Re: First Light for 10" Coil.

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

Original poster: Bart Anderson <classi6-at-classictesla-dot-com> 

Hi John,

Apologies if this gets to the list a little late. I took a trip over the 
Sierra's from Modesto to outside of Reno, Nevada (drop the kids off at 
Grandma and Grandpa's for a winters vacation).

Tesla list wrote:

>Original poster: "John H. Couture" <couturejh-at-mgte-dot-com>
>
>Bart -
>
>You can forget the reduction factors and the 47.4pf isolated toroid
>capacitance for Peter's Tesla coil. The reason is because the surrounding
>conditions that determine the toroid capacitance on his TC are completely
>different. In fact there is no reason to call this a reduced toroid
>capacitance because the toroid capacitance on the TC has nothing to do with
>the capacitance that Inca, etc, calculates. The conditions around a Tesla
>coil have nothing to do with a toroid in isolated space. I don't intend to
>use "toroid capacity reduction" in the future.

Well, I'm not sure I agree. I would say it does, except that it has the 
influence of the ground plane. I really don't see a problem using a factor, 
even if standard Wheeler inductances are used, or maybe I should just say 
standard meter reading capable L's and C's are used, as long as the factors 
agree with the end result.

>So lets start over and also use real numbers of a real TC like 145.49 and
>84.43. For Peter's TC if you use a computer program or manual calcs (brave
>coilers) these two frequencies will not be available to you.

Or will they. If you input the groundplane, secondary, primary, toroid, and 
strike ring into Javatc, here's what follows:
80.87 kHz = loaded Fres, which is pretty close to the measured 84.43 kHz.
146.39 kHz = unloaded Fres. Pretty darn close to the measured 145.59 kHz.

The loaded frequency includes the entire system. The unloaded includes only 
the secondary and groundplane.

>The computer or
>calcs will give you some fictitious resonant frequencies based upon your
>inputs. What you do with these frequencies is up to you. However, if you
>want to know the real world toroid capacitance of Peter's TC proceed as
>follows. The accuracy will depend upon the  accuracy of the real world
>frequency tests.

The frequency's are not fictitious, but are simulating as close to the real 
world as possible. The detail (or number of rings used internally) to 
Javatc is relatively low, but still accurate enough to be useful. Setting 
the detail higher may gain a percent accuracy, but considering the amount 
of time a browsers JavaScript would take to process the data, it's just not 
worth the wait. Even for a user with say 450 MHz processor, it can 
be  annoying waiting for the output. I'm fine with leaving the ring count 
where it is. I think it's a happy place between accuracy and processing time.

>For Peter's Tesla coil he found that the test resonant frequency without the
>toroid was 145.49 KHz. The secondary coil capacitance per the Wheeler
>equation was 69.33 mh. The real world self capacitance of the secondary coil
>without the toroid is
>
>   Cc = 1/(39.5 F^2 L) = 1/((39.478)(145490^2)(.06933)) = 17.26pf

For Wheeler,  I got 72.66 mH
L(uH) = r^2 * n^2 / (9 * r + 10 * l)
where r = 5", n=1150, l=41"

Thus, 1/((39.478)(145490^2)(.07266))= 16.47 pF

Now, regardless of this Wheeler approximation or any of the other (Snow, 
Lorenz, or whoever), this is still the inductance of the single layer 
helical solenoid and does not involve the operating frequency of 145.49 kHz 
(note, it's not even in the Wheeler equation).

 From that, you calculated the self capacitance. However, in order to do 
so, you used an operational frequency of 145.49 kHz to do it. This is the 
problem I continually see going on. The DC capacitance "cannot" include an 
operational frequency unless the frequency is low enough to not disrupt the 
current distribution from it's nice and even distribution along the length 
of the secondary. So what you have is a capacitance that is neither the 
capacitance at 145.49 kHz (because a DC inductance was used to derive it) 
nor a capacitance that is at DC (because a frequency high enough on this 
coil to cause uneven current distribution was used to derive it).

>The test resonant frequency was 84.43 KHz with the toroid on the secondary.
>The toroid + coil capacity is
>
>   Cs  = 1/((39.5)(84430^2)(.06933)) = 51.26pf

I'll just throw in the Wheeler inductance  I found above.
1/((39.478)(84430^2)(.07266))= 48.9 pF

But again, the same "reasoning" applies as above.

>The real world toroid capacity is
>
>    Ct = (Cs - Cc) = 51.26 - 17.26 = 34.00pf

48.9 - 16.47 = 32.43pF (just for the purpose of the corrected Wheeler value).

But again, same reasoning applies. This is just a value of capacitance 
found by using low frequency inductance and a high frequency Fres.

>What could be easier?

