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Re: [TCML] Re: Re: Spark models, revisited



This thread is really interesting. Would be nice, to have a formula for spark capacitance, relevant for TC's. Antonio's appoach seems very convincing, because it only relies on basic physics law's and the model of a transmission line. May be, the transmission-line model can be questioned for this case. On the other hand, the formulas given in Wikipedia http://en.wikipedia.org/wiki/Capacitance seem well established. I see kind of a dilemma.

On the other hand, in trying to measure secondary resonance frequencies, including toroid & sparks, thin wires, attached to the toroid were used, simulating the sparks. If I'm not wrong, none of these experiments were shown on this list. In my experiance the influence of a thin wire on a toroid-tpoload seems quite strong, but didn't yet collect quantitative data. I would perhaps like to do some fairly controlled experiments with different wire-lengths, in order to have an raw estimate of spark capacitance. Perhaps others, having already done these measurements might add their comments.

Kurt

-----Ursprüngliche Nachricht----- From: Udo Lenz
Sent: Monday, October 22, 2012 3:51 PM
To: Tesla Coil Mailing List
Subject: [TCML] Re: Re: Spark models, revisited

If I apply the equations for a wire of 0.2 mm diameter 1 m
above a conducting plane from
http://en.wikipedia.org/wiki/Capacitance
I get 5.6 pF/m. For 11.1 pF/m I would need wire diameter of 2.7 cm.
Antonio Carlos M. de Queiroz wrote:That formula doesn't work if the distance
of the plane is large (gives zero capacitance). A better approach is to
consider the capacitance of a thin toroid in free space, that can be
calculated exactly (discussions in the archives of the list, years ago) and
divide the capacitance by the toroid circunference.
A neat trick and you are right about beingcareful which formula should be
used. The wiki pagegives at its end an equation for infinitely
distantplanes. For my 70cm arc at 0.2mm diameter it works outto 6.5pF/m,
which is more than the value I gave abovebut not really enough to get the
currents and powerdissipation in the arc at the voltage I run on.Udo

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