Capacitor to remove AC distortion in dimmer

Discussion in 'General Electronics Chat' started by Willen, Sep 4, 2016.

  1. Willen

    Thread Starter Member

    Nov 13, 2015
    138
    12
    Hi,
    I just heared, when we use powerful dimmer (Maybe PWM) like in mega structures to control light intensity etc, it causes distortion in AC and distortions can produce unexpected heat in cables and sometime fires. I saw a video and found that to remove the distortion, they used a bigger capacitor like 6 inch in diameter. Where they use the capacitor? I searched some equivalent circuit but found nothing exactly.
     
  2. bug13

    Well-Known Member

    Feb 13, 2012
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    Just curious, can you link in the video?
     
  3. tcmtech

    Well-Known Member

    Nov 4, 2013
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    More than likely it was a common, but large, power factor correction capacitor connected across the main power lines.

    Besides adjusting the power factor up those types of capacitors typically have very low ESR ratings which make them very effective as harmonics traps and HF snubber devices too.

    I use several smaller ones, ~ 2 uF 600 VAC ,around my home and shop electrical system just for that purpose of knocking out HF noise on the AC line sides which in some of the things I experiment with probably gets pretty wild. :D
     
  4. Willen

    Thread Starter Member

    Nov 13, 2015
    138
    12
    Hi
    I cannot see videos in the internet. I saw a engineering program in National Geography channel where they were describing many basic engineering techniques behind a Burj Al Arab, mega structures. And they were talking about light dimmer technology and a big capacitor. I have posted a YouTube link thinking that I found that video by guessing just from its thumbnail picture.
     
    Last edited: Sep 5, 2016
  5. Willen

    Thread Starter Member

    Nov 13, 2015
    138
    12
    Hi,
    Small 2uF 600V capacitors like used in single phase AC motors? How you connect them in mains, any circuitry?
     
  6. DickCappels

    Moderator

    Aug 21, 2008
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    At 40 minutes into the video they start talking about harmonic distortion. That part lasts about two minutes.
     
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  7. tcmtech

    Well-Known Member

    Nov 4, 2013
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    Really? :rolleyes: :(

    How do you imagine they would be connected?
     
  8. #12

    Expert

    Nov 30, 2010
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    Use two wires.
     
  9. Willen

    Thread Starter Member

    Nov 13, 2015
    138
    12
    I know nothing. I am just asking being curious from your first post here.
     
  10. Willen

    Thread Starter Member

    Nov 13, 2015
    138
    12
    Can I connect two leads of capacitor to the two wires of mains to remove distortion? Mains is AC so won't the capacitor kill me?
     
  11. #12

    Expert

    Nov 30, 2010
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    Where are you going to place the capacitor so it can kill you?
    I would suggest, not in your mouth.
     
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  12. Willen

    Thread Starter Member

    Nov 13, 2015
    138
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    I think connecting a capacitor to 220V 50Hz cause short circuit, instead of any improvements.
    Would you suggest rest of the mouth? :)
     
  13. #12

    Expert

    Nov 30, 2010
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    I think you have a lot to learn. I have posted several times that the best test of an oil filled run capacitor is to connect it directly to 240 VAC and measure the current.

    Look at the power poles as you go by and see the capacitors up there.
    They do power factor correction.
     
  14. Willen

    Thread Starter Member

    Nov 13, 2015
    138
    12
    Yes. I am engaged in totally different profession from electronics but I am a kind of addicted to electronics.
    I just heard and seen the oil filled capacitor. I guess electrolytic capacitor are poor choice and oil filled big capacitors are good choice for the purpose.

    Can I say 2uF in 50Hz have almost 1.5k capacitive reactance. So it will consume 0.14A when connected directly to 220V mains?
     
  15. #12

    Expert

    Nov 30, 2010
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    You did the math right but capacitors do not consume current. They allow current.
    If they consumed current, they would get hot. They do not get hot.
     
  16. bertus

    Administrator

    Apr 5, 2008
    15,648
    2,348
    Hello,

    Most noise from a triac circuit will come from the fast switching flange of the triac.
    The switching flange can be influenced by an snubbing circuit.
    The attached PDF will tell you more about this.

    Bertus
     
  17. ian field

    Distinguished Member

    Oct 27, 2012
    4,415
    784
    You'll need to find out whether its PWM, or something else.

    PWM usually implies the standard rectifier/reservoir like in a typical SMPSU. The most common PFC front end is a flyback boost converter interposed between the rectifier and reservoir. It works at a much higher frequency than mains and takes pulses of current from the rough DC waveform that are proportional to its amplitude. On some ATX PSUs they just stick a dirty great iron-cored choke in series with the mains input.

    On a triac dimmer - a PFC capacitor will do little more than take the edges off the switched current waveform.
     
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