587,997 active members*
2,083 visitors online*
Register for free
Login
IndustryArena Forum > CNC Electronics > Phase Converters > Can I convert single phase motor to three phase?
Page 2 of 2 12
Results 21 to 35 of 35
  1. #21
    Join Date
    Dec 2003
    Posts
    24220
    Quote Originally Posted by pennlabs View Post
    On the subject of motors and phases mentioned in this thread no one ever seems to mention that on a single phase system both phases are 180 degrees apart due to transformer coupling at the pole (residential) and not the 120 degrees I think many are assuming and might lead to some confusion. I was told this, researched it and verified this many years ago by doing a phase measurement with o-scope on the home ac line. (measured in my home but that could be different elsewhere.) On a true three phase system you'll have that 120 degrees of separation between phases.

    On a rotary phase converter you start with two phases 180 degrees apart (from residential power) and produce the third phase close to the others by adjusting the power factor with capacitance.
    Actually a RPC uses single phase to produce three phase.
    There is 180 degree difference with respect to centre tap or Neutral, which is still single phase (with a centre tap).
    Not to be confused with two phases. There is no 180° difference between the 240v, because it is 1 phase.
    Also neutral is not involved with WRT to a RPC.
    Think of a motor fed by single phase as an auto transformer, which it is actually what it is, the three phases 120° apart will be produced, without the introduction of capacitors, capacitors are used to improve the power factor.
    There were some good articles published in the late 90's, this is one link
    http://www.metalwebnews.com/howto/ph-conv/ph-conv.html
    Also the Metalworking.com drop box 1998 files FRW- et al.
    show the wave forms in detail.
    Al.
    Attached Thumbnails Attached Thumbnails FRW-4.jpg   FRW-5.jpg  
    CNC, Mechatronics Integration and Custom Machine Design

    “Logic will get you from A to B. Imagination will take you everywhere.”
    Albert E.

  2. #22
    Join Date
    Sep 2003
    Posts
    18
    Get a size O or 1 motor starter off ebay and use one pole of your pressure switch to pull in the coil. It does not take long for all the silver to be worn off the contacts and then they are toast, those little pressure switches are barely rated for your starting current most probably.
    Steven

  3. #23
    Join Date
    Sep 2003
    Posts
    552
    Quote Originally Posted by mxtras View Post
    Is the head pressure being relieved in the line from the pump to the tank? If not, the pump (motor) maybe trying to start up under a load. Check your check valve and unloader - make sure they are doing their respective jobs!

    Scott
    This is where I would put my money. If you don't here the head vent (psssss) after the compessor cycle. The next time it goes to start the head will be under pressure and impossible to start.

    Darek

  4. #24
    Join Date
    May 2006
    Posts
    8

    Thanks Al

    Don't know why I forgot that darn center tap issue. Stuck in a lab all day without windows can play with your mind - :cheers:

    edit>

    I just got done scanning over those pics from the Fitch Williams rotary converter. Is there any other info out on the web that you know of about this that I might go and look at? I poked around for a while and haven't found anything yet. I like the idea of placing the motor on a cart for mobility. I hopefully getting a 7.5hp motor and may give it a try. Although I admit I'm a bit skeptical about having that much motor ready to do a flip from rotational torque. Do you see any problems down the road with that?

    edit>>

    I found it Al, it took me a while! Seems like Fitch Williams hasn't posted anything lately on the forums. However I found
    someone that saved his work in .pdf format on Practical Machinist. Here's the link:

    http://www.practicalmachinist.com/FitchWConverter.pdf

    If anyone would like it email me if the above link fails to load.

  5. #25
    The most common reason for blowing a start capacitor, especially repeatedly, is that the motor is starving for power at startup. The first thing you should be looking at is the circuit size for the compressor. Just because the voltage is fine does not mean the circuit is sized or wired correctly.


    Whoaaa! I just realized that you never told us what type of 3-phase power you have in the shop. If this is a comercial-type building, then you likely have 120/208, but if it is light industrial, then it is likely 120/240 hybrid. This is important!

    If your supply is 120/208, then all of your single-phase 240 tools are running at low voltage (208 volts). In this case, you need a buck/boost transformer to bring your supply voltage up to the 240 volts it wants to see. You don't do this for the entire shop, just the 240 volt single-phase tools.

