Here’s a compact little Solid-State Tesla Coil (SSTC) that you can run INside your home (with the appropriate RF ground). It’s quiet, doesn’t produce a lot of Ozone, and is fun to play with (as-well-as being a good introduction to SSTC’s; it’s my first). Many people have built coils around this design, so there’s a good body of knowledge for it; that’s very important if you find yourself needing some help (search for “Steve Ward mini-SSTC”). Steve spent several years iterating on this design, and the final schematic is here:
If you go-to his website, there are several other (earlier) variations along with pictures and additional information (spark effects, etc). Dan McCauley at Eastern Voltage Research, has a nice “development kit”, the SSTC 2.0, incorporating this design for only $99.00 (resonator not included), which is what I’m covering today.
First, a little background: SSTC’s are differentiated from “classic” TC’s by way of not having spark-gaps (noisy & inefficient, but capable of handling lots of power), or high-voltage capacitor banks. The voltage is low (comparably – hundreds vs thousands of volts, still hazardous), and the power is switched via solid-state electronic components; in this case a pair of IRFP260 MOSFET semiconductors (replacements are a buck or two on ebay) in a half-bridge configuration (don’t worry if you don’t know what that means). A brief historical background on SSTC’s can be found here.
Another neat thing about this design is that it incorporates a self-tuning interface (Jan Wagner/Justin Hayes). The “classic” SSTC has to be manually tuned by adjusting a high-voltage tap (wire placement) on the primary coil.
With that said, let’s get started. The kit as it comes from Eastern Voltage Research contains only parts and a schematic. There are no build instructions and no technical support, so as such, it’s considered an intermediate kit. Access to a voltmeter and oscilloscope is recommended for debugging. Here’s what I received (not shown is the transformer and aluminium frame that the circuit board is mounted in):
Notes on parts: The bridge rectifier labelled KBL01 is for low-voltage (from the transformer) in place of the specified KBL005. The two diodes across the IRFP260’s (labelled FFPF08S60) are not needed, and are not included in the kit. A 2200uf 35V capacitor was substituted in place of the specified 4700uf filter capacitor.
I started by populating the resistors, small capacitors, sockets for integrated circuits, diodes, and DIP switch (selects 555 timing capacitors). Then I populated the components for the low-voltage power supply (5 and 12 volts). There is an important jumper outlined in the errata that needs to be installed. I placed the circuit board into the aluminium frame to set the height for the two voltage regulators; their screw holes need to align with the holes in the aluminium chassis before soldering them in place (same for the MOSFETs, later).
The black and red wires on the transformer (T1) are connected together (red-to-red, black-to-black). The blue output wires are used to power the circuit (connect to CTRL+ and CTRL-); the yellow center-tap wire is not used.
Once the low-voltage supply operation and power paths were verified (checking the power & ground pins on the IC sockets), I installed the diodes, integrated circuits, and remaining capacitors. On my board, pin 4 of U6 was not grounded as the board appeared to be “over-etched”, causing the ground plane to be disconnected. Dan said this wasn’t a problem on his other boards (YMMV). A small jumper fixed the problem.
I wound the gate transformer according to the instructions on page 18 of the Flyback Driver Version 2.0 manual. It’s important to get the wires wrapped tightly and neatly around the core; this effects coupling efficiency and driver capacity. Page 11 of the SSTC 1.0 manual describes the circuit operation, including the antenna circuit. Most of this is the same for the SSTC 2.0 kit. After installing the rest of the components, here’s what it looks like (the missing screw-post arrived later).
Dan suggested using a 100-watt light-bulb as a “dummy load” for testing (across OUT+ and OUT-). Too bad they’re going to be outlawed next year, so be sure to stock up (I’m still not clear on why using less energy is “better” than being poisoned by mercury). I used a Variac and isolation transformer connected to AC+ and AC- for testing:
I had to play with the position of the antenna a bit to get it working. I also found that if my arm was too close to the antenna, the circuit would stop working. I did my testing with position 1 of SW1 closed and the other two open (1000pf capacitor enabled), and the two potentiometers R3 & R4 centered.
Once things seemed to be running, I bolted the MOSFETs and voltage regulators to the aluminium chassis, using the pink insulating pads between the devices and the chassis.
Now for the moment of truth: hooking it up to a Tesla Resonator (coil)! I kept the Variac in-line for power control. Using full power, the MOSFET’s got hot very quickly (30 seconds or so, depending on the frequency settings). Running at 1/2 power, they stayed cool to warm. A three-amp in-line fuse and AC filter were added for line conditioning (some of the “touch lamps” upstairs were observed to be self-actuating 😉
Steve (and others) recommend a 4.5″ by 10″ secondary and 4 turns of 16-gage wire around the bottom as a primary. I had a 4.5″ by 20″ secondary “standing around”, and ran 5 turns of 16-gage around a 6″ form for the primary. I got a bit of corona when I tried wrapping directly onto the secondary. I’ll try again with higher-voltage insulated wire (instead of “speaker” wire):
The sparks & spray shoot off the top of the sphere break-out. A range of effects are achieved by selecting the different capacitors in SW1 and by adjusting the two potentiometers (pots). High-frequency “hissing” with position 1 of SW1 selected. Selecting position 2 yields a range of tones by adjusting the pots, and with position 3, the frequency is so low, that the effect is of intermittent operation. Adjusting Variac voltage yields longer or shorter sparks. Be sure to monitor the temperature of the MOSFETs and don’t let them overheat!
I bent the end of the antenna away from the resonator, as corona was visibly emanating from the tip (it sizzled my finger too!).
Even though this design is relatively low power, it can still pack a wallop. Be sure to follow proper safety guidelines when using your coil, and NEVER use it around anyone that has a pacemaker or other biological implant.
In discussions with Dan, he says that when his current stock of boards runs out, he’s going to discontinue this kit. For $99, I’ve found it to be a great value; I’m ordering my second one tonight!