A Back-To-The-Basics Tesla Coil

[uusedman]

Next question, how do you make them higher or lower frequency?

Thanks

[seth]

Next question, how do you make them higher or lower frequency?

Thanks

I think the frequency depends on...

a) the capacitor you use
b) the spark gap distance
c) the transformer ratings

but again i could be wrong.

Build the one thats on this page and i guarantee it will also be high enough frequency to exhibit ''the skin effect'' thus rendering the arcs harmless. Please correct me Jeff, if im wrong.

Some things that are fairly dangerous are the capacitors, spark gap and transformer - they will certainly give you a shock which bites if you touch them without discharging first. So dont touch them.

[cody]

Next question, how do you make them higher or lower frequency?

This is going to be set by the parameters of the secondary coil you build which will determine its resonant frequency.

You can do a little figuring before constructing the secondary if you have a target frequency in mind. Use something like this online calculator to play with the values of L and C on the secondary.
SSTC Calculator
and dont forget to add C from the topload,
figure the C of the topload and add it in the calculator
DeepFriedNeon - Tesla Coils
Hit "Calc" and it will spit out a frequency below.

I always feel safest by actually testing the coil and topload to determine the exact frequency it resonates at. With a function gen and o-scope like this.
YouTube - Tuning A Tesla Coil with an Oscilloscope

From there, at least with a spark gap coil, you will set up the primary L and C to resonate with that frequency. There are many other things to consider of course, but the secondary is basically whats going to determine the frequency you use.

[Ajay]

Tesla's Bucking Induction Coil

Hello
I recently wound a small multi layered coil similar to the one Tesla spoke about in his London lecture.
The strange thing about this type of coil is that the inductive coupling between the primary and secondary seems to be minimized, while the resonant coupling is maximized.
After reading some of Kinraide's work, I came across an interesting part of his patent that relates to this coil (found on Jeff's page). He says that he wound the primary and secondary with strips of conductors instead of thin wires as they are usually employed. By doing this, he raised the capacity of the coil which, besides lowering the frequency, changed the abruptness of the discharge.
I realized that since Tesla built such massive coils, his coils must have had a rather large self capacitance in the secondary as well. I will rewind my secondary with thin copper ribbon if I can just to see how that changes the discharge, but here was my original mock up coil (insulated with tape, driven by a 50kv induction coil in a Tesla type disruptive discharge circuit)

[Bob Smith]

Hello
I recently wound a small multi layered coil similar to the one Tesla spoke about in his London lecture.
The strange thing about this type of coil is that the inductive coupling between the primary and secondary seems to be minimized, while the resonant coupling is maximized. After reading some of Kinraide's work, I came across an interesting part of his patent that relates to this coil (found on Jeff's page). He says that he wound the primary and secondary with strips of conductors instead of thin wires as they are usually employed. By doing this, he raised the capacity of the coil which, besides lowering the frequency, changed the abruptness of the discharge.
I realized that since Tesla built such massive coils, his coils must have had a rather large self capacitance in the secondary as well. I will rewind my secondary with thin copper ribbon if I can just to see how that changes the discharge, but here was my original mock up coil (insulated with tape, driven by a 50kv induction coil in a Tesla type disruptive discharge circuit)

Ajay, is this the coil winding description you are referring to (below)?
Bob

The coil consists of two spools of hard rubber R R, held apart at a distance of 10 centimeters by bolts c and nuts n, likewise of hard rubber. Each spool comprises a tube T of approximately 8 centimeters inside diameter, and 3 millimeters thick, upon which are screwed two flanges F F, 24 centimeters square, the space between the flanges being about 3 centimeters. The secondary, S S, of the best gutta-percha covered wire, has 26 layers, 10 turns in each, giving for each half a total of 260 turns.

The two halves are wound oppositely and connected in series, the connection between both being made over the primary. This disposition, besides being convenient, has the advantage that when the coil is well balanced—that is, when both of its terminals T1 T1 are connected to bodies or devices of equal capacity—there is not much danger of breaking through to the primary, and the insulation between the primary and the secondary need not be thick.

In using the coil it is advisable to attach to both terminals devices of nearly equal capacity, as, when the capacity of the terminals is not equal, sparks will be apt to pass to the primary. To avoid this, the middle point of the secondary may be connected to the primary, but this is not always practicable.

The primary P P is wound in two parts, and oppositely, upon a wooden spool W, and the four ends are led out of the oil through hard rubber tubes t t. The ends of the secondary T1 T1 are also led out of the oil through rubber tubes t1 t1 of great thickness. The primary and secondary layers are insulated by cotton cloth, the thickness of the insulation, of course, bearing some proportion to the difference of potential between the turns of the different layers. Each half of the primary has four layers, 24 turns in each, this giving a total of 96 turns.
Then both the parts are connected in series, this gives a ratio of conversion of about 1:2.7, and with the primaries in multiple, 1:5.4; but in operating with very rapidly alternating currents this ratio does not convey even an approximate idea of the ratio of the E.M.Fs. in the primary and secondary circuits. The coil is held in position in the oil on wooden supports, there being about 5 centimeters thickness of oil all round. Where the oil is not specially needed, the space is filled with pieces of wood, and for this purpose principally the wooden box B surrounding the whole is used.

The construction here shown is, of course, not the best on general principles, but I believe it is a good and convenient one for the production of effects in which an excessive potential and a very small current are needed.

In connection with the coil I use either the ordinary form of discharger or a modified form. In the former I have introduced two changes which secure some advantages, and which are obvious. If they are mentioned, it is only in the hope that some experimenter may find them of use.
Experiments With Alternate Currents Of High Potential And High Frequency - A Lecture Delivered Before The Institution Of Electrical Engineers - London - 1

[Ajay]

London Coil Clarification

Ajay, is this the coil winding description you are referring to (below)?
Bob

Yes, this is the coil and the lecture which I am referring to.
Ideally, I would like to replicate the coil exactly as Tesla described, but it would be very complicated and time consuming to construct. So I decided to start with a smaller model.
Unfortunately, I discovered that building a smaller model is the same as building a higher frequency model, and since I am using spark gap circuits, this is impractical.
I am rewinding the secondary with about 500 turns of #24 (250 on either side) to lower the frequency.
This coil is very similar to that used in Tesla's one wire transmission of electricity patent. It is basically two counterwound Tesla coils excited at a quarter wavelength and grounded into each other at the neutral terminal.
This way both of the terminals will have a massive difference in potential at any given time, which is why it is referred to by Eric Dollard as the "perfected" induction coil.

[mikrovolt]

Video by spark_starter has a lot of content.
A combination of simulation and maker skills also his presentation is clear
about what coupling factor is. Simulation has more possibilities.

https://youtu.be/JwzjeQVpS2A