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Re: MMC



Original poster: "Daniel Giv'r" <transworldsnowboarding19@xxxxxxxxxxx>


Hey, I have decided to switch from a saltwater capacitor to a MMC. I am planning on getting either a 15KV 30mA transformer and i dont really know how to calculate it. I have tried many online calulators but i dont know what would be the best type.... should I go with hundreds of caps with very small capacitance or a couple with larger capacitance? I am on a fairly small budget ($20-25) for just the caps. please E-mail back with some info it would be of immense help, Thanks a lot
Daniel from Canada


From: "Tesla list" <tesla@xxxxxxxxxx>
To: tesla@xxxxxxxxxx
Subject: Re: AC Resistance of wires - was 8 kHz Tesla Coil
Date: Sun, 02 Oct 2005 22:34:22 -0600

Original poster: "Gerry  Reynolds" <gerryreynolds@xxxxxxxxxxxxx>

Hi Antonio,

Your formula is the same as the one I originally quoted but reduced somewhat. ie:

Rac/Rdc = pi*wr^2/ (pi*wr^2 - pi*[wr-sd]^2) = (wr/sd)^2 / (2wr/sd - 1)

The equation for sd that the web site gave seems to predict a little larger sd than what JAVATC calculated. If this also predicts a little larger sd than what you used, then that would bring the positive errors down some. This approach seems fine to me, but some want something more accurate and doing interpolation on a table lookup is also fine with me. Once the program adds the routine, we dont have to worry about it anymore :-)))

Gerry R.


Original poster: "Antonio Carlos M. de Queiroz" <acmdq@xxxxxxxxxx>

Tesla list wrote:

Original poster: "Gerry Reynolds" <gerryreynolds@xxxxxxxxxxxxx>

The work that Dr Gary Johnson did for AC resistance seems to solve the Rac/Rdc problem for round wires (no proximitry effects).
>...
The following table shows
this for wr/sd up to 8.
wr/sd      Rac/Rdc
------------------
  1            1.020
  2            1.263
  3            1.763
  4            2.261
  5            2.743
  6            3.221
  7            3.693
  8            4.154

A simpler calculation, assuming that all the current is concentrated in a ring with thickness equal to the skin depth and external radius equal to the wire radius, results in: Rac/Rdc = (wr/sd)^2/(2wr/sd-1) The table above becomes: wr/sd Rac/Rdc difference 1 1.000 -2.0% 2 1.333 +5.5% 3 1.800 +2.1% 4 2.286 +1.1% 5 2.778 +1.3% 6 3.273 +1.6% 7 3.769 +2.1% 8 4.267 +2.7% The error is negligible in comparison with the more exact formula. So, the basic skin depth formula can be used with round conductors quite well.

Antonio Carlos M. de Queiroz






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