Rotary Phase Converter

[nisse]

Last weekend I brought home and placed a Bridgeport mill with a CNC control. I am wanting to power it with a rotary phase converter I picked up many years ago at an auction but never have used. It is rated at 5 HP and I have attached a pic of the wiring. The are 4 different bunches of wires, I have hooked up 240 volt single phase to the L1 and L2 wires and it seems to run fine. Am I correct that I connect the 3 power lines from the mill to L1, L2 and the third bunch of wires is the generated leg? I am thinking the other bunch with the wire nut is ground? I have been machining for over 20 years, but never have had to wire up machines and I am looking for a little guidance.
Thanks,
John

 

[Brownie450]

Does the convertor have a plate with the wires numbers
identified? Most units have ID plates.
Is there a manufacturer name available anywhere on the
unit?
Jim

 

[Geo-TH,In]

I think you may have a 3 phase motor used as the rotor.
I don't see the other parts you need to start the rotor motor.
Start Capacitors, run capacitors and 2 contractors. One is for the start and the other is the run contactor.
The last 3 phase converter I made was in 1985. I would have wake up some brain cells to remember exactly
I wired it.
Perhaps go to UTT U-tube Tech to find out how to make a rotary converter.

 

[nisse]

I have attached some more pics, the unit was made by a local company. I tried calling but no luck. There are numbers on the wires but no other diagrams. The compartment with the capacitors has a lid that is riveted on, maybe have to get inside?

 

[Butch(OH)]

Last weekend I brought home and placed a Bridgeport mill with a CNC control. I am wanting to power it with a rotary phase converter I picked up many years ago at an auction but never have used. It is rated at 5 HP and I have attached a pic of the wiring. The are 4 different bunches of wires, I have hooked up 240 volt single phase to the L1 and L2 wires and it seems to run fine. Am I correct that I connect the 3 power lines from the mill to L1, L2 and the third bunch of wires is the generated leg? I am thinking the other bunch with the wire nut is ground? I have been machining for over 20 years, but never have had to wire up machines and I am looking for a little guidance.
Thanks,
John

Yes you are correct, feed one leg of single phase 220 to L1 and also attach one of your 3 phase feed Iines to same bunch of wires. Do same thing for L2. The one marked leg is your generated leg sometimes called wild leg, attached your 3rd 3phase feed wire there. Do not concern yourself with the generated 3 ph line voltage under no load, it will usually be low but picks up voltage when a load is applied. Important, if your machine has magnetic contactors they will be single phase and you need to use the L1 and L2 wires to feed them, not the generated leg. If the 3 ph motor runs backwards switch the 3 ph lines at L1 and L2.

 

[nisse]

Thanks for confirming, what about grounding?
John

 

[Butch(OH)]

Thanks for confirming, what about grounding?
John

There are far more knowledgeable people than me when it comes to per code grounding but the 220 single phase in my shop and the rotary convertor is per the codes when it was built. 4 wire, L1,L2, N and ground. Old style 220 often used the neutral as ground but that does not meet current codes. Three phase doesn't use a neutral and it's important that you do not intermix grounds and neutrals at the wrong places. Im my shop the 3 phase frame grounds carry back to the 220 single phase box that feeds the convertor and connect to a non bonded buss in that box that ultimately terminates at the main panel ground. Now IF your machine has 110 needs then you will need to run a neutral from the 220 single phase sourse, do NOT use the frame ground wire for a 110 neutral.

 

[m16ty]

I've built several phase converters out of old 3 phase motors. What you do in that case is you have L1, L2, L3 wires going to the motor. You hook up your single phase to L1 and L2, and your 3 phase motor you are trying to power to L1, L2, L3. L3 is your generated leg.

Then you have to either rig up a single phase pony motor or start capacitors to get the whole thing started. I've seen people just use a pull rope to get it started but I've never tried that. Your 3 phase converter motor will run fine on single phase, it just needs something to start it.

 

[m16ty]

There are far more knowledgeable people than me when it comes to per code grounding but the 220 single phase in my shop and the rotary convertor is per the codes when it was built. 4 wire, L1,L2, N and ground. Old style 220 often used the neutral as ground but that does not meet current codes. Three phase doesn't use a neutral and it's important that you do not intermix grounds and neutrals at the wrong places. Im my shop the 3 phase frame grounds carry back to the 220 single phase box that feeds the convertor and connect to a non bonded buss in that box that ultimately terminates at the main panel ground. Now IF your machine has 110 needs then you will need to run a neutral from the 220 single phase sourse, do NOT use the frame ground wire for a 110 neutral.

There is no need for a neutral in your feed if your circuit only has 220v split phase or 3 phase loads. Those loads don't require a neutral path back to the panel to run, they work off the phase imbalance between phases.

