Re: Van de Graaff (Toroid Design)

Tesla List wrote:

>   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.

Less, due to the effects of losses and irregularities in the belt
Van de Graaff mentions 1/3-1/4 of the limit (if I remember correctly)
the big Round Hill machine in the 1930's, that used a paper belt in open
air (the machine is now in a museum in Boston).
With a better belt and more controlled ambient conditions it is possible
to get very close to the limit, even reaching your 50 inch^2/uC value.
Capacitance to the down-going belt, specially if it is oppositely
and running close to the up-going belt, can increase the limit a bit.
The limit is valid for other kinds of surfaces, as disks, too.
Measurements that I made with several electrostatic disk machines show 
values practicaly identical to the theoretical limit.
>   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?

The breakdown limit for a Tesla coil appears to be somewhat lower, in 
a way that depends on the operating frequency of the coil. I let more
experienced "coilers" comment on this, as I never made a precise
of this.

Antonio Carlos M. de Queiroz