Using a VFD with a 4:1 Turndown Ratio Motor

[sirdle]

We are installing a VFD on a motor.

We called our supplier to find out if the motor was VFD rated. He contacted the manufacturer.

The response to us was: since the motor has a 4:1 turndown ratio we can run it at 75% of the rated speed.

Er... if the turndown ratio is 4:1 wouldn't that mean we can run the motor at 25% of the rated speed? Or do I have this backwards?

Cheers,
sirdle

 

[BAHTAH]

VFD and Motor Ratio

VFD and Motor Ratio

The short answer is you are correct. I would go on-line and check out the motor data from the mfg to verify the ratio.

 

[Jraef]

Your interpretation of what turn-down ratio is supposed to mean is correct, but honestly, saying a motor is "4:1: is tantamount to saying, "don't do it". That is NOT "VFD rated" if that is all it can tolerate, but your supplier either has no clue, or he knows it isn't but is side stepping the question to try to put the onus back on you for selecting it when the motor fries later. I would find a more reputable / knowledgeable motor supplier.