Single phase current draw

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  • Rayatswan
    Member
    • Sep 2012
    • 47

    Single phase current draw

    If a 415v 5 hp motor wired star draws 8.9 amps full load how much will it draw on 240v single phase when wired Delta using a static phase converter. An explanation of the theory behind the answer would be much appreciated.
    Thanks
  • Jaakko Fagerlund
    Senior Member
    • Dec 2010
    • 3256

    #2
    At full load, you can calculate the current from the maximum power. Though, if you want to be careful, you need to know some other specifics, but you get a good approximation with this.

    At full load it takes 5 horsepowers (really, it is an electrical device, so use kW, as horsepowers need conversions unless you use units like horseamps and horsevolts), which is about 3.75 kW. 3750 W / 240 V = 15.625 A.
    Amount of experience is in direct proportion to the value of broken equipment.

    Comment

    • lakeside53
      Senior Member
      • Nov 2007
      • 10511

      #3
      BUT.... you cannot get the 5hp with static converter. MAYBE 2.5hp to 3hp, but YOU have to limit the current (i.e. the load) - the static converter will quite happily let the motor smoke if you try to load it to 5hp.

      A typical 3hp 240 single phase motor will draw 15-18 amps. Assuming a reasonably efficient motor, your draw off the mains will be about the same AT 3hp.

      Comment

      • becksmachine
        Senior Member
        • Feb 2010
        • 1511

        #4
        Please educate me!

        There are places in the world that use single phase at 415 volts?

        Dave

        P.S. Never mind, he does say something about a phase converter.
        Last edited by becksmachine; 12-11-2012, 10:56 PM.

        Comment

        • joe51
          Junior Member
          • Nov 2012
          • 29

          #5
          Originally posted by Rayatswan View Post
          If a 415v 5 hp motor wired star draws 8.9 amps full load how much will it draw on 240v single phase when wired Delta using a static phase converter. An explanation of the theory behind the answer would be much appreciated.
          Thanks
          "Wired Star"? I've never heard that term. Is that the same as wired in a Y configuration? How many hot legs are you using? Just asking because a star is usually drawn with five points which implies five hot legs and I've never heard of anything that used five hot legs.

          I would think it's going to be very difficult to give an accurate estimate of the 240V current draw because the power factor is liable to change drastically between the two setups. I also have no idea how efficient a static phase converter is or how it would also affect the power factor. Adding capacitors to the input of an AC circuit does some very weird things! For example adding the "power factor correction kit" (2 capacitors) to the input (Primary side of the main X-former) of my Miller Synchrowave 300 welder INCREASES to no-load power draw from something like 12 amps to over 30 amps! BUT it lowers the current draw when running near maximum output.

          Comment

          • Jaakko Fagerlund
            Senior Member
            • Dec 2010
            • 3256

            #6
            Originally posted by joe51 View Post
            "Wired Star"? I've never heard that term. Is that the same as wired in a Y configuration? How many hot legs are you using? Just asking because a star is usually drawn with five points which implies five hot legs and I've never heard of anything that used five hot legs.
            Sorry but it is best to not try to give directions for someoen else if you haven't got a clue of mains voltage stuff.
            Amount of experience is in direct proportion to the value of broken equipment.

            Comment

            • Lew Hartswick
              Senior Member
              • Aug 2002
              • 3666

              #7
              :-) joe51
              Junior Member

              Have you seen the Mercedes "Star"???
              :-)
              ...lew...

              Comment

              • J Tiers
                Senior Member
                • Jan 2004
                • 44281

                #8
                Originally posted by joe51 View Post
                "Wired Star"? I've never heard that term. ..................................which implies five hot legs and I've never heard of anything that used five hot legs.
                hah....... I worked on a client's generator system..... 5 phase, high frequency turbo-generator, the output of which we were converting to high voltage DC. Their 5 phase 200kW generator would fit on the seat of a desk chair, and you could fairly easily pick it up by hand.

                yes, star is the same as "Y" in general.

                Dang... Jaakko can surely serve it up cold and low....... brrrrrrr.
                CNC machines only go through the motions.

                Ideas expressed may be mine, or from anyone else in the universe.
                Not responsible for clerical errors. Or those made by lay people either.
                Number formats and units may be chosen at random depending on what day it is.
                I reserve the right to use a number system with any integer base without prior notice.
                Generalizations are understood to be "often" true, but not true in every case.

                Comment

                • Jaakko Fagerlund
                  Senior Member
                  • Dec 2010
                  • 3256

                  #9
                  Just like a beer, J Tiers, just like a beer 8)
                  Amount of experience is in direct proportion to the value of broken equipment.

                  Comment

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