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Relating frequency and voltage

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EvilTesla-RG

Thu Mar 18 2010, 05:00PM

Registered Member #1523 Joined: Sat Jun 07 2008, 02:05PM
Location:
Posts: 97

I was thinking.

The bigger the Tesla Coil, the lower the frequency, and the higher the voltage.

Meaning that it would be difficult to make both a high-frequency and high-voltage tesla Coil. (Relitivly speaking, as ALL tesla coils are high voltage and high frequency)

So, I am wondering where the bounds are?

Anyone have any clue?

I was thinking, I doubt this boundary is very well know. So, maby I could make an equation relating Tesla Coil size, frequency and output voltage.

Problem is, is there someway to predect the voltage output of a Tesla Coil? Mabe if someone has a list of data points that I could extrapolate a curve from? (Probably using Excell).

Also, what units should the "size" of the Tesla Coil be in? Inductance of the secondary coil maby?

Thanks!

Sulaiman

Thu Mar 18 2010, 05:41PM

Registered Member #162 Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140

There is John Freau's equation;
(Spark length in inches) = 1.7x (square root of input power in watts) (for a 60Hz SGTC)

This is for medium-sized TCs - a few hundred kHz
If you get a better "Freau factor" than 1.7 you're doing very well.
A good benchmark for coilers.

Maybe you could survey published reports of spark length vs power vs frequency and make a table or graphs for us all.

If you do embark on such a project (I hope that someone does)
collect as much data as possible, e.g.
Power drawn from main supply
bps (bangs per second) (E.G. 100 or 120 for sgtc, hundreds for drsstc etc.)
Secondary frequency/diameter/height/turns
Topload Diameter(s)
Spark length/intensity

An excellent benckmark for coilers.

Such a table/graph will make your name immortal .....

P.S. Add an identifier for each coil, e.g. Name, multiple records will be a problem

Steve Conner

Thu Mar 18 2010, 05:46PM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

Sulaiman wrote ...

Such a table/graph will make your name immortal .....

Yes, because a mortal would not live long enough to complete this mammoth and boring task. :)

High frequencies make it more difficult to generate a high voltage, because stray capacitance puts a limit on how high a characteristic impedance you can have when designing the resonator, and the step-up ratio depends on this impedance.

The voltage output is easy to predict by computer simulation nowadays. I've designed coils to a spec for customers who wanted a specified spark length, and every coil I've built turned out in the ballpark of what my simulations predicted, give or take about 20%.

As for "units of size" I like to think of Tesla coils in terms of two parameters:

Freau factor: spark length divided by square root of input power
Watts number: spark length divided by secondary coil length

If you aim to maximise either one, it always hurts the other one.

Sulaiman

Thu Mar 18 2010, 05:53PM

Registered Member #162 Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140

That's why we remember Wheeler, Medhurst and maybe Freau.

Despite a plethora of innovation and mentoring there's not a McConner constant

Steve Conner

Thu Mar 18 2010, 06:02PM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

Well, can I have one then? :P

I suggest spark length divided by the number of components.

Renesis

Thu Mar 18 2010, 06:14PM

Registered Member #2028 Joined: Mon Mar 16 2009, 08:13PM
Location: Norway
Posts: 319

Steve McConner wrote ...

Well, can I have one then? :P

I suggest spark length divided by the number of components.

Succesful run time in seconds divided by the number of semiconductor explosions... A reliable coil would have a high McConner factor

Sulaiman

Thu Mar 18 2010, 06:22PM

Registered Member #162 Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140

Ha ha - On that basis I've already made a TC with a McConner factor of INFINITY,
and sadly one of ZERO.
Quite a wide range.

Not satisfying enough .. need a better McConner constant/factor.

Back to the main topic... I've never heard or read of such data in a neatly compiled set.

EvilTesla-RG

Thu Mar 18 2010, 07:00PM

Registered Member #1523 Joined: Sat Jun 07 2008, 02:05PM
Location:
Posts: 97

Interesting!!

thanks for the info.

However, I'm not interested in a big project of collecting data and building a bunch of coils. I don't have the time, patience, or more importatnly, the money.

I am thinking of just gathering known and approxmate data, and seeing if I can draw up an equation. relating frequency and voltage.

I'v heard of the John Freau equation. Which isn't usefull at All. As it doesn't predict anything. It has an arbitrary constant that has to be calculated through experementation for each individual Tesla Coil.

So the Freu number and Watt Number are indactions of effeincy, not physical size.

McConner- How do you predict a Tesla Coils output voltage (sparklength)?? Do you by chance have a table, or set of information of specs of coils VS their spark length that I could use?

Thanks!

dex

Thu Mar 18 2010, 07:01PM

Registered Member #2566 Joined: Wed Dec 23 2009, 05:52PM
Location:
Posts: 147

EvilTesla-RG wrote ...

The bigger the Tesla Coil, the lower the frequency, and the higher the voltage.

Meaning that it would be difficult to make both a high-frequency and high-voltage tesla Coil. (Relitivly speaking, as ALL tesla coils are high voltage and high frequency)

So, I am wondering where the bounds are?

Anyone have any clue?

Bounds:
The highest 1/4 wave resonant frequency given the secondary size corresponds to a straight wire secondary

.
The lowest frequency given secondary size?.. Hmm..induction coils of very fine wire and multilayer wound coils can be very low resonant (with aircores).

The ultimate upper bound for a max voltage gradient in air is 3000 kV per meter.
In real world the secondary insulation breaks much earlier and it is not recommended to go over 500 kV per meter of secondary lenght.Very wide secondaries could withstand more than 0.5 MV /m.
Tesla's secondary in Colorado Springs was 50 feet in diameter ,and could withstand aprox 1 MV / m .

EvilTesla-RG

Thu Mar 18 2010, 10:06PM

Registered Member #1523 Joined: Sat Jun 07 2008, 02:05PM
Location:
Posts: 97

Yes, but how are these bounds related?

What I really want to do, is create an equation that relates frequency and voltage approxamatly.

So that if we have a frequency X, and voltage Y. Where it is quite possible to build a Tesla Coil at frequency X and a Tesla Coil at Voltage Y.

But this equation could give an idea if it is possible to build a single Tesla Coil that works at both frequency X and Voltage Y.

See what I am getting at?

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