Capacitor Types and Replacements

Is a 20pF electrolytic available now?

Is a 10,000μF polyester available now?

"Horses for courses."

wow, you are familiar with capacitors.

what meaning is horses for courses?

"Horses for courses" -

wouldn't win a race, while

wouldn't plough a field.

Gave you a good one for that... Wangito.

In the long run, over great distance, those plow types would win, they have the heart for the task..

generally speaking, you can. but in some field, you'd better not to do that, they have different attribution. except value and voltage.

for example, loss angle. or loss factor, freq. response etc..

capacitors consist fo two electrodes separated by a gap. That gap filler can be a vacuum, air, various liquids and solids. Each type of filler gives rise to a characteristic type of capacitor.

air capacitor,

vacuum capacitor

mica capacitor, ceramic capacitor

oil capacitor,

paper capacitor,

mylar capacitor

polyester capacitor

virtually any insulating filler will work.

Each filler will have different characteristics, voltage resistance, pinhole absence, degree of polarity, all of which capacitor makers use to meet the circuit designers needs.

electrolytic capacitors can have the plates separated by an electrolyte, in which case they often have a polarity. Electrolytic capacitors can have very high capacitance, but might not be high in voltage or frequency utility. These days they use solid state electrolyte electrolytic capacitors. The wet electrolyte capacitors are rare these days.

when they fail electrytic capacitors can make a bang and a smell.

aluminum electrolytic, tantalum electrolytic and the commonest solid state electrolytic capacitors

do a wiki search on "electrolytic capacitor" +wiki and you get this.

http://en.wikipedia.org/wiki/Electrolytic_capacitor

search on all the others in place of electrolytic and you will get more details

"Horses for courses."

just want to know if its an english proverb?

multilayer ceramic or disc ceramic will normally be good enough as a replacement for paper or polyester (but, check the tolerance and temperature stability if accurate values are needed): disc ceramics will nearly always have a good (low temperature coefficient) insulating layer like COG or NPO.

(For power supply decoupling purposes where multilayer ceramics are now challenging electrolytics, and, accuracy is not so important they often have less stable insulating layers like X5R)

The first part of your question, you answered it yourself... Difference is in the "dialectric material" The other differences are the applications. Each type of dialctric material has different response to different frequencies or capacity to volume ratio... Semi-Solid electrolytics, will work fine from DC to frequencies up to 100kHz while film capacitorswill work fine at higher (audio and up) while vacuum capacitors have extremely low loss values in hi-power hi-frequency hi-voltage applications. there are many types of capacitors and if you are interested go to: http://en.wikipedia.org/wiki/Capacitor_(component)#Fixed_capacitor_comparisons Hope it helps Wangito.

capacitors are constructed specifically on the kind of material for a specific purpose, you can not replace a capacitor with another type even though they have the same capacitance rating and voltage rating.... every material used have their own dielectric strength .... so you can replace one type with another type.... let say a defective an oil capacitor with a rating of 25 micro farad 240 v replaced it with a paper capacitor 25 micro farad 240 v. it cannot be done

Let me try to make both a summation of other people's comments and add a little of my own to attempt a complete answer.

The differentiation of various types of capacitor you listed are because of the insulating material used between the conduction plates. This insulation does give each style of capacitor different secondary characteristics. Frequently these characteristics are of minor importance and thus a polyester capacitor may be successfully substituted with a Mica capacitor. The family of electrolytic capacitors (oil/paper filled and tantalum) have the second highest capacitance for similar volume. These capacitors will typically have a bias preference and require the a specific DC bias direction be maintained to prevent catastrophic failure. The highest capacitance per volume are the ultra capacitors. But both of these families of capacitors have very poor high frequency characteristics. One series of capacitors that does work well at high frequencies are the ceramic and mica capacitor.

Each insulator type of capacitor though has a certain range of capacitance that can be readily fabricated, a 1000pF polyester or ceramic capacitor will be relatively easy to locate but not an electrolytic. Similarly a 100 uF electrolytic will be easy to locate but not a ceramic one. Some capacitors have exceptional parasitic qualities that make them ideal for certain circuits. The low leakage current of a polyester capacitor makes it well suited for the hold capacitor of a peak hold circuit.

A more exhaustive but reasonable capacitor tutorial can be found at http://www.uoguelph.ca/~antoon/gadgets/caps/caps.html - sorry, link no longer available

On power busses (for example) you might find a 220 microfarad electrolytic cap right next to a .1 microfarad ceramic cap. The novice might say "Why bother with the .1 to get 220.1 microfarad?". The 220 uf works fine at low frequencies (say 50 or 60 Hz), but does not work well at high frequencies... so we add the .1 uf to handle the high frequency noise.

One also much watch closely on tolerances. On the .1 uf above, I might use a cap which has +80%/-20% tolerance. For the above application... the more the merrier. In a tuned circuit, this same cap would be a disaster.

With electrolytics and tantalums PLEASE ALWAYS CHECK THE POLARITY!! If these caps are installed backwards, they explode violently and throw crap all over. You might want to consider safety glasses if you value your eyesight. Once or twice over the years, I have seen tubular electrolytics where the manufacturer accidently installed the sleeve over the cap (which has the polarity marks on it) backwards which also goes BOOM!

In active filters, you might change a 1% polystyrene cap with a 1% polyester cap, but I would expect different results over temperature.

In conclusion, in _some cases, you can use a different type of cap, but not generally.

Bill

Sciesis2 wrote, "With electrolytics and tantalums PLEASE ALWAYS CHECK THE POLARITY!! If these caps are installed backwards, they explode violently and throw crap all over". I wholeheartedly agree.

To keep my EE college students on their toes, at the first session of their first Lab course, I would demonstrate this point, usually using a physically small low voltage electrolytic capacitor, say 25 microfarads at 10 VDC, hooked up with reverse polarity to a hefty adjustable DC power supply, capable of putting out, say, 20 amps at up to 50 volts. With the students at the back of the room, I would slowly crank up the voltage, and have a student record the metered V-I values. Not much happens for a volt or two, then the current starts to rise, then it skyrockets as the cap blows - a steam type explosion - as loud as a pistol shot or a "Cherry Bomb / Ash Can / M-80" fire cracker. This dramatically drives home the point that polarity is important with electrolytic capacitors. Interestingly, much larger electrolytics don't blow as loudly, because their cases are usually scored with an "X" scribed into the bottom of the can, which gives way at a much lower internal pressure than that need to rupture an unscored small electrolytic.

Another danger, now mostly obsolete, is the ability of high voltage TV caps (say 5 to 30KV DC) to hold their charge storage for hours or even days, if not equipped with a suitable bleeder resistor. In the 1950's, some early TV sets did not have bleeder resistors, and knocked many a technician for a loop, me included.

Another current danger, which recently killed a power line electrician, concerns exploded high voltage power line capacitors, used to correct power factor on 3 phase "High lines". Lightening hit a 13 KV AC power line in upstate New York, and blew the tops, containing the insulating connecting terminals, right off the caps, which are about the size of a loaf or two of bread. The next day, an electrical crew went out with 3 new caps, to replace the destroyed units on the now deactivated line. A worker climbed the pole and started to unbolt the metallic grounded mounting brackets. He accidentally leaned over and touched one of the torn open caps and a spark jumped to an uninsulated body area. This shocked him off the pole. He was not electrocuted, but the fall killed him. The power was off, the caps were destroyed, so no rubber mats or insulating suits were used, since everything was assumed to be electrically dead. Moral: Big "Dead" Caps can still be deadly.

Thanks for explaination