Introduction: Solid State Tesla Coil
In the following instructable, I will show you how to make a solid state Tesla coil, as well as several helpful tips and hints that will come handy during its construction. I take no credit for the original design, which is Steve Ward's, with some small modifications "here and there."
While fiddling with the antenna, I accidentally burnt both of the Mosfets, so bear in mind this design is far from perfect. I'm still posting the instructable, as some of the techniques I used may be interesting to some. Try at your own risks. Results may vary.
If you like this instructable, please rate it and vote my instructable for the contest.
Step 1: Tesla Coil Parts
A Solid State Tesla coil is made by four main parts: the primary coil, the secondary coil, the topload, and the control circuitry.
The Secondary : The secondary is the long, orange cylinder. It is actually a white PVC pipe covered by a lot of enameled wire. One side is connected to ground, high voltage comes through the other side.
The Primary : The primary is powered by the control circuitry and it generates the magnetic field that the secondary uses to create the high voltage. It is the few turns of thick wire at the base of the secondary coil.
The Topload : The topload is the metallic object at the top of the secondary coil. It provides a capacitance to the Tesla coil.
The Control Circuitry : The circuits that make the tesla coil work at the correct frequency and duty cycle; based on Steve Ward's design.
Step 2: Secondary Coil (Part 1 of 4)
First, the coil former must be prepared. The coil former is the hollow tube in which the enameled wire will be wrapped. The external diameter of the pipe should be 4.5 in. (11.48 cm). In my, case, I used a 4 in. PVC pipe. PVC pipe sizes are not the outside diameter size, so be wary. A 4 in. PVC pipe has a 4.5 in. outer diameter, which is the diameter required. If a 4 in. PVC pipe cannot be obtained, one must use any non conductive hollow cylinder with a 4.5 in. outer diameter.
Usually, PVC pipes will come with a non-straight edge, specially if it is a leftover. To straighten it out, place the pipe inside the flange (see picture). The irregular side must be slightly past the flange's edge(picture 2). Then, with a hacksaw, the irregular edge is cut, using the flange's border as a nice, straight guide.
One can observe the irregular side cut off on picture 3, leaving a nice straight edge in the pipe's end. Now, the flange can be removed for the next step.
Step 3: Secondary Coil (Part 2 of 4)
Now, the secondary former must be cut to the appropriate size. From one end of the winding section to the other end of the winding section, 17 inches must be available. In addition, the former must be able to accommodate two flanges. In my case, each flange had a height of 2 inches, so:
17 in. + 2 in. + 2 in. = 21 in.
Be wary, as the specific height of the flange may vary according to where you buy it, but the principle remains the same. Place the flange so that the required number of inches are in between the flange's edge and the pipe's end and then cut the pipe using the technique described in the previous step.
Step 4: Secondary Coil (Part 3 of 4)
The next step is to glue one flange to the pipe. To do this, place the flange above a disposable surface, and cover only the interior surface of the flange with glue. Regardless of the PVC cement instructions, do not cover the pipe's surface with glue.
Depending on the specific PVC cement you use, it might have negative dielectric properties (it may hurt performance). Besides that, a perfect seal is not needed.
After placing the glue on the flange, place the pipe inside the flange, pushing the extra glue downwards towards your disposable surface. Getting glue on the outside of the flange will not decrease performance, but getting it on the pipe, specifically on the winding area, might.
Sorry for the fuzzy pictures.
Step 5: Secondary Coil (Part 4 of 4)
The final step of this subsection is to wind the secondary. There is no quick way and easy way to wind the secondary without a lathe or similar acting jig, but they can be winded by hand. The materials are, of course, the pipe, 30 AWG enameled wire, and time, lots of it.
