Brushless motor controller output

Thread Starter

Krzysztof Bieda

Joined Jan 5, 2016
Hello everyone,

I have 2 motor controllers. One working correctly and second crashing one.
Both controllers are different but designed for PMSM motors.
I have recorded output voltage signal for one coil ( Motor wire to GND).
My PC scope records signals for some time ( red most frequent one, blue less frequent)
Bellow screenshoots:

Correct output looks like:

Crashing output:
bad.PNG my.PNG

I wonder what causes output voltage to be about -15V?
What should I change in electronic circuit to prevent that negative drop?

When motor crashes then it stops. No component burn.

Best regards,