Xc calcs

Discussion in 'Math' started by roadey_carl, Sep 14, 2010.

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  1. roadey_carl

    Thread Starter Active Member

    Jun 5, 2009
    116
    5
    Hi folks.

    Im sure this is a easy one for you but Im struggling.
    I want to work out what capacitor to use as a series capacitive reactance.
    I know 1/ 2.∏.F.C = Xc. what calculation do I do if I have resistance but want to calculate what capacitor to use?

    Thanks very much

    Carl
     
  2. Ghar

    Active Member

    Mar 8, 2010
    655
    73
    I have no idea what you're asking.

    What resistance? What are you trying to do?
     
  3. Papabravo

    Expert

    Feb 24, 2006
    10,340
    1,850
    A complex impedance has two parts. The real part is the resistance and is plotted along the horizontal axis. Capacitative reactance is plotted along the neagative imaginary axis aka the jω-axis. The complex impedance is:

    R - jXc

    Code ( (Unknown Language)):
    1.  
    2. The magnitude of the complex impedance is
    3.  ___________
    4. √R^2 + Xc^2
    5.  
    6. and the angle is arctan(-Xc/R)
    7.  
    Does that help?
     
  4. roadey_carl

    Thread Starter Active Member

    Jun 5, 2009
    116
    5
    well what im trying to do is get a 12v fan working on 230v supply but using a capacitor in series with a bridge rectifirer to do this.

    Supply = 230vac
    Load = 12v @ 0.11mA.

    so... 230-12 = 218v.

    218/0.11 = 1982Ω

    218x0.11 = 24watts.

    so I know I need a resistor thats 2k @ 24 watts to do this.
    But how can I do the calculation to give me the answer in capacitance... so I know what capacitor to use to do this?
     
  5. bertus

    Administrator

    Apr 5, 2008
    15,806
    2,389
    Hello,

    Sorry, we do not allow circuits directly connected to the mains.
    Please use a small powersupply for the fan.

    Bertus
     
    roadey_carl likes this.
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