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Mini (R)SSTC â€“ my first build

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LAN_403

flannelhead

Sat Aug 08 2015, 09:42PM

Registered Member #952 Joined: Mon Aug 13 2007, 11:07AM
Location: Finland
Posts: 388

9 August 2015

I've been wanting to build a full-blown SSTC since I was 14. Now, at the age of 21 and with much more experience, I thought I could finally give it a try.

2015 is a good time to be a first time SSTC builder â€“ there's such a wealth of good designs and tutorials around. For this project, I chose the tried and tested Steve Ward's Mini SSTC. The coil was built closely following Loneoceans' excellent SSTC tutorial (thanks a lot for this), which is similar to Ward's coil but with a few modifications such as an UVLO circuit. I also chose to employ CT feedback, which worked well after some tweaks in the feedback network.

As I probably can't afford building a second coil soon, I decided I'd make this one a bit more versatile. One feature I wanted to have was staccato control for sword-like streamers like in Loneoceans Ramped SSTC 3. The following additions were made to the basic schematic:

Switchable DC bus smoothing
Zero crossing detector for syncing to the DC bus voltage ramps
Duplex fiber optic communication â€“ interrupter in, sync out
External interrupter using ATtiny84

General coil specs:

Secondary 10x15 cm wound with 0.25mm wire
Aluminium ducting toroid
Resonant frequency ~400 kHz (according to JavaTC)
12 turn primary
Half bridge of IRFP460 MOSFETs
DC bus voltage 325 V

The coil is built inside an old ATX psu casing. The visual design is mostly a replica of Loneoceans' SSTC2 and SSTC3 â€“ they looked all too tasty and practical not to replicate.

The space in the casing was a bit tight indeed, but nothing I couldn't bear with. The built-in fan is a huge plus.

The build went incredibly smoothly. The only hiccup was CT feedback not working properly, which was solved by removing the 1k resistor from the feedback network. In the testing phase I powered the bridge from a 48v step down transformer. In the build process only one MOSFET got blown.

I also built and programmed a little ATtiny84 based interrupter which has a limited duty cycle of 10% as well as a fixed maximum absolute ON time. It also can sync to the zero crossing sync signal provided by the driver circuitry via fiber.

At full 325VDC bus voltage, the coil pumps out streamers extending to ~15 cm â€“ just about the secondary winding length. The electronics seem to be running quite cool and I'm sure I could push the coil even further. However, I rather want this coil to perform steadily and reliably. It's already pretty loud as well. For a first SSTC, I'd consider this a success.

Smoothed DC operation.

Ramped DC and staccato interrupter. The streamers are a lot straighter and sword-like.

Some TODOs include:

Make the mechanic design more durable
MIDI input for the interrupter
Enclose the interrupter in a shielded case
Clean up the interrupter code and publish it

I'll report any progress here.

Finally, I would like to thank Sigurthr and others who helped me understand the RFI issues related to SSTCs. Fortunately, I've noticed no kind of interference with any equipment so far. Should any problems emerge, I've already got a Faraday's cage built to mitigate these issues.

Any feedback is appreciated. I'll upload a video as soon as I have time to capture one.

15 September 2015

I had an issue with a broken ground connection in the coil, which took a while to figure out. Meanwhile, I also acquired a piece of acrylic tube to be used as a primary former. Now I've managed to decrease the number of primary turns to seven. With the new, more powerful configuration, I thought I'd better run it in the Faraday cage. Interestingly, it seemed to have a very positive effect on the spark output! Here's a picture in ramped mode:

Going to take some video and more photos probably tomorrow. Right now I'm not going to bother my neighbours with the noise anymore.

I also made the ATtiny84 interrupter code available here for those interested. It's written in C and has the ability to sync to an external signal. I'm also slowly working on a MIDI interrupter code.

flannelhead

Tue Sept 15 2015, 07:57PM

Registered Member #952 Joined: Mon Aug 13 2007, 11:07AM
Location: Finland
Posts: 388

I gave the coil a huge performance boost. See the top post.

The NEYi

Wed Sept 16 2015, 12:11AM

Registered Member #55086 Joined: Sun May 24 2015, 03:18PM
Location: Ukraine, Kyiv
Posts: 7

Ah, nice result for such a short time.
I started making coils when I was 17 and spent like 2 years to make my first 100% working SSTC.

flannelhead

Wed Sept 16 2015, 03:34PM

Registered Member #952 Joined: Mon Aug 13 2007, 11:07AM
Location: Finland
Posts: 388

The NEYi wrote ...

Ah, nice result for such a short time.
I started making coils when I was 17 and spent like 2 years to make my first 100% working SSTC.

Thanks!

To be fair, though, building this bugger ate all my free time during 2-3 weeks. The success of this project is also mostly thanks to the pioneering work of Steve Ward and Loneoceans' excellent tutorial.

dexter

Wed Sept 16 2015, 05:02PM

Registered Member #42796 Joined: Mon Jan 13 2014, 06:34PM
Location:
Posts: 195

i've build this type of coil last year inspired by Loneoceans's RSSTC
i chosen a unique top load because why not and avoided any external flapping in the breeze wires
i went with antenna feedback because it confuses alot ppl with little or none tesla coil knowledge :)

i also noticed the increase in spark length (50% or more) when putting my hands around the toroid similar to your Faraday cage

flannelhead

Wed Sept 16 2015, 07:55PM

Registered Member #952 Joined: Mon Aug 13 2007, 11:07AM
Location: Finland
Posts: 388

dexter wrote ...

i've build this type of coil last year inspired by Loneoceans's RSSTC
i chosen a unique top load because why not and avoided any external flapping in the breeze wires
i went with antenna feedback because it confuses alot ppl with little or none tesla coil knowledge :)

i also noticed the increase in spark length (50% or more) when putting my hands around the toroid similar to your Faraday cage

That's also a good looking coil! The increase in the spark length is an interesting effect. I think it could partly be related to the change of the resonant frequency when surrounded by some matter.

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