I'm testing a VESC 75V 300A version from Trampa Boards to drive Motenergy ME0907 motor in sensored mode. It works well overall, however I noticed one problem: if the load is high the controller seems to be reducing the motor current which I guess it could be doing to prevent MOSFET overheating. However based on the temperature readings the MOSFET temperature is lower than the cutoff temperature. Basically the reduction in output current starts happening at around 70C degree, while cutoff start if set at 85C. Please see the screenshot attached - the sharp reduction of the current can be easily seen there.
Any ideas what might be causing this current reduction?
Actually it looks like the duty cycle gets reduced first, which causes the output current reduction.
Not that we believe you, but do you also have a temperature graph ? and a printscreen of the temperature settings ? I'm quite interrested in what the cause is, also you're other topic about the torque. I have a bit the same on my ebike that at low rpm the torque/acceleration is less.
Ok so it turned out that the problem lied in "Acceleration Temperature Decrease" setting which is by default set to 25% and reduces the MOSFET cutoff temperature. Although it's supposed to be applied only for acceleration phase, in my tests it was apparently enabled during steady operation too (not sure if it's a bug in the firmware). As soon as I set it to 0%, the output current reduction started happening as expected at 85C (as set by MOSFET Cutoff Start parameter).
It shuold be 14% by default and is applied for any positive drive direction (anything else than braking). This is the headroom for your brakes to keep working. So we cut positive drive power 14% earlier before braking (regen power).
Thanks Frank, now it makes sense.