Re: Why the difference in Fo WinTesla & Fantc?

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

Original poster: "Barton B. Anderson by way of Terry Fritz <teslalist-at-qwest-dot-net>" <classictesla-at-netzero-dot-com>

Hi Brad,

Here's the deal. WinTesla, JavaTC, JHCTES, etc.., are "coil design 
programs" which take our basic coil parameters and output inductance's, 
frequency's, and other relevant data for building and tuning a Tesla Coil. 
FANTC is a program not based on the design of a Tesla Coil but the 
"analysis" of coils and toploads. All external objects near and around a 
coil will change it's overall frequency (various reasons). Obviously, it is 
very handy when used "in conjunction" with TC design programs which have to 
be tweaked to better represent the coil within it's environment.

All the design programs are good and will get you close enough in-tune if 
given accurate input measurements. Depending on the coil geometry, some 
programs may fair better than others on any given day, but they will all 
get you close. It should also be noted that trial and error can get you 
there as well. In all these cases, one should never depend completely on a 
program to determine "exactly" where the coil is tuned. Primary's should 
either be mocked up and tested with scrap wire or built longer than 
calculated to ensure an adjustment window. Secondary's have also been used 
in tuning by removing a turn or two at a time.

More below on your coil:

Tesla list wrote:

>Original poster: "by way of Terry Fritz <teslalist-at-qwest-dot-net>" 
><CoolCorals-at-aol-dot-com>
>
>   Hello, I have recently posted some questions to this group regarding my 
> first attempt at a TC.  I had some primary inductance differences in Win 
> tesla.  I have recently tried the Fantc also.  Now, my coil is pretty 
> well totally built off of Win tesla's program to resonate at 
> 500Khz.  Putting the same info into Fantc shows a secondary resonate at 
> 580-610Khz depending on height from ground plane.  If the Fantc is right, 
> then my coil is WAY out of tune, but if Win Tesla is right, then I should 
> be.  Could you please help me with this problem?  Any info you may offer 
> will be great!!
>
>Thanks, Brad K.
>
>Spec's:
>SECONDARY:  Built on 2" PVC = 2.37" x 22.2" Tall of 22 gauge Magnet 
>wire.  The actual TPI I ended up with was 36.28 which yields 781.15 turns 
>& 485'.  My Tested after built = 3.825mH     Win Tesla = 
>3.68mH     Fantc  =  LDS=3.91mH

Looks like your close on any of the programs here. I would trust your 
measurement. Also, putting in these "exact" numbers into Fantc, I yield 
3.83mH = your measurement. I ran a "Secondary Inductance" Analysis. Here 
are the inputs (note assumed 20" off the ground and 100" on surroundings. 
These assumptions affect any analysis where capacitance is used. It does 
not affect this inductance analysis):
http://www.classictesla-dot-com/temp/bradk1.gif

>TORROID:  From above secondary Win Tesla shows a 4.25" x 13.45" Torroid 
>being 19.47pF.  Fantc shows this at 14.97pF I used AL duct tubing and foil 
>for the top and bottom plates.  It is wrapped on a cardboard form to hold 
>shape.  The built dimensions are exactly that above.  How do you test this C?

This is tested by measuring the frequency of the coil outside away from 
ceiling and walls. Then place the topload on and measure again. Now bring 
the coil into your "coil place" and measure again. All three frequency's 
will be different. Just calc the differentials in capacitance between the 
three and you will have a pretty good idea of your toroid capacitance and 
the capacitance of the resonator (coil + topload) in proximity to your 
running surroundings. Note, the earth can't be moved, so you'll just have 
to know that the earth does effect the coil and topload capacitance. But if 
anyone cares to fund me, I'll volunteer for the next shuttle mission to 
make this measurement some distance away from the earth <grin>.

Fantc gave me 15.13pF when the toroid is modeled by itself, 15.32 modeled 
with your toroid plates, 14.57pF in a "Resonance Analysis" on the coil 
along with everything else. Also note, I assume the coil is 20" off the 
ground and position the toroid to suit. Your numbers and my own will differ 
as I have to assume a few things. The top and bottom plates used on the 
toroid will add to the capacitance (it's effect is small in your case). You 
can use the Disc topload input to add these to the system. I used 2 discs 
and position top and bottom of toroid. Here are images of the topload with 
discs and the inputs used.

http://www.classictesla-dot-com/temp/bradk2.gif
http://www.classictesla-dot-com/temp/bradk3.gif

>PRIMARY:  Primary is wrapped on 4" 1/8" thick clear Acrylic.  I used 6 
>gauge wire and have a total of seven turns.  The final coil width was 2".

