What happens if I’m going downhill and braking and, for whatever reason***, my VESC-compatible ESC starts getting too hot? What would it do?
If it continues to dynamically brake then there is MOSFET heat from the shorting of the motor phases. If it stops dynamic braking then the BEMF-induced current will flow through the MOSEFT’s body diodes, creating lots of heat. If the VESC turns on the MOSFETs to allow regen current to flow to the pack then there is MOSFET heating from that current flow. There’s no way to stop heat from being created.
Or does one of those things create a lot less heat than the others and the VESC will switch to that as it’s the way to create the least amount of heat?
I don’t care what causes it or if this isn’t possible, just curious about what a VESC would do.
Thanks!
So the dynamic braking it does (shorting motor phases to brake) would start to reduce, perhaps by lowering the duty cycle of the PWM pulses that short the phases?
Would that end up increasing the BEMF voltage the VESC would see from the motors and so it would increase the amount of regen current sent to the pack in order to try to hold down the pack voltage and to load the motors to keep their voltage down?
What would happen if the ESC kept staying hot, the VESC would stop all dynamic braking and go up to the max regen current setting to try to keep pack and motor voltage down?
This is the headroom for the brakes. So basically acceleration is cut off earlier than brakes.
Best practice is to provide enough cooling, so that the ESC will not be operated at its thermal limits.
However, with ATC there is enough headroom for the brakes to work.
Worst case scenario: You drive up a hill and arrive at the peak with a very warm ESC, then you descend and brake and the ESC starts to produce more heat and at a certain point it cuts back the braking power to protect itself from blowing up.
Solution:
More safety is gained if you choose an overrated ESC and use higher ATC values.
Same goes for the motor. You don’t want to cook your windings!
Also try to go slow down steep hills. Truck drivers would do the same.
They say: Never drive down a hill faster than you could go up the same hill.
The other safety that is built in: Everything happens gradually. You feel loss of power on brakes and acceleration early. It is not an on-off thing.
What happens to cut back the braking power…the duty cycle of the shorting of the motor phases is lowered?
Does the ATC protection do anything with the regen current level to the pack (if the BEMF voltage is high enough) as part of its response to a high and/or increasing temperature?
The currents are lowered in a linear way in between the two temp values (start & end). You will have less motor max current and motor max regen current.
Batt max regen is not affected directly. However, If motor regen current is zero, you will not charge the battery. As long as you can still regenerate, you will charge the battery.
If you only apply regenerative braking and no forward throttle, would the charge current reach zero if the ESC temperature exceeds 100°C? (assuming default settings unless otherwise noted)
Would the charge current be able to increase past zero if the motor is spun up to its no-load speed? What if the motor is only spun up to half its no-load speed?
Is there any way you could acheive charge current while the ESC exceeds 100°C? (assuming default settings unless otherwise noted)
Once the final cutoff end temp is reached, including the headroom, the ESC will go into free role state on braking commands. You can increase the temp limits to push the braking limits further, but a burned out ESC will also not help with regenerating current…
