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1phase-to-1phase VFD for lathe speed control?

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Deadeye

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Usual story - I have a single phase motor in the lathe but would like to control speed.
Switching to a new, three phase, motor with a VFD is expensive (cheaper to buy a new lathe).
So when I saw single phase output VFDs (ato for example) I got excited.

Then I read about potential overheating the motor and I got unexcited again.

Does it work? Or, if it's "yes, but..." then what is the "..."?
 

CHJ

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Changing frequency will change speed but with a single phase motor under load it will soon loose sync. if it is slowed down and it looses inertia as the magnetic field slip increases, the consumed current will rapidly spike because of lack of back emf (the motor becomes a generator when spinning) that counters the incoming current rush, and either overheat the windings or trip the supply feed.
 

Simon_M

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I have one of the Axminster Trade lathes and it uses a VFD - it works very well however I'm guessing that the 3 phase motor is designed for variable frequency so it works as expected. When adding a VFD to a single phase motor then it's not assured that the motor will cope or that you will be able to program it to work.

My other Axminster lathe (see the forsale forum) avoids the need for a VFD and uses a variable drive that varies the two pulley diameters. This is a proven design that also varies the torque e.g. at lower speeds where more torque is required it delivers it. It works the same as having 10 pulley ratios except that they can be changed as the motor runs.

Some lathes use a DC motor however there are brushes to replace and it's more likely to be used because it's simpler and so cheap to manufacture.
 
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