Re: Calculating and Measuring Resonant Frequency / Inductance of Secondary Coil (magnifier)

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: Bart Anderson <classi6-at-classictesla-dot-com> 

Hi Dan,

I ran your specs from your page in Javatc. I'll pop in the inputs I used 
and show the outputs below. The 606kHz your showing is about double what it 
should show. I showed 312 kHz on the driver. The primary is down around 178 
kHz at 7 turns, so you'll have to tap somewhere around 3.5. turns. 
Something else to note: k at 7 turns is at 0.361 which looks pretty good! 
But, once you tap to resonance, k will drop to 0.288 (so you will probably 
end up raising the primary). BTW, maximum coupling on the system (as is) 
would be 0.466 (when the primary is centered in the middle of the secondary).

Take care,
Bart
PS: Thanks for putting up your maggy page!

Units = inches
----------------------------------------------------
Surrounding Inputs:
100 = Ground Plane Radius
100 = Wall Radius
150 = Wall Height
100 = Ceiling Radius
150 = Ceiling Height
----------------------------------------------------
Secondary Coil Inputs:
Current Profile = G.PROFILE_LINEAR
8 = Radius 1
8 = Radius 2
5 = Height 1
29 = Height 2
216 = Turns
14 = Wire Awg
----------------------------------------------------
Primary Coil Inputs:
11.75 = Radius 1
11.75 = Radius 2
5 = Height 1
10.5 = Height 2
7 = Turns
0.5 = Wire Diameter
0.0185 = Primary Cap (uF)
0 = Desired Coupling (k)
----------------------------------------------------
Top Load Object Inputs (dimensions & topload or ground connection):

Toroid #1: minor=2, major=20, height=31, topload
Disc #1: inside=0, outside=16, height=31, topload
----------------------------------------------------
Secondary Outputs:
311.87 [kHz] = Secondary Resonant Frequency
90 [deg°] = Angle of Secondary
9 = Turns Per inch
1.5 = H/D Aspect Ratio
2.29 [ohms] = DC Resistance
16157 [ohms] = Reactance at Resonance
8.245 [mH] = Les-Effective Series Inductance
9.577 [mH] = Ldc-Low Frequency Inductance
31.585 [pF] = Ces-Effective Shunt Capacitance
70.614 [pF] = Cdc-Low Frequency Capacitance
----------------------------------------------------
Primary Outputs:
178.23 [kHz] = Primary Resonant Frequency
90 [deg°] = Angle of Primary
0.286 [inch] = Average spacing between turns (edge to edge)
3.75 [inch] = Primary to Secondary Clearance
43.102 [uH] = Ldc-Low Frequency Inductance
231.63 [uH] = Lm-Mutual Inductance
0.361 [k] = Coupling Coefficient
2.77 = Number of half cycles for energy transfer at K
7.12 [uS] = Time for total energy transfer (ideal quench time)


Tesla list wrote:

>Original poster: dhmccauley-at-spacecatlighting-dot-com
>In the midst of my magnifier design, I came up with a discrepancy.
>
>Secondary Coil Specifications:
>Coilform Diameter:  16"
>Wire Gauge:  14 AWG (0.064" wire diameter)
>Turns per Inch:  9T (based on my finished magnifier)
>Winding Length:  24"
>
>When I calculate the inductance and resonant frequency of my secondary coil
>(in magnifier coil) using either calculations, or TeslaCad, or WinTesla, I
>get the following
>numbers:
>
>Inductance:  9.76mH
>Fres:  365kHz
>****************************************************************************
>*
>Now, when I measure this secondary coil using an Impedance Analyzer, I get
>the following:
>
>Plot of Impedance vs. Frequency
>http://www.easternvoltageresearch-dot-com/images/mag1_sec_response.jpg
>(Note:  Top vertical line of graph is 14mH and each vertical division is
>2mH)
>
> >From graph, the flat portion of impedance curve is about 9.5mH which
>corresponds to what I calculate.
>However, when impedance is minimum (-2mH), the frequency is about 606kHz.
>I'm using this minimum impedance point as
>where the resonant frequency occurs.
>
>These frequencies don't match one another, yet I would expect them to.  Am I
>missing or doing something incorrectly here?
>(The secondary coil was placed directly across the two probes of the
>impedance analyzer when measuring.)
>
>Thanks
>Dan
>
>
>
>