how to choose capacitor?

[rinaishlene]

Hi,

Does any one know how to choose right capacitor for example if we want to use 100 uF caps but with what suitable voltage because when we want to buy caps, the supplier would ask "what voltage?"

Rina

[nacho1]

you need to know the maximum voltage across the capacitor in your application .
for example if you put the capacitor in parallel with the voltage source, you choose the voltage capacitor higher than  the voltage source. Vsource=12V -> Vcap=16V
tipical values of voltage are 6.3V, 16V, 50V this are normalized

[ckitov]

And you need to know the maximum current in your application. For example if your power supply is for 1A current it might be nessesery to take 100uF capacitor for higher voltage because they are more powerfull and you will can get hier curr ent from them 

[wessoms]

The important things to consider when buying a capacitor for anpplication are the operating voltage. Rule of thumb is 2X the circuit voltage. Example if the volatage of the circuit is 12V then a 25V or greator capacitor is the choice. Secondary choices are the ESR ( equivalent series resistance which will give you the maximum charge the capacitor can supply) , Q of the capacitor ( Based usually on how it is made and the size ) determines the frequency response which is critical in filtering the signal correctly, price ( usally has a lot to do with the previous) , next would be the physical size ( This has a lot to do with the previous things mentioned ).

But for the most part buy either radial ( leads come out one end ) or axial ( leads come out both ends) electrolytic type if you just wan to filter a power. It sounds like it based on the uF you need. Also note electrolytics usually come in polar / non polar which means that their is a polarity with the voltage being applied. if a DC is going to be applied then polarized is easier to find.

Hope this helps

[freddy]

A rule is that one:
 if ripple is not a problem: 470uF for every Ampere RMS of current
 if ripple is a problem: 1000uF for every Ampere RMS of current

The voltage of the capacitor as to be a little greater of the peak of maximum voltage in the circuit.

If you have 24Vac the voltage that you will find after the bridge is: ((24*1.41)-1.4)=32.5V
therefore a capacitor from 35V it goes well, but if it considers that the 24Vac they could have
also a +10% you would have to take one greater of 35V.

Other rule with the circuit have fast current requeste is: better to put 10 condensers from 100uF that 1 from 1000uF
Smaller capacitor have smaller ESR.

[user112]

look here search for word "derating" and you will find the answer (~2/3Vc)
http://www.eee.strath.ac.uk/~bwwilliams/Book/Chapter%2016old.pdf
http://industrial.rell.com/pdfs/IPG_AN_appguide.pdf

[suresh13]

may i ask, what do you intend to use this capacitor for? all the replies so far have been true. But if we know your application, then we can give you more detail information.

[sphinx]

i agree with the last replier since there are lots of types of capacitors and each for its own purpose so there are many types
to chose from so just to ask about voltage and not type thats to me whats most important to choose the right type as well
in your project, i remember some really old type that u dont see anymore in electronics such as tube capacitors. so 4 important
things to think of is type, size, voltage and temperature, at least thats what i think.

/sphinx

[fokker38cc]

Hello
if you are using caps in a high frequency devices, like filtering switching power supply, you must use caps with low internal resistance and low parasitic inductance.
These are special types, and the temperature stamped outside in these caps is 105 degrees Centigrades.
If you use standard caps in this application, the books say it becomes hot and may explode.
See you later
Jose