Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!uunet!mcsun!ukc!mucs!liv-cs!liv!sx43
From: SX43@LIVERPOOL.AC.UK
Newsgroups: sci.electronics
Subject: Ideas please, how to generate arc discharge..
Message-ID: <90351.010238SX43@LIVERPOOL.AC.UK>
Date: 17 Dec 90 01:02:38 GMT
Organization: University of Liverpool
Lines: 37

Please excuse my ignorance if the answer is trivial, Im no electronic engineer.

A friend wants a circuit to generate a discharge of the sort that comes off a
Van de Graaff generator when you point your finger close to it.

Basically he wants to be able to control :

      -- The total charge that gets passed;
      -- The peak voltage;

Being able to control the voltage profile in time would presumably help
but I suppose that would be asking for too much ?

The discharge should have to penetrate both air and some depth of
an insulator, say a tenth of a millimetre, and I suppose it would have
to come off a fine tip in order to be able to localise its passage.

What comes to my mind is something based on a solenoid, where if you
have a steady current flowing and then the circuit is broken the
back-emf generates a discharge.. I thought that setting the initial
d.c. in the solenoid should allow tuning of the total charge passed
in the discharge, but maybe it would tune the power dissipated in
the discharge ?  And how would the discharge be redirected from the
switch which cuts the current to the required discharge-point ?

Also I thought of photographic flash units. They seem to build up a
charge  before discharging it.. I wonder if the principles involved
there would be relevant to my problem. Ideas ?

Any ideas, pointers, or even circuits muchly appreciated.

I would be most grateful if copies of any related posts be emailed to me
(see header) as I may not be spending time on the net nowadays/soon.

Thanks again,

Fazal.