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Detect shorted turns in motor windings...

Discussion in 'Electronic Repair' started by Tor Tveitane, Nov 7, 2004.

  1. Tor Tveitane

    Tor Tveitane Guest

    Hi,

    Can I use a LCR bridge in inductance mode to measure difference in
    inductance if I suspect one of the windings in an electrical motors to have
    shorted turns...?

    What is the preferred way to check for shorted turns within an inductor...?

    Thanks for clues

    Tpr
     
  2. CJT

    CJT Guest

    I don't know what's preferred, but one way might be to ring it like
    a flyback and look at the response.
     
  3. NSM

    NSM Guest

    | Hi,
    |
    | Can I use a LCR bridge in inductance mode to measure difference in
    | inductance if I suspect one of the windings in an electrical motors to
    have
    | shorted turns...?

    Sure. Compare the ratio of inductance to resistance.

    | What is the preferred way to check for shorted turns within an
    inductor...?

    For shorted turns in a motor use a growler.

    N
     
  4. That was my thought/guess as well.

    Tom
     
  5. Tor Tveitane

    Tor Tveitane Guest

    Any urls and info to show how to setup this and to diagnose the response..?

    Tor
     
  6. NSM

    NSM Guest

    | "Tom MacIntyre" <> skrev i melding
    | |
    | > >I don't know what's preferred, but one way might be to ring it like
    | > >a flyback and look at the response.
    | >
    | > That was my thought/guess as well.
    |
    | Any urls and info to show how to setup this and to diagnose the
    response..?

    http://repairfaq.ece.drexel.edu/REPAIR/F_appfaqi.html

    What sort of motor? What's shorted, field or rotor?

    N
     
  7. CJT

    CJT Guest

  8. N Cook

    N Cook Guest

    I've never used one but isn't a growler used for this purpose.

    electronic hints and repair briefs
    http://homepages.tcp.co.uk/~diverse
     
  9. Ross Herbert

    Ross Herbert Guest

  10. Yes, though it would be hard to justify the expense to fix one small
    motor.

    See, for example: http://www.sotcher.com/mre/520.html

    It's just the primary of a transformer connected to 60 Hz along with
    a hacksaw blade, so you could probably build one or improvise from
    something else.

    --- sam | Sci.Electronics.Repair FAQ Mirror: http://repairfaq.ece.drexel.edu/
    Repair | Main Table of Contents: http://repairfaq.ece.drexel.edu/REPAIR/
    +Lasers | Sam's Laser FAQ: http://repairfaq.ece.drexel.edu/sam/lasersam.htm
    | Mirror Sites: http://repairfaq.ece.drexel.edu/REPAIR/F_mirror.html

    Note: These links are hopefully temporary until we can sort out the excessive
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    Important: Anything sent to the email address in the message header is ignored.
    To contact me, please use the feedback form on the S.E.R FAQ Web sites.
     
  11. Jim Adney

    Jim Adney Guest

    Yes, but any electric motor shop, or automotive electric shop will
    have a growler and would charge only a very small fee to test an
    armature for you.

    Disassemble the motor and just take in the rotor, so that they don't
    have to do any significant work.

    If you bring it over here, it would take me less than 2 minutes to
    check it out. ;-)

    -
     
  12. IF, it's a wound rotor motor. Most ac rotors are of the squirrel cage
    variety.
     
  13. Jim Adney

    Jim Adney Guest

    I was wondering about that. Wouldn't a squirrel cage motor still have
    the same magnetic properties? I'm not sure, but I'd bet that such a
    rotor would still pass the growler test, but it's hard to imagine a
    squirrel cage rotor with a short in it, which, I believe is what the
    OP asked about.

    Does anyone know if this happens?

    -
     
  14. NSM

    NSM Guest

    | On Tue, 9 Nov 2004 16:41:01 -0500 "Charles Schuler"
    |
    | >> Disassemble the motor and just take in the rotor, so that they don't
    | >> have to do any significant work.
    | >
    | >IF, it's a wound rotor motor. Most ac rotors are of the squirrel cage
    | >variety.
    |
    | I was wondering about that. Wouldn't a squirrel cage motor still have
    | the same magnetic properties? I'm not sure, but I'd bet that such a
    | rotor would still pass the growler test, but it's hard to imagine a
    | squirrel cage rotor with a short in it, which, I believe is what the
    | OP asked about.

