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Explain these differences in caps, please

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Kris01

New Member
Are there any "real" differences in using ceramic, mica, polypropylene, electrolytic, tantalum, or any other types of capacitors? I mean, when would I choose one over the other?
 

Sceadwian

Banned
This thread will turn into a storm of responses, all different, many contradictory. The differences between types are vast and the experience of people that use them are even greater. I'm sure there is plenty of information available on the Internet already that you could look up as well as the many threads here that describe what the typical usages are.

A basic statement can be made in that the pros and cons of a capacitor type can not be discussed unless you have a specific use in mind. There is no one perfect capacitor type and in any given situation multiple types could be used with equal success.
 

carbonzit

Active Member
The one major difference between types that ought to be pointed out is between electrolytics and the other types you listed. Electrolytics are a "special" case: for one thing, unlike other types, they're polarized (they have a positive and negative terminal). They are also generally used for higher values of capacitance than other types.

Other than this, yes, it's a broad topic that merits research on your own time. It'll be time well spent if you're truly interested in electronics.
 

audioguru

Well-Known Member
Most Helpful Member
I worked for a Japanese PRO audio manufacturer. Most coupling capacitors in their very high quality amplifiers were non-polarized electrolytic.
Thousands of high power amplifiers were sold and there was not a single failure.

I was asked to test an American Name-Brand amplifier at its full rated output power. It smoked then failed after a couple of minutes. Our amplifiers never smoked after running continuously at full power for weeks.
 

stk2008

New Member
I fixed my LCD TV and had to replace the blown ones with Electrolytic caps.

I read its because they can safely run hotter.
 

crutschow

Well-Known Member
Most Helpful Member
I fixed my LCD TV and had to replace the blown ones with Electrolytic caps.

I read its because they can safely run hotter.
That's not true in general. Ceramic caps have a higher temp rating than electrolytics, for example.

The main reason to use an electrolytic is that they are smaller for a given capacitance.
 

stk2008

New Member
Oh hehe ok.

I dont pretend to know much about electrics this is what I was told when I rang up a tv repair company.
Though they where still unwilling to sell me the caps I needed.

I found them on the bay any ways and soldered all 8 in and the tv works fine.

But for some one like me electronics is so fascinating but damn is it complex.
I want to get into it and have purchased a second hand scope.

I have been looking at the Arduino kits they look fantastic.
 

Sceadwian

Banned
That is not true stk2008. Electrolytics will dry out at increased temperatures.
 

Kris01

New Member
The reason why I ask is that I've seen in some circuit diagrams the author specifies tantalum caps (or whatever). As far as I can tell, as long as the Farad capacity is the same and the voltage rating isn't exceeded, then what does it matter what you use? However, I am a novice.
 

Sceadwian

Banned
It matters with stability with temperature, ripple handling ability leakage current inductance and more. Look up each of the different types on their Wikipedia entries it'll become clearer. Wikipedia will give you far more information than you'll get from the posts here and far more references to other sources to understand the why. But it DOES matter.
 

RCinFLA

Well-Known Member
A lot of switching power supplies in many products are running at ripple current exceeding the specs on the electrolytics. The spec for rms ripple current is based on the internal equivalent resistance of the electrolytic caps and running them with too much ripple current causes greater heating within the cap.

One thing you will find in many products is two or three caps put in parallel for the switching supply filter cap. This helps to reduce the heating and allows for better heat dissipation.

Common sign of electrolytics going bad are 'dome' tops where the heat causes excessive pressure build up. The aluminum electrolytics actually have creases in the tops to allow them to split open in the extreme, allowing a more graceful failure venting.

Large 'computer grade' electrolytics have a rubber plug for vent failure relief.
 
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KeepItSimpleStupid

Well-Known Member
Most Helpful Member
Kris:

In some designs you may find a tantalum electrolytic paralled with a ceramic and possible paralleled with a metalized polyester. It's done that way for various reasons, but briefly a capacitor may have a model where there is a lead inductance, series resistance, parallel resistance and an ideal capacitance. Those parameters and their tolerences change with things such as temperature, frequency etc. An electrolytic cap used in a switching power supply is going to different than one used for a line operated power supply. If the latter is used in a switching supply, it may heat up and fail. Tantalum electrolytics do not tolerate overvoltages well at all, but they have an extremely low ESR (Effective Series resistance) and have a large capacitance density. Generally you cannot make electrolytics with say a 1% tolerance. Not all capacitors can be made with the same capacitance or voltage tolerance.

Metalized Polyester is a good compromise for coupling caps on the order of 1 uf or less. Electrolytics are used in the cheap stuff. More exotic capacitor types are used by purist audiophiles. Those will generally be used in instances where tolerances matter such as frequency filters.

Decoupling is where you'll find multiple types. These caps are located very close to the power supply pins of a device. a logic gate draws a brief pulse of power when it switches and an electrolytic won't respond fast enough no matter where it is (at the power pin or 6" away). Ceramics have been used in this application.

Microwave circuits will use surface mount devices because the lead resistance gets in the way. An Electrolytic would be totally inapproprite in this application.

There are variables such as cost, lifetime, reliabilty and appropriateness for the technology.
 

stk2008

New Member
I'm still as confused as ever but I'm still learning! Thanks for the responses guys.

You're not the only one mate these lot make electronics look so easy with all there fancy schematics and numbers :p.

Any way this is a great community and I have all ready learn so much from them.

Thanks
 
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