# Re: Electrum output impedance (fwd)

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---------- Forwarded message ----------
Date: Sun, 12 Jul 1998 01:26:43 -0500
From: "Barton B. Anderson" <mopar-at-uswest-dot-net>
To: Tesla List <tesla-at-pupman-dot-com>
Subject: Re: Electrum output impedance (fwd)

Terry,
Your right <again>. ~1.55M is true in each scope pic. Can you emphasize more on
your reasoning of the voltage dropping to ~1/2 of 1.55M? BTW, I really like your
terminology for the TC " Load Match Piont" as "Tesla Point". I feel this phrase
has been properly assigned. So it is written... so it is done...
Bart

Tesla List wrote:

> ---------- Forwarded message ----------
> Date: Sat, 11 Jul 1998 14:30:41 -0600
> From: terryf-at-verinet-dot-com
> To: tesla-at-pupman-dot-com
> Subject: Electrum output impedance
>
> Hi Greg Leyh and All,
>
>         I was studying the scope photos of the Electrum at:
>
> http://www.lod-dot-org/electrum/electrumspecs.html
>
>         In another post (TC Output Impedance Matching) I propose that the
> "Load Match Point" in a Tesla coil occurs when the load on the coil is equal
> to the following equation:
>
> Rl = 2 * pi * SQRT ( Ls / Cs )  =  195k ohms
>
> For the Electrum:
>
>         Ls = 0.130 H
>         Cs = 135 pF
>         Xls = 31K ohms (the reactance of the secondary at 38kHz)
>
> So the Load Match Point (or Tesla point) calculates out to 195k ohms.
>
> By knowing the current to the sphere, the frequency, and the inductance of
> the secondary, the voltage at the top terminal can be calculated as 1.55
> million volts in the 100, 20, and 10 uS pictures.  By dividing the output
> voltage by the sphere to arc current, the arc impedance can be estimated as
> follows:
>
> In all cases the 50 amps in the secondary multiplied be the reactance of 31K
> ohms gives an output voltage of about 1.55M volts.
>
> 100uS           Io = 15A        Zarc = 103k ohms
>
> 20uS            Io = 5A         Zarc = 310k ohms
>
> 10uS            Io = 8A         Zarc = 194K ohms
>
>         You will notice that these numbers average out very close to the
> calculated value of 195k ohms.  I suspect that the arc may begin at the
> 1.55M volt level but the voltage quickly reduces to ~750k volts and matches
> the arc impedance.  I don't know if the coil finds this point naturally or
> if the Electrum was designed to operate this way.  The close match of the
> Electrum to these calculated numbers is obviously very interesting!
>
> All the best,
>
>         Terry Fritz

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