non-DR QCW's / Tesla Coils / Forums

Forums

4hv.org :: Forums :: Tesla Coils

« Previous topic | Next topic »

non-DR QCW's

1 2 next

Move Thread

LAN_403

Dr. ISOTOP

Mon Apr 02 2012, 06:53PM

Registered Member #2919 Joined: Fri Jun 11 2010, 06:30PM
Location: Cambridge, MA
Posts: 652

Do QCW coils need to be double-resonant to get good spark-to-power ratio? From Steve Ward's measurements we know that the topload voltages are only ~50KV, so it appears that the resonant voltage and current buildup that makes a DRSSTC so wonderful is not necessary.

teravolt

Tue Apr 03 2012, 01:03AM

Registered Member #195 Joined: Fri Feb 17 2006, 08:27PM
Location: Berkeley, ca.
Posts: 1111

hmmmm

Gregory

Tue Apr 03 2012, 03:49AM

Registered Member #2922 Joined: Sun Jun 13 2010, 12:08AM
Location:
Posts: 226

I think that you need a a drsstc because the ressonant swicthing, and, in a sstc you will have some reatance reflected on the primary. This question come in good hour I'm making one QCW, the buck is working good and now I'm working on a sstc to test the buck, so, lets see the results

Goodchild

Tue Apr 03 2012, 06:05AM

Registered Member #2292 Joined: Fri Aug 14 2009, 05:33PM
Location: The Wild West AKA Arizona
Posts: 795

From my experiments I would say you need the DR effect in a QCW. YOU can look at two similar examples a SSTC drive with half rec mains and a VTTC with half rec mains. Both systems are using the same type of input waveform into there main switching section, but the VTTC has one difference from the SSTC, a resonant tank capacitor. I personally think that the higher currents seen in the primary of a QCW are important in the generation of the long sparks because of there inherent current drive nature. i.e. length is more a function of drive current and time than voltage.

Although the currents seen in a VTTC are much lower than a QCW it has a much higher drive voltage to make up the difference.

I don't see this effect being possible with a SSTC unless a insanely high voltage was used or a supper low primary Z. In ether of these cases the SSTC would become a resonant system because the parasitics would then become the resonant component of the primary.

I'm probably totally wrong here so yeah um, yeah! :P

Dr. ISOTOP

Tue Apr 03 2012, 07:42AM

Registered Member #2919 Joined: Fri Jun 11 2010, 06:30PM
Location: Cambridge, MA
Posts: 652

I wonder whether QCW's like high primary currents or long pulses more, i.e. for a given modulator capacity, should one aim for reasonably long ramps that hit a very high Ipk, or long, slow ramps with low slope.
I'm actually sort of inclined to believe its the latter right now, given how low primary risetimes seem to facilitate spark growth. Has anyone tried playing with this?

Avalanche

Tue Apr 03 2012, 08:07AM

Registered Member #103 Joined: Thu Feb 09 2006, 08:16PM
Location: Derby, UK
Posts: 845

I'm building a QCW as an SSTC, or I was - it's been on hold since Christmas!

My theory is that with an SSTC, streamer output is pretty much proportional to DC bus voltage anyway, so my QCW will simply modulate the DC bus voltage (no current feedback necessary). Because streamer growth will be in the rising part of the voltage envelope, I can get away without a feedback loop at all - as it doesn't matter what happens to the DC bus voltage after the streamer has reached maximum length (as long as it dies back down before the next streamer).

Might work

Edit - I should clarify, by "streamer output" I mean total streamer mass - or total volume of plasma. By streamer growth, I mean the shape given to that given volume of streamer mass caused by the shape of the voltage envelope, or it's rate of rise.

Steve Conner

Tue Apr 03 2012, 09:06AM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

Steve Ward's original QCW used DC bus voltage modulation without any current feedback, so that is the approved way of doing it. My experiments with current feedback were none too impressive, and I plan to stop using it.

Goodchild

Tue Apr 03 2012, 03:26PM

Registered Member #2292 Joined: Fri Aug 14 2009, 05:33PM
Location: The Wild West AKA Arizona
Posts: 795

bwang wrote ...

I wonder whether QCW's like high primary currents or long pulses more, i.e. for a given modulator capacity, should one aim for reasonably long ramps that hit a very high Ipk, or long, slow ramps with low slope.
I'm actually sort of inclined to believe its the latter right now, given how low primary risetimes seem to facilitate spark growth. Has anyone tried playing with this?

Well basically if you give the QCW to much PW and not enough voltage you get very fat stubby sparks. but on the other hand if you don't give it enough PW at high voltage the spark with branch. It is a carful balancing act between voltage and PW as you want to make the spark longer you add voltage, but at the same time you also need to increase PW to give the spark the necessary time to heat up the air or it will simply branch out. This is the only way I know of to keep the plasma column straight.

Well correction, you can also use a larger e-field (bigger toroid) to keep it straight, this also needs less voltage.

Gregory

Tue Apr 03 2012, 04:07PM

Registered Member #2922 Joined: Sun Jun 13 2010, 12:08AM
Location:
Posts: 226

I will stop thinking about and try it. yestardey I made a full bridge with two iifp460 in parallel for each switch. I plan to use 30 to 300v or more, last see what hapens.

Gregory

Thu Apr 05 2012, 03:37AM

Registered Member #2922 Joined: Sun Jun 13 2010, 12:08AM
Location:
Posts: 226

I tryed it and I saw that the modulator was making his job bad. I think that is because the reative load of the sstc primary

1 2 next

Moderator(s): Chris Russell, Noelle, Alex, Tesladownunder, Dave Marshall, Dave Billington, Bjørn, Steve Conner, Wolfram, Kizmo, Mads Barnkob