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500W Audiomod PLL SSTC

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Mates

Fri Dec 07 2007, 03:28PM

Registered Member #1025 Joined: Sun Sept 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...

Tom540

Fri Dec 07 2007, 04:28PM

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

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.

Steve Ward

Sat Dec 08 2007, 07:41AM

Registered Member #146 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.

...

Sat Dec 08 2007, 08:34AM

Registered Member #56 Joined: Thu Feb 09 2006, 05:02AM
Location: Southern Califorina, USA
Posts: 2445

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.

Steve Ward

Sat Dec 08 2007, 08:07PM

Registered Member #146 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.

Reaching

Sat Dec 08 2007, 08:21PM

Registered Member #76 Joined: Thu Feb 09 2006, 10:04AM
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 1,5mmÂ² wire and the discharge is hot enough to melt the 1,5mmÂ² copper on the topload within seconds. 4mmÂ² is fine there ,,,only "red hot"

...

Sat Dec 08 2007, 08:36PM

Registered Member #56 Joined: Thu Feb 09 2006, 05:02AM
Location: Southern Califorina, USA
Posts: 2445

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...

...

Sun Feb 24 2008, 10:22AM

Registered Member #56 Joined: Thu Feb 09 2006, 05:02AM
Location: Southern Califorina, USA
Posts: 2445

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.

uzzors2k

Fri Mar 14 2008, 04:03PM

Registered Member #95 Joined: Thu Feb 09 2006, 04:57PM
Location: 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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