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Capacitance of capacitors

Lactuca

Dec 22, 2017
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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
 
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Lactuca

Dec 22, 2017
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Can you show us an example of such a circuit?
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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Laplace

Apr 4, 2010
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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.
 

(*steve*)

¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
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Jan 21, 2010
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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)
 

Lactuca

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

Ratch

Mar 10, 2013
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I haven't heard about this equations before, Thank you very much:)
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
 
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