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Author Topic: Build a Tesla Coil (the way Tesla built them)  (Read 2245 times)

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My work lately has been focused going back-to-basics, replicating Eric Dollard's Borderlands-era experiments like Cosmic Induction Generator and telluric (through-the-earth) signal and power transmission.

The work has brought me to the 'Extra' coil.   Many people have seen the classic 1890's photos of Tesla in Colorado Springs, but few seem to notice how little the coils he photographed look like what we call 'Tesla Coils' today.  His coils had dozens of turns instead of hundreds/thousands.  His primaries were 1-3 turns of copper strap along the wall of the building, and secondary windings of less than a dozen.   I will delve deeper on this covering the Oudin oscillator at some point and how it more accurately reflects 'modern' Tesla Coil designs.

A 'modern' Tesla coil use a primary and secondary.  A few advanced designs (perhaps 1% or less?) employ an Extra coil to generate high voltage, high frequency oscillating currents.
What if I said that every high-voltage coil I've worked with in the last 6 months has had no primary and no secondary?  Just a single Extra coil fed with one wire is enough to generate massive potentials at extremely high efficiency.   Enough that I can light full florescent tubes from several feet away on less than 5 watts (ex: any common function generator). 8)

Instead of starting with a primary+secondary and adding an extra later, I recommend starting with an Extra and working backwards from there.
From a technical standpoint, it is simply a quarter-wave end-fed antenna, but due to the nature and balance between magnetic and dielectric fields, the Q factor of such coils can reach into the hundreds, with tuning so sensitive that moving your hand several feet away is enough to throw them off.   Lots of interesting effects and potential IMO. ;)

Physical construction aside, between Griffin Brock and myself, we have managed to improve the predictive formulas Dollard presented in the Crystal Radio Initiative significantly, to deliver an Extra coil calculator that's quite a bit more accurate than the others online:
https://hakasays.com/DollardTeslaCoilCalculator
(Griffin's page: https://griffingbrock.com/)


This is sort of a teaser-post, I will cover physical construction and design specs in a future post, and eventually some unique and simple experiments we can perform with them.  I will also be covering all of this at the ESTC conference next month in Spokane. ;)
   
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Sirs
A very impressive portfolio ..and inspirational!
I also noticed your seismic work, we had a few
Members here doing seismic work years back ,
one member Groundloop ( who has not been heard from in quite
Some time !
And another researcher wavewatcher, ( I will try to get a message out .

Been sharing your topic with open source researchers globally whenever I can !

Respectfully
Chet K

   

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Another invention in the same era as Tesla was by Paul Oudin, whose oscillating circuit more closely resembles what we call a Tesla Coil today.
When we compare a 'modern' Tesla coil with coils from Colorado Springs, the similarities and differences start to become evident. 

Similarities:

* Both generate high-voltage currents at high frequency.
* Both employ a secondary with a low-impedance path to ground.
* Both employ a dielectric topload.
* Both employ a tuned primary circuit loosely-coupled to a free-oscillating secondary.

Differences:

* Oudin oscillator uses two coils.
*Tesla's used three.

* 'Modern' Tesla Coils have hundreds or thousands of turns of wire, as did Oudin's.
* Tesla's secondary coil @ Colorado Springs had fewer than 3 dozen turns on the secondary, and fewer than 200 turns on the extra (you can see the primary+secondary windings along the perimeter of the room).

* A 'modern' Tesla Coil has a many-turn primary, as did Oudin's.
* Tesla's primary had 1-3 turns.



In-practice, the main difference is that in the Colorado Springs arrangement, the Extra coil was center-stage, with the primary+secondary serving as a loose-coupled step-up transformer.

By having an air-gap between turns of the Extra coil, a certain balance is struck between the dielectric and magnetic fields.  Rather than mutual inductance forcing the coil to behave as a single entity, self-inductance takes over turning the coil into a cascade of single-turn resonators.  The spacing also allows a much greater area to be consumed by the dielectric field creating field effects that stretch quite some distance into free space.

