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Capping the loop end of an electric motor!

Discussion in 'Electronic Design' started by [email protected], Feb 20, 2004.

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  1. Okay, here's a good one... I work with a group of "engineers" from
    the Czech Republic that manufacture DC electric motors (~180 HP).
    We've been having a problem where the loops of the armature are
    destroying the resin wrapping that is supposed to hold them down. The
    centrifugal force of the loops is just tearing this wrapping apart
    after the motor has been in service for awhile. Usually the loops
    flare out enough that they contact the field windings and then the
    motor is toast.

    We've determined that the wrapping process is a very low quality. It
    is almost the consistency of cardboard rather than a very hard
    material like it should be. The proper fix for these motors should be
    to rewrap both ends in the proper manner and then the centrifugal
    force won't tear it apart.

    The manufacturer wants to install a CAP over and around the entire
    looped end of the armature! I've been able to determine so far that
    this cap will probably seriously restrict air flow and cooling. I
    also believe that the cap is just going to tear itself apart

    My question to the group is what other reasons is this a bad idea?
    Also, have any of you seen this capping method used elsewhere? I
    can't find anyone I know that's ever heard of such a thing. The funny
    thing is that this method is coming from a fairly well known company
    in CZ... You can probably think of it.. Thanks.
  2. Whats wrong with the normal steel wire binding just behind the commutator ??
  3. Degaully

    Degaully Guest

    what are the specs on the motor ?
  4. Ian Stirling

    Ian Stirling Guest

    What is the specified wrapping.
    Is it in fact being installed, or are they using strips of old
    T-shirts with flour and water paste?
  5. That's part of the problem. I don't actually know the specs on the
    wrapping, however it is very clear that this wrapping is soft compared
    to every other wrapping I've seen. Most wrappings are almost like
    steel when you tap on them, this one sounds hollow and soft like
    cardboard. It appears to be the reason it can't hold the lops down.
    Typical speed of the motor is 4400 RPM.
  6. Ian Stirling

    Ian Stirling Guest

    Have you suggested that the manufacturer check that the workers are
    actually installing it properly, and that it is the proper stuff?
    It might be worth getting someone with a microscope, and some test tubes
    to have a look at it to find out what it is.
  7. Well you hit the nail on the head there, because this is exactly what
    happens when you buy from a place where English isn't the primary
    language. In addition we are totally separated by a cultural gap in
    terms of manufacturing and quality assurance practices, warranty,
    failure analysis, etc...
  8. Ian Stirling

    Ian Stirling Guest

    It's what happens when you buy from a place where the foreman does not
    understand the design, or does not enforce it, or where management
    substitutes cotton for glass fiber.

    A german factory is quite unlikely to have the same problem.
  9. Big John

    Big John Guest

    See my comments in the text.

    I agree.
    I also agree - not good for cooling. Cheap, quick fixes usually don't work.
    Yes, if the cap is metal. You will have some flux from the main field in
    this area (especially near the core). When the metal cap spins through this
    field you will get an induction braking effect. This will add heat and
    lower the motor's efficiency.
    No, and I worked for a motor manufacturer for 16 years. You should also
    check to make sure they are using an armature design with closed slots.
    This is necessary for a larger motor running at 4400 RPM. A cheap company
    might want to use open slots to make armature winding easier, but
    centrifugal forces will tend to throw the windings out of the armature slots
    at speeds this high.
  10. BFoelsch

    BFoelsch Guest

    It almost sounds like the coils are too long, leaving excess loop length.

    What speed are these units?
  11. 4400 RPM is about normal. The loops extend about a few inches out.
  12. Americans announce technology for the finest drawn wire.
    Japenese drill a hole in it.
    Germans tap it.

    Many thanks,

    Don Lancaster
    Synergetics 3860 West First Street Box 809 Thatcher, AZ 85552
    voice: (928)428-4073 email:

    Please visit my GURU's LAIR web site at
  13. Tim Auton

    Tim Auton Guest

    Then the English claim they invented it all 100 years ago :)

    Tim, an Englishman.
  14. Good grief, I heard that yarn 40 years ago, though it was French,
    Germans, Americans. ...the Japaneese drill bit broke. ;-)
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