    I don't know how to 'growl' a squirrel cage motor. I'd just fire it up and
    check the amps on each leg.

    NM
     
  15. James Sweet

    James Sweet Guest


    I've never even heard of a rotor failure on any type of induction motor,
    usually it's the starting switch, capacitor, or bearings that fail. The
    stator windings can burn out but it's rare.
     
  16. By definition, a squirrel cage rotor is all shorts. :)

    --- sam | Sci.Electronics.Repair FAQ Mirror: http://repairfaq.ece.drexel.edu/
    Repair | Main Table of Contents: http://repairfaq.ece.drexel.edu/REPAIR/
    +Lasers | Sam's Laser FAQ: http://repairfaq.ece.drexel.edu/sam/lasersam.htm
    | Mirror Sites: http://repairfaq.ece.drexel.edu/REPAIR/F_mirror.html

    Note: These links are hopefully temporary until we can sort out the excessive
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    Important: Anything sent to the email address in the message header is ignored.
    To contact me, please use the feedback form on the S.E.R FAQ Web sites.
     
  17. The only way a squirrel cage rotor could fail would be for one or more
    of the shorting bars to open. A quirrel cage rotor is based on all
    the bars being shorted at the end-plates.

    --- sam | Sci.Electronics.Repair FAQ Mirror: http://repairfaq.ece.drexel.edu/
    Repair | Main Table of Contents: http://repairfaq.ece.drexel.edu/REPAIR/
    +Lasers | Sam's Laser FAQ: http://repairfaq.ece.drexel.edu/sam/lasersam.htm
    | Mirror Sites: http://repairfaq.ece.drexel.edu/REPAIR/F_mirror.html

    Note: These links are hopefully temporary until we can sort out the excessive
    traffic on Repairfaq.org.

    Important: Anything sent to the email address in the message header is ignored.
    To contact me, please use the feedback form on the S.E.R FAQ Web sites.
     
  18. Jim Adney

    Jim Adney Guest

    Right, but so is a regular commutator rotor. The only difference, I
    think, is that the squirrel cage rotor is wound with much more rugged
    "wire."

    -
     
  19. Nah. :) A commutator motor happens to be shorted but that is a byproduct
    of how it's wound, not a requirement. A squirrel cage rotor is a bunch
    of copper bars embedded just under the surface of a solid steel rotor
    running length-wise. They are shorted at the end plates. Since these
    are induction motors, they depend on the current flowing in the bars
    as the secondary of a transformer to provide the torque.

    For brush-type motors, current is applied to the rotor windings via the
    brushes. It's possible to build such a motor without "shorted" windings.

    --- sam | Sci.Electronics.Repair FAQ Mirror: http://repairfaq.ece.drexel.edu/
    Repair | Main Table of Contents: http://repairfaq.ece.drexel.edu/REPAIR/
    +Lasers | Sam's Laser FAQ: http://repairfaq.ece.drexel.edu/sam/lasersam.htm
    | Mirror Sites: http://repairfaq.ece.drexel.edu/REPAIR/F_mirror.html

    Note: These links are hopefully temporary until we can sort out the excessive
    traffic on Repairfaq.org.

    Important: Anything sent to the email address in the message header is ignored.
    To contact me, please use the feedback form on the S.E.R FAQ Web sites.
     
  20. Asimov

    Asimov Guest

    "Jim Adney" bravely wrote to "All" (11 Nov 04 20:57:04)
    --- on the heady topic of "Re: Detect shorted turns in motor windings..."

    JA> From: Jim Adney <>

    JA> Right, but so is a regular commutator rotor. The only difference, I
    JA> think, is that the squirrel cage rotor is wound with much more rugged
    JA> "wire."

    The squirrel cage rotor is really a rotating transformer with a very
    low resistance secondary. Any phase difference (slip) between the
    applied field and the transformed field generates very high currents
    in the range of 100's of amperes. To say the rotor is wound with much
    more rugged wire is really an understatement. It is this high current
    that causes a counter emf, applying a mechanical torque to the shaft,
    and results in the desired motor action.

    A*s*i*m*o*v

    .... Electrical engineers deal with current events.
     
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