The result of all this is that the Extra coil (henceforth referred to as the Tesla coil) develops an extremely high magnification factor (Q factor) when wound this way.  One coil I wound has a self-resonance around 960kc, and a measured Q factor of about 280 (under 3.5kc bandwidth). ;D
   

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Buy me a beer
Excellent, a breath of fresh air.

Many ways to do what Tesla did, today we have components Tesla did not have, but what does not change is the principle of operation.

Regards

Mike


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"All truth passes through three stages. First, it is ridiculed, second it is violently opposed, and third, it is accepted as self-evident."
Arthur Schopenhauer, Philosopher, 1788-1860

As a general rule, the most successful person in life is the person that has the best information.
   

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Many ways to do what Tesla did, today we have components Tesla did not have, but what does not change is the principle of operation.

Thanks for the kind words, Contra. ;)

Tesla certainly had a different experience than we have today.  There was nothing in his day.  There were no tubes, no transistors, no scopes, no Farad or Ohm.  Just iron and copper and wood, and that was about it.

In some ways it was probably a good thing, because there were no existing standards or biases to cloud our judgement.
A year ago I would never have thought to make a Tesla Coil that had no primary or secondary.  It simply defies transformer theory (though it makes perfect sense from antenna theory :P).
   
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Hi Hakasays and thanks for your study.

I see three main points: the question of the number of turns of the coils, the question of the single coil rather than separate primary and secondary, and the question of coil spacing.

Regarding the number of turns, modern Tesla coils have many, but they are generally much smaller in diameter than the coils Tesla used. As inductance increases with diameter of the coil, it is clear that the number of turns is an engineering choice rather than a matter of physical principle.

As for the single coil, this is the principle of the autotransformer (like the "variac" when the feed point on the coil is variable).
The autotransformer has advantages and disadvantages compared to the transformer but the principle of operation is the same. Even if the two are merged in the same coil, there is always the "primary" induction circuit (between supply point and ground) and the "secondary" induced circuit (the whole coil between terminal capacity and ground).

One advantage is a better coupling between the two parts. Another advantage, which is less well known, is that the common part between the supply point and the ground, has the "primary" current from the supply superimposed on the "secondary" current from the induced current in the rest of the coil. The resulting current in this part is therefore lower because the secondary current opposes the primary current. For once, Lenz's law is with us. The gain is small, however, because the primary current is much higher than the secondary current due to the high transformation ratio. So even though the primary current is reduced by the secondary current, it is sometimes necessary to provide a larger wire diameter to support the current of the primary part, as is done in a transformer or in Tesla coils with separate windings.
I think that the interest of the autotransformer assembly is also and mainly in the simplification of the realization.

Lastly, the spacing of the coils does not affect the stored energy. This is only proportional to the inductance (and the current of course). But increasing the spacing can improve the quality factor by reducing parasitic capacitive coupling.


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Regarding the number of turns, modern Tesla coils have many, but they are generally much smaller in diameter than the coils Tesla used. As inductance increases with diameter of the coil, it is clear that the number of turns is an engineering choice rather than a matter of physical principle.

This is true, but magnetism is only half the equation in a Tesla coil.  One must also consider the capacitance between turns as well as the inductance.   Having a very small wire diameter means the capacitor formed between each turn has a smaller surface area and thus a smaller peak value.

Quote
Lastly, the spacing of the coils does not affect the stored energy. This is only proportional to the inductance (and the current of course). But increasing the spacing can improve the quality factor by reducing parasitic capacitive coupling.

Spacing between coils has to affect stored energy, since there is stored energy in the dielectric field as well as the magnetic field.  Increasing the wire diameter increases capacitance, while increasing the spacing increases the volume around the coil upon which the dielectric field acts.
This is especially evident as widely-spaced coils will have dielectric fields that can reach several feet out (easily picked up with a bare scope probe).

In the case of the Extra coil, when there is a balance struck between L and C between turns, the capacitive coupling seems to be not parasitic but additive.

