how to drive a capacitor with thyristor or triac

Discussion in 'The Projects Forum' started by mesuthh, Feb 6, 2011.

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  1. mesuthh

    Thread Starter New Member

    Jan 17, 2011
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    Hello People;
    I am trying drive 25uf capacitor with a optocoupler and triac. I have tried so many triacs and huge heatshinks, but always triacs goes fire because the high temperature on triac.
    is there any advice
    thanks from now on
    regards
     
  2. Adjuster

    Well-Known Member

    Dec 26, 2010
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    Please explain in more detail, and post a schematic of your arrangement.

    I advise you not to try it again before finding out what is wrong, as it sounds dangerous - is the circuit connected to the mains?
     
  3. mesuthh

    Thread Starter New Member

    Jan 17, 2011
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    Dear Adjuster you can see my schematic on http://img163.imageshack.us/img163/6451/61125722.jpg or
    kind regards [​IMG]
     
  4. t_n_k

    AAC Fanatic!

    Mar 6, 2009
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    mesuthh,

    you didn't fully answer the question about the supply voltage.

    Your triac is probably failing due to exceeding a critical parameter value.

    The single or repetitive peak current may be an issue. There are transient as well as steady state conditions to consider at the turn-on instant.

    You might consider placing a limiting load resistance in series - such as an incandescent lamp - to make sure the basic function is what you intend.

    What is the point of your experiment?
     
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  5. GetDeviceInfo

    Senior Member

    Jun 7, 2009
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    Your so kind.

    I would have said, your shorting your supply out moron, your going to injure yourself or someone else.
     
  6. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    Dang....I couldn't have said it better !!!!! :D
     
  7. mesuthh

    Thread Starter New Member

    Jan 17, 2011
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    dear Tnk I am trying to make a mini compansating
    regards
     
  8. GetDeviceInfo

    Senior Member

    Jun 7, 2009
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    just being lighthearted,


    if you squeeze afew more amps into that cap you'll make a maxi expansiator.
     
  9. CDRIVE

    Senior Member

    Jul 1, 2008
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    What is that?? :confused:
     
  10. beenthere

    Retired Moderator

    Apr 20, 2004
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    That circuit is not going to "drive a capacitor", but demonstrate the sensitivity of a TRIAC to ΔV/ΔT and/or short circuit current.

    What is the AC source? Is the capacitor rated for AC? Why is there no fuse present?
     
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  11. Adjuster

    Well-Known Member

    Dec 26, 2010
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    I would guess that this is an attempt at switching power factor correction capacitors. That is actually a pretty tough application: professional gear of this kind goes to some lengths to protect the switch elements. This circuit has no snubbing or other filter elements: apart from the inherent switching rate problems, any spikes or higher frequency cr*p on the mains input can come straight through the capacitor to get at the triac.

    The drive to the input LED comes via another unspecified LED in series, so it's not clear how much drive it would get.

    There may however be a far more basic problem. When the LED drive is removed, the triac will turn off when the capacitor current drops to zero. This is however on the peak of the input voltage, when the capacitor will be fully charged. When the input voltage reverses, the capacitor voltage will be added on to the next voltage peak, giving a total of about 678V for a 240V AC supply. This may be enough to break over the triac, in which case it will surely fail.
     
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  12. mesuthh

    Thread Starter New Member

    Jan 17, 2011
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    dear beenthere;
    AC is 240 V Ac.
    regards
     
  13. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    U need a load
     
  14. GetDeviceInfo

    Senior Member

    Jun 7, 2009
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    You need to stop what your doing and take up a different hobby.


    First the fire, then God will speak to you in a soft, beckoning voice.
     
  15. beenthere

    Retired Moderator

    Apr 20, 2004
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    The circuit as posted is not going to work under any circumstances.

    Perhaps the OP can explain what he means by "driving a capacitor", and why there are no fuses present.
     
  16. Adjuster

    Well-Known Member

    Dec 26, 2010
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    Then as far as I can see, the triac will definitely blow up. The problem is due to the phase lead of the current through the capacitor.

    When the gate drive is removed, the triac will turn off at the next capacitor current zero-crossing. The supply voltage will actually be at or near its peak value, so the capacitor will be charged to near peak supply voltage. During the next half-cycle the capacitor voltage will add to the (opposite sign) next voltage peak, bringing the total to about 678V. The triac you mention is 400V maximum blocking, so it will will break down.
     
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  17. beenthere

    Retired Moderator

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    We don't even know if the cap is AC rated.
     
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  18. Adjuster

    Well-Known Member

    Dec 26, 2010
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    Perhaps it's an ordinary polarised electrolytic, with a nice strong can. :eek:
     
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  19. CDRIVE

    Senior Member

    Jul 1, 2008
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    The OP isn't exactly a chatterbox in regards to answering questions. Personally, I think he's a statistic waiting to happen. I also see this thread as more hazardous than most automobile topics that are verboten on AAC.
     
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  20. beenthere

    Retired Moderator

    Apr 20, 2004
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    I would agree about the danger. The questions have been to try to figure out what this is all about and perhaps save the OP from becoming a statistic.

    We'll just close this very shortly unless the OP can say what is it that he is trying to do. A rather complete answer is expected.
     
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