Re: van de graaff tube (fwd)

[<sroys@xxxxxxxxxxxxxxxxx>]

---------- Forwarded message ----------
Date: Thu, 2 Dec 2004 17:26:53 -0600
From: Dr. Resonance <resonance@xxxxxxxxxx>
To: High Voltage list <hvlist@xxxxxxxxxx>
Subject: Re: van de graaff tube (fwd)


We found out the hard way that a PVC tube with 12 inch ID doesn't work at
all --- the leakage current really starts to get high.  We built one like
this and only got a 1 inch spark out of it.  We use 6 inch ID tubes all the
tube for our model HV-750 (750 kV DC) machine and 6 inch wide belt and they
work just fine.  At 8-10 ID you start to seriously lose performance with PVC
as the main column support.

My idea of an ideal VDGRF would be as follows:

Horizontal cylinder 6 - 8 ft long x 48 inch dia.  40 to 46 inch wide belt
runs into this cylinder.  Hemisphere end caps welded on both ends and sanded
perfectly smooth.  Supports would be 4 long pcs of 2 inch dia.
polypropylene.  Sphere support at 4 x sphere dia. from any other metal
objects, floor, or ceiling.

We finally switched our large ball (40 inch dia.) to polypropylene supports
with external belt and it went from 1 inch sparks to 32 inch sparks
immediately.  Belt was 8 inches wide running at 2,000 RPM.  Any faster and
it begins to sound like a machine gun.  1 spark every 1-2 seconds if about
right.  1 spark/sec starts to scare people, especially small kids.

Dr. Resonance


>
> We were only running at 2,100 rpm so, at 3450 rpm, your current would be
> higher.  These values listed were from the direct terminal to ground
> measured short circuit current.
>
> At 3450 the bearing noises become rather high for my liking.
>
> Dr. Resonance"
>
> Thanks for your note and for Antonio's.  As for the bearing noise, I'm
> running small ball bearings and as you say the noise is almost
> unimaginable!  When I rebuild this machine I'm going to use oilite
> bearings which will last longer than my interest in the thing and which
> should be pretty quiet.
>
> This thing was intended to be the prototype for a much larger machine
> which never got built.
>
> Ed
>
>
>
>