Not a thing. This is fine. It's just a matter of understanding what the 
value is, where it is coming from, and what number you are really showing 
(it's simply a value from some point of reference). In the Javatc secondary 
outputs, you will see a secondary Cdc inductance and it's value for this 
coil is about 35pF when the coil is unloaded. This is the low frequency 
capacitance of the secondary and has nothing to do with the toroid (but the 
ground plane does affect it because even at low frequency, the coil is 
still influenced by the ground plane). Note, it is not the 16 or 17 pF 
calculated from Wheeler.

>What do you believe is incorrect with the above calcs?

It's not a matter of "incorrect". It's a matter of understanding what it is 
that is stated (self C). Quite a broad term without some type of reference. 
Like I said, I have no problems with using this value (the combo of an 
operating freq. with a low freq. equation) as long as the end result is 
near to the approximation. In the case your using, your 34pF for topload is 
fine, but don't assume that 34pF is the "real world" capacitance of the 
topload. It's just the value derived after using the method I described above.

>Note that the above calcs are  straight forward and not a back calculation
>as you mention.

I simply meant that C was found from L (nothing more).

>Note that this also includes the minor change in the secondary coil self
>capacitance that you mentioned when the toroid is on top. It also takes care
>of the ground plane, reduction factors, etc.

No it doesn't. It is simply the value you derived from the two mismatches 
of low freq. L with an operational frequency. Yes, it does include the 
entire system (i.e., the loaded freq). But the topload value is still a 
function of the methods stated above.

Here's how I see it.
The end result is to approximate the real world system (loaded Fres and 
other values if desired at this frequency) so that some type of accuracy 
can be counted on during the construction, design, analysis, testing 
against measurement, or whatever the user chooses to do. If the calculated 
frequency is off more than one would like, then it's geek intuition to want 
to know why. Beyond the user inputs, program error, etc.., it's nice to 
breakdown what is going in the program (was something not accounted for?). 
In the past, we always used the "top load" as the default fall guy for any 
error. The topload always takes up the slack, by factor, or whatever.

Thanks to Paul's work in this area, these quantities which were previously 
billed out to the topload are starting to be understood as to their 
relationship with the system. I speak of Paul mainly because he has so 
directly inspired the TSSP measurements and testing (which is basically 
trying to understand and correctly account for the physics involved). But 
it's not only Paul, it's also all the people who made measurements and/or 
helped in discussions and all that stuff which goes into that engineering 
mode of analysis. I don't  claim to understand it all, but I am trying to 
at least get a handle on the pieces of the pie.

>You mentioned that the secondary capacitance changes when operating at Fres.
>Can you explain this in more detail including the frequency equations that
>shows this effect other than the equation shown above?

I will attempt to, but I'll state it in simple terms (as I understand 
things), however, Paul or whoever may want to intercede and add detail.

At low frequency's, the currents measured at different points along the 
coil will measure the same current value. Feed it a 60 Hz signal and 
measure at different points along the coil. You will measure the same 
current regardless of where you measure.

However, apply RF, say 150 kHz signal to the coil, and measure at different 
points. The current at each point will be different (how much a difference 
depends on the coil and source). This is due to fields generated by high 
frequency (both electric and magnetic). The reason for this "non-uniform" 
current and voltage through the coil is due to the change in the 
distribution of electric charges along the surface of the conductor at high 
frequency.

John, I cannot explain correctly how frequency affects the charge at each 
point along the coil (there are better sources than I to explain that 
detail). But I do realize that it definitely does change. At some point, I 
will be able to explain in my own words, but I am still in the learning 
stage here. What I do understand is that there are RF effects on the 
current and potential along the coils length. Because of that, if the 
current isn't the same at the base as say 2/3's up the coil, then there is 
a capacitance of the coil which is not as it was just sitting there with a 
DC meter applied to it. After all, when you measure capacitance, your meter 
is measuring a lumped value (of which the meter decides). If your meter was 
capable of RF measurements (most are not), then you would still measure 
some lumped value. The term "Ces" (effective shunt capacitance) which has 
been thrown around is nothing more than a "lumped' capacitance. It is a 
representation of a capacitor charged to Vtop (since that is what were 
after), a lumped value, which considers the affects of the internal and 
external capacitances at the operational frequency. I wish I could explain 
more exactly how this is done and all that goes into it (but Paul would 
have to do that, and has to dome degree with pn2511 and pn1401).

Paul's Geotc satisfies many terms stated in his pn2511 and pn1401 papers ( 
which are probably still a work in progress ). All I do is provide Geotc 
the inputs from the user, wait for Goetc to finish (in Javascript, these 
solutions can take some time), and then process the information back to 
Javatc's outputs. What I do know for sure, is this particular coil we are 
discussing is a wonderful coil and performed well. Javatc is very close on 
both unloaded and loaded frequency's. The only problem was my initial 
representation of the strike ring. After correcting that, Javatc showed 
pretty darn close the coil (for what that's worth). In your program or even 
the old Javatc, this would not have been possible (hit or miss maybe 
depending on our topload reduction factors). But Pauls' Geotc eliminates 
the need for a topload factor - period! I must also point out that Javatc 
isn't in a high resolution mode here. It is a happy medium between accuracy 
and process time.

