Re: Van de Graaff generator safety question (fwd)

[Steven Roys <sroys@xxxxxxxx>]

---------- Forwarded message ----------
Date: Fri, 26 Dec 2003 11:19:24 -0000
From: colin.heath4 <colin.heath4@xxxxxxxxxxxx>
To: High Voltage list <hvlist@xxxxxxxxxx>
Subject: Re: Van de Graaff generator safety question (fwd)

hi terry,
            i havent done a great deal with van de graaff generators but
have used one this size. poss bigger. i have drawn the sparks to a hand held
metal object while stood on the floor. i cant say wether its safe but get to
about a foot long it starts to hurt a bit! i also witnessed someone get what
you said to the forehead and they are still ok.sorry not to give more
theoretical answers just thought i would share what i have seen done
cheers
colin heath
----- Original Message -----
From: High Voltage list <hvlist@xxxxxxxxxx>
To: <hvlist@xxxxxxxxxx>
Sent: Friday, December 26, 2003 3:13 AM
Subject: Van de Graaff generator safety question (fwd)


> Original poster: Steven Roys <sroys@xxxxxxxx>
>
>
>
> ---------- Forwarded message ----------
> Date: Thu, 25 Dec 2003 10:56:09 -0700
> From: Terrell Fritz <terrellfone@xxxxxxxxxxxxxxxxxxxxxxx>
> To: High Voltage list <hvlist@xxxxxxxxxx>
> Subject: Van de Graaff generator safety question
>
> Hi All,
>
> 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
>
>
>
>