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Em 31/10/2014 04:20, paul wrote:
A sphere is the worst possible shape for this - for a given
size and voltage a sphere is the shape that stores the least
amount of charge.
Something inverted. Anything that can fit inside a sphere has less
capacitance than the sphere, and holds less charge for the same voltage.
A sphere is the shape that, for limited maximum diameter and voltage,
produces the smallest surface electric field. For a given limited
maximum diameter, the sphere has the largest breakout voltage.
A sphere is also poor for controlling the
field around the coil top. Toroids are good in both respects.
I agree.
I'll just add that there is no formula to calculate the ideal
topload size/shape to give max spark length for some given
power level. Coilers have discovered over the years that
large is good, and larger can be even better. But there must
be an optimum size - too small and not enough charge stored,
too large and not enough E-field to push out the streamers.
Remembering the idea of a toroid with flattened outer edge. An idea of
topload where the breakout voltage can be varied,
while the capacitance and shielding of the secondary are not very affected.
Antonio Carlos M. de Queiroz
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