Experimentally, this was confirmed by winding several coils on the same form using the same length of wire, but differing the spacing between turns.   This 'frequency compensation factor' was the hardest to model in the online calculator, and varied based on the height-to-diameter ratio ('tall' coils will have a higher freq than predicted, 'short' coils have a lower frequency than predicted.)  I'll definitely post the raw measured data at some point. O0


I look forward to working with you guys, and will help as best I can to make sure that all of the tools+data are available to you. ;)
   

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tExB=qr
What's your goal with the magnifier coil?
   
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This is true, but magnetism is only half the equation in a Tesla coil.  One must also consider the capacitance between turns as well as the inductance.

I agree.

Quote
Spacing between coils has to affect stored energy, since there is stored energy in the dielectric field as well as the magnetic field.  Increasing the wire diameter increases capacitance, while increasing the spacing increases the volume around the coil upon which the dielectric field acts...

There is probably a misunderstanding, I will rephrase and I think we should agree. The energy stored in an inductor is W=1/2*L*I² and that in a capacitor is 1/2*C*U², whatever their building. L and C are the only parameters that determine the storable energy. For the capacitor this energy is stored in part in the dielectric space.
The spacing has an impact on L and C, and thus has an impact on the stored energy. But whatever the spacing, for a given capacitance and inductance in farad and henry, the energy will be the same, that's just what I said.
I do agree that if you change the spacing while keeping everything else the same, the inductance and capacitance will change and so will the storable energy.



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There is probably a misunderstanding, I will rephrase and I think we should agree. The energy stored in an inductor is W=1/2*L*I² and that in a capacitor is 1/2*C*U², whatever their building. L and C are the only parameters that determine the storable energy. For the capacitor this energy is stored in part in the dielectric space.
The spacing has an impact on L and C, and thus has an impact on the stored energy. But whatever the spacing, for a given capacitance and inductance in farad and henry, the energy will be the same, that's just what I said.

Perhaps it would be better to say that that a critical coil wire spacing exists at-which the capacitive and inductive reactances cancel out.
I agree that a coil that contains X units of energy will always be the product of the coulombs and webers stored in the coil.



What's your goal with the magnifier coil?
Lots of tests on-deck and in various stages of completion. ;)
* Telluric (through-the-ground) radio and power transmission.  (Beer can antenna, sky-high SWR)
* Telluric time-of-flight measurement (since we're dealing with longitudinal waves, as there's a chance the velocity might exceed C (Dollard's prediction based on the Borderlands-era analogue setups was the geometric PI/2*C or ~1.53)
* Cosmic Induction Generator replication.
* Replicating some key Colorado Springs setups that I have not seen replicated by anyone.
* Musical Tesla Coil (partly for show and partly so I have a good way to modulate HF)
* Parametric variation of an intermittently-shorted coil (related somewhat to GiantKiller's work, but with a simpler and more predictable mathematical/conceptual foundation.   Basically, what happens to energy in a coil when the impedance is not constant?
* Replicate a few of Adrian Marsh's experiments (am-innovations.com).  The 'pressure field' surrounding a bulb was something I really want to do study firsthand.

* And of course, being a hyper-efficient Tesla Coil it should make a fantastic lightning show with relatively low power levels >:-)
   

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Perhaps it would be better to say that that a critical coil wire spacing exists at-which the capacitive and inductive reactances cancel out.
I agree that a coil that contains X units of energy will always be the product of the coulombs and webers stored in the coil.


Lots of tests on-deck and in various stages of completion. ;)
* Telluric (through-the-ground) radio and power transmission.  (Beer can antenna, sky-high SWR)
* Telluric time-of-flight measurement (since we're dealing with longitudinal waves, as there's a chance the velocity might exceed C (Dollard's prediction based on the Borderlands-era analogue setups was the geometric PI/2*C or ~1.53)
* Cosmic Induction Generator replication.
* Replicating some key Colorado Springs setups that I have not seen replicated by anyone.
* Musical Tesla Coil (partly for show and partly so I have a good way to modulate HF)
* Parametric variation of an intermittently-shorted coil (related somewhat to GiantKiller's work, but with a simpler and more predictable mathematical/conceptual foundation.   Basically, what happens to energy in a coil when the impedance is not constant?
* Replicate a few of Adrian Marsh's experiments (am-innovations.com).  The 'pressure field' surrounding a bulb was something I really want to do study firsthand.

