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Re: Recommendations for Monster Coil?





---------- Forwarded message ----------
Date: Thu, 02 Oct 1997 11:10:32 +0000
From: Greg Leyh <lod-at-pacbell-dot-net>
To: Tesla List <tesla-at-pupman-dot-com>
Subject: Re: Recommendations for Monster Coil?

Charles S.S. Goodwin wrote:


> Although I have at this point built only one (barely functional) coil, I
> somehow got it into my head that it would be neat to build a really big
> coil.  I have a few friends willing to help me in this endeavour, and am
> looking for some design wisdom as I plan.
> 
> I formed an image in my head of a looming cylinder putting off 12 foot
> streamers from the metal sphere at its top.   With the image in my head as
> a goal, I want to design the apparatus to achieve what sits in my mind's
> eye. Consequently, I plan to have a secondary which is about 10 or 15 feet
> tall and 12 to 24 inches in diameter.  I figure I can use builders tube
> (used for casting concrete pillars) for the form.  

It's true that cardboard tube will work as a coilform, *provided* that it 
never gets wet.  Also, such a tube cannot be stored lying on its side, or 
it will start to deform.  Since your coil will probably have to be stored
and operated outside, these are two important factors to consider.
You should also do some quick calculations and think about the rigging of 
this thing... how will you erect the secondary, and place the toroid?


> I suppose a pole pig is in order (approximate price is...?) 

Perhaps several!!  My 'from the hip' guess is that you'll need about 70kW
to 100kW to bring this coil to full output.


> and I will need a large cap or bank of
> caps (better to build or buy/trade for...?).  Also, for such a large coil,
> which type of gap would be preferable (rotary or...?).
> 
> If anyone who has built such a monster is willing to share their
> (successful?) design specs with me, I would greatly appreciate it.

Check out http://www.pupman-dot-com/, under The latest images... Leyh's coil.
This prototype coil test is similiar to what you want to do;  I even used
a bare cardboard tube coilform for the test!
The cardboard tube is no longer inside the sec winding -- its only purpose
was to hold the winding in place so that a structural fiberglass treatment
could be applied to the outside.  Once the fiberglass set, the cardboard was
removed using a pressurized steam washer!  The sec coilform is now a smooth 
cylinder, with the sec winding embedded inside the fiberglass.


> By the way, I originally wanted to design the system around a cap bank
> which I recently aquired.  It consists of 7 laser discharge caps.  Each is
> rated at 4 Kv (non continuous) or 2.5 Kv continuous and 375 mfd.  I figured
> that if I were to run them all in series, I would end up with a 53 mfd 17.5
> Kv cap bank.  However, this translates to something like 30 amps at 15 Kv
> (leaving 2.5 Kv of headroom so as not to overstress the caps) for a
> resonant frequency of 30 khz, if my quick calculations were correct.  ;)

Such a cap bank would not provide an effective Zchar for the primary, 
resulting in a very low overall efficiency and a molten rotary gap.


-GL