Difference between polarized and non polarized capacitors

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Discussion Overview

The discussion centers around the differences between polarized and non-polarized capacitors, exploring their construction, applications, and reasons for the existence of both types. Participants delve into technical aspects, manufacturing challenges, and cost considerations.

Discussion Character

  • Technical explanation
  • Debate/contested

Main Points Raised

  • Some participants note that non-polarized capacitors are harder to manufacture at small sizes compared to their capacitance, leading to larger physical sizes and higher costs for higher capacitance.
  • Others argue that polarized capacitors allow for smaller sizes and higher capacitance, but they come with the limitation of being polarized, which can restrict their use in certain applications.
  • One participant mentions that electrolytic capacitors provide a way to achieve high capacitance in a compact form but are polarized and have a finite lifespan.
  • Another participant explains that electrolytic capacitors can be connected back-to-back to create a non-polarized version, although this approach significantly increases the cost.
  • A technical explanation is provided regarding the manufacturing of electrolytic capacitors, highlighting the importance of surface area and dielectric thickness in achieving high capacitance.

Areas of Agreement / Disagreement

Participants express differing views on the advantages and disadvantages of polarized versus non-polarized capacitors, indicating that multiple competing perspectives remain without a clear consensus.

Contextual Notes

Limitations include the dependence on specific applications and requirements for capacitor types, as well as unresolved discussions on cost implications and performance characteristics.

hisham.i
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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
 
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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.
 
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.
 
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
 
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