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Re: calculations



Original poster: "Barton B. Anderson" <bartb@xxxxxxxxxxxxxxxx>

Hi Michael, All,

I have to correct my h/d ratio which I stated. I forgot to mention that I was using a base height of 20" (bottom of secondary off the floor). Thus, the h/d of 4:1 is 16" and 5:1 is 20". Wherever I wrote 36" I meant 16" and wherever I wrote 40" I meant 20". Sorry about that.

Take care,
Bart
PS (Thanks Justin for bringing this to my attention).

Tesla list wrote:

Original poster: "Barton B. Anderson" <bartb@xxxxxxxxxxxxxxxx>

Hi Michael,

4" diameter would be good. We average a diameter to height ratio of 4 to 5. Thus, your coil length might be 36" to 40". With the 30awg size you suggested, you can expect 1350 turns for the 4:1 h/d to 1700 turns for the 5:1 h/d. If you desire to build somewhere in the neighborhood of 1000 turns, then 26 awg will yield 1100 turns for the 5:1 h/d coil.

The 4kV, 30mA is a rather low voltage, but it has been done (about 15" sparks are possible). It appears your trying to build around a particular cap size which I assume you have already built or purchased (4800pF)? Ok, you can do that. But first, the .0199uF which Javatc calls out down in the transformer outputs is the resonant capacitor value at which a 60Hz resonant circuit will be established for the transformer parameters you entered. This "does not" indicate that you are required to use this value for the tank cap. The value is there as a reference tool. (Usually, so that you can stay away from this value). There are circuits where this value would be beneficial, but that is beyond the scope of my reply here. For info on resonant charging, see http://www.richieburnett.co.uk/resonant.html#resonant.

Also, the primary using 1/4" copper tubing is perfect. Simply enter the wire diameter. Solid wire or tube is not a factor with non-magnetic inductors, only the geometry is required. Keep about a 0.75" to 1" space between the inner turn of the primary to the secondary (this value measured at the inner start of the primary).

If you were to go for the 5:1 h/d above at 1100 turns, your looking at a self-resonant frequency of 389 kHz meaning the coil has no topload. The primary at 2.75" i.d. and 8.25" o.d. (1/4" tubing w/ 1/4" spacing) will be right at 390 kHz with the 4800pF cap size. Of course, you will add a top terminal for spark discharge. If the terminal is very small (say a 3" sphere placed 5" above the coil), the secondary resonant frequency will drop to 337 kHz. Seems dramatic for a small sphere, but it is what it is. A large toroid or similar object will drop the frequency even farther. The top volts will be low with your transformer (about 130,000) and a large radius of curvature will make breakout difficult. If you do use a toroid or similar, you may need a breakout point of some type.

In any respect, the topload drops the frequency, so with a fixed cap size, you will need to adjust the primary turns. For reference, when you see the secondary frequency lower, you increase your primary turns to lower the primary frequency to that of the secondary for resonance. For the sphere dimensions above, this would work out to 12.6 turns. It's a good idea to run the coil with scrap wire (sloppy is ok) to experimentally arrive at the actual turns you will need, then later build the nice tube primary for the topload size you decide on. If you plan to run different toploads, then build the primary for at least the largest topload you will use.

The gap will likely be a static gap of some type. Due to the low voltage transformer, the spacing will be pretty close and the electrode diameter will be thin. For example, you will probably need to stay in the range of a .125" diameter at a very narrow .08" total gap. It will heat up fast and runs will be short (sparks drop fast as the electrodes heat up and begin to conduct across the gap at lower and lower voltages). A fan will be necessary to aid electrode cooling.

Any questions on Javatc's use, just contact me offlist.

Take care,
Bart



Tesla list wrote:

Original poster: "Michael Ong" <omenowner725@xxxxxxxxxxx>

thanks for your referals to go to those sims they work wonders. also, i think i am going to go with a 4 in diameter instead like you suggested the inductance is a lot higher. however, i do have a few more questions that have been confusing me with these simulators. the first is if the res cap size for a 4kv 30ma 60hz transformer is .0199 uf why does the coil i am trying to build call for a 4800pf cap? the next question i had was that i pan on using 1/4 inch copper water tubing for the primary. since this is hollow is there a way for javatc to take into account that the wire dismeter is not a solid 1/4" but instead a hollow tube with a certian thickness?
thanks again for all your time and willingness to help beginning tesla coilers like myself.


From: "Tesla list" <tesla@xxxxxxxxxx>
To: tesla@xxxxxxxxxx
Subject: Re: calculations
Date: Fri, 11 Nov 2005 21:05:59 -0700

Original poster: "D.C. Cox" <resonance@xxxxxxxxxx>



Since your voltage is so low, I would definitely consider going to a 4 inch dia coil as inductance goes up as square of the radius of the coil and inductance x rate change of current (dI/dt) is what produces voltage.

Dr. Resonance


hello, i am going to be building a tesla coil modled after one on the internet that's a 4kv 4800pf primary 11 turns of 1/4 inch coper secondary 1000 turns of 30 AWG with a pvc diameter of 2.5 inches. i was wondering how do you get these numbers. like how do you know how wide the coil has to be. or the turn ratio, or how do you find the frequency of the coil so you can determine the value of the capacitor you need. any calculations that you guys know to solve for these things would be very helpful. i would like to get to the point where i can make a coil totaly on my own. thanks agian for all the help
-michael