Re: Van de Graaff generator safety question (fwd)

[Steven Roys <sroys@xxxxxxxx>]

---------- Forwarded message ----------
Date: Thu, 08 Jan 2004 22:47:48 -0200
From: Antonio Carlos M. de Queiroz <acmq@xxxxxxxxxxxxxxxx>
To: High Voltage list <hvlist@xxxxxxxxxx>
Subject: Re: Van de Graaff generator safety question (fwd)

High Voltage list wrote:

> From: Ralph Zekelman <hyperion@xxxxxxxxxxxxxx>

> I see references made to the wire brush and the serrated or sawtooth
> comb. The wire brush is in contact with the belt and must charge by
> conduction. The comb with its pointed sawtooth is placed near the belt
> but not in contact. It therefore charges by induction to produce an
> opposite charge on the sphere. Is there a preference?

There is no charging by induction in this case. With the direct
connection or with the comb the terminal polarity is the same of
the belt. The comb points cause ionization of the air and a
conductive path to the belt through it.
I have used combs made of serrated aluminum foil (good because an
accidental touch is not a problem) and also carbon fiber brushes
in direct contact with the belt. The brushes work well even when the
excitation voltage is low.
About the original theme, I have some calculations in my page about
Van de Graaff generators:
http://www.coe.ufrj.br/~acmq/myvdg.html

Antonio Carlos M. de Queiroz