# Rotary converter for 3 phase



## Dan Pantages (Jan 2, 2008)

I have a Rockwell knee mill which has a 3 phase motor on it. It came with a rotary converter. The converter consists of one big motor with 4 wires coming and going from it into a box with a push button on I and then into a box that has a toggle switch on it with a wire going to the 220 plug. There is a cable coming from the first box to the drum switch that runs the mill. When I want to run the mill, I hold the first button in then switch the toggle switch on. This runs the rotary converter. Now I have to do is use the mill drum switch just like a standard switch on any tool.

So here is my question should the rotary converter make so much noise. It sounds like it’s coming apart but when I cut the power to it, the sound goes away, and if I spin it with my hand it runs perfectly smooth. I tell you this because it sounds like bearings but its no


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## Kovacjr (Jan 2, 2008)

The converter will sound loud. My friends on his Bridgeport is the same. Its like having a large motor next to your head. Hard to explain. Just a loud motor buzzing type sounds.


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## Michael Glavin (Jan 2, 2009)

Dan, 

Rotary phase converters are nothing more than standard three phase motors with a bank of capacitors and a relay or two. That said the phase converter should sound just like any other motor of like design and horespower rating while in operation. If your hearing loud and or odd noises you might want to have an electric motor rebuiilder shop take a look at it... 

Michael


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## denray (Jan 5, 2008)

i have a 25HP phase convertor that runs 10 hours everyday, it makes the same sound wether running anything or not, when I first bought it the seller told me they build up some heat if they are not running a motor. 
He suggested to have a non load 5 HP motor running to prevent the heat build up. Never did it. If yours runs quiet when running another motor, find a used motor and set it maybe in a corner or outside let it run to keep 
the convertor quiet. 
Dennis


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## Dan Pantages (Jan 2, 2008)

Dennis - it makes the same loud noise if the mill is running or not. After running it for an hour it is still not hot. As soon as I get a chance I am taking it in to an electric motor shop to have them take a look at it.


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## denray (Jan 5, 2008)

Oh I am sorry I missed read, sounds like you do have a mechanical problem 
Dennis


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## John J (Dec 29, 2007)

On a Rotary Converter is there a switch / contractor between the converter and the load Motor? Do you get the converter running then turn on the load motor? I was just wondering. 

JJ


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## denray (Jan 5, 2008)

JJ 
A 3 phase motor will run on single phase once it is spinning, I have made 3 different size convertors in the past. 2hp, a 5 hp and a 20hp . A 5hp will start one 5 hp motor and run up to an additional 5 hp in smaller motors at the same time. But the biggest one or in this case the 5 HP must be started first. It takes capisitors with single phase power to start a three phase motor. Or you can use a small starter motor to get the big 3 phase motor running or spinning, and then hit it with single phase power and it will run. Now when a three phase motor runs on single phase, the third leg on the three phase motor is generating the third phase. You can hook it up straight to one magnetic contactor on L3 and 1phase power on L1 and L2 legs on a starter, and you can run a 3phase motor. 
We have a big convertor in our business, we can start a 25 hp motor and run up to 50 combined hp. I would prefer 3 phase line power, but we have made over 8000 machines in 21 yrs using a convertor, we have been using the convertor we have now for 15 yrs, greasing the bearings quarterly and it runs 50 hours per week or more. We run all of our 3 phase through 3 phase breaker boxes to protect all the down line wiring. 
They make convertors that are so well balanced they can run high tech cnc equipment. 
Dennis


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## Dan Pantages (Jan 2, 2008)

OK, took it to an electric motor shop and yes it was the bearings that are shot. I will pick it up next week and let you all know if this is the fix.


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## Dan Pantages (Jan 2, 2008)

Sorry, I forgot to finish this thread. Yes it was the bearings. The motor guy put new bearings in it, $90 delivered back to my house, he lives close to me. It just sounds like any other electric motor running, wonderful!


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## modlmkr (Jan 3, 2008)

To bad you spent $90 on a rotary. For about $100 you could have bought a VFD- a variable frequency drive. Then you would not have a wasted motor idling, and your mill would have had full variable speed control from about 20% to 200% of its normal speed. I have all my machines running on VFDs.


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## Dan Pantages (Jan 2, 2008)

A rotary converter for up to 5 HP at Grizzly is $775. A rotary converter operates 3-phase motors at full power with 95% electrical efficiency. A three-phase variable speed drive, 220/230V single phase in with 220/230V three phase out, large enough for my mill looks to cost about $400. I have been told by 2 different people I know, they both own large production shops, that a rotary phase converter is a better option. For $90 I get to keep the original power of the mill and from what I understand using variable speed electronically on a motor like this is very hard on it. The speeds of my mill are varied with the belts and gears. How do you get a motor to run twice it's speed, you can't get something for nothing.


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## gearhead (Nov 28, 2012)

Hello Dan: 

I have a background in industrial maintenance, machining and machine shop maintenance for everything from 1930's multispindle screw machines, to 6000 watt laser cutters, electronics engineering, and various other skills. I also have a complete manufacturing facility at my home including mills, cnc lathe, swiss style screw machine, automatic and manual turret lathes, turret drill press, honing machine, injection molding machine, manual equipment from sherline to engine lathes, automotive equipment including valve grinders and distributor machines, power hack saw, and two air compressors with 200 gallons of capacity. Many of these machines are three phase and all run off a 100 amp service in my slightly over size two car garage and well, I'm not married, and my girlfreind is totally cool, so my dining room as well. Surprisingly, although tight, all machines are accesible and work flow is efficient. I do not run more than two large machines at a time do to the 100 amp service limitations, and of course, I only have one body and two hands. Once in awhile, I will run the automatic turret lathe and cnc lathe in light production while doing second or third operations on support equipment, but I am careful not to tax my electric service to hard at any one time, such as no spindle reversing operations while multiple machines are running. 

