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RE: Calculating and Measuring Resonant Frequency / Inductance of Secondary Coil (magnifier)
Original poster: "Bart Anderson" <classi6-at-classictesla-dot-com>
Hi Dan,
Good point and true. I performed my setup by making all 3 coils the
same. I started measurements last night. There are some interesting
scenario's with magnifiers, and especially in my little situation. For
example, although all 3 are at 180kHz on my own, with the extra coil
over the driver, when the base is driven I'm meausuring 142 kHz (i.e.,
2 coils in series and a single topload affecting both). That kind of
thing. Fun stuff! I'll post details once I have them.
Take care,
Bart
> Original poster: "Mccauley, Daniel H" <daniel.h.mccauley-at-lmco-dot-com>
>
>
>
> Thanks Bart.
> However, the primary coil doesn't have to be at the resonant
frequency of
> the secondary coil.
> The primary coil should more closely match the tertiary coil's
resonant
> frequency.
> But thanks for the calculations. I'm getting closer to finding out
the
> discrepancy.
>
> Because the frequency difference is a factor of 2, this turns out to
be
> only a 25% difference in
> self-capacitance, which could be a possibility. Both the tesla cad
> programs and my impedance plot
> show about 9mH inductance, so perhaps it is the self-capacitance
which is
> the culprit.
>
> Dan
>
>
> > 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
> > >
> > >
> > >
> > >
> >
> >
> >
> >
>
>
>
>
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