Today I ordered a 5HP VFD from Dealers Electric. It's a Danfoss, I think. New but surplus. $265.00. The best price for that size new that I've seen. It goes as high as 1000 hertz . Boy, that would really spin up the drive motor! It is constant torque. My questions are below:1) How much faster can a normal motor be spun? 2) The mill has a mechanical vari-drive, Where should the pulleys be set? 3) Since the drive is constant torque does that normally mean it will power the motor at rated HP at rated rpm but that when the frequency goes up the torque goes down so the motor still produces it's rated HP? 4) If the torque stays constant throughout the frequency range then would it be desirable to adjust the mechanical drive so that the original top spindle speed is reached when the motor is being driven at about 120 hertz? 5) Since the motor will probably be running at 30 hertz or slower some of the time it will have a cooling fan installed. What other kinds of problems should I look for because of the changing frequency? 6) The mechanical vari-drive adds drag to the system so the power available at the spindle is less than the power put out by the motor. I have been told vari-drives of this general size waste about 1HP through friction. But that would make the spindle drive a 750 watt heater and it doesn't seem to put out that much heat. Do they really have those kind of losses? 7) If the mechanical vari-drive does consume that kind of power I will consider replacing it with a belt drive. Would it be worth it to use a toothed belt instead of vee belts to reduce friction and the radial load on the motor and spindle bearings? 8) Will a toothed belt tend to add vibration to the drive train?
Thank You, Eric R Snow