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240 Single Phase to 440 3 Phase

mjc55

Plastic
Joined
May 3, 2023
I recently bought a Wells-Index 747 mill, and we discovered that the motor has been rewound at some point to run straight 440 3 phase, so changing wires around to wire it for low voltage is out since there are now only 3 wires coming out of the motor. It has a nice control panel on it with Allen-Bradley motor starters both forward and reverse, and I am thinking the best (and probably only at this point) course of action is to wire it back 440 again. My dilemma is, I only have 220 single phase in my building. I do have an old Square D 6T5F 240-480,456,432 3 phase transformer laying around. My question is, is it feasible to covert my single phase 220 to 3 phase before I run it through this transformer, and if so what is the best way to do it? I would assume converting to 3 phase after the transformer would be better, but I'm trying to work with what I've got. I'd appreciate any suggestions from you guys who have a lot more experience with this than I do.
 
You'd probably choose a rotary phase converter, which this section is full of discussion about.

A 'Phase Perfect' is a box of electronics that performs a similar function, with lower standing losses but possibly lower robustness and higher cost.

A variable frequency/speed drive (VFD/VSD) can also do the job, but it needs to control the motor directly, and you tell the drive what to do (using front panel buttons or inputs from remote switches). You can't have contactors or other switches between the drive and the motor, though a transformer should be fine. You may need to oversize the drive to cope with the additional reactive current consumed by the transformer.

Another option is to swap the motor, if it's a standard frame size.
 
I recently bought a Wells-Index 747 mill, and we discovered that the motor has been rewound at some point to run straight 440 3 phase, so changing wires around to wire it for low voltage is out since there are now only 3 wires coming out of the motor. It has a nice control panel on it with Allen-Bradley motor starters both forward and reverse, and I am thinking the best (and probably only at this point) course of action is to wire it back 440 again. My dilemma is, I only have 220 single phase in my building. I do have an old Square D 6T5F 240-480,456,432 3 phase transformer laying around. My question is, is it feasible to covert my single phase 220 to 3 phase before I run it through this transformer, and if so what is the best way to do it? I would assume converting to 3 phase after the transformer would be better, but I'm trying to work with what I've got. I'd appreciate any suggestions from you guys who have a lot more experience with this than I do.
run into 3Ph then transformer, I run all my 600V that way.
 
I've run a couple machine for years with a RPC to convert to 220 three phase, then a step up transformer. No problems at all.
 
My question is, is it feasible to covert my single phase 220 to 3 phase before I run it through this transformer, and if so what is the best way to do it?
That depends on the idler motor:
1. What you got is a 220 Vac idler with transformer.
2. Use a transformer and use a 440 Vac idler.

Use #1.
 
I bring my 240v single phase into a 480:240 dry transformer ('backwards'), and connect the 480v single phase primary to two of the three legs of a 480v VFD, whose 3-phase output is directly connected to the motor leads. Works great, it's silent, and you get great performance, dynamic braking, etc. Surplus 480v VFDs are MUCH cheaper than 230v units.
 
I would assume converting to 3 phase after the transformer would be better, but I'm trying to work with what I've got. I'd appreciate any suggestions from you guys who have a lot more experience with this than I do.
All good ideas so far, there are multiple ways to do what you want to do.
What I do is take the 240 single phase and use a RPC to make 240 3 phase and then have a step up transformer to turn the 240 3ø into 480 3ø. That gives me the options of 3 types of power, 240 single, 240 three and 480 3 three phase. I turn on only what is needed to feed whatever each machine needs.
 
I've been doing what you proposed for over 13 years in my shop.

240 single phase goes through a 30hp Phase-a-matic RPC to create 240 3 phase, The output from the RPC feeds a Square D 3 phase load center.

I have a 15hp edger that is hard wired for 480. It is fed from the 3 phase panel through a dedicated dry-pack transformer that turns the 240 3 phase into 480 3 phase.

Works fine.

I also have a 400hp 480V generator that powers the rest of my 480 equipment. It is all too large to run off of a 30hp RPC.
 
I recently bought a Wells-Index 747 mill, and we discovered that the motor has been rewound at some point to run straight 440 3 phase, so changing wires around to wire it for low voltage is out since there are now only 3 wires coming out of the motor. It has a nice control panel on it with Allen-Bradley motor starters both forward and reverse, and I am thinking the best (and probably only at this point) course of action is to wire it back 440 again. My dilemma is, I only have 220 single phase in my building. I do have an old Square D 6T5F 240-480,456,432 3 phase transformer laying around. My question is, is it feasible to covert my single phase 220 to 3 phase before I run it through this transformer, and if so what is the best way to do it? I would assume converting to 3 phase after the transformer would be better, but I'm trying to work with what I've got. I'd appreciate any suggestions from you guys who have a lot more experience with this than I do.
I'm very late to this post. I would open the motor up and see if you can get at the windings to rewire it to 240VAC or I would replace the motor with a new one that has low voltage options with the 9 leads that come out. But I'm guessing you can get into the original connections that some fool decided to connect internally. What does the nameplate show for connections. The bigger problem is keeping the connections phasing correctly so you don't reverse a winding.
 
I'm very late to this post. I would open the motor up and see if you can get at the windings to rewire it to 240VAC or I would replace the motor with a new one that has low voltage options with the 9 leads that come out. But I'm guessing you can get into the original connections that some fool decided to connect internally. What does the nameplate show for connections. The bigger problem is keeping the connections phasing correctly so you don't reverse a winding.
Keep the three ends already there, and when you've found the star point you can buzz out the windings - as long as power goes to the existing terminated lead wires (lets call them "start"), the other three lead wires you've added from the star point, (lets call them "ends") can come out to three more terminals - then bridge those to the next winding's start, apply power and it should spin up. Think of the delta wired triangle, each side is a phase winding - going round clockwise each winding's end connects to the next winding's start to make the triangle. If the motor spins in the wrong direction, just swap TWO of the incoming power phases around to reverse the motor.
 








 
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