Capacitor

Discussion in 'General Electronics Chat' started by Lightfire, Oct 13, 2011.

  1. Lightfire

    Thread Starter Well-Known Member

    Oct 5, 2010
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    21
    Hello everybody,

    I found out recently that a capacitor stores electric charge, which is interesting.

    I am wondering how much voltage and current does a 1 microfarad capacitor can store. How about for a 220 microfarad?

    Is there any formula on how to see how much voltage and current does a specific capacitor can charge.

    Thank you very much everybody!
     
  2. ErnieM

    AAC Fanatic!

    Apr 24, 2011
    7,386
    1,605
    Sorry, no formula per say. Real capacitors you can buy all have a voltage rating for the largest voltage you can put on them. It is best never to get too close to that rating, so if say you expect to put 100 volts on a cap buy one rated for 200 volts.

    Same with current, if you are running lots of current all the time thru a cap check if it is rated for that much current.
     
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  3. kubeek

    AAC Fanatic!

    Sep 20, 2005
    4,670
    804
    A capacitor stores energy equal to 0.5*C*V^2 [joules], so a 1uF cap charged to 50V will store 0.5*0.000,001*50*50 J = 0.00125 J
    Energy of one joule is equal to power of 1W produced over 1 second.

    As for current, that is limited only by the cap's internal resistance, reffered to as ESR - equivalent series resistance. If you short it, the initial current will obviously be V/ESR, if you discharge it in a load R, the current will be V/(R+ESR).
     
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  4. Georacer

    Moderator

    Nov 25, 2009
    5,142
    1,266
    There are formulas that describe the capacitor's operation. Check your trusty wikipedia for more info.

    Most notable ones are:
    Capacitance=\frac{Charge}{Voltage}\\<br />
\text{and}<br />
Energy\ Stored=W=\frac12\cdot C \cdot V^2<br />
     
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  5. Lightfire

    Thread Starter Well-Known Member

    Oct 5, 2010
    690
    21
    Thank you very much for your time, ErnieM.

    So, if there is a voltage and current rating, what is farad rating for?

    Thank you everybody and I hope for an answer.
     
  6. crutschow

    Expert

    Mar 14, 2008
    12,993
    3,227
    If you look at the equations, (which apparently you haven't) you will see that the "farad rating" capacitance (C) is how much energy (charge) the capacitor stores.
     
  7. Adjuster

    Well-Known Member

    Dec 26, 2010
    2,147
    300
    More accurately, the capacitance C in farads defines the charge Q in coulombs required to change the potential across the capacitor by one volt. Q = CV, C = Q/V

    Charge in coulombs is the integral of current in amperes over time in seconds, for a constant current this is simply the current multiplied by the time.
     
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