# Voltage/Length (fwd)

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From:  Bert Hickman [SMTP:bert.hickman-at-aquila-dot-com]
Sent:  Thursday, February 05, 1998 9:05 AM
To:  Tesla List
Subject:  Re: Voltage/Length (fwd)

John and all,

The MAXIMUM voltage a coil will produce can be demonstrated to follow
the Vp*sqrt(Cp/Cs) relationship. However, this assumes no breakout. If
you get breakout, the maximum voltage will always be lower than this
amount. Why?? Because you're stuck with only X joules per bang, and if
you breakout before all the primary energy has been transferred to the
secondary, you're losing some of this energy heating the air, and will
NOT hit the maximum output. I do concur that Maximum (non-breakout) coil
voltage does NOT mean maximum spark length, but for a whole host of
other reasons dealing with repetitive ionization of previous spark
channels and the amount of average power (bangs/second) being dumped
into heating the air...

-- Bert --

Tesla List wrote:
>
> ----------
> From:  John H. Couture [SMTP:couturejh-at-worldnet.att-dot-net]
> Sent:  Wednesday, February 04, 1998 7:11 PM
> To:  Tesla List
> Subject:  Re: Voltage/Length (fwd)
>
>   Greg -
>
>   It should be noted that using the equation
>     Vs = Vp sqrt(Cp/Cs)
>   can give incorrect results when applied to Tesla coils. There are also
> other similar equations for Vs and they will usually all give different Vs
> answers for the same coil.
>
>    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. It is
> obvious that other TC parameters and equations must be taken into account.
> Therefore, the "22.4 x Vp" gain shown above must be viewed with suspicion.
>
>   When Vs and sparks are increased the energy and power must increase, other
> things being equal. This brings us to the energy equation
>     Vs = sqrt(2J / Cs)
>   Here again reducing only Cs will increase Vs with the same energy? If the
> energy is not increased there remains only power gain to increase the Vs.
> The power gain is a function of design.
>
>   This means that equations like the above must be used with caution. In the
> past coilers have said the equations don't work and for good reason. I
> believe the proper utilization of these and other equations is to clearly
> understand and apply the RMS and Instantaneous conditions that are inherent
> with Tesla coil operation. These conditions are still not developed to a
> point where coilers can depend on the results of their calculations when it
> applies to secondary voltage (Vs).. A clearer understanding of power
> magnification is required.
>
>   John Couture
>
> -------------------------------------------------
>
> At 10:53 PM 2/3/98 -0600, you wrote:
> >
> >----------
> >From:  Greg Leyh [SMTP:lod-at-pacbell-dot-net]
> >Sent:  Tuesday, February 03, 1998 8:10 AM
> >To:  Tesla List
> >Subject:  Re: Voltage/Length (fwd)
> >
> >D.C. Cox wrote:
> >
> >
> >> One could strike an arc with a super powerful welder or a 10 kV arc at
> >> perhaps 1000 amperes and surely draw an arc 9-10 feet long so there are
>
> -------------------------------   Big snip
>
> >Assuming 100pF for the total secondary output capacitance
> >and given 0.05uF for the primary capacitance, the transfer
> >ratio (at 100% efficiency) is 22.4, requiring a primary
> >voltage of 45,000V.  If the coil efficiency is only 75%,
> >then the required minimum primary voltage to get 1MV out is
> >well over 50,000V!
> >
> >Clearly I am missing something somewhere, or perhaps my
> >assumption of the secondary C is way off.  I had estimated
> >about 50pF for a single 3ft toroid, and 40 to 90pF of
> >coil self-capacitance.  Does this seem right?
> >
> >
> >-GL

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