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RTillery (Automotive) (OP)
4 Mar 03 17:17
I am looking to purchase a 3 phase milling machine for home use and was thinking about using a VFD to convert my home 230 single phase up to the 3 phase.  Any problem with the 2 speed motor on the mill in doing this?
cbarn24050 (Industrial)
4 Mar 03 17:47
Hi, no real problem, but you need to be sure that you do not disconnect/change windings while the vsd is running.
gcaudill (Electrical)
5 Mar 03 22:27
RTillery, I think you want to supply the VFD with single phase 230V and control a three phase motor. Correct?  

IFF so, the only concern would be to derate the HP rating of the drive (if instructed so by the manufacturer).  Operating from a single phase line will not give the advantage of sqrt(3) in power delivery to the drive as is with a three phase supply.
DanDel (Electrical)
6 Mar 03 18:42
gcaudill, are you suggesting that RTillery can run a 3-phase motor from a single-phase supply with a HP derating?
jraef (Electrical)
6 Mar 03 19:17
DanDel,
Yes, it is done all the time. Actually, many drives 3HP and under do not necessarilly need derating. Check with your drive supplier.

HOWEVER, there is another issue for RTillery. IF the 2 speed motor was a constant HP 2 speed, you will have a problem at low speed because that motor will produce more torque at low speed and if your machine requires it, the VFD will not be able to deliver is running on the high speed windings. If it is a 2S constant torque motor, then no problem. If you don't know, the way to tell is to look at the nameplate. If it has 2 HP ratings, i.e. 3/1.5HP it is constant torque. If it has only one HP rating, it is constant HP.

Check it out and post your answer. If it is constant HP you have a little more work to do.

Quando Omni Flunkus Moritati

DanDel (Electrical)
6 Mar 03 19:50
Sorry, my bad. I didn't see the part about using a VFD with a single-phase supply to supply 3-phase power.
jbartos (Electrical)
6 Mar 03 21:43
Suggestion: The VFD will have to be suitable for a non-inverter type of motor, i.e. it should not produce spikes, ringing, and a high harmonic content on its output.
gcaudill (Electrical)
13 May 03 13:37
jbartos, have you ever found such a drive that was not astronomically expensive?
GusD (Electrical)
13 May 03 22:40
Hi Rtillery

It should work ok ,however;JRAEF is correct on the Torque
requirements.If your motor is a C horsepower than you might have to do some work to get your Hi speed torque.
Proper filters for the Inverter drive will help save your  motor in case it is not Inverter rated.
I don't have a clue as to the cost of a single phase VFD  For the homeowner,it might be cost effective to have a 3 phase motor,usually cheaper than 1 Phase.If the price of the SPhase VFD is low,it might very well be the way to go.

GusD

SteveKW (Electrical)
14 May 03 10:25
There are a lot of hobby mill sites that talk about cheaper alternatives to using a VFD! Try a search.

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