Re: Mini VDG? (fwd)

[Steven Roys <sroys@xxxxxxxx>]

---------- Forwarded message ----------
Date: Fri, 19 Mar 2004 17:10:06 -0800
From: Ed Phillips <evp@xxxxxxxxxxx>
To: High Voltage list <hvlist@xxxxxxxxxx>
Subject: Re: Mini VDG? (fwd)

High Voltage list wrote:
>
> Original poster: Steven Roys <sroys@xxxxxxxx>
>
> ---------- Forwarded message ----------
> Date: Fri, 19 Mar 2004 12:33:54 -0500
> From: dave pierson <davep@xxxxxxxx>
> To: High Voltage list <hvlist@xxxxxxxxxx>
> Subject: Re: Mini VDG? (fwd)
>
> >I am messing around with the idea of a mini van de graaf
> >
>
> > generator and was wondering whether or not a large-ish
> >
>
> > rubber band would suffice for the belt.
> >
>     Sure.  Tho a tad narrow for classic pulley design.
>
> >Also, do you think that it would be possible for one to
> >
>
> > be hand powered?
> >
>     Sure.
>     (see story below)
>
> > (for example, design the unit as a wand, (slightly
> >
>
> > larger than a pen) then hold it and flick a wheel
> >
>
> > with your thumb which rotates the belt, then touch
> >
>
> > it to an unsuspecting victim)
> >
>     Could be done.
>
> >[I'm not sure what the breakdown voltage for a terminal small enough to
> >fit on a "wand" would be, but I would imagine it wouldn't be that high,
> >plus the capacitance would be mighty small too, so *I* wouldn't think you
> >could expect very much performance.  More learned folk than I are sure to
> >respond though... SRR]
> >
> >
>     Good points.
>     Be an interesting exercise.
>     Note that 'the whole body' is the 'terminal' for the 'foot dragging
> ESD machine'.
>
>     True Story
>     (I WAS THERE....)
>     of a hand powered van de Graaff.
> HS Physics class.
>     Some Years Back.
>        Mr Instructor was talking about/demoing the van de Graaff, a ca
> 24" high unit
>         with 8' dia terminal.
>        (Some of us Lab Rats had been 'fiddling with' outside class hours.)
>
>        Had the top half of the top terminal off, holding it under his arm,
>        showed top pulley, belt, comb, described all.
>        rotated machine onto his shoulder, showing inside base:
>         described motor, lower comb, belt, pulley and said:
>              Here is the Ground Terminal.
>              It Must be grounded, regardless of what
>                Dave or Bruce tell you, or it Won't Work.
>
>     At this point he gave the pulley a bit of a spin, by hand.  Didn't
> move the belt
>     more than 6-8".  (recall: its on his shoulder, column over his shoulder)
>     He goes to set it down.
>        Top terminal goes by his ear.
>           SPARK audibly and VISIBLY jumps to his ear
>                 He Jumps, visibly
>     (pause....)
>  he speaks
>        Maybe Dave and Bruce are right.  Maybe It doesn't need to be grounded
>
> (As a practical matter, at the voltages involved, if the base is NOT
> grounded
> by a wire, it will self ground, via 'corona' and leakage to whatever it
> is sitting
>  on....)
>
> best
>  dwp

	My little VDG, which is neither friction free or very well built, will
build up enough charge when the motor shaft is turned by hand a turn of
two that it will run backwards as a motor for perhaps half that amount.
My radial Dirod machine does the same except that it will spin three or
four turns because the friction is less.

Ed