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500W Audiomod PLL SSTC

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Thu Dec 06 2007, 05:46PM Print View
Registered Member #56
Joined: Thu Feb 09 2006, 05:02AM
Location: Southern Califorina, USA
Posts: 2435
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.
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Mates
Thu Dec 06 2007, 08:09PM
Registered Member #1025
Joined: Sun Sep 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…
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Bauerb2
Thu Dec 06 2007, 09:45PM
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.....
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Shaun
Thu Dec 06 2007, 10:56PM
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.
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Dr. Drone
Fri Dec 07 2007, 12:19AM
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Fri Dec 07 2007, 08:03AM
Registered Member #56
Joined: Thu Feb 09 2006, 05:02AM
Location: Southern Califorina, USA
Posts: 2435
@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.
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Bauerb2
Fri Dec 07 2007, 12:05PM
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.


nice coil
-Andrew
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Marko
Fri Dec 07 2007, 12:06PM
Registered Member #89
Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145
To me it really looks like this box is going to melt and disintegrate unless you will be running really low power, <100W or so.

And to be honest, I think coil would look better without it
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Dr. Dark Current
Fri Dec 07 2007, 03:03PM
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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.
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Fri Dec 07 2007, 03:06PM
Registered Member #56
Joined: Thu Feb 09 2006, 05:02AM
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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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Mates
Fri Dec 07 2007, 03:28PM
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Joined: Sun Sep 23 2007, 07:53PM
Location: Czech Rep.
Posts: 566
jmartis wrote ...

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.


I think you are mixing sparks and streamers... Otherwise I can not imagine fly-back giving 8"streamers... You can compare TC and fly-back when the TC is sparking (rather "plasming") against the ground like here that's cca 450W... But anyway, the fly-back efficiency seems higher also in my hands...
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Tom540
Fri Dec 07 2007, 04:28PM
Banned on 3/17/2009.
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Joined: Sun Jul 09 2006, 01:22AM
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My first sstc would draw 12 amps from the line and had a full bridge w/voltage doubler. I could get 15 inch sparks in CW. I have a video but it's sideways and i cant find a program that will rotate it 90 degrees without squashing it.
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Steve Ward
Sat Dec 08 2007, 07:41AM
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Joined: Sun Feb 12 2006, 04:21AM
Location: Austin Tx
Posts: 1055
How are you guys measuring the current? My CW coil used about 7kVA to do over *2 feet* of CW plasma... so 6" at 3kW is downright lousy :P. 6" of CW plasma should be about 1kW or so id say.
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Sat Dec 08 2007, 08:34AM
Registered Member #56
Joined: Thu Feb 09 2006, 05:02AM
Location: Southern Califorina, USA
Posts: 2435
As stated in the first post, it is the current being drawn off the dc filter cap. I haven't put a current probe in the line, but there should be enough decoupling caps on the bridge that the meter is reading the true power.

I think that the reason for the short sparks has to do with some of the work Terry was doing, which showed that for a streamer to be long it has to be both a high enough voltage and a high enough power. This coil puts out tons of power, but relativley little voltage (it has a hard time breaking out from a 3/8" piece of copper pipe). As a result, the streamers are short but roasting hot.

That means that I could probably increase spark length considerably with a better resonator, but for a democoil (at least the demos I am doing... ) 6" of spark is more then enough, so I am happy as it is.
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Steve Ward
Sat Dec 08 2007, 08:07PM
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Joined: Sun Feb 12 2006, 04:21AM
Location: Austin Tx
Posts: 1055
As stated in the first post, it is the current being drawn off the dc filter cap. I haven't put a current probe in the line, but there should be enough decoupling caps on the bridge that the meter is reading the true power.


How much capacitance do you have at the bridge? Also, do you have any way of measuring the RF primary current? Homemade CTs work fine here... I worry that if you are using a DMM, the RF current between your bulk filtering and the bridge may be significantly affecting it.

