View Full Version : wiring 3 phase to 1????

12-17-2005, 09:22 PM
I bought a piece of equipment which has a 3 phase Baldor motor, frame 66, 1/2 HP TE, 208-230/460 volts, 2.5-2.4/1.2 Amps, 1725 RPM, 60HZ, class B, code M ser F 1.25 Rating 40 C AMB-Cont., SFA 2.7-2.6/1.3, Spec 35E29.85, SER F487. Prior to purchase I was told single phase 220 volts.

Is there some way of wiring this to work single phase? Would it be best to buy a new motor? If so What??? The choices are endless. The motor is on a Vernon Mill which I asked about in an earlier thread. Any and all help and advice would be greatly appreciated!!!! Thanks in advance Fred

12-17-2005, 09:52 PM
I don't think you'll find it cost effective to convert single phase to 3 ph to run a 1/2 hp motor. I would be telling the seller you want the single phase motor like was advertized to you. I get the impression that it was a dirty trick played on you- you have a machine you can't use without spending more money and making changes. But to make that motor run, naybe someone here can show you how to rig up a capacitor based 'pseudo converter'.

12-17-2005, 10:00 PM
Where to start.?.?




Many different methods. Rotary phase converters use a 2nd 3 phase motor to generate a 3rd phase but it is not perfect.

Capacators can move a phase out without too mutch extra stuff, but again, not perfect.

VFD - This is an electronic device that uses 220V and convert it electronically to 3 phases. This is supposed to be a nearly perfect phase angle.

The capacators are probably the cheap method.

Rotary, more money.

VFD, lots more money unless you are a good eaby'er.

Too much, not enough, didnt answer the question?


[This message has been edited by rockrat (edited 12-17-2005).]

J Tiers
12-18-2005, 12:16 AM
If you won't run it to full power, you can run it single phase.

Just wire to two of the three wires. Then use a capacitor as a starter, wired from the third wire to one of the others, with a switching device. The switching device has to cut it out as the motor reaches full speed.

Such devices are available that work automatically. Grainger has them, I think.

Starting seems to take about 50 microfarads per HP, but your capacitor must be rated for line voltage plus 50% or so.

It will run on single phase nearly as well as a regular single phase motor.

The catch is that you will get about 2/3 power, based on max current (heating limited current), and if you stall it, you have to switch off and re-start, since it cannot start without the start capacitor.

12-18-2005, 02:04 AM
A 1/2hp vfd runs $140.

This one is 120v single phase in and 220v 3 phase out.

This one is 220v single phase in and 220v 3 phase out.

12-18-2005, 06:14 AM
Thanks to all for the advice. I realize I can do the phase converter rotary route. Would it be better to swap out the motor for a Grainger single phase Dayton motor, capacitor start, open drip proof, 1 HP, 1725 RPM, 66 frame Rigid mount Ball bearing, 15.0/7.5 full load amp, insulation class A of the same frame.

If that would be a straight swap out then It would be worth the extra $40 to do that over trying to salvage the existing motor. Or...am I missing something??? Thanks again to all for the help. Fred

12-18-2005, 06:32 AM
Geez guys, How much can a 1/2 hp motor cost?Go buy a new one or take a chance on a used one.

The tame Wolf !

12-18-2005, 06:34 AM
[Homer Simpson voice] Mmmmmm, instant reversing [/Homer Simpson voice]

12-18-2005, 06:46 AM
I agree. My lack of knowledge in the electrical field and power demand of a milling machine. The choices on puchasing a motor from Grainger are mindboggling. I am trying to make the correct choice with the least problems associated with it.

If a bump up to 1 hp with the single phase 220 motor would this be the best solution in the long run? Thanks Fred

12-18-2005, 07:26 AM
Even with a VFD you dont have INSTANT reversing,so use a drum switch.

The tame Wolf !

12-18-2005, 08:34 AM
If I swap out the motor for a single phase 220 1HP will I have to change the drum switch as well??? Thanks Fred

12-18-2005, 09:31 AM
<font face="Verdana, Arial" size="2">Originally posted by laddy:
If a bump up to 1 hp with the single phase 220 motor would this be the best solution in the long run?</font>

No. Not in the short run either. What benefit do you expect to see from overpowering your machine? It's a machine tool, not a dragster.

12-18-2005, 09:36 AM
<font face="Verdana, Arial" size="2">Originally posted by laddy:
If I swap out the motor for a single phase 220 1HP will I have to change the drum switch as well??? Thanks Fred</font>

No, generally you can wire up any particular drum switch for single phase or 3 phase circuits. Exactly how you need to wire it varies with the switch, though. There are at least three common contact patterns. The wiring diagram may be glued inside the switch housing, or it may be available online if you can find the make and model #. Otherwise you have to figure it out - fortunately it's not too complex.

12-18-2005, 10:01 AM
"Even with a VFD you dont have INSTANT reversing,so use a drum switch."

You don't? I guess not instant, but as fast as you can push the buttons, and depending on the accel & de-accel parameters settings.

12-18-2005, 12:33 PM
Thanks to all. I have decided to switch out the motor for a 3/4 HP 220 volt single phase. I calmed down and realize that the switch can be wired without replacement. My thanks to all for the help. I will post pics on completion, but that will probably be after Christmas. A Merry one to all!! Fred

12-18-2005, 02:55 PM
Dr. see this thread...


The tame Wolf !