Tesla's Flat Coil

[MagnetMan]

Hi Guys,

Can anyone explain how the adjacent lines of the Tesla's bifilar coil are out of phase? Does this have an impact on parasitic capacitance? Aside from Gary "Chemelec" Lecomte, has anyone had any experience with them?

Thanks,
Stefan

[hobbes_lives]

I don't know that they're out of phase, but I do know that a bifilar wound coil will have higher self-capacitance. I'm not 100% sure, but I recall that it's due to the higher voltage potential between the adjacent lines.

[MagnetMan]

Thanks, Hobbes. The higher capacitance due to potential difference makes sense. I've heard it mentioned that the two coils are 90 degrees out of phase, but I am not sure why that would be.

-Stefan

[mikebg]

Useless design

BREAKING "NEWS"!
1. Reinvented is an old method for descreasing resonance frequency of a conventional solenoidal coil.
In the prior art, Nikola Tesla uses flat spiral coil wound bifilar, where both windings are connected in series to decrease the resonance frequency (see posting #1). In the reinvention, a solenoidal coil is used because it is wound easy and can be achieved more inductance at given volume (see position A in the attached figure). The reinvented priciple is shown as position B in the attached figure. Note that there is a soldered region (position S) where leads of windings are connected by solder. The principle can be improved because the S region can be used for addional decreasing of resonance frequency if it is placed to lay direct over turns as shown in position C.
2. Reinvented is the unleaded (environment-friendly) solder wire. The lead-free solders are preferable in EU according European recomendations for health and environmental protection. This last is no joke because the solders are more expensive and have more high melting point.

[MagnetMan]

Thanks, Mike.

So the segment of wire that crosses the coil (flat or solenoid) alters the resonance frequency of the second coil?

-Stefan

[mikebg]

So the segment of wire that crosses the coil (flat or solenoid) alters the resonance frequency of the second coil?

Stefan,
The attached equivalent circuit diagram shows that there are a lot of stray capacitances. They form a lot of resonance frequencies. This fact is used in electronics for delay of wideband analog signals and forming of powerful pulses. If you wish to learn more, search WEB for:
"delay line"
"Blumlein transmission line"
"artifical transmission line"
"synthetic transmission line"
"pulse forming network" or PFN.

[MagnetMan]

Thanks, Mike. I will take a look at those searches for more info!

-Stefan

[chemelec]

In My Tests of all these coils I have made, I am unable to get a Rersonant frequency Anywhere.
Basically these coils are Self Cancelling, killing inductive kickback.

I have created these with two wires as shown below, but also with 3 and 4 wires. (Lots of Fun doing 4 wires.)
And all these seem to give simular results.

[mikebg]

In My Tests of all these coils I have made, I am unable to get a Rersonant frequency Anywhere.
Basically these coils are Self Cancelling, killing inductive kickback.

I have created these with two wires as shown below, but also with 3 and 4 wires. (Lots of Fun doing 4 wires.)
And all these seem to give simular results.

Chemelec, please describe your resonance test setting (equipment and method for measurement).
What is the inductance of the coils created by you?
Calculate the approximate resonant frequency at a value of stray capacitance several picofarads only.

[chemelec]

Chemelec, please describe your resonance test setting (equipment and method for measurement).
What is the inductance of the coils created by you?
Calculate the approximate resonant frequency at a value of stray capacitance several picofarads only.

My Typical, 8" flat wound coils are made to aproximately 400uH.
These are Free Air Resonant at around 2 Mhz.

An Example of a Specific Coil I made is:
36 turns, 22 AWG.
6" ID & 8" OD
Measured Inductance is 402.3 uH
DC Resistance is 1.07 ohms
Q is 2.21 @ 1000 Hz.
Interwire Capacitance is 14.1 pF. (Using my Test setup, as shown on my website.)
Measured Free Air Resonance is 2.04 Mhz.

My Tests are done with the Signal Generator connected to coil, through a resistor. (10K to 100K) Scope leads are across the coil.
(Sometimes I also put a cap across the coil to create a lower resonance.)

I have basically wound Identical Tesla Coils (400 uH) for Comparison.
No Resonance found.

I have also made MANY other Regular, flat and Tesla Coils, Varying in size and Inductances. Same Results.

So What else can I tell you?

[mikebg]

My Tests are done with the Signal Generator connected to coil, through a resistor. (10K to 100K) Scope leads are across the coil.
(Sometimes I also put a cap across the coil to create a lower resonance.)

I have basically wound Identical Tesla Coils (400 uH) for Comparison.
No Resonance found.

Hi Gary,
Stray capacitance between scope leads and input impedance of scope form an impedance Z as shown in attached circuits.
In the left test circuit, the impedance is increased by adding a small capacitor.
In the right test circuit is used a wire connected between scope leads to form one or two turns. Tesla coil has resonance.

[chemelec]

Hi Gary,
Stray capacitance between scope leads and input impedance of scope form an impedance Z as shown in attached circuits.
In the left test circuit, the impedance is increased by adding a small capacitor.
In the right test circuit is used a wire connected between scope leads to form one or two turns. Tesla coil has resonance.

Never Tried that.
But in the second circuit that Resonance may just be a result of your one turn coil.

I only use a 1pF cap and I have also used the X10 input, with no resonance showing.
But I Can't believe that a 1 pF into the 1 meg input impedance will form a Low impedance to not show a resonance.
And It DOESN'T on a normal coil of any kind, so why would it on a Tesla coil?.

Also going into the High scope Input is a 9.5 Meg Input.

[hobbes_lives]

Hi Gary,

Another method to check the resonant frequency of a coil is to place it near the coil of an operating PI. You can calculate the resonant frequency of the coil in question from the ringing that the pulse from the operating PI induces in it.

I bet the resonant frequency of a Tesla bifilar-wound coil is quite low. Perhaps you didn't turn your signal generator to a low enough frequency to find the point where the coil would resonate? Just a thought.