ISSTC (Old Stuff)
Its about time to scale up my mini SSTC design to something large and scary. Well, that's exactly what I did. I name it the ISSTC (interrupted solid state tesla coil). Its basically the same thing as my mini SSTC except I use a full bridge of 48N50s as well as 2X the gate driver chips to drive them. The secondary is my same old 4.5"x19" 30awg winding with an 8"x1.5" toroid on top. The sparks so far are about 20" to free air. I haven't allowed direct ground strikes because the first time I did, I managed to kill a single MOSFET!
Anyway, this coil is incredibly loud and powerful! It only draws a measly 4-6A (depending on the pulse width and rate) but makes big scary sparks. Yep, this is one efficient SSTC! One very interesting aspect of the output is its ability to breakout from the toroid on its own! Most SSTCs do not achieve this. My guess is the very high dV/dT due to the interrupter. The interrupter gives a nice variety of output sparks. This coil does an excellent job of forming streamers, unlike most SSTCs. They form a tight bundle of arcs and it just sort of snakes around. Very cool!
A note of warning: This project is relatively new, thus I can't deem it to be a good project to replicate. It has claimed one fet just from ground sparks. Also, I have no idea how much abuse these MOSFETS are seeing, they get VERY hot.
And now the part you've been waiting for!
Some pictures of the driver and H-bridge.
Sparks produced at a very short ON time but high rep rate (~120bps). These seem like what an OLTC would produce.
Longer ON time and still a high rep rate. Notice how it forms a solid braid of plasma... very cool!
A slightly longer ON time than before. These arcs move enough air to where I could feel my clothes vibrating! Definitely need hearing protection!!!!
Okay, I replaced the MOSFETs with IGBTs (HGT1N40N60A4D). I also put them on a larger, more effective heatsink. At 140VAC they didn't show any signs of warming... cool! I finally got up to 240VAC input! My first attempt resulted in a severe flashover at about 25" sparks. So I lowered the primary winding from 5" to 3". No more flashes, but probably not as efficient. Either way its made 33" strikes to a metal target! I did manage to break it! A direct strike to my antenna some 25" away did it in! Interestingly, when going above 200VAC, the current rose to 10A from 5A, but the arcs DO look so very cool!
Here are some still shots from a video I took:
Today I built a new interrupter that is separate from the main board. I used better values to allow from 60-600us ON time as well as about 40pps to 400pps. My old interrupter was somewhat useless compared to the new one. Its still just a 555. I'm using an RCA cable to connect it to the main driver.
Anyway, I replaced those 2 IGBTs and did some more initial testing, this time with the scope to see what things look like.
The next step is to use a smaller tank cap (.05uF) and more primary turns. This will allow me to add a larger toroid without a drastic increase in primary current.
UPDATE (4/7/04) Note: This is no longer an ISSTC, but a DRSSTC due to the resonant tank capacitor
Okay, this coil is kicking butt now :-) The pictures show 30" arcs to a grounded target. This is my coolest project yet! The cap is .05uf 12kv and the 12kv is no joke, there was actually corona on it my last run! Oh, and I am now happily running off of secondary current feedback! Works perfectly.
To see this develop more, see the DRSSTC-1 page.