Re: topload questions

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Antonio Carlos M. de Queiroz by way of Terry Fritz <teslalist-at-qwest-dot-net>" <acmq-at-compuland-dot-com.br>

Tesla list wrote:
 >
 > Original poster: "by way of Terry Fritz <teslalist-at-qwest-dot-net>" 
<Beans45601-at-aol-dot-com>
 >
 > I was looking around at some of the really big coils and i noticed that for
 > their top loads, they were just using chicken wire on the outside of a
 > wooden frame. since the chicken wire is mostly holes, woulden't a big peice
 > of chicken wire have the same capicatance as a smallish top toroid? My
 > thinking is that the capicatance is caculated by the surface area, and it
 > seems to me that they would need to have a HUGE top load (made of chicken
 > wire) to equal that of a small "regular" top load.

No. Capacitance is almost purely a function of the geometry of the
conducting surfaces, with negligible influence of the surface details.
Actually, a single thin wire loop has great part of the capacitace of a
solid toroid (or even a solid ball) with the same diameter.

A chicken wire toroid would have the same capacitance of a solid one.
The surface electric field, however, becomes concentrated in the
outer surfaces of the wires, and this toroid would cause breakout
with quite low voltages.

 > Also, say you had a
 > medium coil that with a medium top load threw, 5' sparks. Then, you added
 > 100 turnes to the same pricary coil and put a metal trash can (or person,
 > or any large object) on the top of the secondary, could you tune the coil
 > again, so that you would get 5' sparks from the big object on top? or would
 > you have to get a much more powerful coil?

The maximum voltage gain is sqrt(C1/C2), where C1 is the primary
capacitance and C2 is the total secondary capacitance. If you increase
C2, you must increase C1 too to get the same voltage. If you
con't increase C1, I would expect the output spark length to be reduced
by a factor similar to the increase in size of the topload.

An empirical formula relating the input power to the spark length,
as John Freau's formula, but taking into account the output voltage,
would help in the evaluation of these situations.

Antonio Carlos M. de Queiroz