    On the other hand, if the shop is the hybrid 120/240 3-phase, then you need to check the size of the circuit feeding the compressor. If the circuit wire is undersized, then the voltage during startup will drop too low, the motor will start slower than normal, and the cap will blow.

    I am running late and have to wrap this up. In the mean time, why don't you provide more specifics about the compressor and the wiring it is connected to.
    Rick Christopherson

  6. #26
    Join Date
    Sep 2006
    Posts
    8
    IF YOUR AIR COMPRESSOR UNLOADER IS NOT WORKING, YOUR MOTOR IS TRYING TO START AGAINST THE COMPRESSOR LOAD. CHECK YOUR UNLOADER FIRST, IT HAS TO RELEASE THE PRESSURE BETWEEN THE COMPRESSOR OUTLET AND THE RECEIVER INLET CHECK VALVE TO ALLOW THE MOTOR TO START UNDER LIGHT LOAD.

  7. #27
    Join Date
    Jan 2008
    Posts
    136
    NO, NO, NO. unless you have it rewound for 3 phase, but then it would be easier to BUY a 3 phase motor.

  8. #28
    Join Date
    Feb 2006
    Posts
    83

    short ansure....NO!!!!

    I have converted 1 phase,2 pole single phase motrs to 3 phase for building phase converter.The reason I did this is that the 1 phase motor has a governor/start switch that I used through a heavy DPDT relay,to start it.The problem is that you have to strip the windings out of the motor,take dimensions of the slots,core length,ect.I fed all the stator data into the EASA computer engineering program library ,and it gave me the data (span,#of turns,,connection,ect.)to wind it as a 3 phase motor.However,unless you can rewind the motor yourself or,you have a friend that can do it for you,your out of luck.My suggestion is to make certain the check valve and unloader valve are working.When your compressor shuts down,the check valve closes,keeping the pressure in the tank and the unloader valve releases the pressure from the check valve to the compressor head.If it does not,the motor is trying to start under a load.It is my bet,that is where your problem is.

  9. #29
    Join Date
    Sep 2006
    Posts
    8
    Quote Originally Posted by Jim Estes View Post
    I have a compressor motor that is blowing the starting capacitor. I have checked the voltage and it is fine. I was wondering if I could just convert this motor to three phase and eliminate the starting and run capacitor.

    I have searched and found tons of articles about converting three phase motors to single phase. I am sure it goes both ways, but I was wondering if someone else had already done this. I have three phase in my shop and converting this motor to three phase would be cheaper than buying a new three phase motor.

    I have no idea why it is blowing caps, but I suspect that it is from too many starts per hour.

    Any help is greatly appreciated.

    Jim
    I HAD A SINGLE PHASE MOTOR DRIVEN COMPRESSOR THAT HAD A HARD TIME STARTING BECAUSE OF INSUFFICIENT START CURRENT CAPACITY IN THE BUILDING WIRING. I REPLACED THE MOTOR PULLEY WITH A CENTRIFUGAL CLUTCH SO THE MOTOR STARTS UNDER NO LOAD.

    BEING A SINGLE CYLINDER COMPRESSOR, IT DID CAUSE SOME LIGHTS ON THE CIRCUIT TO DIM SLIGHTLY ON EACH COMPRESSION STROKE. I ADDED A FLYWHEEL RIM TO THE DRUM OF THE CENTRIFUGAL CLUTCH TO HELP THE MOTOR OVER THE COMPRESSION STROKE AND ALMOST TOTALLY ELIMINATED THE LAMP FLICKER.

    AS I UNDERSTAND IT, THE FLYWHEEL EFFECT OF THE MOTOR, AS SEEN AT THE LOAD, IS INCREASED BY THE SQUARE OF THE REDUCTION RATIO, SO THE FLYWHEEL EFFECT WAS MUCH GREATER THAN IF THE ADDITIONAL MASS HAD BEEN ADDED TO THE COMPRESSOR FLYWHEEL, AND A LOT CHEAPER.

    FROM THAT EXPERIENCE, I HAVE SINCE MADE 2 OTHER INSTALLATIONS USING 3450 RPM MOTORS INSTEAD OF 1750 RPM MOTORS AND FOUND THE HIGHER SPEED MOTOR STARTS THE HEAVY LOADS BETTER THAN THE LOW SPEED ONES, PRESUMABLY BECAUSE THE REFLECTED LOAD INERTIA IS REDUCED BY THE SQUARE ROOT OF THE REDUCTION RATIO.

