Build Instructions

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• 1

  BUYING THE PARTS

  WARNING: DO NOT PURCHASE IMPORTANT COMPONENTS LIKE MOSFET’S OR DRIVER IC’S FROM GENERAL SHOPPING WEBSITES LIKE AMAZON OR EBAY! MANY PEOPLE HAVE PURCHASED CIRCUIT COMPONENTS FROM SUCH SITES AND FOUND THEY WERE TOTALLY USELESS. DON’T WASTE YOUR MONEY: BUY SEMICONDUCTORS FROM ESTABLISHED SITES LIKE MOUSER OR DIGIKEY!

  Listed on another page is every part needed to build a your very own class-E SSTC. The links provided go to the associated parts on Mouser.com (one of my preferred sites, next to Digikey.com). While the parts I linked to seem to be decently stocked right now, it is entirely possible that one day, they might go out of stock. If you find a part is out of stock, I encourage you to use your common sense and look for alternatives with similar ratings. Please note, however, that most of these part values are not super critical, and substitutions can be easily made. Additionally, if you possess parts of similar values, feel free to save money and use your own parts instead! Owning a 12VAC transformer of your own could save you an extra $10!

  It is also worth noting that having a few extra components on hand isn’t a bad idea. The main components to worry about include the MOSFET, 400V TVS diode, the all of the ICs (74HC14, UCC27524, and NE555), and the high voltage supply’s bridge rectifier. In my experience, the 400V TVS diode is typically the first thing to go, as it essentially sacrifices itself to the high voltage spikes in place of the MOSFET. After the TVS diode goes, the bridge rectifier is typically next in line (since the TVS diode tends to die short-circuited, leading to overcurrent). MOSFETs typically don't die unless you're REALLY pushing your coil or you forgot to replace the TVS diode with a new one. IC deaths are usually the least common, although I have experienced a few. UCC drivers typically die when you crank the frequency above 5MHz (which leads to overheating), and I have had a 74HC14 go bad on me (to be fair, it was used in an experimental context beforehand). ICs are cheap though, so don't be afraid to stock up!

  After ordering the main parts, I recommend ordering a set of official LabCoatz PCBs. To order them, simply take the “Electra Mark III” .zip file (downloadable here) and submit it (as a whole, not unzipped) to a PCB manufacturing website like JLCPCB.com. This .zip file is technically referred to as a Gerber file. If you are asked by the PCB manufacturer for the board size, it should be around 84mm by 100mm. If you want, you can change how many PCBs you order and what color they are. The minimum order size with JLCPCB is 5 copies, which costs around $5 with the cheapest shipping for this PCB.

  Once you have all of the parts, just wind the coils, solder up the circuit on the PCB, connect everything, and proceed to testing!

• 2

  SETTING UP AND OPERATING THE CIRCUIT

  1. Supply 10VAC - 20VAC (or 14VDC - 30VDC) to the low voltage input (listed as "12V" on the PCB). If you have a scope, measure the signal between the MOSFET gate and source, and ensure the circuit is oscillating.
  2. Next, apply a low voltage (under 30V) to the main power input (listed as "12-120V" on the PCB).
  3. Place a fluorescent lightbulb near the coil and start turning the trimmer potentiometers. Stop when the bulb glows the brightest (or, if a discharge is present, stop when it is the longest). The oscillator is now tuned.
  4. Now, tune the class-E portion of the circuit. If you lack an oscilloscope, this will be particularly difficult to do correctly, but essentially, you just need to adjust the number of turns on the primary coil until the MOSFET experiences minimal heating during operation. If you do have an oscilloscope:

  • Connect one probe to the MOSFET gate pin and the other to the drain pin (and the grounds for each probe connect to the MOSFET source pin).
  • Adjust the primary coil until the drain voltage is perfectly out-of-phase with the gate voltage. This will ensure the MOSFET turns on when the drain voltage is zero to minimize stress.
  • As mentioned earlier, if the drain voltage hits zero before the MOSFET switches on, then the primary circuit is tuned too high, and turns should be added to the primary coil. And if the drain voltage extends into the squarewave, the frequency is too low, and turns should be removed from the primary coil. Again refer to the waveform pictures above if you have trouble understanding!

