Talk me out of buying a massive a 460v eletric motor and building a phase converter

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    Talk me out of buying a massive a 460v eletric motor and building a phase converter

    There's a 125hp 460v 3ph motor for sale locally at $300. I'm really thinking about buying it and using it as the rotating portion of a rotary phase converter since DIYing it is so much cheaper than a phase converter even half the size. I know I will only get a little less than 1/3 of the power rating of the motor available for starting other motors (only powering 2/3 of the phases at half the voltage) but even 30hp is plenty of hp for my needs. I just need something that can start 15hp while there's a 10hp load on it or vise versa.

    So IBB, talk me out of it.

    #2
    Research is giving me conflicting answers on whether or not a 460v motor will run on 220. Some say it's fine and just reduces output. Some say it "won't work" but don't say why.


    https://www.practicalmachinist.com/v...0-volt-331540/


    https://advrider.com/f/threads/will-...on-220.269551/
    Last edited by arse_sidewards; 06-04-2020, 07:08 AM.

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      #3
      For $300, it's worth a shot.


      How large is a 125hp 460V motor, size-wise?
      Screw Vertical Scope
      Lugnut4x4.com

      Comment


        #4
        Originally posted by Pt_Ranger_v8 View Post
        For $300, it's worth a shot.


        How large is a 125hp 460V motor, size-wise?
        Browsing similar motors on Surplus Center the shipping weights are in the 1000-2000lb range

        I bet this one is under 1500lb considering the case configuration. If I wind up getting it I'll scale it.

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          #5
          I think it matters how the motor is wired if it's convertible from 480/240 but if you run it on 240v amps will go up and running it at slower speeds (vfd) reduces the airflow passed the winding which will cause it to burn up quicker.
          And op forgot the pic so... Click image for larger version
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ID:	27301 I'm not the one rewinding this motor my friend is.

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            #6
            Originally posted by arse_sidewards View Post
            There's a 125hp 460v 3ph motor for sale locally at $300. I'm really thinking about buying it and using it as the rotating portion of a rotary phase converter since DIYing it is so much cheaper than a phase converter even half the size. I know I will only get a little less than 1/3 of the power rating of the motor available for starting other motors (only powering 2/3 of the phases at half the voltage) but even 30hp is plenty of hp for my needs. I just need something that can start 15hp while there's a 10hp load on it or vise versa.

            So IBB, talk me out of it.
            Check the nameplate, its big, but still small enough its possible that it could be able to be wired for 208.

            Not sure if your location but I've got a bunch of 25-400hp motors I could sell for scrap price if you have some kind of a business name to run it through.

            Comment


              #7
              Do you have nameplate info for this motor?

              also, some power companies require motors over 100hp to be on a soft start due to the demand load at startup. Might want to check on that.

              Comment


                #8
                Originally posted by Tin Roof View Post
                Do you have nameplate info for this motor?

                also, some power companies require motors over 100hp to be on a soft start due to the demand load at startup. Might want to check on that.
                Could pull start it or spin it up with a small motor first. I've seen people rope start an RPC to keep from tripping the breaker.

                VFD pc is the right answer

                Comment


                  #9
                  Nameplate

                  Click image for larger version
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                    #10
                    I have 200A of service. If this motor can run on 220 with double amperage that puts me 40A over before you take power factor and efficiency into account. I am going to be way the fuck over 200A when I start this no mater what I do so I will have to come up with a soft start solution. If I can run this motor on 220v and derate it by half then I'm comfortably within my 200A service. This entire thing hinges on whether I can wire this motor up and expect it to draw the same amperage at any voltage. I would prefer a ~30hp motor since that's more in line with my power needs but I don't think I'm gonna do better than $300 at any size above 10-15hp.

                    Comment


                      #11
                      Originally posted by arse_sidewards View Post
                      Nameplate

                      Click image for larger version
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                      Looks like a hammered asshole. What does it actually say?

                      What is the cost of a VFD to run the motor you have VS all the time you would pour into an alternative?

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                        #12
                        Originally posted by Johann View Post

                        Looks like a hammered asshole. What does it actually say?

                        What is the cost of a VFD to run the motor you have VS all the time you would pour into an alternative?
                        $200 for the cheapest Chinese 15hp one so $400 to run both machines plus another $100-200 each time I want to run something that's 3ph. Considering how cheap sub-5hp 3ph motors are compared to their 220v single phase counterparts having a phase converter that can provide 3ph to my basement and garage stands to save me a lot of money in the long run.

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                          #13
                          Tried something similar. 25 hp 3 phase motor. Running it on 2 legs of single phase just spinning it (started it with another smaller motor) it was pulling 61a per legs when it tripped the service. I now have an American rotary that I run off of.

                          Comment


                            #14
                            Originally posted by Tin Roof View Post
                            Do you have nameplate info for this motor?

                            also, some power companies require motors over 100hp to be on a soft start due to the demand load at startup. Might want to check on that.
                            How would a soft start for 240v 200 amp single phase look/work/exist?

                            Comment


                              #15
                              Originally posted by Blacksheep10 View Post
                              Tried something similar. 25 hp 3 phase motor. Running it on 2 legs of single phase just spinning it (started it with another smaller motor) it was pulling 61a per legs when it tripped the service. I now have an American rotary that I run off of.
                              How exactly did you design your VFD. What was the capacitor setup?

                              Originally posted by larboc View Post

                              How would a soft start for 240v 200 amp single phase look/work/exist?
                              Spin the big motor up to speed with a small one.

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