But just like any program on this planet, the user must get the inputs correct.

>What equations show the capacitance changes when the currents are displaced?

Yes, good question. Not something that is easily put down in an email very 
easily. But, pdf format is easily read by probably everyone on this list, 
so there are  almost no excuses.

Please go through the equations and explanations of
http://www.abelian.demon.co.uk/tssp/pn2511.html
http://www.abelian.demon.co.uk/tssp/pn1401.html

and for examples of the distribution, please see
http://www.abelian.demon.co.uk/tssp/pn1710/

>I agree it would be silly to think only the top load capacitance is
>affected. The above calcs show the secondary self capacitance also is
>affected.
>
>I agree it is "misleading" to state the top load capacitance is reduced,
>etc. This refers to a reduction from the INCA capacitance. As I said above
>the INCA capacitance has nothing to do with the toroid capacitance when on
>Tesla coils. The INCA capacitance conditions never match the conditions
>around Tesla coils.

No, of course not, but they are "part of it". The part missing is the 
influence of the ground plane and anything else around it that is within 
close enough proximity to affect the toroid to some degree.

>I agree with your equation for solving for C. Why can't the Wheeler
>inductance L be used in this equation?

Oh, it can, but sure helps if clarity is given to it's use. So can Snow, 
Lerenz, Lundin, Kirchoff, Maxwell, whoever... The idea is just to set the 
stage correctly. Let the low frequency inductance be stated as such. Let 
the operational frequency be known as such. Let whatever capacitance you 
derive from these two values be a derivation of these. You could even let 
the free-space capacitance be just what it is. If these values are "used" 
(as they are) in conjunction with a factor to derive a correct loaded 
value, then super! That is the goal. There's nothing "wrong" about it. 
Except to say that "this" equals "that", when there are far more factors 
that go into "that", and it's not always something easily jotted down on 
paper (at least by me).

>The L and C inputs you are using give
>you frequencies that do not agree with the test resonant frequencies. Why
>bother using these inputs?

No, they agree just fine as shown above. What makes you say that?

>If you have the two real world resonant test frequencies and a computer
>program why not use this combination to find the real world secondary coil
>and toroid capacities as I show above?

Sure, why not. But if the program can show what you should be measuring, 
then better yet. The horse in front of the cart.

>A relatively simple job. Note that
>this takes care of the distributed current effects, the toroid reduction
>factors, etc.

>Bart - My Ctop calcs are not recent. I have been trying to point out to
>coilers for many years how the real world TC coil self capacitance and
>toroid capacitance   can be found by using the real world resonant test
>frequencies. The problem is that most coilers are not interested.

I think they are (not everyone of course, but a select few, even a few who 
rarely post on TCML I think). I am one of those coilers that was interested 
and is why I became involved in the first place.

I've gone through frequency measurements with different sized toroids on 
the same coil, changing toroid positions from zero to nearly a couple feet 
above. I noted the frequency changes with position and posted here. During 
that time, I was attempting reduction factors for the old Javatc. These 
factors are nothing new to me. If you remember, at that time, the List 
consensus was that the toroid factor was typically about 20%. I was stating 
that in my findings, I found it to change from 10 to a little over 30% 
based on the coil geometry, toroid geometry, and position.  In other words, 
one coil might come out "right on the money", but the next might not. The 
toroid reduction was eventually realized to be a little more variable than 
20%, "if we are looking at C as based off a low frequency L".  That was the 
viable method at the time.

But now my brain has been forced open. I have come to realize that L and C 
are affected at high frequency, I have come to terms that the change in 
topload previously stated, even by myself, must now be put in perspective. 
Paul's "gift" of Geotc is something that evaluates much of the items 
identified here and much more not identified. Geotc isn't simply a Javatc 
or Fantc "thing". Anyone could use it in the same way (or maybe 
differently). I know JCHTES runs with an ASP shell for online calculations. 
Geotc is written in JavaScript, and ASP has no problems with running 
JavaScript. I would imagine the integration would be pretty easy. It's just 
a matter of passing inputs to Geotc, let Geotc do it's thing, and pass the 
answers back which can be displayed, as well as used for other misc. items 
(which is one with some items in Javatc).

If you should ever decide to go that route, let me know. I'll help in 
anyway I can and show you how Javatc processes info to and from. I am not 
glory bound with Javatc. Paul's Geotc does all the real work and deserves 
all the glory if any is given. Heck, I'm just a garage coiler like most on 
the TCML.

Take care,
Bart