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Re: Some new DRSSTC numbers



Original poster: "Paul Benham" <paulb@xxxxxxxxxxxxxxxxxxxx>

Thanks Steve.

I really need to get around to building one of these, albeit a small model
that I can use for taking measurements and move around easily.

Cheers,

Paul.

----- Original Message -----
From: "Tesla list" <tesla@xxxxxxxxxx>
To: <tesla@xxxxxxxxxx>
Sent: Friday, January 21, 2005 2:34 AM
Subject: Re: Some new DRSSTC numbers


> Original poster: Steve Ward <steve.ward@xxxxxxxxx> > > Paul, > > Comments: > > > On Thu, 20 Jan 2005 11:38:25 -0700, Tesla list <tesla@xxxxxxxxxx> wrote: > > Original poster: "Paul Benham" <paulb@xxxxxxxxxxxxxxxxxxxx> > > > > Hi Steve, > > > > So is the best efficiency is seen when the burst is just long enough to > > ensure breakout? > > This is a good question. Efficiency increases almost linearly with > burst length, less than 100uS burst length is in fact MORE efficient, > at the expense of more bus voltage needed on the IGBTs to get the same > spark lengths. You also have the benefit of reduced current stress > (the peak current is less due to less cycles to ring up, and the > duration is less... both very good things!). The lower tank impedance > may cancell these benefits compared to a setup with higher Z and > longer burst lengths. > > So does the toroid size then set the length of spark > > achieved if the burst length is adjusted accordingly? > > Another great question. As i have found emperically, larger toroids > do help, but at some point you just dont gain anything. I think its > similar to spark gap coils where really huge toroids dont really pay > off all the time. Now one thing to consider is that perhaps a greater > Q is required to drive a larger toroid, and now that you mention this > i am curious to put a bigger toroid up top (will have to steal the 26" > toroid ;-)). So to answer your question... i dont think we know for > sure yet! But yeah, trend suggests that bigger toroids = better > sparks, but just how big can they get? dunno yet. Notice that Jimmy's > first DRSSTC used a blimp-sized toroid, extremely low tank Z, and > again, not too many cycles driving the coil (i beleive he found 14 > cycles to work well). > > > > > Is the ring up time to breakout just set by the coupling factor and toroid > > size or is there more to this eg input voltage? > > The input voltage of course matters, but basically i think you nailed > 2 important factors. I often use a breakout point, but i do find the > coils work best when it breaks out *just* before something BAD happens > instead, so we want to elevate that breakout voltage it seems. The > coupling factor will of course change how many cycles are required > before breakout. Im using about 14 cycles with this setup, and > breakout is achieved (at full input voltage) within about 2 cyces!! > The other 12 are driving power into the streamer :-). You can tell > when breakout has occured as the RF envelope is clamped, and along > with noticing that "clamping" effect, you also hear corona ;-). > > It would be interesting to > > see if the primary current ringup is faster with higher voltages or lower > > primary resistance. > > Seems as simple as manipulating ohms law? And by resistance i assume > you mean impedance? We really do want to get rid of dc resistance, > though it has been shown to act as a nice current limiter, but i think > there are maybe better solutions to that, though i cant argue with > success. > > I think the important thing is to get the energy into the streamers > quickly instead of forming a streamer and then driving it for > toooooooo long ;-), then it starts to look like the "old" SSTCs with > the flaming thorny sparks that arent nearly long enough for the input > power. > > Seeya, > > Steve > > > > > Cheers, > > > > Paul. > > > > ----- Original Message ----- > > From: "Tesla list" <tesla@xxxxxxxxxx> > > To: <tesla@xxxxxxxxxx> > > Sent: Thursday, January 20, 2005 3:03 PM > > Subject: Some new DRSSTC numbers > > > > > Original poster: Steve Ward <steve.ward@xxxxxxxxx> > > > > > > Might interest the DRSSTC folks... > > > > > > I recently rebuilt my very first DRSSTC: > > > > > > http://www.stevehv.4hv.org/DRSSTC1.htm > > > > > > I recorded some numbers and made some interesting discoveries. > > > Numbers are posted on the webpage at the bottom. Seems my setup is > > > really starting become *quite* efficient. 60" vertical arcs were > > > achieved at only 800W of real power into the coil (PF is about .83 for > > > my setup!), and this is mainly limited by my space, i could probably > > > get about 66" or so. Im working on getting a current transformer so i > > > can monitor the primary current accurately as this is very important > > > to gain further insight on things. > > > > > > I feel i have some reasons to back up the coil's increase in performance. > > > > > > 1) new secondary with a higher Q (that is, lower winding resistance). > > > Also, it is larger, allowing for longer sparks before any racing > > > sparks. Old secondary: 4.5"x19" 30awg magwire. New secondary: > > > 6.5"x22" 26awg magwire. > > > > > > 2) higher coupling between primary and secondary (went from .25 to .3). > > > > > > 3) lower tank impedance. Started out with a 75nF cap and 20uH primary > > > inductance, now im running a 300nF cap and 10uH of inductance. > > > > > > 4) due to implications of #3 (faster ring up achieved) i only require > > > about 100uS to achieve excellent results (i think Dan M's coil uses > > > around 300uS!). Longer burst lengths result in much poorer efficiency > > > (see table on website). > > > > > > The thing that really hurts my "experiment" is that I didnt take down > > > these numbers for the original setup for a "direct" comparison. But i > > > knew the older setup well, and i will say that i never achieved > > > efficiencies quite this high! > > > > > > I have 4 working DRSSTCs and haven't killed an IGBT since... hmmmm, > > > well i cant remember ;-)))) (several months now). Must be getting > > > closer ;-). Just takes some design revisions and lots of > > > perserverence to get a reliable DRSSTC (or 4!) that kick(s) out some > > > super sparks. > > > > > > Seeya, > > > > > > Steve > > > > > > > > > > > > > > > This message has been scanned for viruses by MailController - > > www.MailController.altohiway.com > > > > > > > > > >