Will I Need A Run Capacitor?

Discussion in 'The Projects Forum' started by shane73, Aug 29, 2014.

  1. shane73

    Thread Starter New Member

    Aug 29, 2014
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    Hello greetings all. Would like some help with a little thing i'm trying if anyone could possibly answer my question please :)

    I'm running an old 2 speed desk fan through an electronic fan controller so as to lower the speed. The fan starts up fine so I know I don't need a start capacitor but my question is, before I run it for any length of time and possibly cause damage, do I need a run capacitor in place????

    The fan is a 10" AC 240v 50Hz desk fan and the electronic fan controller is a Vent-Axia 3-speed fan controller (an industrial version of the T-Series).
     
  2. inwo

    Well-Known Member

    Nov 7, 2013
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    Possibly, did it use one before?
     
  3. shane73

    Thread Starter New Member

    Aug 29, 2014
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    No the original fan had no caps at all and was a 2 speed fan with horrible plastic click switches (which i assume changed the voltage). Its an old fan probably 20-30yrs old, i wana use it as a pc case fan but wana slow it down so it dont sound like an airplane, had enough of cheap plastic pc fans which always need cleaning and dont last long. I would have thought the fan controller would smooth the current as its not a cheap unit but dont wana burn out the motor. The motor has a big what i assume is a magnet which the axle runs through and then a big coil below that. It runs fine without the cap and had it running a good couple of hours but i have a 450v 2uF cap ready if i need it.
     
  4. shane73

    Thread Starter New Member

    Aug 29, 2014
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    i assume its better to put it in line and it not be needed rather than not put it in line and it be needed?
     
  5. shane73

    Thread Starter New Member

    Aug 29, 2014
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    has 4 wires live, neutral, earth and switching wire if that helps.
     
  6. Johann

    Senior Member

    Nov 27, 2006
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    Without a start/run capacitor, this appears to be an ac squirrel cage motor with shaded pole(s) to create a rotating magnetic field. Is this an open-frame type construction and can you post a photograph of it?
     
  7. shane73

    Thread Starter New Member

    Aug 29, 2014
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    Theres an image of the motor, i'm running it with a capacitor at the moment and seems fine. Ive also included a picture of the project so far :)
    IMG_20140830_043913_798.jpg 10629771_699867853432968_6051616416921514721_n.jpg
     
  8. ISB123

    Well-Known Member

    May 21, 2014
    1,239
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    Better safe then sorry!
     
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  9. Johann

    Senior Member

    Nov 27, 2006
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    You see the two loops of copper wire on the laminated core? These create an out of phase magnetic field (out of phase with the main magnetic field created by the big coil below the rotor), therefore no provision was made for any running capacitors. Are you connecting the capacitor in series with the power to the fan?
     
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  10. Johann

    Senior Member

    Nov 27, 2006
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    Also, the rotating part (rotor) is what they call a squirrel cage rotor, very common to ac induction motors. This is not a magnet, but becomes magnetized due to the induced current in the rotor bars embedded in the rotor itself.
     
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  11. shane73

    Thread Starter New Member

    Aug 29, 2014
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    Ive got a single capacitor wired through the live switching wire (grey wire), as this was the wire which ran the fan on low setting with the original switches, and this is the setting i will be running the fan on most of the time. I assumed from looking at how another capacitor was wired to a fan i looked at and from reading that would be the logical place to put it. Do i not need it then? It's all a bit of guesswork with some research but im just a bodger def no sparky :D
     
  12. Johann

    Senior Member

    Nov 27, 2006
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    No harm in trying things! That is how one learns. Regarding the capacitor, I don't think you need it. Remove it and connect the supply (with or without your speed controller) directly to the motor and monitor the performance for a while. Just make sure that your supply voltage matches the required voltage of the fan motor.
     
  13. Johann

    Senior Member

    Nov 27, 2006
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    On second thoughts, the capacitor most probably was used to limit current, causing a reduction of speed, but now you have a speed controller, so get rid of the capacitor and adjust the controller accordingly to give you the desired speed.
     
  14. shane73

    Thread Starter New Member

    Aug 29, 2014
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    Yes it did seem to be running fine without the capacitor i just didnt wana burn out the motor. It's a 2 speed fan as standard and never had a cap anyway, also terribly clunky buttons where you could see the connection spark so one would assume that adding a good quality fan controller the current would be further smoothened without the need for a cap. I'll disconnect the cap a bit later and test it all day tmorow. Must remember they hold a charge :D
     
  15. shane73

    Thread Starter New Member

    Aug 29, 2014
    9
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    the capacitor wasn't from this fan sorry, this motor never had one, the cap was from an industrial fan which would be just overkill for cooling, though i did consider it and may yet happen if i overvolt my pc :)
     
  16. shane73

    Thread Starter New Member

    Aug 29, 2014
    9
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    thank you kind people i will keep you updated :)
     
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