Re: Van de Graaf and 3/4" grounded sphere (fwd)

[Steven Roys <sroys@xxxxxxxx>]

---------- Forwarded message ----------
Date: Mon, 12 Jan 2004 11:02:47 -0800
From: John Pepper <jspepper@xxxxxxx>
To: High Voltage list <hvlist@xxxxxxxxxx>
Subject: Re: Van de Graaf and 3/4" grounded sphere (fwd)



High Voltage list wrote:

> Original poster: Steven Roys <sroys@xxxxxxxx>
>
> ---------- Forwarded message ----------
> Date: Sat, 10 Jan 2004 18:54:27 -0600
> From: Dr. Resonance <resonance@xxxxxxxxxx>
> To: High Voltage list <hvlist@xxxxxxxxxx>
> Subject: Re: Van de Graaf and 3/4" grounded sphere (fwd)
>
> With most Van de Graaffs, maximum impact is delivered with a ground terminal
> 33% x HV term. dia.     This gives a high capacitance value and delivers
> very fat, bright sparks.  Smaller terminals deliver longer sparks but with
> considerably less energy.  You can use 6-12 inch dia. smooth copper plumbing
> floats available from McMaster-Carr Supply Co., Chicago, IL.   They work
> great.
>
> Using this 33% formula, output potential works out to approx 26.5 kV/inch of
> bright spark length.  Ignore the long thin streamers as they usually emit
> from sharp and not large rounded objects.
>
> Dr. Resonance
>

Greetings,
I have tried a variety of discharge spheres (some of which I purchased in the
garden department of Rite Aid).  The 8" diameter sphere produces VERY loud and
bright sparks but only about 4-5" in length.  I believe that this short spark
length is due to the inability of the main electrode to store enough voltage
without corona leakage.  As I mentioned in a previous email, the sphere has only
a 3/4" radius rolled lip where the support column enters the sphere (not very
oblate).  The ideal shape for the bottom of these terminals should be similar to
one half of a toroid (i.e. maximum radius).

-John