VFD Resonance

Thanks GaryS,


I didn't actually try to measure the VFD voltage, I just meant reading off the internal value on the VFD. I expected to see 208V, but the reading says 240V at setpoint 100%.


The VFD can take single or 3-phase, right now I have it hooked up to a single-phase 240V, 50A circuit. The motor is 3-phase 3hp, the VFD rating is 5hp (current rating is around 20+ amps) so I don't anticipate an issue with it running on single-phase. The drive is rated for this size motor on 1-phase.



The motor speed reading was also taken from the VFD, the motor doesn't have a tach or encoder. I expected more slip but it's running under no load so I assumed the speed value is likely accurate near synchronous. The motor speed at rated load is 3520, I have this value as well as an absolute max speed of 3600 set as setup parameters in the drive. Speed reading was around 3600rpm at setpoint = 100%. I will check the pole number setting in the drive, but I'm assuming it calculates this based on the motor rated speed and input frequency.


I've triple checked now, and the motor nameplate data matches the VFD parameters. I hear what you're saying about moving the noise frequency up to inaudible, this is my concern as well. I do expect a bit of singing but the "mormon tabernacle choir" was a pretty accurate way of describing it.

Actually the vfd calculates the motor speed using the number of poles and output frequency 2 poles 60hz = base speed 3600 rpm, 4 pole 60hz = base speed 1800 rpm
2 poles 50hz = base speed 3000 rpm you get the idea.
it looks like you did everything right
if the singing is as loud as you say and you are the only one to judge that I would try to run it on a different motor and see if it acts the same. most any 3 phase motor will work
it it quiet's down with a different motor then i would thing there is something wrong with the motor if not it may be something in the vfd.

Or just put the 10ga SO back on it and it will quiet right down.

Keith