Re: Slightly off topic- Van DeGraff Generator / other E&M experiments

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

Original poster: "D.C. Cox by way of Terry Fritz <twftesla-at-qwest-dot-net>" <DR.RESONANCE-at-next-wave-dot-net>


Ed:

The current doublers are commonly referred to as, "spray up and spray down"
on the charge transport belt.

We spray up at 7 kV DC using a small screen.  Very important to be sure the
screen does not go "to the edge of the belt" or else it will leak charge
directly to the pulley (ground) and not spray the belt evenly.  Leave a 1/2
gap at each edge of unsprayed belt.  Check this with the upper terminal
grounded (so you don't get hit in the head with 1 MEV like my brother did
once --- and only once he says!!) in a dark room to see even spray across
the belt without it "bunching" at the edges of the belt.

On the upward run of the belt remove the charge with a screen on both
outside and inside of the belt.  It seems most of the charge ions end up on
the inside of the belt (consider the charing belt as it passes the screen,
belt (dielectric), and grounded pulley to be a capacitor and it makes more
sense.

Both upper screen are connected to the upper metal pulley usually on the
vertical bearing support (drill & tap).

Now the "spray down" part.  Attach a wire and a 10 - 20 meg Ohm 50 kV rated
resistor to the dome (dome must be well insulated from the pulley and
bearing assemblies) and this terminates on an insulated (1-2 inch high PE
rod stock) which feeds an insulated spray down screen.  The resistor makes
the dome "live" electrically with respect to the pulley and causes the spray
down screen to dump equal and opposite charge on the downward run of the
belt.  Grounded screen on the bottom removes it as does the lower pulley
itself.

Happy Van de Graaffing,

Dr. Resonance



----- Original Message -----
From: "Tesla list" <tesla-at-pupman-dot-com>
To: <tesla-at-pupman-dot-com>
Sent: Thursday, June 27, 2002 5:36 PM
Subject: Re: Slightly off topic- Van DeGraff Generator / other E&M
experiments


> 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: "Ed Phillips by way of Terry Fritz
<twftesla-at-qwest-dot-net>"
> <evp-at-pacbell-dot-net>
>
> >         In this post you mention a "current doubler".  I've never been
quite
> > sure what this means or how to modify a simple machine to use the
> > principle.  Can you give some help on this?
>
> This is usually mounted on a metallic pulley mounted inside the
> terminal.
> Consists of an insulated metallic pulley and two combs.
> A comb A collects charge from the up-going belt, at the point where it
> touches the pulley. At the other side of the pulley, a comb B is
> connected to the terminal.
> The connection between the comb A and the pulley equalizes their
> potential, that due to the "ice pail" effect goes above the potential of
> the terminal. Comb B then not only takes charge from the belt
> transferring it to the terminal, but also charges the down-going belt
> with opposite charge, that is attracted to the belt by the charged
> pulley.
> The effect is that similar opposite currents flow in the up-going and
> down-going sections of the belt, doubling the charging current.
> The charging comb A can be omitted, as an insulated pulley will also
> become charged soon.
> This, at least, is the ideal situation. Sparks between the pulley and
> comb B, over the belt, can discharge the pulley periodically, resulting
> in irregular charging current, and corona from the terminal to the
> down-going belt (if the belt is not well insulated from the terminal)
> can cancel the effect.
>
> The connections for systems with two current doublers, that should
> work as an influence machine, is shown as the "Toepler system" and
> the "Holtz system" (charging combs omitted) in the picture:
> http://www.coe.ufrj.br/~acmq/vdgself.jpg
> The Toepler system was what I originally tried to make with my
> double VDG, but due to the exposed belts the system didn't work:
> http://www.coe.ufrj.br/~acmq/myvdg.html
>
> About my calculations for power in a VDG, I was wrong in saying that
> mechanical losses are small. See what I measured in my machine, in
> the address above. The losses there are more than 10 times greater than
> the electrical output...
>
> Antonio Carlos M. de Queiroz
>
>
>
>