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PlasmaSonic II based SSTC, with poor performance

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Cotlone

Tue Sept 30 2008, 11:49PM

Registered Member #1383 Joined: Mon Mar 10 2008, 11:09AM
Location: Wollongong, NSW
Posts: 27

Hey guys, this is my first post here so firstly Iâ€™d like to say gâ€™day to everyone. This is also my first attempt at building a coil of any sort.

Ok but the real purpose here is to see if anyone can help me out with my SSTC and its apparent lack of output. Iâ€™ve based my coil nearly completely on the PlasmaSonic II, though Iâ€™ve culled its ability to generate long sparks and I am focusing on its acoustic performance. I can only get the device to generate spark/discharge with the base of the secondary moved within reasonably close proximity of the discharge terminal. This spark is at best about 20mm when my input is 200V but does play music, despite the terrible quality. The system should be well capable of delivering corona discharges on its own, so far - nothing. Iâ€™ve attached a couple of photos and schematics to help explain my setup and circuit.

I had initially made an error on the schematics prior to printing the board. I forgot to inverse the gate signal on two of the gates. To do this Iâ€™ve been running the wires from the incorrect GDT to the appropriate tracks on the board. These wires need to run past the toroid itself coming pretty close, I was wondering whether this will cause the not so clean switching signals Iâ€™m getting.

I should also say that the MOSFET driver chips were getting pretty hot and occasionally still do (will this happen if poorly tuned?) and the old GDTs became very hot too. That is until I blew one of them up (broke into pieces), along with two MOSFETs. I thought that I'd perhaps wound my previous GDTs too tightly. There shouldn't be a problem with heat in my current setup as I've since added a fan directly above the MOSFET heat sinks.

... and here are some details,

Primary coil : 12 turns, 3.15mm diameter
Secondary coil: 1220 turns, 0.4mm diameter
Secondary cap: Total capacitance > 8pF, but not sure
Resonant freq: I think it is around 300kHz, but this could be my problem
GDT : 12 Turns trifiliar, type 77 material
MOSFETs : IXFN48N50

Ok so let me know what else youâ€™d need to know about the setup. Thanks very much for any help I really appreciate it.

- Cotlone

]schematics.pdf[/file]
]pcb_layout.pdf[/file]

MRacerxdl

Wed Oct 01 2008, 12:14AM

Registered Member #989 Joined: Sat Sept 08 2007, 02:15AM
Location: SÃ£o Paulo, Brazil
Posts: 476

Some times here, it happens to the Mosfet Driver burn and doesnt get killed, it only makes a very poor GDT Driving and heats much, and the sparks at secondary stay at few mm. And when I trade the mosfet drivers for new ones, it back to work. Try that, maybe it work.

Cotlone

Wed Oct 01 2008, 12:29AM

Registered Member #1383 Joined: Mon Mar 10 2008, 11:09AM
Location: Wollongong, NSW
Posts: 27

Yeah I had replaced all of the driver chips, and changed them from TC4422s to UCC37322s. I had hoped that was the problem before. I have also replaced all of the MOSFETs since the failure.

KresoLiubov

Wed Oct 01 2008, 06:51AM

Registered Member #1153 Joined: Mon Dec 03 2007, 07:27PM
Location: Croatia
Posts: 213

Simple enameled wire for GDT? You need to use wire like from CAT5 cable

Cotlone

Wed Oct 01 2008, 12:37PM

Registered Member #1383 Joined: Mon Mar 10 2008, 11:09AM
Location: Wollongong, NSW
Posts: 27

So the insulation is rubbish in the enameled wire? This would be contributing to poor gate signals then? I'll try rewinding them then with other stuff.
Cheers

KresoLiubov

Wed Oct 01 2008, 02:22PM

Registered Member #1153 Joined: Mon Dec 03 2007, 07:27PM
Location: Croatia
Posts: 213

Cotlone wrote ...

So the insulation is rubbish in the enameled wire? This would be contributing to poor gate signals then? I'll try rewinding them then with other stuff.
Cheers

In such use you need to consider enameled wire insulation as it does not exsist

Dr. Drone

Wed Oct 01 2008, 03:17PM

Registered Member #290 Joined: Mon Mar 06 2006, 08:24PM
Location:
Posts: 1673

Tom540

Wed Oct 01 2008, 08:32PM

Banned on 3/17/2009.
Registered Member #487 Joined: Sun Jul 09 2006, 01:22AM
Location:
Posts: 617

I find it weird everyone is so anti magnet wire. Thats what it was designed for. Just paint your core and youll be fine. The main reasons I use cat5 is simply because its easier to strip is color coded and is cheaper that magnet wire. Not because im worried about shorts. Ive never had a short from using magnet wire.

Dr. Drone

Wed Oct 01 2008, 08:34PM

Registered Member #290 Joined: Mon Mar 06 2006, 08:24PM
Location:
Posts: 1673

Cotlone

Wed Oct 01 2008, 11:59PM

Registered Member #1383 Joined: Mon Mar 10 2008, 11:09AM
Location: Wollongong, NSW
Posts: 27

Thanks for the replies everyone,

I've rewound the cores this morning and I'll stick them in soon as I can. I tied a knot in one end of my three wires and then twisted them together, I've then wrapped 15 loops around the toroid cores.

Is there a general rule for the coupling of coils? I thought that SSTCs were generally pretty highly coupled ie over about 0.35 or so, I could be quite wrong though.

So once I get these new GDTs tested I'll see how the performance is and have a look at my DC blocking caps.
Thanks for your help guys, I'll post my findings up soon.

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