RE: Toroid size selection

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "John H. Couture" <couturejh-at-mgte-dot-com> 


Luke -

There are many ways to determine the toroid size for a Tesla coil using
manual calculations. Here is a simple and easy way to do it. The toroid
capacitance should be sized according to the electrical energy it must have
to store in the TC. For example for your 1800 watts proceed as follows. The
overall efficiency from 1800 watts input to the toroid is assumed to be 15%.
The number of bangs is 120 BPS.

     Watts per bang = 1800 x .15/120 = 2.25 watts

     Volts on toroid = 10^4 x sqrt(1800) = 424264 Volts

     Toroid capacitance = 2 x watt seconds/V^2
                        = 2 x 2.25/424264^2 = 25.00 pf

     For toroid with a 6 inch minor diameter
     Toroid major diameter = (cap^1.2368)/2.0233
                           = (25.00^1.2368)/2.0233)
                           = 26.48 inch

You can pick the size of the primary capacitor in a similar manner. The
efficiency would be higher and the voltage would be lower. The capacitance
would be about .03 uf and the voltage gain and Ccoil would be about 10 pf.

         Voltage gain = sqrt(Cp/Ctor+Ccoil)
                      = sqrt(.03^-6/35^-12) = 29
         Voltage gain = SEC volts/NST volts
                      = 424264/15000 = 28.28 gain

The TC must also be in tune and I suggest that you use a computer program
like JAVATC or JHCTES to keep everything in tune.

  John Couture

-------------------------------------


-----Original Message-----
From: Tesla list [mailto:tesla-at-pupman-dot-com]
Sent: Sunday, January 11, 2004 5:40 PM
To: tesla-at-pupman-dot-com
Subject: RE: Toroid size selection


Original poster: "Luke" <Bluu-at-cox-dot-net>

Is this 2.0 to 2.5 times the sec
coilform dia. a general rule of thum?  When designing a coil is this
always the range to shoot for at first?   Where did the 5 or 6" chord
dia. come from?  Why was that chosen?
I know there are probably no set rules for an exact dimension and it
requires trial and error to get it all inline. But I would like to know
the thoughts behinde why you chose those dimensions so I can apply the
thoughts toward another coil if I build another in the future.



Resonant Rise?  Help me out here.  That one lost me, although I have
heard the term.  I was under the impression if I were to go any larger
on my MC there would be a large current draw from my xformer and it
would stress it out.

I do not want to blow my transformer and am willing to move up in size
of my cap.  But I am also one of those people that has a very hard time
doing something "just because they say so".  Even if I don't really
fully get the why of things I at least need to hear it and feel it makes
some sense.

And if I do bump up the MC vaule what current do I use for playing with
formulas for the primary circuit?
Do I use the current the reactance would draw or the 120mA the
transformers are capable of delivering since they are current limited
any way?

Sorry if I ask too many newbie type questions.

Thanx

Luke Galyan
Bluu-at-cox-dot-net

-----Original Message-----
From: Tesla list [mailto:tesla-at-pupman-dot-com]
Sent: Saturday, January 10, 2004 10:56 PM
To: tesla-at-pupman-dot-com
Subject: Re: Toroid size selection

Original poster: "Dr. Resonance" <resonance-at-jvlnet-dot-com>


For efficient operation you need a toroid of 2.0 to 2.5 times the sec
coilform dia.   With your specs a nice 24 x 6 or 20 x 5 inch toroid
would
work very well.

Your .0214 cap selection sounds very close to a resonant match with your
transformers impedance.  You might go up to 1.6 x the transformers
impedance
to prevent unwanted potential resonant rise which could blow your xmfr.
You
might try .03 to .035 value to keep above this undesireable range.

This will also provide more energy for pri-sec transfer.

Dr. Resonance

Resonance Research Corporation
E11870 Shadylane Rd.
Baraboo   WI   53913
----- Original Message -----
From: "Tesla list" <tesla-at-pupman-dot-com>
To: <tesla-at-pupman-dot-com>
Sent: Saturday, January 10, 2004 8:41 PM
Subject: Toroid size selection


   > Original poster: "Luke" <Bluu-at-cox-dot-net>
   >
   > I just joined the group and this is my first post.
   > I have played with TC's bout 12 years ago and my last one took up too
much
   > room for me at the time so I dismantled it.
   > I have regretted it since.  So now its time to make another.
   >
   > My question is what is the best method / formula for selecting a
toroid
   > size?  And why?
   > Various opinions and methods would be appreciated so I can get an
over all
   > view of what everyone thinks.
   >
   > I will be using 2 NST's in parallel each rated at 15KV 60mA.  For a
total
   > of 1800 watts.
   > The capacitance I have chosen is 0.0214 micro farads.
   > I will be winding a coil with a diameter of 8 inches and a 36 inch
coil
length.
   > How do I go about figuring out the best size toroid with the above
information?
   >
   > Thanx.
   >
   > Luke Galyan
   > Bluu-at-cox-dot-net
   >
   >
   >
   >