Flat Secondary Coil on PCB?

[profdc9]

I was thinking about designing a small kit-based Tesla coil where rather than the seconary coil being a solenoid, it is a flat spiral.  Of course the secondary inductance goes down, but is there any reason this shouldn't work?  Flat spirals are already used for resonant power transfer applications (e.g. wireless charging and induction cookers).

The board I designed has (I calculate) about 1 mH of inductance.  It is about 150 turns of 0.13 mm wide traces separated by 0.15 mm.  This is the thinnest I could fit in the design rules of the process.

Anyways I was up late last night and drew up a PCB.  The hole in the middle is for a post to put the topload on sticking up from the PCB.  The hole on the edge is to connect the ground.  There is a six turn coil on the back that is used to sense the current in the secondary for feedback purposes.

I was thinking too that I could stack the boards to get more turns and place a thick HDPE insulator between them.    The center of each coil would be connected to the ground of the next in series, and these would be stacked as to be placed over the primary coil  so that the board would intersect  the magnetic field lines of the primary coil.

Here is what I drew up last night:



Any comments about this design?  I want to call it the "Conversation Piece" which would be a little tabletop SSTC coil.  It would be powered by 12-30 VAC.

Dan

[Phoenix]

Hello

I know that such tesla coils work, because they are sold commercially: https://highvoltageshop.com/epages/b73088c0-9f9a-4230-9ffc-4fd5c619abc4.sf/de_DE/?ObjectPath=/Shops/b73088c0-9f9a-4230-9ffc-4fd5c619abc4/Products/TESLA_MINI_v1.2_

In the description you can see the technical data of the coil, it has 120 turns: https://highvoltageshop.com/epages/b73088c0-9f9a-4230-9ffc-4fd5c619abc4.sf/de_DE/?ObjectPath=/Shops/b73088c0-9f9a-4230-9ffc-4fd5c619abc4/Products/TC12_flach

Greetings
Phoenix

[profdc9]

You wouldn't happen to know of a video of it in use?  I am curious to see how they work.  I was thinking of adding a buck converter before the half/full bridge so that I could modulate the power with an audio signal.

Dan

Hello

I know that such tesla coils work, because they are sold commercially: https://highvoltageshop.com/epages/b73088c0-9f9a-4230-9ffc-4fd5c619abc4.sf/de_DE/?ObjectPath=/Shops/b73088c0-9f9a-4230-9ffc-4fd5c619abc4/Products/TESLA_MINI_v1.2_

In the description you can see the technical data of the coil, it has 120 turns: https://highvoltageshop.com/epages/b73088c0-9f9a-4230-9ffc-4fd5c619abc4.sf/de_DE/?ObjectPath=/Shops/b73088c0-9f9a-4230-9ffc-4fd5c619abc4/Products/TC12_flach

Greetings
Phoenix

[Phoenix]

No, i do not have a video about this coil. But if you look at the image from the second link, you can see that the primary is on the same PCB as the secondary. There are 2 bigger traces after the secondary coil.

The description says that this is a class E SSTC. I think you could use any normal Audio PLL Class E SSTC schematic and simply hook this coil up instead of a classical resonator: http://uzzors2k.4hv.org/projectfiles/classesstc1/classE_SSTC.GIF

Maybe you need to adjust some component values according to your resonant frequency, but the basic principle is the same.

Greetings
Phoenix

[oneKone]

The only thing I can offer here is another reference. This coil is still early days but it is a drsstc.
https://hackaday.io/project/165112-pcbtc-gan-edition

[profdc9]

The only thing I can offer here is another reference. This coil is still early days but it is a drsstc.
https://hackaday.io/project/165112-pcbtc-gan-edition

Thanks for the link.  That looks like an awesome project.

Thanks to you both for the info.  It gives food for thought.  I didn't think I was the only one who thought of this, but obviously there's been some movement here.

I was thinking of keeping the primary and secondary on separate PCBs so I could stack several secondaries to get more turns, and also I put the sense coil on the other side of the secondary board so that it there is less of a chance of having a coil strike damage the circuity (if it is possible to have a streamer that long).

dan

[Mads Barnkob]

You could stack multiply PCBs as its done with planar transformers where the PCB are connected with VIA and the primary/secondary are interleaved for highest possible coupling.

I know this might not work as well with a high voltage output like this, but at least it is a common used practise to make these electronic layer cakes.

[nick]

I coincidentally came across the project below today while looking for something else. Your post immediately rang a bell. Maybe some of his info is helpful.

http://www.megavolts.nl/en/projects/tesla-coils/201-pcb-spiral-teslacoil-en

[klugesmith]

The board I designed has (I calculate) about 1 mH of inductance.  It is about 150 turns of 0.13 mm wide traces separated by 0.15 mm.  This is the thinnest I could fit in the design rules of the process.

Dan, what's your estimate of the DC resistance, and resulting effect on Q of primary circuit?
A simple rule of thumb: Sheet resistance is about 1/2 milliohm per square for 1 ounce copper foil (about 35 um thick).  The resistance of your fine-pitch spiral can be a good indicator of actual trace width after etching.

[edit] Oops, you were proposing the flat spiral coil for _secondary_ TC winding.  Point still stands:  Resistive damping is strong unless L/R (in seconds) is large compared to period of oscillation.