* And of course, being a hyper-efficient Tesla Coil it should make a fantastic lightning show with relatively low power levels >:-)
I look forward to seeing your work and hopefully replicating it should the opportunity arise. It sounds fascinating.  I have nothing technical to add. :) I always wondered about that pancake coil on a a large fram e in the background of this portrait.
   

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tExB=qr
What is a "Cosmic Induction Generator"?
   

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What is a "Cosmic Induction Generator"?

Two monopolar Tesla Coils pointed end-to-end, such they create a powerful 'null' zone where the two fields would cancel.  Interesting formations show up when certain vacuum bulbs are placed in the 'null' zone, especially at higher power.
It's on the same tangent as Philo Farnsworth's later multipactor/Fusor works as 'stars' and other formations that resemble ball-lightning or galactic formations will appear.

https://youtu.be/o-YK5hdKh40

It's also an interesting experiment thermodynamically because you can pump many hundreds of watts into such an arrangement and no heat shows up in the wires and no appreciable EM is emitted into space.  The energy 'disappears'. (or at least that is what appears to happen, that's why I need to replicate).

I have a high-power (2kw+) linear amplifier that I have been trying to modify to demonstrate this properly on the bench before the conference.   Needs a firmware hack to disable a 'gain too low' interlock. C.C  These 'smart' amps tend to to trip-out when any small frequency or impedance change; almost like they're not meant to run Tesla Coils with them C.C :P

As a future test I intend on winding two coils that have the same resonant frequency, but different physical size.  That way one coil can be placed inside the other creating a fully-encapsulated 'null zone'.  I haven't seen Dollard attempt this yet so looks like unexplored territory. ^-^
   
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Gentlemen
Just so you are aware
We have access to full private lab on east coast
Full material analysis and even electron beam microscopes
Total analysis of bulbs prior to ?, so you know what can be contributing( effect or ? ) unaware …. in the experiment !

A member at Stefan’s open source community has offered use from time to time !
Thanks
Chet

   

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It was an arduous week, but I finally managed to do a firmware hack on a powerful linear amplifier so I do some higher-power tests.
Amp is rated 2-2.5kw so.... ^-^ ^-^ ^-^

A bit more detail here:  https://hakasays.com/blog/2022/06/successful-linear-amplifier-firmware-hack/


Next 'build a Tesla Coil' part should be up soon as well, now that the dragon has been slain ;)
   

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Next part's up, covering physical design+construction: ;)
https://hakasays.com/blog/tesla-highvoltage/build-a-tesla-coil-design-and-construction/

Please feel free to AMA and I will do my best to answer.  The more questions I get, the more I can fine-tune for presentation and web content.

The next part should cover the basic steps to measure and tune the coil once it is built, then after that a couple simple experiments/demonstrations to show it off. :P
   

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The process of tuning quarter-wave coils is deceptively simple; all that is needed is a function generator and scope.

* The active lead of the function generator is attached to the lower leg of the coil and fed with sinewaves.
* To an oscilloscope, a short bare wire is attached to the probe lead end and is left dangling a foot or two from the coil.
From there, you simply tune up and down until you begin to see a peak register on the oscilloscope.  For a well-constructed coil with minimal loading, this peak may be EXTREMELY sharp.  My better coils tend to have a bandwidth around 2-15kc in the common HAM bands.

The dielectric field produced by these coils can extend very far into space, so do not be surprised to see >10v P/P on the scope probe a couple feet away with only 1/10w-1/4w input (10-20v p/p on most function gens).

Because of this effect, you'll also find that moving your hand or body anywhere near such coils will throw the tuning off dramatically.


