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Testing a motor with a megger and multi meter

Discussion in 'Repairing Electronics' started by Gregory, Nov 2, 2017.

  1. Gregory

    Gregory Member

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    I have a 3 phase motor When testing with a megger do you only test from each winding to ground.
    When I do a ohm meter test of the 6 wires I get a reading wirer green 1&2. 9.7ohm White 3&4. 9.7 ohm Yellow 5&6 9.7 ohm readings .( these coloured are the ones I painted on the terminal. )
    This is the order in witch they wer connected to the terminal block.
    When I connect any black wirer or white wirer in any order I get a ohm reading between 17 and 10 ohm black to black or white to white black to white.
    I do not under stand this layout.
    Are all the wind endings joined inside.
    The windings do not go to earth.
    Attached is a photo.
    Greg
     

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  2. Gregory

    Gregory Member

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    IMG_2165.JPG IMG_2168.JPG Having don further investigation into the use of the megger one connection goes to ground and the other goes to one end of the winding.
    The motor has a internal star connection.
    Having disconnected the star connection in the motor I have now have all the individual windings which have been marked 123456 as showen in the photo also with ohm readings of each individual winding.
    Can someone tell me how to connect the windingsin of this motor into a 4 pole singel phase also using a start and run capacitor
    Thank you
     
  3. cowboybob

    cowboybob Well-Known Member Most Helpful Member

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    You can't make a 4 pole motor from a 3 pole configuration.

    That said, there are a number of methods for converting a motor from a 3 phase to single phase source, from simple to not so simple.

    And it's important to note that motor performance (startup torque and run torque) is considerably reduced by the conversion.

    You might start here.
     
  4. dave

    Dave New Member

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  5. MaxHeadRoom78

    MaxHeadRoom78 Active Member

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    There are two types of Megger, high voltage-resistance tester and the low voltage very low resistance type.
    Presumably you have the former, these are only really used and useful for resistance test and breakdown using high voltage.
    So when used on a 3ph motor it is generally a reading from winding to ground.
    Or for short between separate winding coils.
    Max.
     
  6. Gregory

    Gregory Member

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    Having viewed the you tube vido I do not understand how to connect the 6 coils , ends to get the motor to run on singel phase .
    They wer connected internally as star I decided to disconnect the star connection and start with 6 individual windings but require help to connect them up for a singel phase motor. Or change them to delta
    Can you advise me in regards this.
    Greg​
     
  7. MaxHeadRoom78

    MaxHeadRoom78 Active Member

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    Maybe look up RPC circuits.
    This is the basis for operating on 1phase.
    Max.
     
  8. Gregory

    Gregory Member

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    Could you explain what RPC circuits are
    Thank you
    Greg
     
  9. MaxHeadRoom78

    MaxHeadRoom78 Active Member

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    Rotary Phase Convertors.
    Use a 3ph motor to convert 1ph to 3 ph.
    Max.
     
  10. Gregory

    Gregory Member

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    I am not happy with the 3 phase motor .I have decided to remove all the windings and rewind the motor.
    The motor I require is a singel phase motor.2.5 Hp 4 pole 2500 RPM If it can be done Cap start cap run.
    The motor has 36 slots.
    I require help with the wirer size and the winding sequence.and connections forward and reverse
    I realise that there could be 2 different wirer sizes.
    For run and start.
    This motor I will use on my milling machine as the motor is flang mounted.
    I only have singel phase to the shed.240 AC VOLTS
    I would apperiate all the help I can get as I do not have the money to replace it with a new one.
    I am prepared to have a go. And learn.
    The question will be asked what happened to the original motor.
    I baught it very cheep as I can not afford a new one. The miller did not have a main motor.
    This one was given to me as a 3 phase .
    I need Singel phase.
     
  11. MaxHeadRoom78

    MaxHeadRoom78 Active Member

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    IMO if the motor runs on 240v then a VFD would solve the problem without the hassle of rewinding, and also you will have RPM control.
    A 240v VFD usually accepts 1ph or 3ph and converts to 3ph variable frequency out.
    Max.
     

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