Scarily similar half-bridge SSTC

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Scarily similar half-bridge SSTC

Postby Party Scratch » Wed Oct 23, 2013 5:44 pm

Hi guys, when I first saw the video of the "oneTesla" on vSauce I thought it was a SGTC, but when I saw the schematic I was kinda shocked (hehe) because it is very similar to my design...I've built it maybe a half year ago and I think the schematic should be pretty self explanatory. The feedback is done by an little antenna because I was lazy to wind the feedback coil.

Here are the schematics: Image and the power part: Image
The MOSFETs I'm using are IRFP460 and the secondary coil is about 25cm high and has a diameter of 75mm, the copper wire has diameter of 0,2mm/SWG 36. The primary coil is wound with 1,75mm alu wire and has 12turns on 105mm diameter. Here are some photos: http://rpsx.eu/upload/czfiyMiG.JPG http://rpsx.eu/upload/d1ncg0xI.jpg http://rpsx.eu/upload/BLi9gIRd.jpg http://rpsx.eu/upload/GYjqk0Zl.jpg
Here's the coil: http://rpsx.eu/upload/PWx4iDrm.jpg

and here are some vids: http://www.youtube.com/watch?v=AYW8AQwzRvg
I've tried to audio modulate by rectifing the utility AC (I used transformer to limit power to around 110VDC on primary, The FETs heats like hell) and adding a MOSFET which is biased so it's only half open and then I put the audio signal from my PC (through cap ofcorse) to the biased GATE of the FET, it works pretty well: http://www.youtube.com/watch?v=eNCC2kJk5gM The FET is heating like hell thou, that's why I want to use PWM modulation and use the "ENABLE" pin on the UCC drivers to modulate the amplitude by PWM.

I have already tried to put MIDIish square wave there (MCU is connected to PC via serial port which sends the note frequency and length to the MCU which then uses timer to generate square wave with the proper frequency which then controls the ENABLE pin on the UCC drivers) and it works pretty well. I didn't make a video and sadly the MCU went dead (7805 failed somehow). Anyway rate my coil and/or ask me anything :)
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Re: Scarily similar half-bridge SSTC

Postby Bayley » Thu Oct 24, 2013 2:30 am

There's really not much difference between SSTC's and DRSSTC's - you can sort of get an SSTC to run as a DRSSTC by just sticking a capacitor in series with the primary, but it will not be reliable because of the lack of a synchronous interrupter.
Conversely, you can turn a oneTesla driver into a SSTC by replacing the tank cap with a piece of wire and the CT with an antenna (not just theorizing, Kramnik has done it before).
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Re: Scarily similar half-bridge SSTC

Postby DJKOR » Thu Oct 24, 2013 4:20 am

Bayley wrote:Conversely, you can turn a oneTesla driver into a SSTC by replacing the tank cap with a piece of wire and the CT with an antenna (not just theorizing, Kramnik has done it before).


Not that I plan on doing this but since Tesla coils are a bit new to me, what would changing the oneTesla to a SSTC do to it? What's the main advantage of having a DRSSTC over a SSTC? Output capabilities? Music modulation ability?
Image
My build thread: viewtopic.php?f=15&t=998 | 246kHz Primary / 267kHz Secondary
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Re: Scarily similar half-bridge SSTC

Postby ican » Fri Oct 25, 2013 6:18 pm

DJKOR wrote:
Bayley wrote:Conversely, you can turn a oneTesla driver into a SSTC by replacing the tank cap with a piece of wire and the CT with an antenna (not just theorizing, Kramnik has done it before).


Not that I plan on doing this but since Tesla coils are a bit new to me, what would changing the oneTesla to a SSTC do to it? What's the main advantage of having a DRSSTC over a SSTC? Output capabilities? Music modulation ability?


I'd like to know how this changes things as well... If I can change it to an SSTC just by pulling the tank capacitor and the top collector, and be able to use another Interrupter designed for an SSTC, then I may just build a "switch" into the board where one side uses the Tank and the other uses a wire instead.
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Re: Scarily similar half-bridge SSTC

Postby stegu » Fri Nov 01, 2013 4:28 am

I would strongly advise against adding a switch to the primary circuit. The peak current is upwards of 100A, and you need a very solid connection. Few switches are fit for the purpose, and the shorting of the tank cap needs to be made with thick wire and good connectors. Also, a switch is an invitation to make mistakes by having it in the "SSTC" position while still trying to use the CT for feedback, or in the "DRSSTC" position while using the antenna for feedback. Either of those will probably fry the circuit.

A DRSSTC has a higher output than an SSTC, at least in theory, because of the dual resonance. The primary can be pumped up to a higher amplitude than the bus voltage because you time the pulses with the self resonance of the primary. On the other hand, an SSTC will never be out of tune. It will always resonate at the secondary frequency.

I doubt that an SSTC mod of the oneTesla would be able to handle continuous operation (100% duty cycle) because of the heat buildup, but I don't really know enough to tell. Any thoughts on that from someone who knows better? There won't be any problems with overvoltage from long pulses, and no potentially destructive kickback from "bucking" due to frequency mismatches between the secondary and primary, but the IGBTs will still need to handle a lot of power.
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Re: Scarily similar half-bridge SSTC

Postby ican » Sat Nov 16, 2013 4:04 pm

I'd like a bit more information about converting to a SSTC... Since my friends and I are working with a fairly large amount of coils now - 2 oneTeslas, a custom DRSSTC, a few SSTCs and a SGTC, I have been playing with the idea in my head to just turn my oneTesla into an SSTC.

I don't plan on running anywhere near 100% duty cycle, or even 50%... I get long enough sparks out of 1.9% duty cycle with the toroid mounted when I used the GeekGroup interrupter. If all it takes is pulling off the Toroid and replacing the Tank Capacitor with a fat wire, then I also have bigger IGBTs available that we can use to prevent those from frying as well... We've already added bigger diodes that don't fry when the IGBTs pop, so now it's just a matter of keeping the IGBTs cool enough to keep running. We're planning to immerse the electronics in Mineral Oil at some point, which should keep the IGBTs at room temperature even at 50% duty cycle.

How fat does the wire have to be, and I'm assuming CT = Top Collector = Toroid, so all that would be needed is a breakout point (the bolt on top of the secondary) and that wire to use the GeekGroup's interrupter? Could a small (4") toroid or brass ball (also 4" diameter) be used in place of the 8" oneTesla toroid to achieve the right results? I'm kinda attached to the look of having a toroidal top.
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Re: Scarily similar half-bridge SSTC

Postby Alex » Sat Nov 16, 2013 6:05 pm

CT=current transformer (the little black thing with the wire through it)
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Re: Scarily similar half-bridge SSTC

Postby ican » Mon Nov 18, 2013 4:05 pm

Thanks Alex, I actually figured that out after posting, and forgot to come back and edit my post. lol... So instead of having the transformer there with the wire through it, how would you set up the antenna? Do you just remove the CT entirely, and stick a straight wire antenna in one of the holes? I'm imagining it must be more complicated than that.
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Re: Scarily similar half-bridge SSTC

Postby E.TexasTesla » Sun Dec 29, 2013 4:59 pm

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