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Re: resistance of tank circuit

Original poster: Vardan <vardan01@xxxxxxxxxxxxxxxxxxxxxxx>

Hi Daniel,

The "power factor" is normally the SIN of the angular difference between the voltage and current sine waves in a steady state system. A Tesla coil is not very steady state at all so the power factor varies over time and may lack any real meaning.

Pure inductors and capacitors have very low power factors since the voltage and current waveforms are out of phase by 90 degrees (SIN(90) = 0).

The "reactance" might be what you are looking for and that can be calculated from the equations on page 1 here:


At resonance, the reactance of the capacitor and inductor will be the same.

You might also refer to "surge impedance" on page 6. Surge impedance is sort of a measure of resistance of the primary circuit as a whole. That is often used for things.

There is a similar thing here but for dynamic output impedance:


I think programs like Bart's JAVA program calculate these numbers too but the equations are pretty easy to use directly.

Spark gaps typically have an "average resistance" in the 2 to 4 ohm range. That is measured by checking the ring down time of the bare primary system to determine the series resistance.

Maybe this helps, or maybe you could be more specific if not.



At 10:13 PM 4/30/2006, you wrote:
Hello, I am interested in finding the power factor and phase angle of my voltage and current waveforms for my primary coil and tank cap. What is the best way to do this? The inductor has a reactance of 51.7 ohms at 144kHz, and the capacitor has a reactance of 51.5 ohms at 144kHz. How do i find the resistance of my capacitor, inductor, and spark gap? (no multimeter)

Thanks for the help