Difference between polarized and non polarized capacitors

[hisham.i]

Hello,

I googled the difference between polarized and non polarized capacitors and all i found was differences in construction and the material that they are formed from.

I want to know why there is 2 types of capacitors, what are the differences (cost, technical, etc), why there is not only non polarized?

thanks

 

[Runei]

Non-polarized capacitors (the ones we learn about in physics at first), at hard to manufacture at a small size compared to their capacitance (they become very big if we want a big capacitance). Also, they can be quite expensive when they become bigger.

Polarized capacitors give us a way to manufacture smaller capacitors, but with a high capacitance. The drawback however, is that they are polarized.

Some places with high requirements, it is not allowed to use polarized capacitors.

 

[NascentOxygen]

Electrolytic capacitors are a way to manufacture a high capacitance relatively cheaply and in a small sized package. They are definitely a compromise, and have a finite life.

You can connect two electrolytic capacitors back-to-back (electrically) so as to form a non-polarized electrolytic capacitor. Obviously, it will be about 4 times the cost of a single polarized capacitor giving the same capacitance.

 

[jim hardy]

The answer to your question is:
Electrolytic capacitors pack thousands of times more capacitance into a given volume than you can get with film dielectric types.
But - electrolytic capacitors are necessarily polarized because of how they're made..

capacitance= area / distance.

Area is the area of the foil

Etching an aluminum foil gives it more surface area per square inch. The microscopic hills and valleys have more surface area than would a mirror flat sheet. Remember the old saying "Colorado would be bigger than Texas if you ironed it flat" ?
Etching gives a large [STRIKE]denominator [/STRIKE] NUMERATOR (golly I'm doing everything backward today !)
Distance is the thickness of the dielectric.

In electrolytics the dielectric is not a plastic or paper film but a thin layer of aluminum oxide on one the aluminum sheets. It's only a few atoms thick so you have a very small denominator.
This little paper by Cornell-Dubelier explains it well.

http://electrochem.cwru.edu/encycl/misc/c04-appguide.pdf

old jim