DRSSTC

Seven Nation Army played as a first musical test.

A DRSSTC (dual resonant solid state Tesla Coil) is a specific type of Tesla Coil that allows for a few improvements over tradition SGTCs:

  • It is typically far more efficient when it comes to arc length vs. power input.
  • The output can be easily modulated, allowing for playback of music.

There are many excellent resources on the operating principles and design of DRSSTCs, so I'll link them below. Here I want to discuss more the trials and tribulations it took to make mine actually work.

Work on my DRSSTC started as my high-school senior project. I only began to revisit it last summer. Wow was I naive. This took hundreds of hours, minimum, to even begin to see the proper waveforms on my oscilloscope. (Green is primary current, yellow is bridge output.)

Scope

I'll go over a few of the issues I had to deal with to get everything working:

  • Getting the random Chinese UD2.7 to work with essentially zero documentation.
  • Gate drive leads being too long, leading to noise and switching instability.
  • Current and phase feedback transformers' core material saturating at too high of a frequency.
  • Impedance mismatch between primary and secondary leading to very small output.
  • Poor IGBT choices leading to very violent and exciting bridge failures. (9900uF 340V caps can dump A LOT of energy.)
  • Poor choice of TVS diodes also leading to IGBT failures.
  • Accidentally connecting my scope ground to the driver while it was also grounded. (RIP drive MOSFETs)

The final working version of the bridge was a complete resdesign of the original, and only came after two rounds of explosions from the original IGBTs.

Telsa

I will say the one thing that remained solid was safety. I always had a fire extinguisher on hand (which was only needed once). I put bleed resisters across all capacitors and never went near the bridge until I could verify the bus caps were discharged.

I also recently designed a new custom RP2040 based interrupter as the old setup required custom software to control everything. The new one is plug and play and simply shows up as a MIDI device.

PCB CAD

I feel I learned a lot about my personal motivations and obsessive nature, honestly. When I’m truly interested in something, I have zero problems putting in the effort. I also learned a ton about electrical engineering and real-world engineering difficulties. Test and measurement skills were also massively improved. Out of any project or class I’ve ever partaken in, I think I learned the most about my field of engineering pursuing this.

P.S. I have a picture of myself at ten years old after building my first miniature spark-gap Tesla Coil. (I will not share that here due to my bowl cut) Nonetheless, I have always been fascinated by them. As I grew older, I always wanted to build a larger DRSSTC with the skills and resources I had acquired. I spent literally my entire summer working on this, spending upwards of 18 hours a day during certain periods. After a certain point, I was fueled by spite and obsession.