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Registered Member #56
Joined: Thu Feb 09 2006, 05:02AM
Location: Southern Califorina, USA
Posts: 2445
UPDATE: Look down, the only thing left of this coil is the controller/bridge/power supply
Well, it has been a while since I have done any coiling, but I got inspired to get a working one built for the JPL invention challenge (more about that in the Self Playing Xylophone thread ), and then I decided to make it a finished coil.
The power scheme is pretty simple, 'just' a variac feeding a bridge rectifier to a nice fat storage cap, then off to a full bridge of ixfx55n50 MOSFETS (big fat monster mosfets, they fit in a to-247 package, but the die covers the entire copper heat spreader, even where the hole would go with a normal to-247), and into a 7 turn primary. The secondary is a 4" by 11" phenolic former, wound with 32awg wire. I had too add a small topload to keep the top turn on the secondary from arcing.
To drive the beast I have Steve Conner's pll driver, driving a pair of the to-220 tc4422/tc4421. I had to tweak the resistors on pin 11/12 of the pll to get the coil to track properly, and then I ended up switching over to secondary base feedback instead of the antenna. That helped performance a ton, the pll was not nearly as picky, and there wasn't an antenna to worry about any more To do that just took a classic 'goldmine core' and wrapped 50 turns of 32awg wire, put a 390r resistor across it, and hooked it from pin 14 to ground. Works like a champ!
In any case, this thing is a beast! It pulls 15a off the dc bus (about 200v), so it is running 3kw of real power into that ark. There is well under 100w going up in that heatsink, so I am guessing something like 97% efficiency The sparks are about 6" long, sometimes a bit more, with audiomod a bit less.
Although I can't say much about the audio quality, it is loud (at least 90dB if you don't mind the horrible distortion...), but it sounds horrible. But it definitely recognizable, and still impresses everybody.
On the bright side, those mosfets are robust little buggers! I was messing with it and couldn't make it fry them even at 200v on the bridge pulling 15+ amps with moderate detuning. Abet, I called it indestructible and sure enough as I was taking pictures I had an arcover from the fets to the main heatsink, which took out a pair of fets, my gate drivers, and my 2nd to last pll driver. I rebuilt it last night, but I don't want to do any more high power runs until I get more pll's and really some more big MOSFETS (only 2 left IIRC :o )
Some pics.. with flash: (notice how the air is all ripply around the plasma, that is a HOT flame
without flash:
UPDATE: Got Chris to host the video on 4hv.org, so now you might actually be able to watch it. The run was done at about 70v on the variac (much more than that and the audio just more distorted, not any louder). The first 30s or so was me messing with the tuning, then the song starts, and I pull arks with an insulated point (piece of copper wire on a ceramic rod). Then I attach a ground lead, and pull some flames. Then I go back to air arks, and then finally a few hits to my finger.
Registered Member #1025
Joined: Sun Sept 23 2007, 07:53PM
Location: Czech Rep.
Posts: 566
... wrote ...
In any case, this thing is a beast! It pulls 15a off the dc bus (about 200v), so it is running 3kw of real power into that ark. There is well under 100w going up in that heatsink, so I am guessing something like 97% efficiency The sparks are about 6" long, sometimes a bit more, with audiomod a bit less.
Maybe it is only my feeling, but that sparks you show on those two pictures do not look like 3KW of power. Where the hell is all the energy? I would expect at least shinning-melting tip of the break out point…
Registered Member #973
Joined: Tue Aug 28 2007, 07:32PM
Location: Pittsburgh, PA
Posts: 66
i was going to say, i ran my new sstc with at around 500W (40V 9-12amp) and i get "almost" the same output (inch or two shorter), with some very hot arcs to ground. 3 KW should give you much more than what you have.....
Registered Member #690
Joined: Tue May 08 2007, 03:47AM
Location: New Jersey, USA
Posts: 616
I couldn't get the video to play, but judging by the pics you must be losing power somewhere, unless that plasma is WAY hotter than it looks. My SSTC looks about like that and it wont blow a 5A fuse at 120VAC in.
Also, my secondary is about the same size as yours (1.5" shorter) also wound with 32ga. I would have thought 3kW would merit a much larger resonator. Your mosfets can certainly handle it.
Registered Member #56
Joined: Thu Feb 09 2006, 05:02AM
Location: Southern Califorina, USA
Posts: 2445
@andrew: Looking at your videos, you seem to have 2-2.5" of spark to air at 500w, which would correspond to 6" at 3kw (keeping in mind that these things go by the ratio of sqrt input power). Surprisingly enough I get about 6" of spark.
And yes that plasma is roasting hot, I don't think I have ever seen anyone else's coil with such a dramatic amount of heating in the air surrounding the plume. Heck, you can almost see it in the thumbnail
That copper breakout point (#12awg wire) gets glowing red/orange, and if I use a steel nail as the breakout point I get some lovely sparklers.
(both taken with 70v on the variac pulling about 10a off the DC buss)
In any case, the idea behind this coil was so that I could have something that would sit on shelf, and be ready to rock whenever needed. Just plug it in and hook up a MP3 player or variac for added fun. the whole being able to pump 3kw into it came as an added bonus, that made the coil a heck of a lot more fun to play with
BTW, there is a working link to the video in the first post now.
Registered Member #973
Joined: Tue Aug 28 2007, 07:32PM
Location: Pittsburgh, PA
Posts: 66
yeah the heat from my coil is immense, it's almost uncomfortable knowing how much power is getting dumped into it. At full power i can feel this giant woft of hot air getting propelled off of it. it's fun to burns things though. I put a needle tip point on mine and it just melted away. what fun hehe.
after looking, your coil may not show the full power by arc length, but it sure shows its power by its current output, i suppose... that arc is brightttt.
I was lookign at one of steve wards coils 1.6kW 21". 3kW for your coil seems a bit like overkill, especially for that size, but if it works, it works.
Registered Member #152
Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384
Yea I too wondered about the power thing.. With 500W I can get 6-8" white hot arc from flyback, but from SSTC at the same power I hardly get 3-4" white-purple spark at CW or ~5-6" purple spark with halfwave input. The spark from the SSTC looks like it has much less power than the one from a flyback.
Registered Member #56
Joined: Thu Feb 09 2006, 05:02AM
Location: Southern Califorina, USA
Posts: 2445
Yes, that box is just to make it so that I can say it is enclosed. It totally screws with the audio quality and the sparks hit the top if I run it at high power. Not to mention that it does nothing to stop the RF burns you get fro touching anything metal within a 5ft radius of the coil :p
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