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# Re: Van de Graaff (Toroid Design)

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Antonio -

The 26.5 ucoulombs/m^2 (58.5 inch^2/ucoulomb) is for a smooth metal
surface. I would expect that the charge condition for belts would be much
different. My question is, would the belt charge be more or less than the
58.5 inch^2/ucoulomb? The only info I could find was 50 inch^2/ucoulomb for
real belts.

Have you tried to model the current (coulomb) passage thru the Tesla coil
system as compared to the usual energy model? The coulomb conditions on the
Tesla coil terminal would end up the same as the VDG for a 1 meter dia
sphere charged to 1 million volts. The timing and efficiencies would be
different. I wonder if this could explain the random extra long spark?

John Couture

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At 09:17 PM 1/6/99 -0700, you wrote:
>Original Poster: "Antonio Carlos M. de Queiroz" <acmq-at-compuland-dot-com.br>
>
>Tesla List wrote:
>
>> Other info for designers is, in theory, 50 uA of terminal to ground current
>> is produced with every sq. inch of belt passing over the pulley, however,
>> in actual practice 28 uA per sq. inch is a much more reliable design value.
>
>The correct figure (and units) is 2.65 nC/cm^2, or 17.n nC/in^2,
>or 26.5 uC/m^2, for a flat belt transporting charge at one side.
>This value comes from the surface charge density that produces
>a field of 30 kV/cm: D=e0*E=8.85e-12*3e6=26.5 microcoulombs/square
>meter.
>
>Antonio Carlos M. de Queiroz
>
>
>
>

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