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I have a 1 HP, 4-pole, 3-phase, AC motor which is inverter rated.

I need to select a Single Phase VFD to drive the motor. Some of my options are as follows:

  • 1 HP, 120V, 3.7 amp
  • 1 HP, 240V, 3.7 amp
  • 1.5 HP, 120V, 4.8 amp
  • 2 HP, 240V, 7 amp

What should be my considerations? Should I just get the cheapest option (the first listed one above), or are there advantages to getting the more powerful ones? Other things being equal, is there any advantage to using a 120V VFD input, versus a 240V input?

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2 Answers 2

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Things are not equal if you already have the motor. You need to know your motor rated voltage.

The two 1HP VFD have the same power but the 120V one handles double the current because it needs to in order to achieve the same power with half the voltage. So 3.7A for both motors cannot be correct.

Motors are the same: if same power rating but is designed for half the voltage means it will need double the current. Therefore your motor voltage needs to be close to the VFD voltage and the VFD needs to support the supply you have available.

If your supply voltage is not close to your motor voltage, then things get messy and expensive.

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Generally, just match your VFD power rating to your motor power rating. Your VFD shouldn't be widely larger than your motor rating, but a 2HP VFD would drive a 1HP motor.

The higher input voltage will lessen the current on your line side. Also, there will be less current in the winding of the motor, so your motor will run cooler.

Also, not sure how complicated your application is, but I have never used a McMaster-Carr VFD. However, the prices there are just slightly less expensive than a very high quality, industrial grade VFD. I would recommend an Allen-Bradley PowerFlex 525 VFD. They are absolutely fantastic and supremely reliable. I would suspect a 1HP would cost around $700.

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  • $\begingroup$ Prices vary - don't give them. $\endgroup$
    – Solar Mike
    Commented Nov 16, 2023 at 8:26

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