# connecting an older two speed motor with a  VFD



## rogee (Apr 18, 2013)

Does the fact that my Mill has a two speed motor cause any additional problems in getting it's 3ph motor to run on single phase with a VFD or a static phase converter?


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## Alan Douglas (Apr 18, 2013)

Shouldn't be any.  You probably want to use the higher-speed windings; I would expect the motor to have more rated horsepower at that speed.  If you're keeping the original two-speed switch, you could use either.


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## British Steel (Apr 19, 2013)

I've added a VFD to my lathe with its 3-speed motor, had to do more than a basic plug-and-play conversion to allow speed switching on the fly, but if you won't swap speeds while running (doubt you will on a mill, but useful on a lathe) then no problem. If you want to.use both speeds, look for a VFD that allows 2 sets of motor parameters so you can set one for each speed (full load Amps etc) and perhaps a spare pair of contacts in the 2-speed switch or add a microswitch it operates to select between 'em.

Dave H. (the other one)


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## Alan Douglas (Apr 19, 2013)

I may have given you some incomplete information.  There's a discussion in another forum on this subject:

http://owwm.org/viewtopic.php?f=82&t=131342


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## LEEQ (Apr 19, 2013)

This picture illustrates a 1hp, 3 phase, 2 speed motor. The wires for two speed are wired together into pairs. The 3 pairs go to three hot legs coming from the vfd. the triple that is numbered 4,5,6. is left alone. Now it is a one speed motor powered by vfd. My vfd controls forward and reverse very simply on it's keypad. It has a dial on the front that I use to control speed. You can also use the up and down keys for this.  It's so simple to use to control, I opted not to put the original switch back in as a 12v control wired into the vfd. I mounted it within reach of the mill. Now my step pulley is a variable speed.

- - - Updated - - -

. My knowledge is in big part thanks to Ulma Doctor. Someone like that can tell you better how to determine what to wire together to make this work, but that's the idea. Best of luck


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