  These setup steps probably won't need to be repeated again, unless the coil falls out of tune for some reason. Once tuned, you can start cranking up the input voltage! If you have a scope, try to monitor the drain and gate waveforms as you increase the voltage. Class-E tuning tends to be somewhat dependent on the input voltage, so what works at 20V might not work so well at 60V. Just something to keep in mind!

  The other thing to watch is the peak voltage at the drain. You should stop increasing the input voltage when the drain peak voltages get close 400V (in fact, to be safe, I would recommend staying below 375V at the drain).

  And now for a few design tips to ensure you get the most out of your build!

  1. For one, you want the primary and secondary coupling to be high, but not too high. A coupling coefficient of 0.25 or lower is recommended to avoid throwing off the class-E waveform.
  2. Next, you want a good balance between resonant capacitor size and primary coil turns. For best results, you should have fewer turns on the primary coil and more tuning capacitance across the MOSFET. A higher capacitance tends to mean less voltage stress on the MOSFET, but keep in mind that primary coils with fewer turns allow higher current flow, which could cause other issues. I personally recommend finding a balance that results in less than 6 amps of current draw during uninterrupted operation, but you are welcome to go higher if you are confident in your tuning and setup.
  3. One last thing to consider is the MOSFET’s gate capacitance. At super high frequencies, more current is demanded from the gate driver IC to switch the MOSFET on and off, and if the gate capacitance is too high, your UCC27524 will overheat. Just something to keep in mind!

  Honestly, given how reliable and easy it is to get this circuit oscillating, there isn't much to say for troubleshooting. There are a few small things though:

  1. If the circuit shorts out (indicated by lots of current being pulled, and possibly some components "popping"), disconnect the power and feel the MOSFET. If it isn't blisteringly hot, the failure probably resulted from the input voltage being too high. In this case, the TVS diode is the most likely component to have broken.
  2. If the MOSFET is extremely hot, it probably died from overcurrent or overcoupling, and it should be tested. To test a MOSFET, use a multimeter to check the resistance between all of the pins. Normally, there should be near-infinite resistance (or maybe a few megaohms) between all pins, unless you apply a voltage between the gate and source, in which case the drain-to-source connection will have nearly zero resistance (this is how MOSFETs switch "on"). If the MOSFET appears shorted between any of the pins, even after you discharge the gate-to-source voltage, it is most likely dead.
  3. If there is no perceptible output, try messing with the interrupter potentiometers. If the interrupter duty is too low (i.e. the coil is only "on" for less than 1% of the time), it may appear as though nothing is happening.
  4. If the circuit is drawing a normal amount of power (usually 5A or less for near-100% duty), but no output is seem (or less output than expected), your oscillator most likely fell out of tune. No worries, some quick adjustment of the trimmer potentiometers should fix the issue!
  5. If the circuit is not pulling power, you either have a bad connection or your UCC driver isn't supplying a signal to the MOSFET. If the UCC27524 feels hot, it may have burned out and you should try replacing it.
• 3

  FIRING IT UP

  With standard 500V MOSFETs, my coil can handle roughly 75VAC (about 100VDC) before the peak voltages across the MOSFET and TVS diode exceed 400V. Using a 1.5MHz coil and a 3.5 turn primary coil (3.5" in diameter), I was able to produce burning-hot CW arcs over an inch in length, all without any MOSFET heating! However, the real treat comes when you dope the electrode with chemicals: baking soda and table salt both color the arcs a brilliant yellow, lithium compounds produce a deep red or magenta hue, boric acid (sold in stores as a human-safe ant killer) generates a blinding white-green, and potassium nitrate gives a strange mix of orange and purple (and the longest sparks out of all of them)! And if you put a thin piece of steel in contact with the burning-hot CW flame, it ignites into a glorious shower of sparks!
  

  Playing music with this Tesla coil is also super easy: just connect the circuit to the audio player of your choice using a standard 3.5mm headphone cable, crank up the volume, and enjoy the show! I personally used my laptop to play the audio, and I'm happy to say the coil didn't damage it in the slightest. If you want to play it safe though, you might consider picking up an old-school .mp3 player and using that.

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