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Unpredictability is part of the nature of Van de Graff's.

It doesn't take much for them to stop working or to
perform really poorly.  Two things are particularly bad
for building a charge... any moisture in the air and the
charge will bleed off into the air very quickly... and any
tarnish or dirt on the ball and it won't hold a charge.

Depending on what your ball is made of (probably
spun aluminum) you could try cleaning it with an
alcohol pad (inside and out) before you run it.  Clean
the belt too...

Good luck...

Dave Taylor
------------------------------

> From: Jesse Alexander <[log in to unmask]>
> Reply-To: Informal Science Education Network
> Date: Sat, 14 Feb 2004 02:56:24 -0800
> To: [log in to unmask]
> Subject: VDG Questions

> Hey Folks,
>
> I'm looking for inexpensive ("pre-owned" is ok) Van de
> Graaff generators that can be easily taken on the road
> during traveling science programs. I am also looking
> for "care and feeding" guides for VDGs.
>
> The generator should be about 24" tall so that it can
> be easily seen during assemblies of 300+ kids.
>
> We have had a lot of problems with "unpredictable" VDG
> behavior on the road. Something seems to be shorting
> out the globe. I can develop a charge by holding my
> fingers about a 1/4" from the belt, but the charge
> somehow doesn't make it to the globe (once I remove my
> fingers-of course). The rubber belt is exposed on our
> Pasco SF-9722 VDG.
>
> Any ideas?
> Jesse Alexander, WB2IFS
> Science Evangalist/Demonstrator
> Liberty Science Center

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