Relation between size of a capacitor and its capacitance

Discussion in 'General Electronics Chat' started by Mohamed Bouakoura, Aug 26, 2015.

  1. Mohamed Bouakoura

    Thread Starter New Member

    Aug 26, 2015
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    Hello everyone,

    a simple question, why a bigger capacitor have less capacitance and more voltage than a small one ? , check the picture below :

    thanks for your answers in advance.
     
  2. ISB123

    Well-Known Member

    May 21, 2014
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    Size of capacitor is determined by its breakdown voltage and capacitance.Only reason for capacitor on right side to be bigger is because it has higher breakdown voltage.
     
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  3. tjohnson

    Active Member

    Dec 23, 2014
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    I've observed through experience that the voltage rating of an electrolytic capacitor has more effect on its size than its capacitance. For example, I have a 1000μF 10V capacitor which is less than half the size of a 470μF 35V capacitor that I have.
     
    Last edited: Aug 26, 2015
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  4. alfacliff

    Well-Known Member

    Dec 13, 2013
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    the size of a capacitor, if the capacitance , and voltage are thge same is determined by the dielectric constant of the diaelectric. for a high "k" factor dielectric, the size is smaller.
     
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  5. Mohamed Bouakoura

    Thread Starter New Member

    Aug 26, 2015
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    indeed the bigger the capacitor the more voltage it can support, but why the bigger capacitor has less capacitance ? ...
    In my opinion, in the bigger one we use more dielectric matter so the breakdown voltage would be greater and obviously the capacitance smaller , is this correct ?
     
  6. ISB123

    Well-Known Member

    May 21, 2014
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    Breakdown voltage is determined by K value of dielectric,distance between the plates and thickness of dielectric.
     
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  7. Mohamed Bouakoura

    Thread Starter New Member

    Aug 26, 2015
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    the bigger capacitor(420v 120µF) is defective, and i can't find a similar one to replace it, so can i use 8 small capacitors of (16v 1000µF) ?
     
  8. MikeML

    AAC Fanatic!

    Oct 2, 2009
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    Study this formula. With a bit of work, you should be able to derive a formula for the volume of a capacitor once you understand the link.
     
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  9. #12

    Expert

    Nov 30, 2010
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    Major advances in thin film technology have made capacitors smaller over the years. At this point in time, a 30 year old aluminum electrolytic capacitor can always be replaced with a smaller size that has the same electrical qualities.
     
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  10. alfacliff

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    Dec 13, 2013
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    absolutly not! the voltage must be equal or greater in the cap you are using to replace the bd one.otherwise there will be either an explosion, or something equally bad. series connecting capacitors must use eqqualising resistors in paralell with each cap to equalise the voltage.
     
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  11. AnalogKid

    Distinguished Member

    Aug 1, 2013
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    Within any capacitor construction type (aluminum electrolytic, ceramic, film, etc.), the total energy stored per unit of volume is approximately constant. However, the total energy in a capacitor is 1/2cV^2 -- 1/2 times the capacitance times the square of the voltage. So if one capacitor has twice the voltage rating of another (with the came capacitance), it has to be 4 times the volume.

    ak
     
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  12. alfacliff

    Well-Known Member

    Dec 13, 2013
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    the dielectric constant is also in the formula, thats why tantalum caps are smaller than electrolytics of the same ratings. and how large would a ceramic of the same rating be? or a vacuum cap, or an air cap? or an oil filled cap? a 1000 mfd ceramic cap would be huge compared to an electrolytic, at the same voltage rating. different caps have different charistics for different uses. you wouldnt use an electrolytic at rf would you? ceramic, mica, vaccuum, and such are what to ue at rf.
     
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  13. cmartinez

    AAC Fanatic!

    Jan 17, 2007
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    I've noticed that too... but I wonder if the newer designs last as long as the older ones.
     
  14. gerty

    AAC Fanatic!

    Aug 30, 2007
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    Sometimes it's all just an illusion anyways....
     
  15. cmartinez

    AAC Fanatic!

    Jan 17, 2007
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    Wow! that's unbelievable!... made in China?
     
  16. nsaspook

    AAC Fanatic!

    Aug 27, 2009
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    At least the used a quality 'fake' inside but then it might have a 'fake' inside it.
     
  17. ISB123

    Well-Known Member

    May 21, 2014
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    Its fake Rubycon cap guys:D.
     
  18. gerty

    AAC Fanatic!

    Aug 30, 2007
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    Not sure of it's origin, picture from an article on bad/counterfeit caps I read several years ago. I saved the picture to show my students..
     
  19. AnalogKid

    Distinguished Member

    Aug 1, 2013
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    All true, but I'm not sure what your point is.

    ak
     
  20. alfacliff

    Well-Known Member

    Dec 13, 2013
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    my point is that the size of the cap (as in the origional post) dosnt really determine its ratings.
     
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