Re: Some new DRSSTC numbers

["Tesla list" <tesla@xxxxxxxxxx>]

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
>  > >
>  >
>  >
>
>
>