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Re: Top Toroid



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> From: Tesla List <tesla-at-poodle.pupman-dot-com>
> To: Tesla-list-subscribers-at-poodle.pupman-dot-com
> Subject: Re: Top Toroid
> Date: Friday, January 31, 1997 1:05 AM
> 
> Subscriber: rhull-at-richmond.infi-dot-net Thu Jan 30 22:56:39 1997
> Date: Thu, 30 Jan 1997 18:27:28 -0500 (EST)
> From: richard hull <rhull-at-richmond.infi-dot-net>
> To: tesla-at-pupman-dot-com
> Subject: Re: Top Toroid
> 
> At 09:10 PM 1/29/97 -0700, you wrote:
> >Subscriber: c604313-at-showme.missouri.edu Wed Jan 29 20:57:23 1997
> >Date: Wed, 29 Jan 1997 13:33:57 -0600 (CST)
> >From: c604313-at-showme.missouri.edu
> >To: tesla-at-pupman-dot-com
> >Cc: Tesla-list-subscribers-at-poodle.pupman-dot-com
> >Subject: Re: Top Toroid
> >
> >
> >   Jeff,
> >    Here is a small list of Toroids and there capacitance in picofarads:
> >
> >   Toroid (height X diameter)         Picofarads
> >
> >          3 X 12                        12.95
> >          5 X 14                        16.08
> >          5 X 20                        21.58
> >          7 X 30                        32.17
> >          6 X 36                        37.18
> >         12 X 36                        40.84
> >          8 X 48                        49.58
> >         12 X 48                        51.79
> >         12 X 60                        63.32
> >         20 X 60                        68.07
> >
> > 
> >    The Toroid is measured in inches.
> >    One quick remark. try to construct the cap with the least amount of
> >metal just a thin shell of metal is best (aluminum duct tape on 4 pvc
> >joints fitted together works well) The reason being is that the top cap
is
> >also in the midst of the magnetic field that is set up by the primary
ind.
> >If the terminal cap was a solid chunk of metal, the changing magnetic
> >field would set up an E field in the cap and induce current flow causing
> >heating of the Terminal cap which is a waste of energy. you don't want
the
> >toroid to soak up the energy of the magnetic field you want that energy
to
> >be soaked up by your secondary coil.
> >     There is a good toroid home brew description on Bill Beaty's Tesla
> >web page.     
> >                       enjoy!
> >                           --Bert S.
> >
> >
> >
> 
> Bert,
> 
> I trust these are calculated values!!!  I can almost tell due to the fact
> they are all in error from real world, honest to God, measured values.  A
> true, relative isolated toroid is usually about 25-30% lower in capacity
> than the calcs say it is.  My 12X3 spun unit is 7.8pf and my 5X20 is 15.1
> pf.  put them on a coil and they can appear to be even more than
calculated!
> It's a crap shoot!  The thrust is that the math isn't even close for  any
> form of critical engineering purposes. Especially on small toroids.
> 
> 
> Richard Hull, TCBOR

Richard, Bert, Anyone Else,
What do you actually mean when you say a toroid is 7.8pf anyway? In a
classic capacitor the capacitance is a function of the Area of the
plate(s), the Distance that separates the plates, and the dielectric
Konstant of the insulating material that separates the two plates. 

i.e.		C= (KA)/(D^2) 

When you say a toroid has a 7.8 pf capacitance, is this based on some
standard distance away from earth in dry air, or what? The reason I ask
this, is twofold: 

1) If measuring the capacitance of a toroid using a sensitive capacitance
meter, what are the actual test conditions. For example, is it measured
between earth and ground at a distance of one meter in dry air at Standard
Temperature and Pressure (STP)? I would definitely think that the distance
from ground would influence the value tremendously, but also any
surrounding objects (especially if THEY are connected to ground or are
simply very large in comparison to the toroid). For example, a person might
not THINK about it, but a ROOF and the WALLS would probably contribute a
significant amount to any actually measured capacitance. It also seems to
me that to make any valid repeatable measurement you would have to also
define the orientation of the toroid with respect to earth.
Any object up close (such as a human being!) would add a significant error.
The closer the object/person, the greater the error.

2) If Toroid capacitance IS subject to such large variations in value due
to surroundings, then any value derived by formula would only give proper
results if the formula accounted for all the extraneous forces, and if the
experimenter ENTERED all the required data into the equation. A formidable
task, even if you decide to remove all such variable elements by doing it
inside a Huge building. Outdoors you have OTHER things to contend with that
we probably don't want to get into! (Outside, an insulated body will pick
up a charge from several sources. Tesla actually filed a patent based on
this!)

It seems to me that what should be done is measure real-world toroids under
real-world conditions, and then use the results to come up with a corrected
formula that would generate an answer that is reasonably close to the
observed values. Then the result from the formula would be more useful in
practice. I think you would also have to caution people that the calculated
value could actually vary from the real by up to plus or minus so much
percent.

Since we coilers are generally interested in the toroid as it applies to
our secondary coil, what we need is a method for measuring toroid
capacitance AS A TOP LOAD on the secondary. A first approach might be to
measure the self resonant point of a secondary coil with and without the
toroid. Or even better yet, with several different toroids! The more the
better!! Then do the same thing with every one of your coils, each time
also trying every one of your toroids (even ones that you think are *the
same*). The results might be something other than what you suspect. And
then the Hunt is ON! If results are consistent and reproducible by others,
then one might be able to gather enough data to come up with a reasonable
formula applicable to coiling. If not, the results in themselves would be
useful as-is as a kind of sampling of What To Expect.

My reason for proposing using the self-resonant frequency of a secondary
with and without toroid as the meausrement means is simple: Almost all of
us can do THAT with very simple equipment. I might not have a picoammeter,
but I do have a sine wave generator, and two LED's. An oscilloscope and
frequency counter are NICE, but not NECESSARY for getting some working
data. I am still concerned by the distance factor of the toroid to earth or
its nearest component.  A reasonable isolation of the toroid from
surrounding objects may be enough to get useable results.

Just a thought.

Fr. Tom McGahee