Im really curious if you are consuming that much power in such a short arc, because it sort of messes up my understanding of the impedance of an arc produced by a tesla coil. What is the operating frequency of the coil? I know spark length per watt is dependent on the frequency too, since the capacitance of the arc is an increasing load as frequency goes up.
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Reaching
Sat Dec 08 2007, 08:21PM
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Location: Hemer, Germany
Posts: 458
yeah steve is right. i was curious about the the 3kW too.
my new 13,5mhz vttc is drawing around 600watts at full power and i get white hot streamers which are about 5 to 8 cm long, .. at 13,5mhz CW!! not at 250khz or so according to your secondary..

my vttc coil has 28 turns of 1,5mm² wire and the discharge is hot enough to melt the 1,5mm² copper on the topload within seconds. 4mm² is fine there ,,,only "red hot"
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Sat Dec 08 2007, 08:36PM
Registered Member #56
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Posts: 2435
There are 2x 2ufd caps on the bridge, and I am using a mechanical ammeter. The power into variac blows the 15a breaker on a power strip after a few minutes...

It is running at 319kHz (maybe a little lower with that top load)

I did have a CT on the primary coil for a little while, I was seeing about 50A p-p (although that was with a really rough calibration on the ct). The primary could be improved a little, right now it is loose wound and up about an inch on the secondary. (tuned for max current into the bridge). I suspect that I could do a helical coil with a few more turns and keep the power about the same due to higher coupling.

I am getting a nice 2 channel 100Ms/s DSO for Christmas, so I should be able to post some nice shots of everything that is going on next month

The secondary base current is about 500ma p-p for those who care. I am considering running a dedicated ground for it to see if that helps at all, right now there is about 50ft of wire between it and the house's ground. I don't expect much. Next time I run it I will put a few light bulbs on top and see how much current is actually being fed into the plasma. Not sure how one would go about measuring the voltage up there...
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Sun Feb 24 2008, 10:22AM
Registered Member #56
Joined: Thu Feb 09 2006, 05:02AM
Location: Southern Califorina, USA
Posts: 2435
UPDATES:

I could have sworn that I called the coil done back in December, but it just seems to keep changing...

The most notable events are:
*A new case was build out of hardwood, and a new cover made out of Plexiglas to replace the original Plexiglas box that looked like it was made by a stoned 2 year old.
*Several new secondaries have been wound for it, all on a 4" diameter by 11" tall wound with 32awg wire. They were all done using a new technique with I am going to put in another thread, which produced coils that have a thin paper former. I kept getting arcovers from the primary supports, so I have had to wind 3 of them now (and the current one is damaged and needs to be replaced).
*To solve the arcover problems the secondary was lowered 3/8"
*A soft start relay circuit was added as to eliminate the need for a variac--now you just plug in power/audio and go
*The audio source was changed from a cheep mp3 player to my laptop, which outputs a much greater voltage, and allowed for much better audio to be produced. I still need to design some kind of preamp so I can go back to the mp3 player, but for now I am using a sony clie' which has a reasonable audio output but is not capable of driving the coil into clipping
*The tuning in general has caused power consumption to drop to about 5a, and likewise spark length has been reduced to about 3". This led to a quieter spark that is still big enough for a small room of people to see it and a produce a sufficient level of audio (about equivalent to a set of laptop speakers in both quality and volume).

Some pics:
The secondary wound over a layer of paper on a temporary former, and with the former removed


overall system streaming music over wifi, and a pic with the plastic cover on (but an old resonator and rats nest of wire)


Playing with a piece of quartz tubing from a broken xenon flashlamp


And of course some streamer pics



I have a few videos of the coil operating with audio modulation, but I need to compress them down to something reasonable in size and get them hosted here. The output volume is about enough to fill a classroom with audio, and the quality is about the same as a laptop's speakers. Turning on an equaliser to give and extra 15db or so boost at the lower frequencies and roll of the higher ones helps a lot. It is also possible to take the instability of the pll circuit and drive the coil right at the break between +/- 90deg tuning, which gives a result very similar to an interrupted coil (drsstc, etc). The streamers are about 1" long with no audio in and then shoot to a good 4" long spindly streamer when you start to feed it sound (of course in this mode it works best to play only a few chords at a time). The audio in that mode sounds like crap (as do all interrupted coils), but it is still fun to play with. I would assume it is also very hard on the fets.
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uzzors2k
Fri Mar 14 2008, 04:03PM
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Location: Asker, Norway
Posts: 1308
Wonderful streamer pictures! The sound quality of your coil is better than mine, despite your discharge being larger, gj.
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