Path: utzoo!utgpu!watmath!att!dptg!rutgers!cs.utexas.edu!uunet!garfield!leif!andrew
From: andrew@kean.mun.ca
Newsgroups: sci.electronics
Subject: My HV experience.
Message-ID: <10719@kean.mun.ca>
Date: 8 Aug 89 17:51:21 GMT
Organization: Computing Services, Memorial University
Lines: 42

My first (and really only) experience with hive voltage was when I built a 
little device for making Kirillian photographs.  It wasn't that bad... only 
around 25kV.  Anyway, for those that don't know the Kirillian setup:


    (ground - *omitted for live subjects*)
-----------------------------------------------V                   thin
============================================================== < insulator
______________________________________________________________
   (High frequency high voltage surface)



Basically, I was using a cookie sheet as the HV carrier, an overhead 
projector's transparency film as the dielectric, and a car's ignition coil as a 
HV source.


Well, I heard that the best way to find out the correct polarization of a car's 
ignition coil is to hold a pencil between the live wire & ground, then see on 
which side of the graphite tip the spark is.  (I'm not sure if it works...).


Well, to make a long story short, I had this pencil _point_ sitting _real_ 
close to the _pointed_ HV electrode when the rollers on my chair slipped and I 
shifted my hand so that I touched the metal eraser holder on the pencil.
Basically, everything on my upper body contracted in one spasm of pain.  Hurt 
like the flaming devil, too.  

Turns out that when the chair slipped, I had lain my elbow on a grounded lathe, 
and the pencil tip had fleetingly come closer to the live electrode.  I'll tell 
you this... the little bit of wood that surrounds the guts of a pencil and the 
air gap between the electrode points might as well be a short as far as that
current was concerned...  ('course, it _was_ HF AC ~100 kHz).



Haven't played with HV again yet.



-Andrew.