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Capacitance of capacitors

Discussion in 'Electronics Homework Help' started by Lactuca, Dec 22, 2017.

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  1. Lactuca

    Lactuca

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    Dec 22, 2017
    Good afternoon, Could you please help me? I need to solve one problem with capacitors . Is it possible to use some transformation ( similar to delta- star for resistors) for capacitors? (to calculate final capacitance, when it is not possible to use basic equations for series or parallel circuits) thank you
     
    Last edited by a moderator: Dec 22, 2017
  2. Harald Kapp

    Harald Kapp Moderator Moderator

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    Nov 17, 2011
    Can you show us an example of such a circuit?
     
  3. Lactuca

    Lactuca

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    Dec 22, 2017
    In my opinion, there I am not able to use this equations, because capacitors which looks like to be parallel are not exactly in parallel circuit.. but I am not sure..
     

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  4. Laplace

    Laplace

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    Apr 4, 2010
    I believe this circuit calls for using the same sort of analysis technique as would be used for an unbalanced resistance bridge, only here it is more like an unbalanced reactance bridge. Ground one end of the network, and apply a voltage source to the other. This circuit has 4 nodes in addition to the input & output (source & GND) nodes. Write 4 node equations using capacitive reactance Xc instead of resistance R. Xc = 1/(jωC) but since all currents will be capacitive in this circuit, it seems like it should not be necessary to carry through the 'j' in all calculations. And since the capacitance will not change as a function of frequency, select a value for ω that is most simple (ω=1?). Solve for the node voltages, find the total source current, and from that the equivalent reactance & equivalent capacitance.
     
    Harald Kapp likes this.
  5. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Jan 21, 2010
    Yeah, when looking at it I considered that all the capacitors could be replaced with reactances an solved as if it were a network of resistors. After reading Laplace's reply it seems that is what he suggested (in a far more detailed manner)
     
  6. Lactuca

    Lactuca

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    Dec 22, 2017
    I haven't heard about this equations before, Thank you very much:)
     
  7. Ratch

    Ratch

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    Mar 10, 2013
    The circuit has 4 nodes and 5 loops. You can use either loop or node analysis to find the voltages, currents, and the impedance of the circuit. You will have to solve 4 or 5 equations for 4 or 5 unknowns. Once you know the impedance, you can find the resultant capacitance.

    Later edit: Looks to me like you could simply the circuit directly by using wye-delta transformations.

    Ratch
     
    Last edited: Dec 23, 2017
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