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Re: DRSSTC eye candy (sparks)

Original poster: Steve Ward <steve.ward@xxxxxxxxx>

First order of business:

More sweet arc pictures from my large DRSSTC run tonight (bottom of page):


Now if that doesnt get your attention, i dont know what will ;-).  I
think i managed to set off a car alarm as well.

Now to respond to Ken: (sorry for all the snipping)

On Fri, 18 Mar 2005 16:34:35 -0700, Tesla list <tesla@xxxxxxxxxx> wrote:
> Original poster: "K. C. Herrick" <kchdlh@xxxxxxx>
> Steve (& all)-
> Thanks kindly for the added info.  Leading to a few more queries/comments
> interspersed...
> 1.  So the 1T primaries of T1 & T2 are connected in series (& in series
> with, of course, the primary ckt)?

If i understand you, yes, that is true.  Both CTs reside on the
primary conductor... the primary of the CTs IS the output wire from
the bridge.

> 2.  Why D19-D22, when 2 back-to-back zeners might do it?

I wanted to make sure that the slow recovery time of the zeners
wouldnt foul anything up.

> 3.  Have you thought to try eliminating one of T1-T4 by connecting, say,
> T4's secondary to drive T1's & T3's primaries in series?

I did try this once, but it didnt seem to work quite right, but i was
having other problems at that time as well, so it might actually be
ok.  I get these ferrite cores 5 for $1, and wire is cheap, so i dont
mind using 4 of them.

> 5.  Perhaps one should always choose the lower freq. so as to minimuze
> efficiency-loss due to the IGBTs' transition-times.

Ah yes, that was one of my reasons too, forgot to mention that.

> 6.  So basically, U1's /CLR=low forces /Q high, enabling the drive while
> blocking CLK from affecting /Q.  /CLR must then go high for > 1/2 CLK
> period but < 1 full period, whereupon CLK is enabled to toggle /Q low, thus
> cutting off  the drive exactly @ the primary-current z.c.  Do I have that
> right?


  If so, then the /CLR=high duration must be kept adjusted dependent
> on primary tuning.

If you wanted to keep the number of cycles constant, yes.  That is not
hard to do, i have a remote controller, its just a twist of a knob

  Would be nice if there were a way around that...

> 7.  I'd had somewhat the same problem with my feedback-t.c., in assuring
> that oscillations would start when I gated the drive on.  I solved that by
> incorporating enough linear gain in the amplifying chain so that
> noise--picked up + internal--would provide the needed impulse to get things
> going.  I had to use 3 linearized CMOS inverters in series followed by 1
> digital, with the input-drive just the +/- 0.7V across a pair of
> back-to-back diodes in series with the secondary return.  Couldn't employ
> all stages w/in one IC due to intra-substrate coupling; had to use 2,
> 74Cs--& not HCs.

There was no good place to inject some starting noise, so i decided to
make the circuit start up by having the gate drivers send out a pulse
when they are enabled.  This is quite realiable and seems to work

> I really like your implementation; much less complex than mine was!  Your
> gate-drive xfmrs I especially like.  I'd gotten part way thru building a
> variable-L 4-6T primary, to use with a spark-gap and my 12"-dia. secondary
> coils, when a good part of my motivation & energy went.  I hope to get some
> back & to continue w/ that project, but perhaps trying s.s. yet once again.

Hopefully those new pics i just post will motivate you a bit as well
;-).  You can get those brick IGBTs (CM300DY-24H) on ebay for about
$30 a pop.  1 of them would easily handle sparks in the 6' range.  Im
using 2 for up to 11' now, but hope to eventually achieve 12' after i
raise the whole coil up on some bricks (to avoid ground strikes) and
to get a better spark target (something 10' tall or so).  Most of my
sparks just fly off 9' or so into the air with nothing to connect



> Ken Herrick
> [snipped]