Re: Van de Graaff generator safety question (fwd)

[Steven Roys <sroys@xxxxxxxx>]

---------- Forwarded message ----------
Date: Fri, 26 Dec 2003 00:08:23 -0600
From: Dr. Resonance <resonance@xxxxxxxxxx>
To: High Voltage list <hvlist@xxxxxxxxxx>
Subject: Re: Van de Graaff generator safety question (fwd)


Our 20 inch dia. VDGRF will produce a max of 550 kV on a dry day (30%
humidity).  The re-entrant hole drops the 3 mV/m value considerably.

We obtain sparks at 26.5 kV per cm at this potential.

Dr. Resonance

Resonance Research Corporation
E11870 Shadylane Rd.
Baraboo   WI   53913
>
> I was thinking of making a Van de Graaff generator out of a 50cm diameter
> (20 inch) stainless steel sphere I have laying around.  I got it from
> Waterscapes:
>
> http://hot-streamer.com/temp/Old2001Files/2001-04/Orb.jpg
>
> http://www.waterscapesweb.com/orbs.html
>
> If I calculate the top voltage assuming 3MV/m radius:
>
> 3MV / m x 25cm = 750VDC
>
> If I calculate the top capacitance I get:
>
> C = 4 x pi x Eo x R  =  4 x 3.1415... x 8.85E-12 x 0.25  ==  27.8031pF
>
> Where I got worried was the stored energy:
>
> E = 1/2 x C x V^2  =  1/2 x 27.8pF x 750000^2  ==  7.81 Joules!!
>
> Assuming one is grounded and the thing arcs to one's forehead, assuming
the
> human is the biggest resistance in the path, then all the 7.8 joules is
> dissipated in the human....
>
> My question is how dangerous is it??  Making this thing would not be fun
if
> it was capable of killing anybody (well...  "easily").  If it would be
> really dangerous, I would not want to build it since it would not be fun
to
> demonstrate if I had to really worry about it.
>
> It is pretty much like a 30pF 750kV cap I would think.  But I am not a
> great expert on this stuff so I thought I would ask.
>
> Cheers,
>
> Terry
>
>
>
>