First, have something to hold the wire that permits it to spin freely. This can range from a small, eager kid to some books and a stick. I recommend you to (before starting the Tesla), try to break a small section with your hands for you to know what is the maximum force you can apply without breaking it. (Although not exact, an idea does help)
Enameled wire is sold by weight, not by length. You will need slightly less than 3/4 of a pound, or almost 1/4 of a kilogram. The exact weight, assuming perfect winding (which probably will not happen) is 0.246 kg. To start winding it, you may either glue a few turns of wire with super glue, or place some electrical tape sticky side up to hold the first turns.
It is extremely important to avoid spaces between wires, as well as overlapping turns. One overlapped turn will not ruin the entire coil, but try not to make a bad job in here, it will be worth it. You can use electrical tape to hold the wire if you are stopping halfway through the coil for any reason. If for any reason, you break the wire midway, it is best to start over.
When you finish, add a bit of glue(epoxy, hot glue, etc) to hold the last few turns. Varnishing the secondary coil after winding is extremely recommended, but not necessarily needed. For a note, mine is not varnished.
If the difference between summer and winter temperatures is large in your region, varnishing the secondary is a must. Metal expands during summer and contracts during winter. If not varnished, you could end with an unusable pile of twisted wire by summer.
The secondary coil presented below is a compromise between speed and quality. For maximum quality (and slowest time), check the links at the end of this instructable.
Step 6: Toroid (Part 1 Out of 4)
To make the toroid, you will need aluminum duct, a plier, wire, and a second flange. First, cut the aluminum ducting so that it can do exactly a full revolution to the flange. Then, cut a piece of wire whose length is slightly larger than the aluminum duct. Using the pliers, bend the wire to bring the two edges of the aluminum duct as close as possible.
Make sure the wire is inside the toroid; having it in the outside would be detrimental to the Tesla coil. The missing slice can then be covered using either aluminum tape or scraps of aluminum duct.
Ideally, if you can find a piece of tube with a diameter just smaller than you aluminum duct's diameter, you should glue it as described in one of my links at the end of the instructable, titled A new 8.5 x 34.5 Toroid for the 'Phoenix' . Since I could not find this material, I had to use a wire. It will still be okay as long as the wire remains in the inside of the toroid.
Step 7: Toroid (Part 2 Out of 4)
Now, glue the toroid to the flange using hot glue. Avoid using any other glues without checking flammability first.
Paste the toroid to the flange well, going around the circumference. Depending on how you are going to connect the Tesla secondary to the toroid, you can glue the remaining notch in the ducting either now or later in the process. Please see the next step for further clarification.
Step 8: Toroid (Part 3 Out of 4)
Before continuing, the way to connect the secondary to the tesla coil has to be thought out. If you have either conductive glue or aluminum tape (glue preferred), you can skip away this step.
Being too cheap to buy these. I decided to make a screwed connection. I drilled a hole through the flange and the aluminum ducting. Afterwards, I inserted a screw through the aluminum ducting from the inside of the aluminum duct towards the flange, and used nuts to hold it . See pictures for an explanation. This is not ideal; but it works good enough.
Then, I placed the toroid over the secondary and attached the wire to it. Some of you may ask: How did the cable got from the outside to the inside of the pipe? The way I used was to drill a small 1/16" hole through the pipe. Bear in mind that drilling a hole limits the maximum arc length of the Tesla coil to the separation between this hole and the base of the secondary; any greater would arc inside. Nevertheless, I consider 17 in. arcs good enough for me.
If using conductive glue, just glue the secondary cable to the outside of the toroid. After finishing this step, use hot glue to close the notch that remained in the toroid if you have not done so already.
In all cases, remember the secondary cable has an enamel coating. Remove it with sandpaper before connecting.
Step 9: Toroid (Part 4 Out of 4)
The final step in the tesla coil construction is to fill the top hole of the toroid with aluminum. If you can obtain a pie pan that fits in the toroid's inner circumference, use it. If not, take a pie pan and cut a circle that can fit in the toroid. Place the toroid in its final position on top of the secondary, and hot glue the flange to the pipe.
Then, place the cut pie pan on top of the toroid and glue it with hot glue.
