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RE: [TCML] BIG solid state
An excellent build and infinitely more complex than a lot of us could
manage.
A YouTube video to see the 'type' of streamer it produces would be great. I
say 'type' as I like the lazy wandering sort as produced by the Biggg one,
rather than the more frantic output of some SS types.
There are many I am sure who want to know about the fire Dept. issues, which
were briefly mentioned as a teaser.
PS: I can't say I agree with Vasil's rather cheeky comment of >> " and
they win compared with "those old spark gappers"
Regards
Phil Tuck (an old spark gapper)
www.hvtesla.com
-----Original Message-----
From: tesla-bounces@xxxxxxxxxx [mailto:tesla-bounces@xxxxxxxxxx] On Behalf
Of Steve Ward
Sent: 15 June 2011 04:36
To: Tesla list
Subject: [TCML] BIG solid state
Hi Everyone,
Just a post about a recent project of mine. Many hands involved on this one
(see credits later). So far its just a prototype, but results are
promising:
http://www.flickr.com/photos/kickermagnet/5811280440/in/photostream
This is, as far as im aware, the largest Double Resonant Solid State Tesla
Coil built and working as intended. The machine stands 15 foot tall (to the
top of the toroid). With breakout point at 16 foot above the ground, its
made some 25 foot sparks. Power input at 200bps was measured at 33kVA
(480VAC 3 phase, about 40.5A RMS). I estimate a power factor of .92 given
the line reactor used to smooth the current peaks charging the 2kJ of DC bus
storage. The secondary is 24" diameter and wound to just over 8 feet
length. The toroid is 96" by 16", and is indeed very ugly.
For now, i dont have many photos of the detailed construction (this is
something i should get to soon) but you can sorta see whats going on here:
http://www.flickr.com/photos/kickermagnet/5487415037/in/photostream
<http://www.flickr.com/photos/kickermagnet/5487415037/in/photostream>On the
lower level, you can see banks of white electrolytic DC capacitors, 3300uF
400V X 16 total, wired in series parallel banks, one per each of the 4 IGBT
inverters. The inverters consist of a full-bridge of CM300DY-24H
transistors. So each pair of half-bridge bricks (there are 8 total, 4
H-bridges) drives its own .625uF 20kVAC capacitor, and 2-turn primary coil.
There are 4 MMCs and 4 primaries. The mutual inductance between primaries
and equal MMCs force current balancing of the 4 drives (each drive sees the
same load impedance). This was chosen to avoid some possible issues with
directly paralleling modules, such as, what happens if 1 device fails? Does
it take out all the rest? In this scheme, there is DC isolation between
inverter outputs, so one inverter failure should not take out the other 3.
And, in fact, if i did lose an inverter, i should be able to short its tank
circuit (using its energy storage of the MMC to maintain tuning) and
continue operating at 3/4 power. Hopefully it never comes to this!
The coil has a natural resonance of about 45khz, but i found that de-tuning
the drive down to 40khz or so was best to keep it in tune with large
streamer loading. The primary current peaks at 6000A after about 6 cycles
of excitement. The coupling coefficient of the system is fairly high, at
about .19 (estimated by a 5 cycle beat period that didnt quite notch). So
detuning the primary seemed to work well at efficiently transferring energy
to the secondary in the event of being detuned by streamers.
The primary copper is 3/8" diameter to keep the surface area down (which
happens to reduce AC losses as the eddy currents are lessened). I pump tap
water through the primary to keep it cool, as the RMS current is something
like 80-100A per primary coil! Me (tall guy) and friend Mike working on the
primary coils:
http://www.flickr.com/photos/kickermagnet/5487414563/in/photostream
The MMC is made out of giant polypropylene snubber capacitors, rated 5uF,
2500VAC pk, 3600Apk and 80A RMS each. They make the CDE MMC caps look very
small indeed. I think the whole MMC bank (32 of these caps) weighs
something like 150lbs. Total bank is 4 strings of 8 in series, 2.5uF 20kVAC
effectively.
RF grounding was primarily a 4x20 foot sheet of metal "cloth" (1/2" square
steel mesh) laid on the parking lot, and also clipped to the building ground
rod (about 40 feet away). Would have preferred an even larger sheet of
metal down there, but this was available and quick, and seemed to do the
trick!
Spark performance ended up being right on target, at 25 feet, with
extrapolations from smaller DRSSTCs (that make 10-12 foot sparks).
I gotta thank the help of many friends, Jeff Larson for his use of materials
and labor on the secondary coil for this beast. Big thanks to the guys in
Arcattack, who stayed at my house for a week this january to help me crank
out this prototype (we actually got it running by the end of a week!).
Terry Blake has been supportive in helping setup and teardown of this
system, which isnt trivial, and for being the guy in the suit. And recently
Jimmy Hynes (who got me working with DRSSTCs originally) who visited and
instigated the testing of this machine, and helped tune it up to almost
perfectly match our expected outputs. And Dave (who isnt on the TCML) for
being such an awesome host, letting us run and store this machine at your
shop, and dealing with the city and fire department on issues that really
dont concern them, thats a story for another time.
Steve
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