Weird AC/DC mini SSTC build review

[Michelle_]

I'm just posting this in case anyone else searches for information on this.

"Mini SSTC IV"

https://www.vn-experimenty.eu/teslov-transformator/sstc/mini-sstc.html

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(this is not my video, it's where I found the idea)

I thought the circuit looked interesting and I had basically everything to build it, so I decided to give it a try because I was curious what such a simple circuit can do.

My feedback is that in DC mode it is really stressing the transistor and even with fans things get pretty hot. The two diodes in particular got hot, and I put a 24V mini blower fan pointed directly at them. In CW mode the transistor could get hot enough to die after 5-10 minutes or so even with a heat sink and fan, running at full output. Full output required a stronger PSU than my lab PSU so I used a 20A 24VDC din rail mounted PSU that could adjust to 28V. The difference between that and the lab PSU was dramatic, even though I ran it through a 6A breaker (which was a good idea because it popped a couple times). The secondary got hotter than I would like as well in CW mode and I had concerns about its long term survival.

Ultimately I killed all 5 of the transistors I bought during testing so I wouldn't really recommend this as a long term solution.

I tried a few different top loads, primary windings and positions, and they all had an effect on the current draw and to some extent the performance.

I did run it off AC using a variac and isolation transformer. It did appear to be able to run continuously without any overheating in this mode but the performance was not particularly inspiring. Arcs were maybe 6cm at most. I would have maybe kept it in this configuration as it was stable and only drew 3A, to give away to someone, however it would require a 48V transformer, which is $47+ shipping from digikey and 6lbs (3kg) for a 4A unit which seems dumb to do.

The most impressive thing this setup can do however is light up tubes. It can light up tubes and CFL bulbs from 3+ feet away in CW mode.

Overall it would be a good build for a first tesla coil because it's easy but significantly more powerful and robust than a regular slayer exciter.

That said I built a fairly nice secondary so I'm going to repurpose it with a nicer driver, and I think I'm going to build the steve ward mini SSTC driver for it, which is more complicated but will be a good learning experience and presumably work more reliably long term.

I've attached a picture of the schematic, bare driver board (before I added a bigger heat sink, mounted it to a platform, and added fans), and a couple shots of it running in CW mode. I didn't take any good pictures of it with the toroids or running in AC mode but I'm going to reuse the secondary and toroids so I will post it after I build the steve ward driver.

EDIT: Actually I might have to wind a new coil for the steve ward SSTC anyway because of the resonant frequency, so maybe I will see about a smaller transformer and trying to cool this properly and give it away after all. Maybe there's something I can do to boost the performance on AC.

[Michelle_]

So I realized I can't reuse this secondary for my next project so I spent some more time tinkering with it and now I feel a lot more optimistic about the design. Running on AC anyway.

Now it draws only 2.5A and hardly gets warm with 15+ minutes of use which is good, even pulling arcs won't trip my 3A circuit breakers.

Arcs are quite small as stated about 6cm but again it lights things up pretty well. Since it draws less than 3A I can use a much cheaper and lighter transformer than the 4A unit I was looking at before, so I will probably put it in an enclosure and either leave it on my desk at work or give it away, especially since it can just run off of a wall outlet. I will keep the circuit protection and probably use a small 5V PSU for fans.

The unit is pretty quiet besides emitting a quite pleasing (to me) deep humming, and the arcs seem relatively safe to touch. After messing around with it for a pretty long time it seems solid now and even though it's weak it's fun to play around with.

Thought I would mention the secondary is only 4" winding and 2" in diameter so this thing actually is super small. The steve ward "mini" sstc I realized has a 10" tall secondary lol and his "micro" sstc is 6" (?) and has less output than this one so I feel better about it to be honest. That said my output is less than in the video but I'm not totally sure why, on the other hand my current draw is a lot lower which seems good for what I'm using it for, not sure if it's because of my isolation transformer limiting the current somehow or if I made a mistake in the design.

[Michelle_]

Finishing this will be good practice for the upcoming SSTC5 build. After that I'm going to build a RSSTC, upgrade the SSTC5 to full bridge, then ultimately build a DRSSTC. I still think this weird little tesla coil will be a fun desktop toy once I get the power situation finished up. Maximum spark length I've gotten is 70mm so about 2.75" lol.  Resonant frequency apparently is 714KHZ and it still lights up a CFL (if you're holding it) from around 3 feet.

[Michelle_]

OK I'm done playing around with this, time to move onto SSTC5.

Now it has a transformer and a 110v fan so it all runs off of one wall socket. The power unit is off to the side but it's not that interesting it's just packaged together for easier access to the circuit breakers. I was going to integrate it all into a lower level of the tesla coil assembly but I guess I don't feel like spending any more design time or filament on this so I just connectorized it and packaged it together instead.

Kinda weird results with the 115 to 48v transformer, it runs way more powerfully from this than the isolation transformer and variac, and pulled more amps too. Unfortunately the mosfet started getting really hot really quick, so I changed the jumpers on the transformer to 24VAC and interestingly it is still more powerful than it was than with the isolation transformer and variac at 48v, despite now drawing only 3.5A at 24V versus 2.5-2.75A at 48V before. Not sure what to make of that, but whatever, lol, it's running well and staying cool and now it's time to move on.

I'm starting to rethink my giving tesla coils to people plan, it just doesn't seem like a good idea; so I'll probably put it on my desk at work so I can scare away anyone from the quality department that comes to bother me.

Pictured is running 24vac, max spark length now is 3". BTW I haven't killed a single mosfet on AC even stress testing it.