Hi Bluesman7,

Thanks for the information. I'd been using the grinder for around 60 minutes, hollow grinding, when the VFD went Pop.

Quote Originally Posted by bluesman7 View Post
Actually AC voltages are measured RMS [root mean square] so 220 volts AC will dissipate the same energy as 220 DC through the same resistance. The peak voltage of a 220 AC supply will be 1.41 times the RMS voltage or 310 volts. None of this has anything to do with the OPs question.

Induction motors are designed to operate at a given voltage at a specified frequency. The labeling on the motor does not make any sense to me as the speed is listed at 2800 and the freq. specified as 60 hz.. A 2 pole induction motor has a synchronous speed of 3600 at 60hz and with the slip at full load it is usually around 3450 or so. The same motor will run around 2800 at 50hz. The VFD label doesn't really make sense either as the voltage should vary proportionately with the frequency. Running an induction motor at a voltage lower than specified for a given freq. will increase the slip at load and can over heat the motor by drawing too much amperage. It's possible that excess current was the cause of the failure of the VFD.

Were you loading the grinder heavily [sensing slow down] around the time of the failure?

In my mind the VFD should have a spec. in volts/hz that matches the volts/hz of the motor.