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Registered Member #2893
Joined: Tue Jun 01 2010, 09:25PM
Location: Cali-forn. i. a.
Posts: 2242
I have two paper mica caps, .5uF at 1kV but those likely will not work. Maybe a MMC of "regular" silver mica caps like these could work. It'd certainly be cheaper/easier to obtain.
What I currently have; * Plenty of 24, 25, 26 and 28 AWG wire * Two dead XRTs, could be used to supply 600VAC if 1200 turns were piled on their big cores. * Alu wire for making a toroid * Maybe some other stuff
I am thinking about using vacuum tubes instead of IGBTs for this coil. Not only would a VT bridge be awesome looking, but it would also be a lot tougher to kill than expensive IGBTs. Of course high impedance might be a problem, but one can always just crank up the bus voltage.
A high voltage GDT would need to be made, but that's not exactly a tough thing to do.
Registered Member #1875
Joined: Sun Dec 21 2008, 06:36PM
Location:
Posts: 635
I was just talking about the bus supply synchronous buck when I mentioned the class D amplifier, not anything having to do with the coil or its 350kHz H-bridge.
Careful modulation of the bus supply is what sets the QCW apart, and the power supply much more critical than in a standard SSTC. The actual part that supplies the primary with its power would typically be a standard H-bridge capable of withstanding the power dissipation associated with those long on times.
I have seen standard tube coils with very similar effects to the QCW, but the QCW's bus supply scheme allows you to fine tune the effects so you can get longer spark length for a given power input, swordier or branchier streamers, etc.
Registered Member #2292
Joined: Fri Aug 14 2009, 05:33PM
Location: The Wild West AKA Arizona
Posts: 795
Grenadier wrote ...
I have two paper mica caps, .5uF at 1kV but those likely will not work. Maybe a MMC of "regular" silver mica caps like these could work. It'd certainly be cheaper/easier to obtain.
What I currently have; * Plenty of 24, 25, 26 and 28 AWG wire * Two dead XRTs, could be used to supply 600VAC if 1200 turns were piled on their big cores. * Alu wire for making a toroid * Maybe some other stuff
I am thinking about using vacuum tubes instead of IGBTs for this coil. Not only would a VT bridge be awesome looking, but it would also be a lot tougher to kill than expensive IGBTs. Of course high impedance might be a problem, but one can always just crank up the bus voltage.
A high voltage GDT would need to be made, but that's not exactly a tough thing to do.
Ummm so your going to build a VTTC? A VTTC runs in the same mode but as said before what sets the QCW apart is being able to have longer ramp so that you can push more spark out of the system.
A VTTC is also a high impedance tank circuit and Dual Resonant. If you are interested in making a VTTC with a modulated bus supply you should talk to Phillip Slawinski over at Tesla Universe. He converted his 833C VTTC to what he calls a SSVC (Solid State Valve Coil). He also uses a solid state supply that puts a ramp onto the plate of the tube, but instead of a 0 to 300VDC ramp like the QCW, he uses a 0 to 20Kv ramp from what I understand, so that it is suitable for tube use.
From what he has told me and other over at TU the SSVC is even more expensive to construct than a QCW for a similar spark output. When you get right down to the nuts and bolts the operation mode is the same among VTTC QCW and SSVC, the differences comes from implementation. Each variant has it's advantages and disadvantages that must be considered when designing something like this.
Registered Member #2292
Joined: Fri Aug 14 2009, 05:33PM
Location: The Wild West AKA Arizona
Posts: 795
Dr. Kilovolt wrote ...
What about running a standard SSTC on half wave doubled voltage, similar to VTTC supply? Would this give longer sparks?
Yes it would to some extent, but because it's not a dual resonant system, you will be hard pressed to get much more than 2 feet out of a normal SSTC with a reasonable input power.
Registered Member #2893
Joined: Tue Jun 01 2010, 09:25PM
Location: Cali-forn. i. a.
Posts: 2242
From what I'm understanding, the only thing special about a qcw coil is the ramped bus supply.
People seem to be using class D amps to change the voltage. But since the transistors are not part of the resonant tan, and do not see the huge tank currents, you do not need expensive IGBTs to make the bus supply? If that is the case, yay.
What /me needs is a 15ms 100 to 600V ramp. Now I've got to figure out how to make it...
Registered Member #2292
Joined: Fri Aug 14 2009, 05:33PM
Location: The Wild West AKA Arizona
Posts: 795
Grenadier wrote ...
From what I'm understanding, the only thing special about a qcw coil is the ramped bus supply.
People seem to be using class D amps to change the voltage. But since the transistors are not part of the resonant tan, and do not see the huge tank currents, you do not need expensive IGBTs to make the bus supply? If that is the case, yay.
What /me needs is a 15ms 100 to 600V ramp. Now I've got to figure out how to make it...
They are subject to huge tank currents!! :P The current flowing through the IGBTs in regular DR where do you think it's pulling that current from? Thin air? No, the bus capacitor. But in a QCW, because the bus is modulated there is no tank cap on the main bridge and you pull your large current out of the class D amp. So your class D IGBTs and the filter inductor have to be able to handle the same peak current you plan to run in your tank.
The IGBTs in the H bridge for the coil see currents in the 100A to 200A peak range, much lower than a regular DR but for much longer periods of time (10mS to 20mS) so thermal dissipation becomes a very large factor as well.
Registered Member #2893
Joined: Tue Jun 01 2010, 09:25PM
Location: Cali-forn. i. a.
Posts: 2242
True...
Basically my goal is to get the biggest musical sparks out of the smallest possible coil (I want to replicate the first video). So it looks like the first step is to build the DRSTTC. I've never built one before, so I really have no clue what I'm doing :p
I get how it works. Basically you turn on the bridge, then turn it off before the IGBTs explode. But a qcw would run for 15ms, and that is a hell of a lot of cycles. That means that current must be controlled via the bus ramp?
I don't want to explode expensive parts, so I'm trying to figure all of this out. Speaking of exploding parts, what is the best DRSSTC driver for this system? I could design one, but since this is my first experience with all of this I'd prefer to not make my silicon go boom...
Registered Member #2919
Joined: Fri Jun 11 2010, 06:30PM
Location: Cambridge, MA
Posts: 652
Grenadier wrote ...
True...
Basically my goal is to get the biggest musical sparks out of the smallest possible coil (I want to replicate the first video). So it looks like the first step is to build the DRSTTC. I've never built one before, so I really have no clue what I'm doing :p
I get how it works. Basically you turn on the bridge, then turn it off before the IGBTs explode. But a qcw would run for 15ms, and that is a hell of a lot of cycles. That means that current must be controlled via the bus ramp?
I don't want to explode expensive parts, so I'm trying to figure all of this out. Speaking of exploding parts, what is the best DRSSTC driver for this system? I could design one, but since this is my first experience with all of this I'd prefer to not make my silicon go boom...
On a QCW, you control the primary current using a high-impedance tank circuit. The hard part of the coil is the sync buck powering it; the DRSSTC is just a standard DRSSTC.
Registered Member #2893
Joined: Tue Jun 01 2010, 09:25PM
Location: Cali-forn. i. a.
Posts: 2242
Assuming a 20uH primary and a f=350khz, I'd need a 10nF tank cap and the impedance would be 50 ohms. I'm not sure if I'd call that high...
As for the buck, hell not sure where to begin there. I happen to have a pair of these that could probably be used. Only 600V though, so the bus can't exceed 440V if there is a safety margin :-/ Also have 8 of these which I could //
Wish I had some sort of block diagram of the huge buck to look at.
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QCW coil
