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muffin fan at lower than rated voltage?

Discussion in 'General Electronics Discussion' started by Heimhenge, Jul 19, 2011.

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  1. Heimhenge

    Heimhenge

    13
    1
    Jul 12, 2011
    I have a muffin fan rated for 220-240 VAC. When I feed it 110 VAC it self-starts and seems to run just fine. Would there be any long term danger running it at that lower voltage? I ask because I want to use it to vent a battery room for my solar electric system, and just happened to have it in my "spare parts" bin. Also, it gives me just the CFM I'm looking for.

    Note that, as a battery room vent fan, it would run 24/7.
     
  2. Resqueline

    Resqueline

    2,848
    2
    Jul 31, 2009
    My not-so-educated guess would be that it'll be ok, but it won't give quite the RPM & CFM as the spec'' says.
    I figure that the higher slippage leads to a higher % of the magnetic field turning into heat in the rotor, but since the field is only half as strong as designed then it's ok.
    The copper loss will certainly be lower, so in total it should run cooler. It'll be more sensitive to stalling due to bad bearings though, due to poor torque reserves.
    Correct me anyone if my reasoning's wrong.
     
  3. Heimhenge

    Heimhenge

    13
    1
    Jul 12, 2011
    Yeah, I was worried about the torque issue too. But it does self-start at 110 VAC, and seems to be running cool. I'll run it longer tomorrow to see how it behaves. It'll be mounted horizontally, and I don't know if that causes more or less stress on the bearings, but the one it's replacing ran for close to 10 years 24/7. And the old one was rated for 110 VAC.

    I'm pretty good at basic electronics, but electric motors are a whole 'nuther animal, so I thought I'd start this thread and see what the experts had to say.
     
  4. daddles

    daddles

    443
    3
    Jun 10, 2011
    In general it's a poor idea to run induction motors at voltages other than their rated voltages. But, the proof is in the pudding: if it's not overheating and there's enough torque, it might be suitable.

    Question: should you test it with a locked rotor? The computer fans often fail when the bearings go bad and they can freeze up.
     
  5. Resqueline

    Resqueline

    2,848
    2
    Jul 31, 2009
    The run torque of these motors is much higher than the start torque so once it gets going it should keep going. A horizontal axle usually gives less friction & wear.
     
  6. duke37

    duke37

    5,364
    772
    Jan 9, 2011
    Muffin "light flat round spongy cake eaten toasted and buttered". Yumm.

    If it is a shaded pole motor it should be all right, these are often controlled by input voltage (series resistance).
     
  7. Resqueline

    Resqueline

    2,848
    2
    Jul 31, 2009
    Muffin fan just got a new meaning here.. ;)

    I believe these have a squirrel cage rotor. They tend to either run or not.
     
  8. Heimhenge

    Heimhenge

    13
    1
    Jul 12, 2011
    Ran some tests today based on all your suggestions ...

    1. It does say on the label "impedance protected." I think that's what Duke37 was talking about. I have no idea if it's a "shaded pole motor."

    2. It self-starts just fine in the horizontal orientation (vertical rotation axis), just as it does in the horizontal axis orientation. No torque problems. The thing continues spinning for over a minute after I cut the power, so it must have good bearings.

    3. Draws 29.5 mA at run speed. When I manually stop the fan blade, that rises slightly to 30.5 mA. No obvious heating when stalled, as will eventually happen when it wears out and the bearings freeze up.

    I was concerned about what would happen with a bearing freeze, and was prepared to add an inline fuse to avoid overheating. But at 30.5 mA that's only about 4 W of energy being dissipated, and the fan will be mounted in a sheet metal duct. So I don't think there's any fire hazard.

    Many thanks for all the input! I do feel "safer" now.
     
  9. TBennettcc

    TBennettcc

    292
    2
    Dec 4, 2010
    30mA, huh? That's quite a bit smaller than the motor / fan I was thinking of...
     
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