# Re: Toroid Design .

```to: John

Belt running at 90 ft/sec.  You are right -- my journal is back in Wis and
I reversed it.  The theorectical value of 1 uA per 50 in squared does give
an incorrect value in measured practice.  The value is usually almost exact
1/2 this value.

DR.RESONANCE-at-next-wave-dot-net

----------
> From: Tesla List <tesla-at-pupman-dot-com>
> To: tesla-at-pupman-dot-com
> Subject: Re: Toroid Design .
> Date: Thursday, January 07, 1999 12:30 PM
>
> Original Poster: "John H. Couture" <COUTUREJH-at-worldnet.att-dot-net>
>
>
>   D.C. -
>
>   Thank you for your test data on the 40 inch dia VDG generator. Is the 9
> inch wide belt running at 90 ft/sec or at 90 inches/sec? Also shouldn't
the
> 50 ua/sq inch be 1 ua/50 sq inches as I show in my post?
>
>   This gives -
>   9 X 90 x 12 = 9720 sq inches/sec x 50 ua = 486000 ua/sec
>   This is 486000 ucoulombs/sec - way too high
>   This would indicate efficiencies of less than 0.5 percent??
>
>
>   Should be? -
>   9 x 90 = 810 sq inches/sec divided by 50 = 16.2 ua/sec
>   This is 16.2 ucoulombs/sec - possible - see my post
>
>
>   Sphere capacity = 56.4 pf
>   Voltage = 1 million volts
>
>   Charge time  56.4/16.2 = 3.48 secs at 100% efficiency
>   What was the rate of sparks per second?
>
>   The max theoretical breakout voltage at 70 KV/inch rad
>   V = 40/2 x 70 KV = 1400 KV = 1.4 million volts
>   32 inch spark - what do you think the voltage was?
>
>   My voltage equation
>   KV = 65 x inch^0.7 = 65 x 32^0.7 = 735.4 KV
>
>   Note that the rate of sparks and the actual voltage is required to find
> the efficiency of this VDG.
>
>   There is much more to this type of problem. Nothing? in the VDG text
books
> is of any help when it comes to real world VDG work and efficiencies.
Only
> actual tests are of value. Ask Richard Hull. Fortunately we have plenty
of
> test data for Tesla coils thanks to the work of coilers. The graphs in my
> books use much of this data. However, much more TC test data is required
> from coilers.
>
>   John Couture
>
> ---------------------------------
>
> At 09:38 PM 1/5/99 -0700, you wrote:
> >Original Poster: "D.C. Cox" <DR.RESONANCE-at-next-wave-dot-net>
> >
> >to: John
> >
> >Good post on the theory John.  One caution to watch is the leakage
current
> >from the relatively large area of very large balls.  Point in case, we
> >built a 40 inch dia 1 MEV Van de Graaff several years ago and attempted
to
> >charge it with a 6 inch wide belt running at 75 ft/sec.  It barely
worked.
> >Output spark was only 4 inches.  Terrible error.  With experimentation
we
> >discovered it required a 9 inch wide belt running at 90 ft/sec which now
> >produces sparks around 32 inches (bright spark from side of terminal) in
> >length.  It nows works properly but, in theory, should have worked ok
with
> >the first design.  The large surface area and per sq/inch leakage rate
> >reduced the output to under 100 kV on our first tests.  Also, note at
> >around 100 ft/sec or greater bearing noise becomes quite irritating.  We
> >prefer 65-70 ft/sec as a better design value.  Charge is also "blown"
off
> >the belt as the charge collides with stationary air molecules on its
upward
> >run.
> >
> >Other info for designers is, in theory, 50 uA of terminal to ground
current
> >is produced with every sq. inch of belt passing over the pulley,
however,
> >in actual practice 28 uA per sq. inch is a much more reliable design
value.
> > Output potential is usually around 68% of theorectical max (30 kV/cm
> >breakout value).
> >
> >DR.RESONANCE-at-next-wave-dot-net
> >
> >
>

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