Re: TCforVDGinjection

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

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

Tesla list wrote:
> 
> Original poster: "cd by way of Terry Fritz <twftesla-at-qwest-dot-net>"
<vbprg1-at-hotmail-dot-com>
> 
> I dont want to agrivate anyone by presenting a subject that is to far
> offtopic, but
> next on my list of mad scientist devices
> is building a Vandegraf generator
> I am wondering if anyone has recently found any good info on the net about
> vandegraff construction. Especially injection type VDG devices...

There is something in my site:
http://www.coe.ufrj.br/~acmq/myvdg.html
An old paper by Van de Graaff is excellent about this:
L. C. Van Atta, D. L. Northrup, C. M. Van Atta, and R. J. Van de Graaff, 
"The design, operation, and performance of the Round Hill electrostatic 
generator," Physical Review, Vol. 49, May 1936, pp. 761-776.
I don't know if it is available online somewhere.
 
> I think you can build 2 types of Vandegraf machines
> 1 is a belt / pulley driven system with specific rollers for generating a
> charge
> and the other is
> an injection system. I know very little of this type

The active system replaces the friction excitation by one of two
methods, that essentially are:
1 - Induction method: The lower pulley is conductive and is connected 
to a high-voltage DC supply. It attracts charge from a grounded comb 
to the surface of the belt.
2 - Spray method: The lower pulley is conductive and grounded. A high-
voltage DC supply is connected to the comb that deposits charge in the
belt.
The induction method is better, as it doesn't require any significant
current from the HV source.
My VDG machine can be connected in any of these ways, or can operate
by rolling friction alone. As a DC supply I use a small electrostatic
machine, that can easily produce the few uA required, even by the spray
method. The active methods work better, specially in humid weather, but
the maximum performance is similar in all cases.

> I am curios know if tesla coils are used as the electron injection device
> onto the vandegraf belt sytem?
> The information I have read kind of hinted at this but went on to say that
> you didnt want to mess with this dangerous stuff...

A Tesla coil would not produce the DC voltage required, and is far, 
far, too powerful and complex for this use even if you manage to
produce some DC from its output. 
A simple electronic power supply made around a flyback, and ignition
coil, or even a multiplier with diodes and capacitors would be enough.
You need only about 10 kV and negligible current (just enough to ovecome 
leakage) for the induction method. 

Antonio Carlos M. de Queiroz