    ON PORTABLE COMPRESSORS THAT ARE DIRECT CONNECTED TO THE MOTOR PREVENTING THE ADDITION OF A CENTRIFUGAL CLUTCH, I SIMPLY INCREASE THE VOLUME OF THE PIPING CONNECTING THE COMPRESSOR TO THE RECEIVER SO THE COMPRESSOR HAS SEVERAL REVOLUTIONS TO BUILD ENOUGH PRESSURE TO OPEN THE TANK CHECK VALVE. THIS ALLOWS THE MOTOR TO COME UP TO SPEED WITH REDUCED LOAD. STARTING CURRENT TIME IS REDUCED, MAKING A SAVING IN ELECTRICITY AND ALLOWING OPERATION ON EXTENSION CORDS.

    ON ONE DIRECT COUPLED PORTABLE COMPRESSOR THAT HAD A STARTING SWITCH FAILURE BUT HAD TO BE USED IN THE FIELD THAT DAY, I TEED A PRESSURE SWITCH INTO THE COMPRESSOR DISCHARGE LINE TO OPEN THE START CIRCUIT AFTER PRESSURE BUILT UP AND STARTING TORQUE WAS NO LONGER NEEDED.

    IN EVERY CASE, THE PRESSURE SWITCH, CHECK AND UNLOADER VALVES WERE VERIFIED TO BE IN GOOD WORKING ORDER.

  10. #30
    Join Date
    Feb 2006
    Posts
    71
    Quote Originally Posted by tool_man View Post
    When your compressor shuts down,the check valve closes,keeping the pressure in the tank and the unloader valve releases the pressure from the check valve to the compressor head.If it does not,the motor is trying to start under a load.It is my bet,that is where your problem is.
    Usually you will hear the pressure valve, a loud hiss as when the motor shuts down.
    A lot of the little compressors I have played with havn't had any sort of unloader, the ones that did had the unloader built into the auto on/off switch.

  11. #31
    Join Date
    Jul 2003
    Posts
    9
    Quote Originally Posted by integerspin View Post
    Usually you will hear the pressure valve, a loud hiss as when the motor shuts down.
    A lot of the little compressors I have played with havn't had any sort of unloader, the ones that did had the unloader built into the auto on/off switch.
    The pressure switches that have the additional connection for a small tube to connect to the compressor pump side of the check valve are the first thing to fail over time since they are a mechanical overly complex design. Most use a diaphram that operates a plunger that operates the actual air release valve. An alternative to these devices is a unloader called a "genie unloader valve" sold be grangers, no tubes from the pressure switch, no diaphranms, it is about the size of a check valve installing inline between the pump and check valve. It is preset to unload pressure via a small orafice. Never had a problem with one whereas I've has the pressure switch activated unloaders either not release, not shut off, or simply wear out the activation mechanism in the pressure switch and fall apart....the only catch is that the "genie unloader" costs about 20 bucks, which I consider a small price to pay for the increased reliability it offers. In addition to this I usually add a solid state relay for the switching of the motor power, the contacts of the pressure switch activate the "coil" of the solid state relay (less than one amp usually), the "load" side of the solid state rely then switches power to the motor at the point where the supply voltage crosses zero, minimizing noise spikes and the pressure switch contacts will usually last longer than the rest of the components in the system as a result. The solid state relay will usually require a small dc voltage to operate the "coil" via the pressure switch contacts, I usually adapt a "wall wart" dc power supply of the proper voltage from radio shack or similar type store, ebay usually has solid state relays (new) for extremely low prices. Make sure the voltage and current ratings are sized like you would for a start or run cap, more is better. Finish off the system with a automatic drain valve, power twist link belts and synthetic compressor oil in the crankcase of the compressor pump and there is a good chance the only time you will be looking at your system is when giving a shop tour! Unless of course you enjoy the challenge of discovering you have no air at just the time you need to use it the most, I hate those kind of surprises. Hope this helps, needless to say my suggestions all were as a result of having to deal with a failed component that would usually decide to go "belly up" sometime after 3pm on Friday afternoons....maybe you have better luck. Best regards, Joe.

  12. #32

    Re: Can I convert single phase motor to three phase?

    Quote Originally Posted by Jim Estes View Post
    I have a compressor motor that is blowing the starting capacitor. I have checked the voltage and it is fine. I was wondering if I could just convert this motor to three phase and eliminate the starting and run capacitor.

