Brushless AC Motor Questions

Discussion in 'General Electronics Chat' started by tracecom, Jun 9, 2010.

  1. tracecom

    Thread Starter AAC Fanatic!

    Apr 16, 2010
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    I have a brushless AC motor (attic vent fan) that quit. I disassembled the motor and see no apparent damage. I have two questions.

    1. There is a component in series with the winding that I am guessing may be a diode. It is a rectangular shape .340" tall, .260" wide, and .100" thick; it has two wire leads and is marked as follows:
    X23 UMI
    3A 130°C
    250V M6
    <PS> JET
    It has no continuity in either direction (as measured with my cheap DMM).
    If it is a diode that has gone open, then replacing it might fix the motor. Can anyone confirm that this is a diode and suggest a US source for a replacement?

    2. The rotor shaft passes through (on both ends) what I think is a sleeve bearing. The bearing seems to be packed with shredded fiberglass and is allowed some movement (presumably to accommodate minor shaft wobble.)
    Should I add some lube to this packing and if so, what?

    Thanks for your input.

    ETA: The motor winding measures 6.3 ohms.
     
    Last edited: Jun 9, 2010
  2. beenthere

    Retired Moderator

    Apr 20, 2004
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    That is most likely an induction motor, which is a very common kind of AC motor. The component is probably a thermal protection device that has opened because the temperature of the motor coils got beyond 130 C.

    You might try getting to the motor number (Fasco is a good guess) to see about a replacement. Exceeding the temp limit may mean bad insulation in the coils, or bad bearings causing drag. It is unsafe to operate an attic fan without a overtemp protector, as an attic fire can total your house in just minutes.
     
  3. Bychon

    Member

    Mar 12, 2010
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    41
    Oil...I used to use Hoppes gun oil because it has no enamel causing impurities, until some new motors came out with bushings so tight that the oil flashed into flames!:eek:

    You don't seem to be having tight bushing problems.

    Now I use common, whatever they have in stock, oil in the zoom spout containers. 3-in-1 oil would work, too.

    Adding oil to an old motor like yours is a good thing.
     
  4. beenthere

    Retired Moderator

    Apr 20, 2004
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    Not 3-in-1. The stuff turns to varnish and hopelessly gums up everything. I have spent hours cleaning it off printer mechanisms and out of bearings. If you want to oil a motor, use SAE 20 or 30 wt motor oil.
     
  5. tracecom

    Thread Starter AAC Fanatic!

    Apr 16, 2010
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    You are correct. I Googled a few things containing "thermal" and finally hit on "thermal cutoff" which led me to a picture of the component I removed. I haven't found an exact replacement yet, but there's hope. The motor had been in use for about two years and I just assumed it (like most of the Chinese junk that I am forced to buy) had worn out.

    Now, it seems that the real question is why did it overheat? The rotor spun freely in the bearings, and the housing wasn't restricted by dirt or debris. Maybe the motor was overworked by restricted airflow due to clogged soffit vents or dirty exhaust screen.
     
  6. beenthere

    Retired Moderator

    Apr 20, 2004
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    Good question. You might want to make the repair and run the motor where you can monitor it's temp for a day or two before reinstalling it in the attic.
     
  7. 203

    New Member

    Jul 3, 2010
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    I'm working on my attic fan this AM, since it's so hot I gotta do something up there to keep the A/C from running all the time. THe motor was not turning, I took it apart, just like you did. I googled X23 UMI and ended up with your post (c:

    I'm facing the exact same failure.. motor is two years old and trashed because of this little thermal device. I am afraid to put it back in the attic, so I gotta go get another. Mine is also China made..

    My motor is 'made' by Air Vent Inc. model DOW 136 0 40 XIN 3/4" FWIW

    For grins, I bypassed the safety device, and ran the motor. The bearings are failed in mine.. it has a 'planetary' action to the shaft and runs way slow.. but turns fine by hand.

    So I guess the little safety device did a good job here.

    Off to find a motor.
     
  8. tracecom

    Thread Starter AAC Fanatic!

    Apr 16, 2010
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    I buy them at Lowe's - about $50.

    Next year, I am recovering my roof and the attic fans are going in favor of a ridge vent.
     
  9. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    Ridge vents are the bomb. Operating costs: zero.

    [eta]
    Related to lubricating oils;

    Most petroleum-based lubricants will eventually turn to varnish, gumming up the works as Beenthere said.

    Use a synthetic lubricant instead. Make sure you clean any remaining lubricant/varnish out first.
     
    Last edited: Jul 3, 2010
  10. 203

    New Member

    Jul 3, 2010
    2
    0
    Now here's page 2, as Paul Harvey once said....

    Went to Lowes, it's not obvious where the fan motors are. So went to the info desk, and there's a motor just like mine. I ask about it, the gal says somebody just returned it, it was bad. Hmmm. I asked how the previous person was compensated.. and learned that they got a store card. Hmmm. Ask for a store card for my failed motor, and without receipt or anything, they give me a store card.

    I go look in the millwork section ( that's where I'd keep a fan motor, too :) ) and find that these attic fans have a lifetime warranty, based on the packaging. And a pile of $58.95 motors stacked beside the fans. So it appears that they'll warranty the lifetime warranty if you ask for it. Or they will gladly sell you a fan motor if you fail to ask.

    Hope others who google get some benefit out this thread. Y'all have a nice day :)
     
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