Re: Is this design OK?

["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 Karen & Ramon,

I went through JavaTC and Fantc on your coil and have some info for you 
below. However, I would like to point out your coil is quite low on 
secondary turns compared to the normal Tesla Coil. This doesn't mean it 
won't work well. I haven't experimented with such low turn coils, so I 
can't give much in the way of experience. I was curious to see how the 
programs would do on your coil.
More below:

Tesla list wrote:

>Original poster: "Ramon van der Hilst by way of Terry Fritz 
><teslalist-at-qwest-dot-net>" <enqrypzion-at-yahoo-dot-com>
>
>Hey all,
>
>We've mailed to the list before, after checking our NST. The question 
>raised whether the 54.8VAC measured with an input of 2VAC was the RMS 
>value. When we connected the measuring device to the wall :) it gave 220 
>VAC, so we're sure it's the RMS value. As we need the coil to be taken in 
>an airplane, we'll try to make it quite small. The following specs are 
>estimates for our final design, we wondered what your opinion is on them 
>(calculations made using JavaTC):
>
>Secondary:
>
>Diameter: 2.7759 in
>Height: 11.81 in
>#18 magnet wire:
>Bare wire Diameter: 0.0403 in
>Insulation Thickness: 0.0015 in
>Spacing: 0.0009 in (errors...)

So, 267.2 turns.

>Top Load:
>
>Spherical: 7 inch diameter
>Top Terminal Reduction: We have no idea so we entered 10 percent.

Yes, this is very misleading. It is actually an adjustment which should be 
used to adjust the resonant frequency of the coil and affects the total 
system capacitance (not just the topload). Fantc shows 8.58pF with 
conditions I set up for the program (that info is below), but note, Fantc 
also shows 11.76pF shunt capacitance. JavaTC has difficulty with some 
geometry's. This has come to my attention since the advent of Fantc and 
obviously affects the resonant frequency. When I run JavaTC, I also use 
Fantc. I usually go back and forth between programs adjusting the Top Load 
Reduction in JavaTC to match the frequency Fantc delivers. When JavaTC is 
adjusted, the system should be auto-tuned which changes the turns and 
primary outer diameter (for flat coil). I update Fantc with this new info 
and run the Resonance Analysis again. I repeat this procedure until I get 
convergence of the resonant frequency between the two programs. This sounds 
a little nuts, and is why JavaTC has been updated off-line to run some 
Fantc iterations and remove this redundancy, however, until I can fix a 
specific issue I am having with the auto-tune feature, the new version of 
JavaTC will have to wait.

For your system, the Top Load Reduction should be set to 39.7 for a loaded 
resonant frequency of 1464kHz.

>Secondary self resonant frequency: 2158.95 kHz
>Loaded Resonant Frequency: 1313.23 kHz

>Primary: We would like to use copper tubing yet we haven't got a clue 
>where to get it 'in a box' > already in a spiral :S
>
>Inner Diameter: 5 in
>Wire Diameter: 0.3937 in (1 cm)
>Wire Spacing: 0.3937 in (1 cm)
>Number of Turns (tuned): 3.3714
>Angle: none
>
>Coupling (calculated): 0.0579 (dunno wheteher that is good or bad)

That's BAD (probably). You didn't give information about the location of 
the primary to secondary. I performed my routines with the assumption that 
the flat primary is "even" with the bottom turn of the secondary. JavaTC 
showed coupling at 0.1296, Fantc showed 0.1285. I suspect an input was left 
blank either in the secondary or primary inputs when you acquired the 
number above.

>Tank Cap:
>
>7x in series: a .022uF 2000V MKP cap and a .015uF 2000V MKP cap in parallel
>giving 5.3 nF -at- 14kV > 5.3 nF is the resonance amount for the NST.
>
>NST:
>
>Rated Vin: 220
>Rated Vout: 6028
>Rated mA (we didn't measure this actually, really should do that soon :S > 
>value that is on the box): 10 mA
>Hertz: 50
>Applied Vin: 220 (eventually ;-) )
>
>Amps across the spark gap (vented by a 1400W vacuum cleaner motor): 371.7
>effective Vout: ~164000
>Spark Length (John Freau): 13.2 in
>
>to us it seems fine, yet on some sites people warn you for a little amount 
>of turns on the primary, would that be a problem or should we simply raise 
>the primary/secondary to spread the magnetic field better?

As mentioned, the turns are low. You top volts will also be low and I 
suspect the surface field stress at the sphere will be low and possibly 
problematic. But, I'm a firm believer in proving out suspicions. In other 
words, if you already have this coil built, why not try it and see how the 
low turn coil reacts. I would suggest the same as far as coupling (try 
various ratios of mutual inductance).

>any other comments are really appreciated aswell!
>thanks in advance,
>
>Karen Oud & Ramon van der Hilst



Ok, here are some numbers provided by Fantc which I feel will accurately 
model the real deal based on my own experience and use of the programs:

* The coil is in a enclosed room with approx. 100" to nearest wall and 150" 
from ground to ceiling (my garage).
* The coil is 20" above the ground plane.
* The sphere top terminal is setting just above the coil.


Primary Inductance (L1): 2.179 uH
---------------------------------------------
Secondary Inductance (L2): 1.049 mH
---------------------------------------------
Mutual Inductance (L1,L2): 6.163 uH
Coupling Coefficient(K): 0.128883
---------------------------------------------
Secondary Resonant Frequency: 1464.53 kHz
---------------------------------------------
Effective Series Inductance (Les): 1.01 mH
---------------------------------------------
Effective Shunt Capacitance (Ces): 11.76 pF
---------------------------------------------
Total Topload Capacitance (Ctop): 8.58 pF
---------------------------------------------

I'll think you will find these numbers very accurate. Measurement will tell 
the tale.

Take care,
Bart