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6919 Views 2 Replies Latest reply: Aug 30, 2014 10:22 AM by lou.key RSS
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Aug 5, 2014 4:56 AM

Single phase 4 pole motor running slow with little torque


Can you help me on this one using basic terms please.

I have an old desk fan which has a 4 pole single phase(230v 50hz i think) motor fitted to it,the coils are rated at 80 ohms a piece.

The problem i have is that it is running very slow, so slow in fact you can stop it with you fingers.

I have had the motor checked by a re-winder, he says that the integrity of the motor is OK.

The rotor sits in two bushes, everything is free to move but i can't get it to run any faster.

If i re-assemble it the fan just about starts until i engage the reciprocating part then it stops.

The motor does not get hot.

Any ideas i am at a loss?


  • Mariner Novice 3 posts since
    Aug 18, 2014
    Currently Being Moderated
    Aug 18, 2014 12:22 PM (in response to stevieh)
    Single phase 4 pole motor running slow with little torque

    If the motor has brushes and it has an ac rating on its nameplate, it is a "universal" motor- it will run on ac or dc. Assuming that the "motor integrity is OK", make sure that it is operating at rated volyage, in your case 230 volts, (And not 110 volts). If the motor is only getting 110 volts to run, it will likely operate as you describe. Make sure that the brushes are not worn down too much also- but you rewinder probably checked that.


    I have found with small room fans, the real problem is eventually the bearings- which are just plain sleeve bearings, get dirty and sticky, and the motor becomes "stuck" in the bearings. This is why fans usually start on the fastest setting.


    I hope that helps.

  • lou.key Novice 1 posts since
    Aug 30, 2014
    Currently Being Moderated
    Aug 30, 2014 10:22 AM (in response to stevieh)
    check the capacitor

    if the winding and bushing is fine then you have to check your capacitor it might have deteriorated and way below its rated capacitance

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