If you have a well-built coil, a simple experiment you can do initially is to try and power a florescent tube wirelessly with just one lead from the function generator as your power source.
You will have to continually adjust tuning as you move the tube closer and further from the coil, but with some effort you may be able to light the tube from 1ft away or even further, using less than a watt of input power.
   

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Hello Hakasays,

you are doing very nice coils and experiments, thank you for sharing your work.

I have a question - why you are tuning to 1/4 wave resonance ? Any specific reasons behind this ?
Have you tried 1/2 ?  :)

Thanks!


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I have a question - why you are tuning to 1/4 wave resonance ? Any specific reasons behind this ?
Have you tried 1/2 ?  :)

Thanks!

That is a very good question! :)

Pic attached might help visualize why we usually use quarter waves.   Quarter-wave lets us separate a voltage node and a current node but without using a normal transformer.

You can indeed use half-wave and other harmonics in such coils, and they do seem to retain the high-Q properties with air-gap, but the strongest voltage peaks seem to happen at quarter-wave resonance (or at least what I've personally measured).

Of course this is just talking about a normal single coil; when we start adding things like sparks or modulation we can change the impedance of a coil dynamically, turning it into a quarter-wave coil for part of a cycle and half-wave for another part... ^-^   That is more advanced and something I hope to look into eventually, but short-term goal is getting more people up-to-speed on the crash-course basics O0


One option too is to drive a half-wave coil from the center to retain balance and avoid needing to use a ground.  In that config it's basically two quarter-wave coils back-to-back.
   

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On your picture, I think dashed line is not current


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On your picture, I think dashed line is not current

Thanks.  Your pic does a much better job illustrating the separation. O0 ;D

If current tends to accumulate at one end and voltage tends to accumulate at the other, then a single coil can become a transformer at the right frequency. 8) :o ;D

In the case of a Tesla Extra coil, the 'transformer ratio' appears to be proportional to the magnification factor of the coil.
So a coil with a Q factor of 200 will act as a roughly 200-1 transformer (excluding losses).   That's been my experience, anyway.
   

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I'm currently working on getting demos together for upcoming conference so I thought I'd share a couple clips >:-)

Tesla brush bulb replica illuminating under RF:
https://www.bitchute.com/video/VvUFuPXK1nV8/
The brush bulb is a replica made by Griffin Brock, with a partial vacuum on the inner bulb and a deep vacuum on the outer bulb.

High voltage transformer action using one wire to a Tesla Extra coil.  No primary and no secondary:
https://www.bitchute.com/video/COwdkKgDxJ5b/
System is being powered with a high-power ham radio linear amplifier through a T-match tuner, fed from a primary oscillator.

You'll notice the voltage produced is lower than a 'modern' Tesla/Oudin oscillator, but the current within is much higher.  That arc is a standing flame that instantly ignites wood/paper.

To reach extreme potentials such as those at Colorado Springs, an Extra coil would be fed from a loose-coupled resonant primary+secondary arrangement, somewhat reminiscent of a modern Tesla coil.

Since the system is matched near to 50 ohms, at peak power the input is only ~200vRMS (600v p/p).  So from the length of the spark we can conclude the magnification factor is likely 200 or greater.  Of course this could also be measured using lower power (function generator) input and a scope, or by using the standard 'Q calculator' using bandwidth sharpness and frequency.

I do plan on doing a proper 3-coil Colorado Springs replica eventually for the 'big cool sparks' demonstration but it probably won't be until sometime post-conference. C.C
   

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Buy me a beer
Nice work😎

Regards

Mike


---------------------------
"All truth passes through three stages. First, it is ridiculed, second it is violently opposed, and third, it is accepted as self-evident."
Arthur Schopenhauer, Philosopher, 1788-1860

As a general rule, the most successful person in life is the person that has the best information.
   

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Did a livestream last weekend to try modulating a Tesla Coil with AM to play music.
Was a little rough around the edges but at least it recorded this time C.C
https://www.bitchute.com/video/V39hv0YpLItT/
Enjoy ;)
   

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Congratulations! You now built half of Tesla's FE system :)


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The only way of discovering the limits of the possible is to venture a little way past them into the impossible.
   
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