Lewm,
What I was getting at was that ac controllers that change speed between 45 and 33.3 without splitting the phase cannot really do a good job. The capacitor that then does the phase split/rotation, cannot be of the right value to do the job correctly for two different frequencies. That is why I think that plug-in motor controllers that electronically switch speed are of dubious value. The right way is for the controller to do the splitting optimally for whichever speed, in which case, there are, in effect, two separate supply lines leading from the controller to the motor (the capacitor is then removed from the motor).
What I was getting at was that ac controllers that change speed between 45 and 33.3 without splitting the phase cannot really do a good job. The capacitor that then does the phase split/rotation, cannot be of the right value to do the job correctly for two different frequencies. That is why I think that plug-in motor controllers that electronically switch speed are of dubious value. The right way is for the controller to do the splitting optimally for whichever speed, in which case, there are, in effect, two separate supply lines leading from the controller to the motor (the capacitor is then removed from the motor).