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Registered Member #29
Joined: Fri Feb 03 2006, 09:00AM
Location: Hasselt, Belgium
Posts: 500
BP.. It's outstanding work!
Perhaps if you made all the wiring as compact as possible (short leads, no "big" loops where your primary connects to PCB, etc.) and shielded everything, your bench instruments should not go crazy (I noticed this too before I put my coil in a faraday cage.) You are no doubt radiating significant harmonic power as well as possibly inductively coupling into power-supply leads... Just a thought....
Registered Member #63
Joined: Thu Feb 09 2006, 06:18AM
Location:
Posts: 1425
Thanks Peter, Avalanche, WaveRider =)
In these pics here, you can see the output board from close up:
My primary is connected straight to the drain, i.e.: +VE >> PRIMARY >> MOSFET >> GND
On that circuit board, the DRAIN and +VE are the big pads on the left and right of the FET, respectively. I've snuggled the decoupling cap in there as best as I can, and you can see where the big negative pad connects straight to SOURCE.
I could connect the primary straight to the heatsink underneath the positive pad (not using insulators, for now, which greatly helps with removing heat from the TO-220 package).
It's interesting to note I'm getting ~100V peaks on the drain with a 32V supply. The IRF730 is a 400V FET, so if I can keep it well enough in tune, I'd consider tripling the supply voltage =D You guys can flame me later.
I should also play around with the turns and coupling on the primary -- I'm sure that two turns isn't optimal.
Registered Member #63
Joined: Thu Feb 09 2006, 06:18AM
Location:
Posts: 1425
I raised the secondary by putting two tiny C-shaped aluminium heatsinks over the primary to sit it on, and now he resonates at 12.7MHz. I also get a higher voltage (or at least, longer breakout) at the top of the coil. The plasma appearance is just breathtaking at such high frequencies -- it looks less and less like an electrical discharge and more and more like a tiny blowtorch flame.
The wire forming my secondary (0.5mm, or 0.02in)gets ridiculously hot after a few minutes of operation... considering the skin depth (or lack of!) in copper at 12+MHz, I shouldn't be surprised.. If I had thicker wire, I'd like to rewind it with more turns and a smaller diameter.
I will also adjust primary turns and consider enclosing in a cage.
Registered Member #103
Joined: Thu Feb 09 2006, 08:16PM
Location: Derby, UK
Posts: 845
Nice pictures! How does the discharge compare to your 'lower' frequency class-e coils (in terms of appearance/impressiveness more than size)? I'm seriously considering cutting my frequency in half with my current setup, as it should be easy to get 6Mhz at quite a bit of power with this lot.
Registered Member #63
Joined: Thu Feb 09 2006, 06:18AM
Location:
Posts: 1425
The angle of the photo doesn't help, but that spark is ~9-10mm in length.
When the signal generator is stable, the arc makes NO noise. In still air it does NOT even appear to move.
If you didn't already see them, the pics from my 6.5MHz coil can be found here: http://www.infringingwebsite.com/matt/6.5mhz/ Notice how in all the pics, although the edges of the discharge are a very fuzzy plasma glow, it *still* branches out into 'streamers' of some description.
The 6.5MHz discharge still retains a lightning-like appearance that causes hissing/rippling noises, which is why I set my aspirations at 13.56MHz.
As I coax more and more power from the coil (I need to get my Variac operational for this), things will get more interesting, and I think the rippling noises will start again.
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