Solid state Tesla coils require a breakout point to work properly. A breakout point is a pointy object that protrudes from the toroid. I have decided to not place a fixed one so that experiments using different breakout points can be made, but never run the tesla coil without a breakout point. For example, a screwdriver placed on top of the toroid is commonly used.
Step 10: Primary
The primary of a Tesla coil is made by another coil of wire. Fortunately, it only requires ten or less turns of a thick wire (16AWG or thicker).
Just wind a ~16 AWG wire ten times around the lower part of the secondary. Hold it temporarily with tape, as the precise number of turns may be adjusted later on if deemed necessary.
The number of turns affects how much current passes through the circuit (see next step for the circuit). The less turns, the longer the arcs, but the hotter the MOSFETs will get. Ten turns is a good starting point, then one can reduce the number of turns until the MOSFETs start getting warm.
If the number of turns is too low, the MOSFETs will blow up eventually; on the other hand, if you have too many turns, the performance will be sub-par to what is achievable.
Step 11: Control Circuitry
I strongly recommend you to employ Steve Ward's design. (Scroll to the bottom of his page for his final design).
...But, sometimes you will not be able to find some components. For example, I could not find locally the UCC37322 or UCC37321. So, I made my own variation of his circuit. See the schematic below.
In this instructable, I will not teach you to make a circuit out of a schematic; if you can't read them you should try simpler projects first. A disadvantage from my spinoff is that there is no isolation; bear this in mind when working. This is why I recommend Steve's Design if possible.
You may build this circuit in a strip board, veroboard, printed circuit board, point to point, etc; but do not use a breadboard (Protoboard); there is too much parasitic capacitance.
As always, place a fuse between the circuit and the mains plug. 5A or similar.
Brief Technical Explanation
A solid state Tesla coil works by switching the primary at a resonant frequency. This frequency varies due to the height of the coil, the topload, and the environment. Thus, a fixed frequency oscillator is not ideal.
The following driver changes its frequency based on what the antenna gets from the Tesla coil. The antenna could be any straight piece of wire connected to the circuit. The other end is left unconnected. Thus, this SSTC uses antenna feedback.
To avoid overheating the mosfets, usually an interrupter is used. It's role is to turn the Tesla coil on and off at a certain frequency. This doubles as a power control if one varies the duty cycle of the circuit. A full explanation on how the Tesla coil works can be found on Steve Wards site. I also recommend to follow his schematic (the last one), and fall back to mine if some of the parts are not available on your area.
The only difference between mine and his is that I did not use the gate drive transformer and the ucc chips. If you can find these elements, by all means do his design, as it has galvanic isolation between the half bridge and the rest of the circuit. (which is a good thing)
---The capacitors on the half bridge are must withstand at least 170V.
---This tesla coil is not audio modulated, but it could be made so by just changing the interrupter for an audio one.
---The 5v and 12v signals can be obtained from a transformer followed by a LM7812 and a LM7805 (plus capacitors).
Step 12: Test It
-The bottom part of the secondary goes to ground. Mains ground works out at this power level, but do not have sensitive stuff plugged nearby. A dedicated ground is ideal, though.
Hopefully, you will get the Tesla Coil working. If it doesn't, read below:
-Sometimes one needs to connect the primary the other way around; see if swapping the connectors solves the problem.
The Tesla Coil has capacitors that will remain charged after you turn it off. Be sure to discharge them before fiddling with the circuit, and double check that they are discharged before poking anything.
Bonus: Add some salt to the breakout point and the streamers will be orange instead of blue. Unfortunately, I did not take any photos of this before the MOSFETS died.
Step 13: Links and References
Useful links, better methods (although more time consuming), and references
Stephen Kludge: "How to build the perfect secondary coil"
"A new 8.5 x 34.5 Toroid for the 'Phoenix'"
Steve Ward: "Solid State Tesla Coils"
Disclaimer: I am in no way associated, in any way, with any of the authors linked. If any of the authors would want their links or respective information taken down, please tell so.