Ok, I have to ask. Is this a helical primary, conical, or flat spiral. When 
you use the term "coil width", it's easy for one to assume a 2" flat coil 
width. But, if that were the case, the inductance would be much higher and 
the turn to turn spacing would be "squeezed" together (not a good idea). 
However, if the 2" is the "height" from the bottom winding to the top 
winding measured center-of-conductors, then the inductance and coil work 
out ok. Thus, my inputs in the first gif image above. There, the bottom 
primary winding is parallel to the bottom secondary winding. Here is what 
the whole system would appear if these assumptions are correct (50/50 shot).
http://www.classictesla-dot-com/temp/bradk4.gif

>   I had asked on this before and tested actual Inductance is 
> .005945mH.  Win Tesla .0097.  Using formula.0054mH and I was answered 
> fantc showed .0055 I believe.  I have since finished the spark gap and 
> tank wires.  The connecting wire is 6ga stranded power cable.  With these 
> on I retested the whole primary inductance with tank wires.  I now 
> test  .0095uH  This should be the TRUE FINAL inductance.  This is all of 
> the wire that will be in there.

Use your measurement. Due to the small inductance to begin with on this 
coil, the cabling is obviously significant. The shorter, the better. If you 
can reduce lengths, it will help. As it is now, 4uH of cabling inductance 
will mean the actual tuning on your coil will be less than 7 turns. You do 
realize the coils h/d ratio is large? I'm not sure how this coil is going 
to perform.

>NEON:  Franceformer 6000v -at- 30ma.  the max cap would = .0133uF.  I don't 
>want to blow the ballast so I thought I would run a smaller cap.

Well, due to the tuning issues you will be running into, I wouldn't go up 
in capacitance. Reducing capacitance will allow more turns.

>SPARK:  4-1/4" Brass Tubes adjustable spacing.  This makes a 3-series gap.
>
>TANK CAP:  I am going to use a sort of adjustable MMC setup for tuning the 
>primary.  I have Hi-Q .005uF -at- 4Kv and have hooked up 18 total.
>3-series & 6-parralled.  This totals 12Kv and tested at .0107uF.
>Going from the actual final inductance this should be 499.1 Khz.  I have 
>some others so I can change the C if I need to.

Good idea. This will indeed help with keeping the coil within a tuning window.

>Now, win tesla shows that with the above stats, my secondary will resonate 
>at 505 Khz, but it's Inductance was low.  Using the formula plus win 
>tesla's Torroid C and self C shows now a Fo at 495.6Khz.
>Pretty close to my tank and the whole 500Khz starting point.  Here's the 
>kicker, Fantc, (as long as I inputed everything right) shows the resonance 
>test at 589-610 Khz!!!   That's a HUGE difference.  Before I fire this up 
>for the first time I thought I should ask you experts.
>Sorry for being so long, I just wanted you to have all of the info.
>Also, my last post I found I messed up on parameters, but these shown are 
>right.

Well, I'm showing even a little higher at 652kHz if built with my 
particular assumptions. Don't worry too much about what one program sees 
over another. In the end, it appears you have a good idea with the MMC 
adjustability. You can make this coil stay within the confinements of your 
primary. If not, you can always change something. Most of us have improved 
on our coils one component at a time, one mistake at a time, one success at 
a time.

Don't get bogged down with program discrepancy's. These are just tools to 
help. But if it's a first coil and the first time using these tools, they 
can be confusing. A coil can be built with paper and pencil in hand or 
less. Trial-n'-error is as good a teacher as any, and sometimes better (if 
one works at finding out "why the error/success"). The only way programs 
pop out exactly the same numbers is if they use the same inputs and 
equations. Often, this actually happens, but not for every item. Fantc is 
not a calculator like the other programs, so it will never run exact same 
numbers as the calculator programs (except by chance). It's accuracy is 
"very" high, but only with all the parameter inputs for the analysis you seek.

Take care,
Bart


>Thanks for your help and sorry for asking so many questions.  I hope they 
>don't sound dumb.
>
>Thanks, Brad K.
>