# Voltage/Length (fwd)

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From:  Alfred A. Skrocki [SMTP:alfred.skrocki-at-cybernetworking-dot-com]
Sent:  Saturday, February 07, 1998 7:56 AM
To:  Tesla List
Subject:  Re: Voltage/Length (fwd)

On Thursday, February 05, 1998 6:17 AM Greg Leyh
[SMTP:lod-at-pacbell-dot-net] wrote;

> John H. Couture wrote:
>
>
> >   It should be noted that using the equation
> >     Vs = Vp sqrt(Cp/Cs)
> >   can give incorrect results when applied to Tesla coils.
> [snip]
> > If the Cs is reduced in the above equation (reduce toroid size) with no
> > other changes the Vs and sparks can be shown to be greatly increased. We
> > know this is not true because it is contrary to tests of real coils.

The  above is wrong because it does not consider the fact that the
equation Vs = Vp sqrt(Cp/Cs) refers to the distributed or parallel
secondary capacitance. The toroidal capacitance is in SERIES with the
secondary and actually decreases the total secondary capacitance and
this is why adding a toroid usually increases a coils output.

Ctotal = 1/(1/Csecondary + 1/Ctoroid)

yet it's own capacitance holds the necessary energy for increased output.

> But Vs isn't the the only factor that affects spark length!
> Real world factors, such as break rate and terminal capacitance
> both _dramatically_ affect spark length, independent of Vs.

This is definitely true! All these factors influence the efficiency
of the coil.

> When you increase the toroid size and see longer sparks,
> Vs has actually _decreased_, but the coils' effectiveness
> at propagating the spark channel has improved by an even
> greater amount, due to bigger toroid's improved capacity
> to provide fast currents to the base of the spark.

That's not really true for the reason I explained above.

> The equation Vs = Vp sqrt(Cp/Cs) follows directly from
> Conservation of Energy, and simply sets an _upper limit_
> for Vs.  It's true that Vs can drop below this amount
> if the coil is inefficient, but Vs can never be _larger_
> than this quantity.

Unquestionably true!

Sincerely

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Alfred.Skrocki.Sr-at-JUNO-dot-com
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