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Calculating capacitive reactance 
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#1
Feb713, 05:39 AM

P: 4

Hi,
Apologies if this has been posted/answered else where but I could not find it. I am trying to develop a model in matlab for a simple (short cylindrical coil) air cored transformer. So far I am capable of defining the coil such as core diameter, turns, length etc.., calculate the coil resistance, input current, magnetic field produced, flux density at a given distance along the central axis, and potential emf for the secondary coil. The next thing I need to work out is the impedance Z. Z = sqrt(R^2 + X^2) where X = XL  XC I can calculate XL because I have found an equation to work out the inductance of the coil, L. L = (r^2 * N^2)/(9r + 10l) *from the wiki inductor page so XL = 2πfL. I run in to problems with capacitive reactance XC. I cannot find anywhere online explaining how to work out the capacitance of a coil so I can calculate the capacitive reactance XC. XC = 1/(2πFC) Does anyone here know how to calculate the capacitance of a coil, or even if my understanding is completely off? 


#2
Feb713, 06:49 AM

Sci Advisor
PF Gold
P: 3,679

Here's a fellow experimenter who gives a formula for selfresonant frequency, and some references:
http://www.pupman.com/listarchives/1.../msg00227.html maybe you could back into capacitance... 


#3
Feb1313, 11:05 AM

P: 4

Thanks for a reply, its been useful, but seems to be for coils greater in length than I am dealing with. I tried using the suggestions anyway but they maths doesnt seem very dependable. I think I am best off just measuring it from a physical coil, then compare it back to the maths.



#4
Feb1313, 04:42 PM

Sci Advisor
Thanks
PF Gold
P: 12,182

Calculating capacitive reactance



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