# Relation between size of a capacitor and its capacitance

#### Mohamed Bouakoura

Joined Aug 26, 2015
6
Hello everyone,

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

#### Attachments

• 73.4 KB Views: 21

#### ISB123

Joined May 21, 2014
1,236
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.

#### tjohnson

Joined Dec 23, 2014
611
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:

#### alfacliff

Joined Dec 13, 2013
2,458
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.

#### Mohamed Bouakoura

Joined Aug 26, 2015
6
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.
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 ?

#### ISB123

Joined May 21, 2014
1,236
Breakdown voltage is determined by K value of dielectric,distance between the plates and thickness of dielectric.

#### Mohamed Bouakoura

Joined Aug 26, 2015
6
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) ?

#### MikeML

Joined Oct 2, 2009
5,444
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.

#### #12

Joined Nov 30, 2010
18,224
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.

#### alfacliff

Joined Dec 13, 2013
2,458
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) ?

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.

#### AnalogKid

Joined Aug 1, 2013
11,055
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

#### alfacliff

Joined Dec 13, 2013
2,458
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.

#### cmartinez

Joined Jan 17, 2007
8,257
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.
I've noticed that too... but I wonder if the newer designs last as long as the older ones.

#### gerty

Joined Aug 30, 2007
1,305
Sometimes it's all just an illusion anyways....

#### Attachments

• 69.3 KB Views: 22

#### cmartinez

Joined Jan 17, 2007
8,257
Sometimes it's all just an illusion anyways....
Wow! that's unbelievable!... made in China?

#### nsaspook

Joined Aug 27, 2009
13,305
Sometimes it's all just an illusion anyways....
At least the used a quality 'fake' inside but then it might have a 'fake' inside it.

#### ISB123

Joined May 21, 2014
1,236
Its fake Rubycon cap guys.

#### gerty

Joined Aug 30, 2007
1,305
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..

#### AnalogKid

Joined Aug 1, 2013
11,055
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.
All true, but I'm not sure what your point is.

ak

#### alfacliff

Joined Dec 13, 2013
2,458
my point is that the size of the cap (as in the origional post) dosnt really determine its ratings.