Re: Some new DRSSTC numbers

["Tesla list" <tesla@xxxxxxxxxx>]

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 -
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> >
>
>