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Re: The worlds Largest Coil



Comments interspersed..

Main comment... On large scale projects the mechanical aspects will greatly
outweigh the electrical ones.. After all, how complex is a coupled tuned
circuit, electrically... 

You're looking at hundreds of thousands of dollars to build something like
this, without considering any of the electrical components, just for
structural materials, equipment rental (cranes, etc.), and crew (riggers,
ironworkers, etc.)


----------
> 
> Original Poster: "Christopher Boden" <chrisboden-at-hotmail-dot-com> 
> 
> comments gently folded throughout to add texture...
> >Original Poster: "Jim Lux" <jimlux-at-jpl.nasa.gov>
> >
> >Some more calculations..
> >
> >Assume a spherical top load 10 m in radius (32.5 ft, 390 inches) =
1100pF
> 
> I love how you just toss that out....lol....a 10M stainless monocoque
sphere 
> is a rather impresive item by itself. It will be beautifull.

It's always good to just ballpark your plan, just to see if it is even in
the realm of feasibility... Make those simple assumptions, run the numbers,
and then, if it looks like it might work, start looking at the
implementation details..

> >Assume a secondary 20 ft in diameter and 100 ft high with windings every
3
> >inches = 166 mH
> 
> That's the full tower size, will such a large sec be required?

Don't know.. just threw it out to get a feel for it.  In general, though,
yes, because of the voltage stress along the L, it will need to be quite
long.  
> 
> What would the best method of construction be? Fiberglass encased tower? 
> What are the options for tower construction other than wooden form (the 
> costs of the Sitka would be staggering for such a design).
> And I don't think they make PVC that big :)

Personally, I am a big fan of Extren(tm) pultruded fiberglass structural
members (http://www.strongwell-dot-com/pult/EXTREN.htm) for larger HV
structures. Structurally, they are much like aluminum (at least for
strength and weight), although more flexible. The cost is about the same as
aluminum.  It's available from most large steel distributors in all
standard structural shapes (I beam, angles, tubes, etc) and sizes.

You'll need a structural engineer to design something this big, and make
sure they know how to design with composites which have nonisotropic
characteristics.

> 
> Also, with a tower of this size there comes another problem. We cannot
wind 
> it with conventional means. The tower will have to be built, erected,
then 
> wound by a suspended spool and a guy in a rappeling harness. Plan on that

> person spending the better part of a full day in that harness laceing
wire 
> into pre-machined slots in the tower while another person either operates
a 
> crane holding the spool, or a dolly on the ground traveling a circular
path 
> (though supporting the wire weight for the winder would be hard like
this).

No one said it would be easy.  It will probably take weeks to wind. But,
the idea of precutting slots and driving around it (or set up a temporary
scaffold around it like window washers use) as you lay the wire into the
slots is proabably as good as any.  You could also just rent a 100 foot
"snorkel lift" for the weeks, but it's a pain to drive around a tower, so
you'd probably need two, one for each side. I'd go with the scaffold on
winches.. you'll need it for maintenance.

> >Self C of secondary is another 500 pF
> >Resonant frequency is about 10 kHz..
> 
> That's nice and low, well under most broadcast radio (FM is 88 to 108
MHz).
And lower than AM, which is 550-1600 kHz, and right at the Omega Nav
frequencies (10-14 kHz), where you get worldwide single mode propagation.
> 
> 
> >At this frequency, the impedance of the secondary is about 10.4 Kohm.
> >
> >Say we want the Q of the secondary system to be at least 10.. The wire
> >resistance needs to be <1 K.
> >There is about 25000 ft of wire in the secondary, so we want our wire to
be
> ><40 ohms per thousand feet.. or AWG 24.   In reality, you'd probably
want a
> >design Q of 100, so you'd want <4 ohms/thousand feet, or AWG 14...  This
is
> >readily available in long lengths at a reasonable price.
> 
> What's the largest spool we can get from Beldon? 5000'? How do we splice
it 
> while winding? With 3" between turns it should be easy.

You can get arbitrarily long lengths (think about cross country power
lines) of wire.. Splice it like any other wire, twist, solder, crimp,
whatever..  You better look into copper futures (or use aluminum)... The
60% increase in resistance won't make much difference, and it will be much
cheaper and lighter...
> 
> >
> >With the 10 meter diameter top load, the maximum stored energy would be
> >1000pF * (10*3MV)^2/2 = 448 kJ. so your pump energy (per pulse) would be
> >45kJ per pulse.  At 720 pulses/second, the power draw would be about 
32MW.
> >The secondary winding would be dissipating that much heat, by the way.
> 
> We will dissapate 32 MILLION WATTS through the windings? Wow.....
> Is there any way to NOT waste so much energy?

Make the Q higher... or make wimpy sparks.. your choice...If you want to
use resonant rise to get the high voltage, you're sort of constrained.. 
> 
> 
> >
> >It would be a relatively feeble lightning stroke too, at 15 kJ/meter. 
(But
> >still mighty impressive...)
> 15000 joules per meter.....what is average for a good coil?

A whole lot less.... Run the calcs..  Most likely a few joules/meter..


> Would a smaller tower (80') get us more power, thicker strokes?
> I want the longest hottest discharge we can get. I want to be able to see

> this from miles away.

Consider the visual horizon.. how many miles?  

> >How much would this cost?  A bunch, but mostly in structural
components..

A data point.. I built a 50 foot high artificial tornado using standard
structural stuff, renting cranes, etc,
(http://www.reelefx-dot-com/Tornado/40footVolvo.htm), and it cost somewhere
between $100K and $1M (actual cost is a trade secret of Reel EFX). This was
a temporary structure, and not designed to be particularly durable or safe
(it met the requirements of the entertainment industry job).  It took a
crew of something like a dozen people a month, and some wretchedly
expensive rental gear, as well as a BIG crane.