share of the 80A being discharged) but the actual reason isn’t all that important because of the obvious manufacturing defect (unsoldered bus bar / contact).
The main lesson for me is to carefully inspect any of these cheapo Chinese electronics before putting in service for power applications.
The second lesson for me is that these all—in-one BMSs may be fine for lower current levels, but for high sustained current levels of 100A or more, the Chargery architecture with external contactor is starting to strike me as a far superior architecture (separate the ‘brains’ from the disconnect where all the heat is generated and active cooling can be used...).
And to be fair, I’m a bit surprised, but it seems I have stress-tested my BMS far more severely than most on this Forum.
I ran 80A continuously for 1 hour before I saw the plume of smoke and halted the test. My actual goal for the test was to fully discharge at 80A for a full 3-1/2 hours.
