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Some new DRSSTC numbers

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

Might interest the DRSSTC folks...

I recently rebuilt my very first DRSSTC:


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.