Logan Brown
After building a functional Tesla coil out of Snap Circuits, I became obsessed with designing and constructing an improved version. This project went through many iterations, and failures to achieve the final result. With each failure I analyzed, learned, and improved my design and process. I like to refer to this project as "The Box of Scary".
Tesla Coil:
This project originally began as a Tesla coil. I was originally using a slayer exciter circuit, which is extremely basic, and I was only able to get mediocre performance at best. After I learned more about electrical engineering, I came to the realization that this circuit was not very good, so I switched to using a ZVS circuit which uses primary side resonance rather than secondary side making it much more reliable and powerful.
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ZVS Driver Circuit:
ZVS (zero voltage switching) circuits switch the polarity of the voltage applied to an LC circuit when the voltage crosses zero. Since the crossing happen at 0 volts, they have relatively low switching losses making them reasonably efficient. I decided to solder the components mid-air for improved high frequency performance compared to a breadboard, and because I was using SMD MOSFETs. I originally tried using additional MOSFETs to limit the gate voltage instead of using resistors and zener diodes. This was highly effective and produced huge arcs, but could only run for a couple seconds at a time before resonance was lost. I eventually switched to a standard design which was slightly less powerful but worked continuously.
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After I had a working design, I switched the MOSFETs I was using out for ones with a lower ESR, and I added an extra capacitor. This made the circuit significantly more powerful. Unfortunately, my design updates worked a little too well, and the transformer arced to itself and caught on fire. I corrected this by casting a new transformer in a block of silicone to insulate it.
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My prototype worked well, but it was a loose jangle of wires. I needed to design a case and packaging so I could use my High Voltage supply in future projects.
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ZVS (zero voltage switching) circuit​
Prototype
Testing the loose prototype
Packaging:
I designed a case using Fusion 360, and 3D printed it. I added power input, a switch, and a cooling fan to extend operation time. I used 30kV high voltage wires that a friend donated to me after he saw that I was using wires with 400V insulation.
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A couple of months after creating the Box of Scary, I learned how to make my own low pressure discharge tubes to produce plasma. I made a makeshift vacuum pump using a brake bleeder kit, a syringe, and some one-way valves. I used the vacuum system to partially evacuate a narrowed glass test tube, then heated the neck of the tube with a MAPP torch to seal it off.
Finished Product:
After many failures, iterations, and testing I managed to complete my Box of Scary. I worked in this project over an extended period of time, coming back to it as I learned and incorporated new skills and knowledge.
It is worth mentioning the Box of Scary produces high-frequency electricity that is not picked up by your nerves. This means it does not shock you like a wall outlet and will not stop your heart or force you to grab onto the wires, which are some of the biggest dangers of electricity. By no means does that make the Box of Scary safe. The arcs it produces can burn you, but it is unlikely to kill or maim you.