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  • Motors Question

    The motor on my tool and cutter grinder I have .I think is buggered.
    The original was three phase.
    I have another motor that is around the same size but is single phase.
    it is 2850 rpm just like the other and says "fan motor" on it.
    SAYS ON THE PLATE
    250 watts
    12 uf
    2.0 amp
    220 volt
    0.88 cos
    Problem is there is no capacitor with it .
    The question is...
    Do all single phase induction motors have caps...........or do I need to get one ..............and how do I wire it in.
    and what size of one do I need.
    I can get caps no problem.....does it matter if the cap is more powerful than what it needs to be.
    The motor drives a belt and pulley and spins a spindle at 5000 rpm plus.

    This is a wiring diagram found inside the box for the wiring on the motor.



    all the best.............mark


    [This message has been edited by aboard_epsilon (edited 12-01-2005).]

  • #2
    motor is capacitor start and run.If motor does not start but hums pull pulley or belt. if it starts and runs rough either cap or starting winding down, cap size is approx 20 mfd for half hp on 240 volts 40 mfd for 1 hp pro ratio
    do not exceed these values or motor will overheat and may burn out' cap start has switch to turn of cap

    Comment


    • #3
      Cap size is 12 mfd, it says so on the plate.

      Sir John.
      .

      Sir John , Earl of Bligeport & Sudspumpwater. MBE [ Motor Bike Engineer ] Nottingham England.



      Comment


      • #4
        where's the switch Mal ....I thought that switch on the diagram was the overheat switch
        all the best.....mark

        Comment


        • #5
          No switch that funny thing with two black boxes is the cap.

          Sir John.
          .

          Sir John , Earl of Bligeport & Sudspumpwater. MBE [ Motor Bike Engineer ] Nottingham England.



          Comment


          • #6
            OK thanks John........all is clear .....off to the tip in the next few days to grab a cap off a washing machine.

            all the best..........mark

            Comment


            • #7
              Also, the cap doesn't have to be EXACTLY 12uf. Anything from about 8 to 16 should work ok. If it is lower expect a little less torque. If higher a bit more torque but will run hotter.

              [added]

              You can also parallel caps to get the right value, two 6s in parallel gives a 12. You can also put them is series and it will reduce the value. Two 20s in series gives a ten.

              [This message has been edited by Evan (edited 12-01-2005).]
              Free software for calculating bolt circles and similar: Click Here

              Comment


              • #8
                Thanks Evan that's good news.
                because I was thinking .the last caps I had off washing machines were for 1000 watt motors.
                These would not do .....
                The other motors on washing machines are the pump motors these are about 125 watts....so maybe two caps off these will do the job.
                all the best.mark

                Comment


                • #9
                  As stated above, but be sure to use RUN cap. and not start cap. There is no cent. sw. to disconnect start winding so cap. is connected at all times.
                  Jim

                  Comment


                  • #10
                    HI JIM
                    how do you tell one from the other
                    does it have run and start printed on them.
                    all the best.mark

                    Comment


                    • #11
                      Uhhh .... sure it's not a reversible split-phase motor? In which case, there would be no capacitor, and the mystery marks would be motor contacts indicating a centrifugal switch. The "fan motor" label is a clue, as fans are the classic low-starting-torque load, which is about all a split-phase motor is good for.

                      Comment


                      • #12
                        I've just dug a cap out of my archives
                        it says 10 uf on it .
                        it also has a circle with a plus and an S in it.
                        it has only two terminals.
                        what's this.. a start cap or run cap
                        .it also has many other numbers and letters on it...
                        shrugs shoulders

                        sauer38h said
                        "Uhhh .... sure it's not a reversible split-phase motor?"


                        The mystery marks aghhhh.
                        I assumed that the all knowing ,very wise Sir John had diagnosed them as well known electrical symbols meaning it has a cap there .

                        So who's right and who's wrong
                        all the best.mark



                        [This message has been edited by aboard_epsilon (edited 12-01-2005).]

                        Comment


                        • #13
                          http://library.thinkquest.org/10784/...t_symbols.html

                          here
                          http://www.kpsec.freeuk.com/symbol.htm

                          here about half way down the page it is described as .....Unpolarised capacitors (small values, up to 1آµF)

                          http://www.kpsec.freeuk.com/components/capac.htm


                          and here aboput half way down is a general symbol i supose for any capacitor

                          http://www.bcae1.com/capacitr.htm


                          all the best.mark

                          Comment


                          • #14
                            John is correct, the diagram shows a capacitor. On the one you have is the circle with the plus and S near one of the terminals? What shape is the capacitor and what material is the case of the capacitor?
                            Free software for calculating bolt circles and similar: Click Here

                            Comment


                            • #15
                              You can't tell from the schematic alone if the mystery marks indicate a capacitor, open switch contacts, or open relay contacts.

                              There is another schematic symbol for a capacitor which removes the ambiguity, but it's not used as often as it should be. Here she is -
                              http://www.electronics-tutorials.com...apacitance.htm

                              If the motor has a centrifugal switch, that would resolve the mystery.

                              Comment

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