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08-13-2011, 10:40 AM
 gyula Silver Member Join Date: Apr 2007 Posts: 817
Quote:
 Originally Posted by drak Xenomorph, I don't understand reactance that well myself, but accordingly somehow you can lower the frequency with resistors using the reactance chart. I won't be doing it this way though, but would love to have a basic course on exactly how reactance works. in the smith pdf it says Suppose that your neon-tube driver is running at 30 kHz and you are using a capacitor of 100 nF (which is the same as 0.1 microfarad) and you want to know what is the AC resistance of your capacitor is at that frequency. Also, what coil inductance would have that same AC resistance. I don't understand that at all, i was just going to work around it by charging a cap bank then pulsing it at 60 hz into a basic transformer. Unless someone can recoomend a reactance for dummies book that i can read.
Hi Drak,

Perhaps you are confused by the incorrect usage of the word resistance by Don Smith in the above quote? Because he should have used the word reactance instead of resistance, ok?
We normally talk about AC reactance in case of capacitors or coils, saying a capacitor has a capacitive reactance or a coil has an inductive reactance, and reactance also has a dimension of OHM like a normal resistance.
The nomograms also show these in Ohms, for capacitors the reactance formula Xc=1/(2*Pi*f*C) or for coils XL=2*Pi*f*L where f is the AC frequency in Hertz, C is the value of the cap in Farad and L is the coil inductance in Henry. Using these you get the reactance in Ohm, and the nomograms used these formulas.
(You can see from the formulas that a given value capacitor has an decreasing reactance value when you increase frequency and coils behave just on the contrary: they have an increasing reactance when you increase frequency.

rgds, Gyula
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