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Voltage/Length (fwd) (the Kevlar thread)




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From:  Jim Monte [SMTP:JDM95003-at-UCONNVM.UCONN.EDU]
Sent:  Friday, February 06, 1998 10:33 AM
To:  tesla-at-pupman-dot-com
Subject:  Re: Voltage/Length (fwd) (the Kevlar thread)


Hi,

Recapping the relevent parts of some recent posts on output voltage
being determined based on energy considerations,

> 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)
<snip>
>                                            I had estimated
> about 50pF for a single 3ft toroid, and 40 to 90pF of
> coil self-capacitance.  Does this seem right?
>
>
> -GL
>
>From:  Greg Leyh [SMTP:lod-at-pacbell-dot-net]
>Sent:  Thursday, February 05, 1998 6:58 AM
>To:  Tesla List
>Subject:  Re: Is 0.5*C*V*V vaild?  (Was Output Voltages and Voltage/Length)
>
>Jim Monte wrote:
>
>[snip]
>> A Tesla secondary has distributed capacitance rather than a lumped C.
>> Circuit theory indicates that ac variation is with time only, not with
>> time and position.  For example, if a 60 Hz ideal current source is
>> applied to several resistors in series, they will all see the maximum
>> current at the same time.  This is due to the assumption that circuit
>> dimensions are small relative to a wavelength.  This is not true for a
>> Tesla coil.  Suppose that the maximum voltage distributes itself with
>> respect to position so that only some of the total C sees most of the
>> voltage.  This would seem to possibly allow a higher voltage than would
>> be obtained by finding the total C and solving for Vmax based on energy
>> considerations.
>
>This is almost certainly true, especially for TC's
>with little or no topload (such as Tesla's Magnifier
>at CS).  For TC's with large toploads, where Ctop is
>comparable or larger than the distributed capacitance
>of the coil, the E= 0.5*C*V*V equation is more accurate,
>since Ctop is a lumped element, and will store most of
>the energy due to the V*V term.
>
>Even with the most optimistic projection of TC output,
>where _all_ of the secondary energy is in the toroid, and
>none of it is in the distributed capacitance of the coil,
>many coils fall far short of their advertised output values.
>
>
>-GL
>From:  D.C. Cox [SMTP:DR.RESONANCE-at-next-wave-dot-net]
>Sent:  Thursday, February 05, 1998 12:35 PM
>To:  Tesla List
>Subject:  Re: Voltage/Length (fwd)
>
>to: Greg
>
>I checked the old notes.  Cap was 0.1 MFD on the primary side.  Good
>efficiency but certainly not "magic".
<snip>
>> From:  Greg Leyh [SMTP:lod-at-pacbell-dot-net]
>> Sent:  Wednesday, February 04, 1998 10:01 AM
>> To:  Tesla List
>> Subject:  Re: Voltage/Length (fwd)
>>
>> D.C. Cox wrote:
>>
>>
>> > I will check my notes but I believe the total cap including electric
>field
>> > was closer to 200 pF.  We were running at 14.4 kV RMS with resonant
>peaks
>> > in the primary measured at approx 24-26 kV.  No where near the 50 kV
>you
>> > mentioned.  Output was at 985 kV in the one-shot mode and in the RSG
>> > "running" mode the streamers were solid connecting at 9 ft. with some
>at
>> > 11-12 ft. but only very intermittant.
>>
>>
>>   Primary Energy = 0.5Cp x Vp^2 = 16.9J (at 26kV)
>> Secondary Energy = 0.5Cs x Vs^2 = 97.0J (at 985kV)
>>
>> Perhaps some of JHC's 'engineering magic' is at work? :)
>>
>> If you can transform that secondary energy back down to
>> the power grid voltage with greater than 30% efficiency,
>> I need several hundred thousand units right away!!  ;)
>>
<snip>

You may be able to argue that even the toroid is large relative to the
wavelengths of some harmonics, but assume we store all the energy
in the topload cap.  Redoing with a primary cap of 100nF and only the 50pF
toroid cap in the secondary,
   Primary Energy = 0.5Cp x Vp^2 = 33.8J (at 26kV)
   Secondary Energy = 0.5Ctor x Vs^2 = 24.2J (at 985kV)
Maybe that order for several hundred thousand units can wait a bit.

Jim Monte