AC Motor Turning Faster than Rated RPMs

Discussion in 'The Projects Forum' started by Runfish, Aug 26, 2014.

  1. Runfish

    Thread Starter New Member

    Aug 26, 2014
    3
    0
    Hello all,
    I've been working on a simple little project the past few days that required a 110V AC 1 rpm motor. I was able to pick one up off eBay for very cheap (from China). When I first installed it everything seemed to be moving along just fine, but then I noticed something. My 1 rpm motor was moving FASTER than 1 rpm. After some timing of its rotation I noticed it was moving ~8 seconds too fast (That's one rotation every 52 seconds). The solution to this that I have is an AC Motor Speed Controller (That I have already ordered).

    My question is two fold:

    1. Is this the ideal solution?
    2. What could be causing the motor to turn faster than its rated?

    Here is a stock photo of the motor that I am using with all its markings.

    [​IMG]
     
  2. ericgibbs

    AAC Fanatic!

    Jan 29, 2010
    2,503
    380
    hi,
    Looking at your measured time of 52Secs.
    50Hz/60Hz= 0.866' * 60 = 52Secs.

    The internal gearing seems wrong.?
    Whats your local mains frequency.?

    E
     
  3. Sensacell

    Well-Known Member

    Jun 19, 2012
    1,131
    267
    Note that the label says SYNCHRONOUS motor- that means it rotates in sync with the applied ac voltage- exactly in sync. A speed controller will not alter the speed- only make it malfunction, to alter the speed you must change the frequency of the AC power applied to the motor.

    What is the AC line frequency in your country? It will turn slower if you are in a 50 Hz country, but faster than 1 RPM? Strange?

    Does it have a capacitor with it to shift the phase? if so, check that it is: (a) properly connected (b) the correct type and value for the motor.
     
  4. Runfish

    Thread Starter New Member

    Aug 26, 2014
    3
    0
    I live in the US (Las Vegas to be more precise) so I'm assuming that it is 60 Hz? The motor came in "all as one" kind of package. So to check those things I will have to open it up. I'm not sure if this would effect it (Just trying to give all the info I can) but when I tested it I had it plugged into a power strip.
     
  5. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
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    very cheap + China = enough said
     
  6. tracecom

    AAC Fanatic!

    Apr 16, 2010
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    I would guess that the motor is actually built to turn 1 rpm based on 50Hz. At 60Hz, it turns faster. Notice the label.
     
  7. alfacliff

    Well-Known Member

    Dec 13, 2013
    2,449
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    it is marked .8 and 1 rpm. if it works right, the 1 rpm would be the 60 hz, and the .8 would be 50 hz.since a synchronous motor like this can not change speed without changing the line frequency, they muxt have made the gear ratios wrong. synchronous means sunchronous with the line, not a motor that lags the line. its called slip, thats why a motor is rated at 1750 rpm on 60 hz, not 1800 like a synchronous motor would be.
     
  8. #12

    Expert

    Nov 30, 2010
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    I'd say you got fooled by the advertising. There is no such thing as a synchronous motor that has a range of speeds (when plugged into a standard power line).
     
  9. MaxHeadRoom

    Expert

    Jul 18, 2013
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    I suspect their intention was to give a range based on the frequency of the supply 50/60hz.
    Max.
     
  10. #12

    Expert

    Nov 30, 2010
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    It's still wrong according to the label. 1 RPM should be the 60 Hz speed and .8333 RPM the 50 Hz speed.
     
  11. Bernard

    AAC Fanatic!

    Aug 7, 2008
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    Every thing on the lable is markad from lowest to highest, 100V-127, .8-1, 50-60.
     
    MaxHeadRoom likes this.
  12. THE_RB

    AAC Fanatic!

    Feb 11, 2008
    5,435
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    It's just mislabeled.

    Its a standard 50Hz 1 RPM motor, and you are running it on 60Hz so it runs fast.

    One other point; Do you need it to start turning in the same direction each time? ;)
     
  13. Runfish

    Thread Starter New Member

    Aug 26, 2014
    3
    0
    Yup, I need it to be going CW every time.
     
  14. Bernard

    AAC Fanatic!

    Aug 7, 2008
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    Some old microwave ovens used a simple oneway clutch to insure one direction turntable rotation- do not remember mech.

    Welcome back Edit- could not live with out you.
     
  15. MaxHeadRoom

    Expert

    Jul 18, 2013
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    Usually the old synchronous clock motor mechanisms used a kick start to make sure it rotated in the correct direction, occasionally you would see a clock run backwards when the spring kick starter failed.
    Max.
     
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