Original poster: Steve Ward
<mailto:steve.ward@xxxxxxxxx><steve.ward@xxxxxxxxx>
First order of business:
More sweet arc pictures from my large DRSSTC run tonight (bottom of page):
<http://www.stevehv.4hv.org/DRSSTC2.htm>http://www.stevehv.4hv.org/DRSSTC2.htm
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
<mailto:tesla@xxxxxxxxxx><tesla@xxxxxxxxxx> wrote:
> Original poster: "K. C. Herrick" <mailto:kchdlh@xxxxxxx><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?
Exactly!
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
great.
>
> 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
to...
Seeya,
Steve
>
> Ken Herrick
>
> [snipped]
>
>