Tesla's Bifilar Pancake Coils

[Jiffycoil]

Ooops,

How to wind a pancake tesla secondary coil

Sorry about that.

[elias]

I have done one wire transmission of energy using two such coils.
I suppose that the TPU is also based on such effects: http://www.zpenergy.com/modules.php?...p=getit&lid=94

[greenliving]

I understand clearly..thanks for explaining..

[7imix]

Here is a bifilar pancake coil I wound yesterday as a test. It's too small to do anything really interesting, I think, but it proved that this construction technique is fairly easy and produces beautiful results.



Balsa wood is glued together to form the frame. I then cut slits in the balsa with an xacto knife all the way around. Finally, I wound the spiral all the way from the inside out, then turned around and wound it on top of the other coil in the opposite direction from the outside in.

This method will allow me to control the inter-turn spacing, which I believe is one of the methods tesla is referring to to match the capacitance of the coil to it's self-induction.

Jiffycoil, that is a beautiful device! I would like to build one of those!

[Jiffycoil]

@7imix
That is a brilliant idea. I can clearly see the benefit in having the ability to tap various point on the coil. I guess I building on of these now. Great thinking.

[Zooty]

I saw a video by woopy YouTube - bifilar Tesla pancake wireless coupling.wmv where he uses a bifilar pancake coil wired as a joulethief then another single wound pancake coil as the receiver. I was wondering what the result would be if he used a tesla bifilar as the receiver. Has anyone tried this?

[synchro]

bifilar

@Zooty,

Yes, they make excellent output coils. Wired in series, the bifilar pancake will generate twice the voltage.

[Mike2kt]

Building large bifilar coil

I originally posted this in the Joulethief SEC exciter and variants thread...Jiffycoil recommended I post over in this thread as well. So here it is...!


I'm going all out on making a flat bifilar coil. Rig is in place to wind a set of 28 AWG magnet wires between two plates of glass. Shooting for 1,200 turns. Space between the glass will be sealed along the edges and brought to a hard vacuum (at least 1 atmosphere, hoping for 2). Wire showed up today the fun starts this weekend! Yes, I understand the dangers. I have a theory that many projects fail not because the idea is unsound, but at a small-scale any minor deviations can ruin the results.

Now if only I can get the glass place squared away...they thought I was crazy...untill I said it wasn't for a "table top."




-----

Speaking of glass, thoughts on Lead-alkali glass vs Borosilicate glass? I know the Lead-alkali glass will be a better insulator...but how will all that lead affect the magnetic field?

Given the size of the flat bifilar coil, the voltage coming off the coil is going to be insane. So insulation is good (less voltage leak)...as long as the magnetic field between the two windings is not substantially impacted.

Crud, now I have to make two of these with each type of glass. LOL

[7imix]

I'm going all out on making a flat bifilar coil. Rig is in place to wind a set of 28 AWG magnet wires between two plates of glass. Shooting for 1,200 turns.

Awesome. Have you considered putting fishing line between the turns to reduce the capacitance of the coil? This will reduce the number of turns, but it might be significant. Just a suggestion.

[Mike2kt]

Awesome. Have you considered putting fishing line between the turns to reduce the capacitance of the coil? This will reduce the number of turns, but it might be significant. Just a suggestion.

Hmmm, actually no, I was going to wind it with no additional spacing between wires. Didn't even think of using fishing line...thanks for the idea!

I was originally going to order 42" diameter cercal glass which would have left me extra room anyway...I still have time to up that to a 48" diameter, but will probably need to jump from 1/2" thick to 3/4" thick for stability.

Forgive my ignorance...I come from the world of small digital circuits so these are new concepts at this scale. Is the spacing used to act as additional insulation between turns resulting in lower capacitance? Or is it the physical spacing/separation that lowers the capacitance?

I welcome (and appreciate) any and all ideas at this point!! Once this sucker is made, going back and making changes is a non-starter. It will have to wait for Rev II. ...at some point.

[Jiffycoil]

By doing this your coils voltage output can be optimized. Also you minimize the skin-effect and proximity effect losses.

[Mike2kt]

By doing this your coils voltage output can be optimized. Also you minimize the skin-effect and proximity effect losses.

Got it! Guess I'll be making a trip to the "Bass Pro Shop." lol I take it nylon fishing line is the way to go?

At this point I may just push back construction one weekend...given I still don't have the glass. I'm more than happy to turn this into a forum-driven design (within minor constraints like max diameter, max cost, etc) that I will then construct and share the results.

I'm absolutely not an expert at this, so if there are improvements to the design I'm all ears!!

[7imix]

The closer the conductors, the more the capacitance. Eric Dollard mentions this in "Introduction to Dielectric & Magnetic Discharges in Electrical Windings & Electrical Oscillation". In section 13:

This gives rise to an interesting paradox that will be noticed with capacity. This is that the smaller the space bounded by the conducting structure the more energy that can be stored. This is the exact opposite of magnetism.

The point of Tesla changing the capacity of the coil by adjusting the turn spacing is to match the capacity required to cancel self-inductance in the coil. It's not super important, because as Tesla says in the patent, one can always add an external capacitor ("condenser") to cancel the coil's self-inductance. However there may be other disadvantages to having a coil with a large capacitance, I don't know.

Have you estimated how long the final wire length will be to wind this coil? It would be interesting to calculate the frequency required for quarter-wave resonance.

Good luck building this, I will probably build one too if you share pics and construction details!

[Mike2kt]

Have you estimated how long the final wire length will be to wind this coil? It would be interesting to calculate the frequency required for quarter-wave resonance.

Assuming no additional spacing and a 120mm center diameter***, it's ~2,063 meters or ~6,768 feet for 1,200 turns. This is with 28 AWG wire and I have two spools, so running out is not a big issue.

***I'm under the impression that the inner most coils provide the least benefit...so to make starting the coil and centering everything (120mm CD) easier it's worth giving up that space. Or am I wrong and this needs to be made much smaller?

I don't have an exact number on the spacing with nylon fishing line yet...but it looks like 900 turns will fit in a slightly larger area. I'm trying to find line that is closer to the 28 AWG wire external diameter of 0.014in

I'm going for a multiple of 300 if that wasn't obvious.


I will be posting pictures and details as I build it for sure!

[7imix]

Assuming no additional spacing and a 120mm center diameter***, it's ~2,063 meters or ~6,768 feet for 1,200 turns. This is with 28 AWG wire and I have two spools, so running out is not a big issue.

6768 feet * 4 = 27072 feet. The wavelength of the resonant frequency will be around this.

I plugged some numbers into wolfram alpha and 36.29 kHz has a wavelength of 27103 feet. It should be quite easy to create a driver circuit that can impulse the coil at 36.29 kHz!

36.29 kilohertz - Wolfram|Alpha

That's over a mile of wire man! Crazy!

I think the center of the coil being empty is fine.