    I have searched and found tons of articles about converting three phase motors to single phase. I am sure it goes both ways, but I was wondering if someone else had already done this. I have three phase in my shop and converting this motor to three phase would be cheaper than buying a new three phase motor.

    I have no idea why it is blowing caps, but I suspect that it is from too many starts per hour.

    Any help is greatly appreciated.

    Jim
    Jim, as for blowing caps;
    Check voltage while actually starting, see if it dips more than 5, maybe 10%.
    Check your unloader. When the compressor gets to pressure and cycles off you should hear a brief hiss as it releases the air from the cylinder, if no hiss, your unloader is not working and the motor is trying to start against a cylinder of high pressure air. If you hear a continuous hiss, your check valve is bad.
    As for rewinding a single phase motor to 3 phase, I have done it several times and can coach you, but unless you work in a rewind shop it would be much cheaper to buy a 3 ph motor.

  13. #33
    Join Date
    Sep 2006
    Posts
    6463

    Re: Can I convert single phase motor to three phase?

    On the subject of a quick fix in times when you are without a place to buy or get the necessary correct parts, I had a small home made air compressor bought from a deceased estate made from a small stripped down 4 stroke lawn mower engine and a 1/3 HP single phase motor.

    In my infinite wisdom, which is normal for any DIY graduate with a degree in nothingness, I decided to guild the lily and connect it to a large 50 litre air tank as it was originally made with a couple of square tubes in the frame that served as a rudimentary reservoir.

    Catastrophic results would be a new way of stating things went pear shaped.......OK, it started and did pump up to 80 PSI but it couldn't restart when the pressure dropped down to 50 psi.......motor go hot wouldn't turn quickly and the start windings shed magic smoke.....it couldn't get up to speed for the centrifugal switch to cut out the start windings.

    It was soon realized that the motor was unable to lift the load once the load was fully loaded.........no load and it went for it big time.

    As I am the tightest miser you can imagine when it comes to buying parts that I can't source from the scrap box, I just added a tee piece to the outlet pipe to the tank and a small gate valve.

    On starting against a pressurised tank I just opened the gate valve and then closed it once the motor started, it's not on an automatic cycle for restarting as that was too sophisticated for the initial build plan, but it does have a pressure relief valve once it gets to 80 psi...........simple and it worked.

    Some years ago I parted it from the big tank and just ran it direct on line as a wheeled portable for pumping tyres and blowing things off as I now have a 2 cylinder bigger compressor for all my needs, and I'm getting lazier by the day once something works and doesn't need improving.

    I don't mess with single phase motors anymore now that you can buy a 3 HP VFD for under a $100 and get an automatic 3 phase supply speed controllable for cheap to get 3 phase motors
    Ian.

  14. #34
    Join Date
    Dec 2003
    Posts
    24220

    Re: Can I convert single phase motor to three phase?

    Quote Originally Posted by ElectricSteve View Post
    Jim, as for blowing caps;
    Check voltage while actually starting, see if it dips more than 5, maybe 10%.
    The OP posted 15 years ago.
    Hopefully he has cured the problem since!!!
    Al.
    CNC, Mechatronics Integration and Custom Machine Design

    “Logic will get you from A to B. Imagination will take you everywhere.”
    Albert E.

  15. #35
    Join Date
    Sep 2006
    Posts
    6463

    Re: Can I convert single phase motor to three phase?

    LOL.....I forgot to look at the posting date........probably all over bar the shouting by now.
    Ian.

Page 2 of 2 12

Similar Threads

  1. how to connect single phase spindle motor with 3 phase inverter
    By pdsherathia in forum Benchtop Machines
    Replies: 10
    Last Post: 01-19-2014, 07:15 PM
  2. Convert three phase transformer to single phase?
    By jimjovan in forum CNC Machine Related Electronics
    Replies: 5
    Last Post: 09-16-2013, 11:32 PM
  3. Vacuum Former Change from 3 phase to Single Phase
    By the1toyplace in forum CNC Machine Related Electronics
    Replies: 90
    Last Post: 11-19-2012, 03:46 AM
  4. Replies: 12
    Last Post: 10-13-2009, 03:53 AM
  5. CONVERT SINGLE 240/480V POWER TO THREE PHASE 415V OUTPUT
    By PhaseChangeConv in forum News Announcements
    Replies: 0
    Last Post: 09-03-2008, 05:45 AM

Tags for this Thread

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •