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Need help repairing electric motot

Discussion in 'Electronic Repair' started by PSI, Aug 30, 2004.

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  1. PSI

    PSI Guest

    My faithful oscillating fan has given up the ghost. I know I can
    go buy a new one but I like tinkering and fixing things so I'm looking
    for some help.

    The facts:

    1) Its a three speed table fan with thermal protection that is about
    20 years old.

    2) There is no hum indicating its trying to spin and giving it a hand
    doesn't help.

    3) I removed the capacitor and tested with a multi-meter on the ohm
    range. The "resistance" increases steadily to a large number and then
    goes to zero ( its a 4 uf 230V cap ). I think this means its OK??

    4) There is a "device" in the circuit coming from the neutral to the
    cap (ie . white---> "device" ---> cap ). Its tied with string on top
    of the winding and inside a clear plastic sleeve, is cylindrical in
    shape with one end pointed and coloured orange. There are some
    markings on it but I can't read them without removing it first). The
    AC voltage before the "device" is 115V. Voltage after the " device"
    is 11V.

    Is this the thermal-protection? If so does this indicate it's fired
    and should be replaced? ( I haven't tried to bypass it because it
    means snipping some more wires)

    5) Near as I can tell there arre no "brush's " but I haven't fully
    dissasembled ( because I don't figured how to get some of the parts
    off :)


    Most important: I'm reasonably handy but my electronics/motor
    knowledge is basic high-school level( ie I know what a stator,
    rotor,armature,commucator etc. are but not sure I can relaibly tell
    you if its a split-phase, or induction etc type motor :) )

    Any suggestions are appreciated

    Frank
     
  2. The device inside tied to the windings is, indeed a thermal fuse. Sometimes
    they open for no apparent reason - no indications of excessive heat. To see
    if that's the problem, either check it continuity or jump across it and see
    if the fan runs. If it's open, you then have the decision to make as to
    whether or not to run the fan without the protection.

    WT
     
  3. Yes. If you measure across it with an ohmmeter (fan unplugged!!!),
    it is now open.
    These usually use a shaded pole induction motor, or possibly since you
    mention a capacitor, capacitor run induction motor. No brushes.
    There are plenty of Web sites with basic motor info.

    Your motor may have failed due to gummed up or worn bearings and overheating,
    a winding short and overheating, just a tired thermal fuse, etc.

    What I'd probably do is confirm the thermal fuse is open and bypass it for
    testing. Also check for mechanical problems. To be doubly safe during
    testing, consider placing a light bulb in series with the fan so that if
    it has a serious short, you won't smoke anything beyond the fan motor.

    More info in the small appliance repair guide at the site below.

    --- 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.
     
  4. Richard

    Richard Guest

    So it does have thermal protection
    and probably the field coils are not activated
    Yes I have repaired such a motor by replacing the thermal protection
    you could verify this by bypassing this device. This of course if
    there is no evidence of shorts or burned coils. The thermal protection
    is there to prevent over temperature conditions in the coil usually
    due to shorts and or course over temperature means more shorts and
    possible fire!
    no these are induction or shaded pole motors, no brushes
     
  5. PSI

    PSI Guest

    Replaced the "device", which I now understand is correctly called a
    thermal fuse, cleaned out the dried grease and dust, applied some
    "electric motor oil" to the shaft and the fan is blowing again -
    maybe another 20 years.

    Thanks to everyone for the help.

    Frank
     
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