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Registered Member #2292
Joined: Fri Aug 14 2009, 05:33PM
Location: The Wild West AKA Arizona
Posts: 795
Ok folks, we have have had enough progress on this project that we figured it was time to start a project thread. I will start out with saying this is a joint project between myself and Steven Caton. We have been designing and gathering parts now for a little more than 6 months. Let there be no illusions this is a long term project and we don't expect to have it running anytime soon.
So what are we building? Simple the worlds largest QCWDRSSTC! The design goal on the system is 12+ feet of sword sparks. This is to be a very complex build. Most of the system is designed we just have to get the rest of the parts and build it.
Some Specs!!! Fres: 450KHz Secondary MMC for spark capacitance compensation. Peak primary current 800A Pulse widths on the order of 100mS+ Tank cap: MMC consisting of 12 10Kv 5.6nF high RMS current MICA caps Primary: 3/8 water cooled conical Controller: ZVS driver with full phase shift modulation
Power electronics: 32x IXYN82N120 100A 1200V high speed IGBTs with positive tempco (that's right 32 of them!) Topology: full bridge 8x Current sharing/impedance matching network (8 ferrite transformers) A grand total of 120mF of bus capacitance with an energy storage of 30KJ Water cooled copper heatsinks (that are 1" think) fully laminated copper bus structure.
Here is one of the 4 bridge assemblies. It has 8 IGBTs inside and 30mF of total bus C
An exploded view of the bridge assembly:
All the parts on the bridge are to be water jetted and laser cut.
A large amount of simulation and modeling has been conducted regarding the modulation topology and spark loading on the secondary circuit. We still have plans to measure the capacitance added by sword sparks by extrapolating a general equation from data we plan to collect from my small QCW. This will give use the numbers we need to accurately choose the secondary MMC size based on our 10 to 12 foot design goal. Without the secondary MMC the resonant frequency will easily shift many 10's of KHz possibly pulling the system out of resonance by the end of the burst (below the magic 380KHz zone).
I will add more info and photos later. But this gives a good idea of the magnitude of the project.
As usually high res photos can be found here:
UPDATE 11/24/12 Ok So some of the parts have come in for the HOG. We now have all the water cooling parts, ferrite cores for the sharing networks, wire, bridges and transistors, DC block caps, and copper (note shown). Also in the photo is the two radiators that will cool the water in this closed system. Each radiator has three 120mm fans with speed control, so we should be able to keep this coil rather silent.
The water blocks and transistors have been assembled for some time now and as soon as the bus caps come in we can start fabricating the bridge modules.
UPDATE 12/28/12 Ok so probably the last update on this project for this year. All of the MICA caps for the Tank circuit have come in and 8 of the bus caps have arrived. We plan to build one bridge module to start and then once we have tested it fully build the remaining 3.
UPDATE 8/26/13
OK so we actually built something.... We changed our bridge design drastically from out last design, we even changed the transistors. We plan to change the modulator again however from a discrete logic and analog to a full 100MS/S ADC front end with a FPGA DSP doing the heavy lifting. That's right folks we are going to do phase lead all in digital!
The great thing about our new controller is the it will be highly configurable, simply by changing the software it could act like a a UD1.3 UD2 or in ZVS phase shift modulation mode. It's truly a universal driver!
Until then here are some photos of the new bridge and the older analog controller.
Registered Member #3908
Joined: Tue May 24 2011, 09:40PM
Location: Gilbert, Arizona USA
Posts: 68
Goodchild wrote ...
Power electronics: 32x IXYN82N120 100A 1200V high speed IGBTs with positive tempco (that's right 32 of them!) Topology: full bridge 8x Current sharing/impedance matching network (8 ferrite transformers) A grand total of 120mF of bus capacitance with an energy storage of 30KJ Water cooled copper heatsinks (that are 1" think) fully laminated copper bus structure.
Wow, that certainly fits into the "go big, or go home" arena. I can hardly wait to see how you'll drive the eight parallel IGBT's comprising each quadrant of the bridge, and the balanced output transformers. P.S. nice modelling!
We still have plans to measure the capacitance added by sword sparks by extrapolating a general equation from data we plan to collect from my small QCW. This will give use the numbers we need to accurately choose the secondary MMC size based on our 10 to 12 foot design goal. Without the secondary MMC the resonant frequency will easily shift many 10's of KHz possibly pulling the system out of resonance by the end of the burst (below the magic 380KHz zone).
I find this very interesting, since I've been attempting to model QCW spark characteristics myself. Maybe you want to share some of your results.
Steve Wards tesla gun requires about 25kW peak power for a 50" spark. By Freaus relation you would need about 210kW for 12'. According to my current model, QCW spark length rises with the square(!) of the voltage. This is a bit radical, but it seems to agree with my own measurement for shorter (30") sparks. Extrapolation from Wards data 65kVpk for 50" would require a voltage of only about 110kVpk for 12'. The arc load resistance is then 29k. By the hungry streamer model, which seems to hold for my shorter arcs, reactance of the arc load capacitance and the arc load resistance are the same. For 450 kHz frequency that amounts to a 12pF capacitive arc load. This is heavily extrapolated and speculative. What do you think?
Registered Member #30
Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
I think crank the sucker up and see what happens!
Did you leave room for a bunch of plastic film caps in your buswork? If you're switching at 500kHz, your DC bus decoupling will have to be good up to several MHz.
Registered Member #2292
Joined: Fri Aug 14 2009, 05:33PM
Location: The Wild West AKA Arizona
Posts: 795
Uspring wrote ...
