Re: Van de Graaff (Toroid Design)

to: Antonio

I've been in the lower section of the Boston VDGRF.  They are using what
appears to be a leather belt at present approx 4 feet wide.  There is also
a heater system to drive out the mositure near the lower upward run of the


> From: Tesla List <tesla-at-pupman-dot-com>
> To: tesla-at-pupman-dot-com
> Subject: Re: Van de Graaff (Toroid Design)
> Date: Monday, January 11, 1999 3:56 AM
> Original Poster: "Antonio Carlos M. de Queiroz" <acmq-at-compuland-dot-com.br> 
> 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
> > different. My question is, would the belt charge be more or less than
> > 58.5 inch^2/ucoulomb? The only info I could find was 50 inch^2/ucoulomb
> > real belts.
> Less, due to the effects of losses and irregularities in the belt
> surface.
> Van de Graaff mentions 1/3-1/4 of the limit (if I remember correctly)
> for
> 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
> charged
> 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
> > system as compared to the usual energy model? The coulomb conditions on
> > 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
> measurement
> of this.
> Antonio Carlos M. de Queiroz