Hi,
Thanks - the Phase to Phase Kt value is critical to getting the motor to run at maximum speed - it is set at the motor manufacturer's specified value of 6.4 mV/Hz - I have tried changing it plus and minus, but then the motor doesn't run fast properly. Everything is running fine except at low speed - if I start it then reduce the speed to low it will get to a point where it only rotates at low speed pulling a relatively high current and will not respond to increasing the speed demand. The motor is not required to run at low speed in the application, but the problem is that it can get into this state on startup if the fan is rotating at the time it goes into startup. At low speeds the measured velocity constant goes up to about 100!