Re: Spark Gap Coils vs. SSTCs

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Original poster: "Eastern Voltage Research Corporation" <dhmccauley-at-easternvoltageresearch-dot-com> 

Steve,

I can summarize it in a few tables.  Not only is cost a major comparison
point, but so is availability.
I'm going to compare my ISSTC coil with a similarly sized spark gap coil
using a PT transformer.
Arc appearance and length are about identical.  I also won't get into
secondary and toroid since these are
identical.

As far as MTBFs compare, the spark gap coil is still the all out winner.
Just remember, spark gap coils have been around
for more than one hundred years.  The DRSSTC / ISSTC / OTLC type coils have
only been kicking around maybe 2 years
and only a handful of the coils have been built altogether so far of that
particular type.

Remember, the comparison is between two coils which have IDENTICAL output in
my experience.

MAJOR DESIGN FACTORS - SPARK GAP COIL
*****************************************
1.  For 3kW operation, you need either (3) 15kV / 60mA NSTs or (1) 14.4kV
Potential Transformer (1.5kVA)
      Probably not the easiest thing in the world to get ahold of.

2.  Spark gap - May require rotary spark gap at these power levels (>3kW)
Mechanically complex

3.  Requires high current 120VAC (20A + ) or 240VAC

4.  Higher voltage primary tank capacitor required (typically at least 20kV
+  rated capacitor for 14.4kVAC operation)


MAJOR DESIGN FACTORS - ISSTC COIL
************************************
1.  Switching components (MOSFETs / IGBTs) may be expensive ($20-$50 each)
depending on size

2.  Requires some sort of custom PCB board whether its perfboard, wired
point-to-point, or custom PCB board.

3.  Typically requires much more knowledge, troubleshooting, and test
equipment (oscilloscope) to get running then conventional spark gap coil.

4.  Reliability is an issue.


ADVANTAGES - SPARK GAP COIL
*******************************
1.  Very reliable and repeatable operation
2.  No complex circuitry to troubleshoot etc...
3.  No custom PCB boards required

ADVANTAGES - ISSTC COIL
*******************************
1.  Requires much less power for same arc (1.5kW vs. 3.5kW in my examples)
2.  No heavy high voltage transformer required
3.  No mechanically complex spark gap

Dan


 > Dan,
 >
 > Good point.  But for those of us who haven't yet moved into SSTCs, please
 > give us some idea of cost comparisons between SS & SG style coils.  For
 > instance, what would it cost to duplicate your ISSTC?
 >
 > And what is the typical mortality rate of IGBTs with experimental coils?
 > That is, how do the MTBFs compare?
 >
 > Thanks,
 > --Steve Young