Re: Mini VDG? (fwd)

[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