So I thought I'd throw in my two cents on your comments. 

There are 3 ways to run 3 phase motors off of single phase power. First is the venerable "buzz box", or Phase-O-matic. These boxes use a large capacitor to energize the third leg of a three phase motor to get it started turning, then the motor continues by "single legging". Meaning not all three phases are are there during operation and the motor does not put out full power, although the rpm does not change because that is based on the 60hz line frequency. The motor must be de-rated and can overheat during heavy load operation. These are best used for low power constant load devices. My automatic turret lathe has two 2hp motors, one for the coolant pump, and one for the spindle and hydraulics. I use a home made phase-o-matic for the coolant pump and it works well for that light duty job for over ten years now. 

Second is a rotary phase converter as you have described. These work well and use a single phase motor to drive a 3 phase motor working as a generator to provide three phase power to your device. The biggest draw back is the space they take up, second drawback is your paying for the power of two motors instead of one, third no variable speed or other options. However, as you stated and I agree, they work quite well and if you already have one then there aren't alot of good reasons to change. I do not use one due to space and option concerns. 

Third, VFD's(Variable Frequency Drives) and this is why I write this diatribe, you were provided with erroneous information from your large production shop sources. Most modern machine are controlled by VFD's as original equipment. 3 phase power is typically very dirty power with voltage variations and spikes on all three, or just one or two legs of the circuit. Factories and job shops install expensive transformers to help regulate this, as well as step down the power from other voltage levels. Even if the machine is a constant rpm and no other features are needed, there will usually be a Frequency drive installed, because it takes the incoming power and all its poor qualities, and digitally generates three, high quality, uniform phase legs to run the motor. It effectively cleans up the power and stabilizes the load to ensure efficient continuous operation at the manufacturers motor specificatioons. 

Variable Frequency Drives, have the added bonus of being able to generate those three legs at any frequency you want, not just the line freq. of 60hz. Although the motors design parameters such as winding wire dia., # of turns of wire, stator diameter, etc., determine its rpm at 60hz, and power output and torque ratings, the motor doesn't know it was designed for 60hz, that is smply a function of the power grid, to some extent designed so that electric clocks would keep proper time. Since the 3 phase motor is basically just magnetic feilds chasing each other around in a circle, the frequency of the magnetic feilds determines the rpm. Again, at 60hz, the design parameters decide the rpm and other characteristics, but if you change the Hertz, you change the rpm, and the motor will not know or care as long as you don't exceed the design limitations such as, to much rpm for the bearins or balance specifications, or to much load, or to quick a load change, etc. 

All this means that a VFD will provide you with complete control over your motor with absolutly no harm unless you do something with it you shouldn't be... 

My CNC lathe has virtually all its functions controlled through a VFD that is factory installed. My Hardinge DSMA automatic turret lathe has been running for twelve years with a VFD I installed. I have a plug that allows me to simply switch the output from that VFD over to my manual turret lathe for second operations in just moments. 

All of the large CNC milling machines and Lathes I used to work on before my entire crew and I were replaced by temps, were VFD controlled spindles except for the machines made before VFD's existed. I'm not sure your freinds understood what you were asking or if they simply don't know that much about how their machines actually are wired and function, but VFD's are the best way to control your 3 phase motor and is standard industry practice. Some VFD's are even capable of positioning, with the addition of an encoder to provide feedback, they can control the c-axis(spindle position) on a lathe so that live tooling can provide indexed cross drilling and milling operations. This is how swiss lathes work their magic. 

Almost all VFD's can convert single phase 220v home power into three phase, even if the company doesn't state it or sell it that way, its just how you wire it. However, what you will see is that ones that are rated for single phase are more expensive. They are not more expensive because of the conversion of single to three phase. The price of VFD's is based on the horsepower rating they are designed to control, and to operate on single phase you need to double the capacity of the VFD if it is a three phase rated unit. In other words, if you have a 2hp spindle, you need a 4hp VFD. So if you are shopping for a VFD that the factory has advertised as a single to three phase capable converter, it will be called a 2hp unit, but already be a 4 or 5hp unit and priced accordingly. If you shop for a three phase only unit and simply wire it like a single phase converter then you shop for a 4-5hp unit in the first place. 

Once you have a VFD, many cool features await you. The abiliity to have remote run/stop, or/and emergency stop buttons is simple, a couple wires on a screw terminal on the VFD. RPM can be controlled using the input pad in usually 2 rpm increments, or a simple potentiometer from Radio Shack will provide you with infinite speed control up to the max rpm you place in the parameters while setting up the unit. Also, motor reversing, either keypad or remote(I could use this on my manual mill but it has already been converted to single phase motor and I'm to lazy to change it). You can add a breaking resistor and it will give you remote braking, or you can program the spindle to brake immediate or with a ramp down of rpm. For that matter, you can program rate of acceleration as well, amongst many other features most of us will never need and are for specialized applications. 

So this is how you can double your rpm, simply increase the frequency. As long as your bearings can handle it, it will just spin happily away for as long as you need. 

Hope that helps everyone understand the basics of running 3 phase equipment at home. 

Gearhead 
AKA Karl


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## Dan Pantages (Jan 2, 2008)

Thank you Karl, best explanation I have had. I still think the $90 was the way to go, I am not that skilled to use a quarter of the equipment you talk about and changing a belt to change the speed of my mill is not a big deal to me, I am a hobbyist, I'm not running a production shop where time is money. Now the dinky little motor on my Myford Super 7 lathe is making noises, off to my motor guy.


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