Now you are correct about pulling 110v loads off of a 220v split phase or 3 phase circuit, in that case you either need a neutral or a transformer to change the 220v to 110v split phase. It was common practice in the days of old to run things like 110v lights on a machine just by pulling off one leg of 220v and connecting the other leg to ground, but this can result in a dangerous condition where you a making your grounding conductor energized. Your whole machine is energized, and the only reason you don't get shocked is the ground conductor is a better path than your body and if for some reason that ground path is interrupted it will get you.

 

[buickanddeere]

Should have thermal protection on the single phase supply to the rotary . And on the three lines to the mill.

 

[wore out]

Check out the Forum linked below, all you could ever want to know about phase convertors.

https://www.practicalmachinist.com/forum/categories/transformers-phase-converters-and-vfd.11/

 

[nisse]

Here is an update: I connected the converter as planned and everything seems to run fine. However, the 120 volt outlets on the machine cabinet for the light, and the controller check at 140 volts with the spindle off and 130 volts with the spindle running. I checked the single phase legs feedng the converter and they check at 121 volts and 123 volts. Should I be changing the third leg wiring? Also, do I need to be concerned about there still being voltage at the converter even with it being disconnected? I Don't know much about capacitors, but I know they can be dangerous.
Thanks,
John

 

[Janicholson]

Because L1 and L2 are connected to the supplying 240, it will show up there. Shutting off the 240 supply will (should!!!) kill it. Jim

 

[m16ty]

Here is an update: I connected the converter as planned and everything seems to run fine. However, the 120 volt outlets on the machine cabinet for the light, and the controller check at 140 volts with the spindle off and 130 volts with the spindle running. I checked the single phase legs feedng the converter and they check at 121 volts and 123 volts. Should I be changing the third leg wiring? Also, do I need to be concerned about there still being voltage at the converter even with it being disconnected? I Don't know much about capacitors, but I know they can be dangerous.
Thanks,
John

How are is your 120v outlet connected? Are you just pulling off one leg of the 240v? If so, do you have a neutral in your feed?

 

[nisse]

How are is your 120v outlet connected? Are you just pulling off one leg of the 240v? If so, do you have a neutral in your feed?

There is a large electrical cabinet on the back of the machine that contains everything. I will have to take a look inside tomorrow.
Thanks
John

 

[m16ty]

There is a large electrical cabinet on the back of the machine that contains everything. I will have to take a look inside tomorrow.
Thanks
John

It could be fed by a transformer that reduces the voltage from 2 legs of 220v to 2 legs of 60v (giving you 120v phase to phase), I have seen that before. Otherwise you’re going to need a neutral going to the machine.

 

[wore out]

It could be fed by a transformer that reduces the voltage from 2 legs of 220v to 2 legs of 60v (giving you 120v phase to phase), I have seen that before. Otherwise you’re going to need a neutral going to the machine.

WHY is it necessary to use the 120 Volt accessory outlets on the machine at all? Cover them and ignore them.

 

[Butch(OH)]

There is no need for a neutral in your feed if your circuit only has 220v split phase or 3 phase loads. Those loads don't require a neutral path back to the panel to run, they work off the phase imbalance between phases.

Now you are correct about pulling 110v loads off of a 220v split phase or 3 phase circuit, in that case you either need a neutral or a transformer to change the 220v to 110v split phase. It was common practice in the days of old to run things like 110v lights on a machine just by pulling off one leg of 220v and connecting the other leg to ground, but this can result in a dangerous condition where you a making your grounding conductor energized. Your whole machine is energized, and the only reason you don't get shocked is the ground conductor is a better path than your body and if for some reason that ground path is interrupted it will get you.

I guess you missed the part where I said the 3 phase doesn't use the neutral?

 

[m16ty]

WHY is it necessary to use the 120 Volt accessory outlets on the machine at all? Cover them and ignore them.

That’s probably what I would do, and it’s how my lathe lights are. Just run a cord to a wall socket to power your lights.

 

[Butch(OH)]

Here is an update: I connected the converter as planned and everything seems to run fine. However, the 120 volt outlets on the machine cabinet for the light, and the controller check at 140 volts with the spindle off and 130 volts with the spindle running. I checked the single phase legs feedng the converter and they check at 121 volts and 123 volts. Should I be changing the third leg wiring? Also, do I need to be concerned about there still being voltage at the converter even with it being disconnected? I Don't know much about capacitors, but I know they can be dangerous.
Thanks,
John

There are several ways that it could be making 110v First, as I said previously be sure that your wild leg is not hooked up to your control circuits. Some simply grab one leg of the 220 and use a neutral, as another said do NOT use the machine ground for that. My Giddings boring mill and my Summit lathe both have a step down transformer with various taps to set the 110 Voltage. My surface grinder just grabs a 3 Phase 220 leg and a neutral. If you are beyond your understandings you might want to have someone take a look at the whole deal?