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I have a Crompton Greaves single phase induction motor that powers my drill press (image below). I believe it’s rated at 1/2HP. I wanted to control the speed of this motor so that I can use the drill for tapping operations too. I’m guessing a VFD would be the way to go? If yes, how do I connect this motor to the VFD? Also would a VFD rated for 0.75KW work?

motor description

user3418620
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Single-phase motors do not perform well with any type of speed control. The motor in question is particularly problematic because it has both a start capacitor and a run capacitor. The start capacitor must be disconnected above a certain speed when the motor is started.

There are few manufacturers (perhaps only one) that make VFDs for single-phase motors. Initially, the VFD for single-phase motors was sold only to drive centrifugal pumps and fans. Only single-capacitor motors were said to be suitable. More recently, they may have expanded their recommendations.

You will probably find that the best alternative is to buy a three-phase motor and a VFD from one of the many manufacturers that sell VFDs for three-phase motors. Many VFDs with ratings up to at least 2 Hp are available for use with single-phase input power at 220-230V. There are some lower power VFDs for 120V single-phase input and 220-230V 3-phase output.

  • Would those VFDs require a three phase power input because I currently have a single phase in my garage and getting three phase is expensive and quite tedious in my part of the world. – user3418620 Oct 01 '21 at 14:04
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    The smaller VFDs are available with a single phase input option. For tapping, use a tapping head - it does the reversal. – Kartman Oct 01 '21 at 14:09
  • @Kartman, thank you, see revised answer. –  Oct 01 '21 at 14:30
  • @electrophile No, the whole point of a VFD is to take available power, turn it into DC. So the input phases don't matter. Then, once it's DC, they turn it back into AC *at a frequency and phasing of your choosing*. I completely agree, dump the 1-phase motor and get a 3-phase. It will play much better with VFDs. – Harper - Reinstate Monica Oct 01 '21 at 22:34
  • It seems that in the US and Australia there is a ready supply of dead exercise treadmills. These usually have a 1.5HP or thereabouts DC permanent magnet motor in them. A simple triac speed controller works well. About $30 AUD for the speed controller and a 4 digit tacho from the Ebays. Job done. – Kartman Oct 02 '21 at 13:20
  • Would the 3-phase motor operate at 415V? Or would the VFD take care of that? I realize that these are noob questions... – user3418620 Oct 03 '21 at 04:46
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    The VFDs with 220-230V, single-phase input are generally for 220-230V, 3-phase motors. You would need to search to see if any include a voltage boost for 415V motors. In the North America market, 230/460V dual voltage motors are common, so that influences the availability of VFDs. In your market, VFD availability likely also matches the commonly available motors. –  Oct 03 '21 at 12:44