7i77 > Huanyang GT series VFD issues

fungus wrote: Even a tiny (0.001) Ki caused the spindle to exponentially increase in RPM.

That suggests that your velocity feedback is backwards.

Does the encoder velocity show positive numbers for positive PID output?

andypugh,
I always have a bit of trouble deciphering what's what in the HALScope channels, but abs.spindle.out, lowpass.spindle.out & hm2_5i25.0.encoder.05.velocity are all positive.

Include pid.s.command in that. It is also positive. This is while commanding M03 S50, and it is rotating the correct direction for M03.