Hi Eric,
you wrote:
We still have plans to measure the capacitance added by sword sparks by extrapolating a general equation from data we plan to collect from my small QCW. This will give use the numbers we need to accurately choose the secondary MMC size based on our 10 to 12 foot design goal. Without the secondary MMC the resonant frequency will easily shift many 10's of KHz possibly pulling the system out of resonance by the end of the burst (below the magic 380KHz zone).
I find this very interesting, since I've been attempting to model QCW spark characteristics myself. Maybe you want to share some of your results.
Steve Wards tesla gun requires about 25kW peak power for a 50" spark. By Freaus relation you would need about 210kW for 12'. According to my current model, QCW spark length rises with the square(!) of the voltage. This is a bit radical, but it seems to agree with my own measurement for shorter (30") sparks. Extrapolation from Wards data 65kVpk for 50" would require a voltage of only about 110kVpk for 12'. The arc load resistance is then 29k. By the hungry streamer model, which seems to hold for my shorter arcs, reactance of the arc load capacitance and the arc load resistance are the same. For 450 kHz frequency that amounts to a 12pF capacitive arc load. This is heavily extrapolated and speculative. What do you think?
I'm glad you bring this up because I can't claim I know a whole lot on the subject yet. From my experimentation with the little QCW it seems that QCW sparks need way more power than a regular DR for a given length of spark and this makes sense given they are thicker brighter, higher energy plasma. However we run QCWs at drastically lower break rates than a regular DRs. Hence at least from my QCW experiments assuming I stayed at 5 to 10 Hz I was able to match regular DR spark length with the same input power.
I think that regular DRs follow a very similar model to that of the QCW spark in terms of amount of voltage needed in relation to length. So if once again we keep the break rate reasonable 5-10Hz we should be able to make 10 or 12 feet at a similar input power to an equivalent sized DR.
This is however speculator. I need to gather more data before I can make any concreate assumptions. The main info we need is capacitance added per foot. It's probably not linear because that would be too easy. Most likely it is logarithmic or exponential. We plan to find this data by looking at shift in frequency and relate this to spark length.
Any other info you have gathered on your model or just general DR model would be of great help. I welcome others that have data or theories on this subject. One of the main reasons for this project is to help answer some of these questions.
Steve, Thankfully our caps only have to be 5-20nF due to the ZVS operation but they have to be rated for a lot of current due to the commutation of the current on the rising and falling edges that can be as high as 80 to 100 amps. We are thinking of using some of the 940C caps for this application. GO figure we are finally using 940C's for their designed purpose...
We did leave a generous amount of room for caps so no matter the solution we should be in good shape.
From my experimentation with the little QCW it seems that QCW sparks need way more power than a regular DR for a given length of spark and this makes sense given they are thicker brighter, higher energy plasma. However we run QCWs at drastically lower break rates than a regular DRs. Hence at least from my QCW experiments assuming I stayed at 5 to 10 Hz I was able to match regular DR spark length with the same input power.
Yes, the main difference between QCW coils and others is the duty cycle. They don't differ as much in peak power. A SGTC might have a burst length of 100us and a bang energy of 10J, which amounts to a peak power of 100kW. The 210kW value I guessed at for your project is meant as a peak value at the end of the rampup.
I think that regular DRs follow a very similar model to that of the QCW spark in terms of amount of voltage needed in relation to length. So if once again we keep the break rate reasonable 5-10Hz we should be able to make 10 or 12 feet at a similar input power to an equivalent sized DR.
I agree that you can probably get the same performance in terms of spark length with similar power values, but I believe, that the voltage required is much lower for QCWs. A SGTC has a very short burst length so there is little time to heat up the plasma and make it conductive. The low conductivity requires more voltage from the coil to transport charge to the tip of the arc, which is needed to make it grow.
The main info we need is capacitance added per foot. It's probably not linear because that would be too easy. Most likely it is logarithmic or exponential. We plan to find this data by looking at shift in frequency and relate this to spark length.
I'd be very interested in seeing that data and also info on spark length versus voltage You need to be careful in your analysis of the data, since your coils frequency also depends on the resonant frequency of your primary tank.
I know only 2 theoretical approaches relating to the arcs capacitance. The simpler one is based on a wire model, where the arc is assumed to have the capacitance of a perfectly conducting thin wire. That would predict a linear growth of capacitance with arc length. I've posted a more complicated theory on TCML a while ago That model is base on some unproven assumptions, but it seems to work for the smaller (30") arcs, that I measured. It also predicts a linear rise of capacitance with arc length.
Registered Member #30
Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
Very interesting TCML thread. There are some good pointers for possible experimental work there.
I'll add in a puzzler of my own. Is all the power consumed by a streamer fed in through the root from the breakout point? Or does it draw some from the surrounding E-field? I've seen people try to measure breakout point current before, but that could be the wrong approach.
I've noticed that longer breakout wires lead to an earlier flattening of the primary current. That can be due to an earlier breakout or a higher top load capacitance or some effects of the field on the arc or whatever. Hard to tell. It's definitely worthwhile considering the toroids E-field in arc models. I've seen breakout current measurements with the electrum. Do you know of any others?
Registered Member #2292
Joined: Fri Aug 14 2009, 05:33PM
Location: The Wild West AKA Arizona
Posts: 795
Another interesting thing that I have noted is that high frequency needs less voltage as well. If I remember right Steve Ward showed this with his QCW when he took voltage measurements at 380KHz and then 500KHz and was able to get the same sparks but with less voltage. I'm curios if this also relates to less spark capacitance with an increase in frequency or if it's strictly based on overall volume and density of the plasma.
I will have to find some time to sit and read your TCML thread it look very interesting!
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"The HOG" Supersized QCWDRSSTC
