Weekend Projects: Make a 100KV Singing Arc Plasma Speaker Flyback Driver!

Today on Weekend Projects, we will be constructing an epic Singing Arc Plasma Speaker, which superheats air to create plasma, and by modulating that plasma arc with music, we get a singing arc! (Sorry for the lousy editing. It took longer than expected to get this video as perfect as possible and some reason the audio is out of sync after rendering, possibly due to a bug in Kdenlive I have never had experienced before with the h.264 codec.)


Note: If you plan on duplicating this circuit yourself, please be aware that it is not entirely "safe." Research high voltage safety. I have been shocked many times, and have learned the hard way to stay safe. The output of this can cause severe burns (obviously), heart issues, and nerve damage if you come into contact with the HV.

Also, make sure to buy PLENTY of spare part's ahead of time. This is also not going to be a cheap project. Think around $20-$60 depending on how much scrap you have. (Speaking of, please do not bother asking me if XXX transistor, YYY transformer, or ZZZ oscillator/timer chip will work. The part's you see in the video is all that I got to work reliably.) Even then still have managed to kill:

* 1x flyback transformer ($8-$20)
* 4x NE555's / SE555's (~$5)
* 1x IRF250. (~$0.25)

I have also made this driver long in the past, and just could not get it to function for longer than 5 minutes without killing MOSFET's and 555's, especially when packed into a housing as a full-fledged project. I think there the reason's were as follows:

* I was attempting to go as cheap as possible, and as the old saying goes, you get what you pay for. Esp. when it comes to power supplies and MOSFETs.

* For a while, I thought my MOSFET's were blowing due to the transient voltage spikes from the kickback and every time I ordered a new batch of MOSFET's, A tried to go after higher and higher Vds rated one's. Initially buying mass quantities of IRF540, then IRF640, then IRF740, then finally IRF840 (each one can handle more voltage, but less current) before I gave up and came to the realisation this was not the right approach. I now think it was overcurrent (high internal resistance) and thermal management issue's that were the dominant factors in killing them, along with no protection from kickback and the continuous beating they took with each cycle.

* Also, I was not using a tank capacitor as shown in the video. I was relying on the large, sudden changes in current (di/dt) from the square wave drive to induce high voltages in the secondary, however, this leads to the transient voltages on the primary climbing so high until something gives out, usually the MOSFET. Adding any form of dampening would reduce the output, but as it turned out, adding a tank capacitor allows the flyback to operate a bit more like a resonant ZVS circuit, so that it oscillates and rings, effectively recycling otherwise lost power.

* Using potentiometer's instead for R1 and R2 to "tune" the output is not a great idea to my finding, it is too difficult for starter's, and has lead to the 555 latching up, and really unless the thing is far out of tune to begin with, it really is not that necessary (at least not in this case.). I was driving the first flyback with 49HKz switching frequency, at approximately 66.6% duty cycle (2 10K resistor's and 1nf capacitor), and the 2nd flyback in the video at 96KHz, again, at 66.6% duty cycle (2 10K resistor's and 2 1nf capacitors in series). Changing either R1 or R2 causes both the duty cycle and the frequency to change. You cannot control the 2 independently. I believe the circuit should be operated close to 50% duty cycle in this "better" resonance mode, to reduce harmonic content down to closer to just the base freq.

* Another issue may be power supply choices. A easy to work with 100-200VA transformer would be better, but I do not have one that large. Instead, I modified an old Xbox power supply, which is a overly sophisticated SMPS, which will work fine once you hack it to bypass all the protection and overcurrent shut off BS that the engineered into it! Even then, I have some weird intermittent issues with voltage sag on the output, possibly due to inrush current or strong EMI interference with the regulating section internally.
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