Re: Optimal toroid elevation

• To: tesla-at-pupman-dot-com
• Subject: Re: Optimal toroid elevation
• From: "Malcolm Watts" <malcolm.watts-at-wnp.ac.nz> (by way of Terry Fritz <twftesla-at-uswest-dot-net>)
• Date: Sun, 28 May 2000 20:24:24 -0600
• Approved: twftesla-at-uswest-dot-net
• Delivered-To: fixup-tesla-at-pupman-dot-com-at-fixme

Hi all,
          You might care to take this with a grain of salt right now but I 
have something for you all to consider when determining terminal 
capacitances:

On 26 May 00, at 6:29, Tesla List wrote:

> Original Poster: "Barton B. Anderson" <tesla123-at-pacbell-dot-net> 
> 
> Jeff & Marco, 
> 
> I just measured this, and it is definately large enough to be significant.
> However, as Marco pointed out, if the toroids out of reach, then it's out of
> reach (definately stick with the primary). 
> 
> Here were the results of my test. The winding dimensions are 12.5" x 44.5",
> 18awg, 
> CS=21.6pF, Ls=87.6mH. 
> 
> Ctop = 34" x 7.4" and calcs to 36.9pF (70.3kHz) 
> 
> Test #1: 
> Toroid at top plane of secondary. Measured 86.2kHz. 
> Ctop then calcs to 17.2pF (53% error from original calc). 
>   
> 
> Test #2: 
> Toroid raised 22" up. Measured 75.7kHz. 
> Ctop then calcs to 28.2pF (23.5% error from original calc). 
> 
> This test also held true for a 16" sphere. Of course, capacity's were
different
> but the results were the same (11pF gain in Ctop is significant). Jeff,
did you
> model this with E-Tesla5? I took E-Tesla5 to work today to run on a faster pc
> and ran the setup mentioned above (true measured values were input into the
> program). The program showed 76kHz for Test #1 (but this is not what I
> measured). I need to rerun E-Tesla5 for Test #2 as I put in the wrong toroid
> height. I have a feeling it is going to be near 73kHz. I'll post this result
> tomorrow. 

It is worth bearing in mind that using Medhurst's C and measured 
frequency with added top hats is not going to give the correct 
answer for Ctop (or Ctot) since Medhurst's C is not the intrinsic C 
for the coil. I have a preliminary indication that adding a top hat 
might well add more capacitance than is currently inferred from the 
frequency measurements. Later today I will do a measurement on 
my work coil (which clocks in at 67pF-odd intrinsic C vs Medhurst's 
19.? pF and post the comparative results with and without the 
topload I am presently using.

Regards,
Malcolm

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