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Original poster: "Michael Grimm" <mgrimm@xxxxxxxxxxxxx>



-----Original Message-----
From: Tesla list [mailto:tesla@xxxxxxxxxx]
Sent: Thursday, November 10, 2005 10:02 AM
To: tesla@xxxxxxxxxx
Subject: Re: LTR vs. STR for pigs was Re: PFC Question


Original poster: Shad <shenderson@xxxxxxxxxxxxxxxx>

Hi Steve, All,

Comments interspersed,

On Wed, 2005-11-09 at 15:30 -0700, Tesla list wrote:
 > Original poster: Steve Conner <steve@xxxxxxxxxxxx>
 >
 > Hi all,
 >
 > This debate got me thinking and I thought of a few
 > things I'd like to bring up.
 >
 > 1) What decides whether a cap is LTR or STR? The
 > answer is the leakage inductance of the transformer.
 > Now in a NST that is built in, but a pig has
 > practically none so you need to provide your own
 > external ballast. So, it is not the pig itself that
 > determines whether the cap is LTR or STR, but the
 > ballast. (And the transformer turns ratio too, I
 > suppose.)
 >
LTR operation for a pole pig is determined by the ballast setting.  I've
personally used an LTR cap on a pole pig, and in short, it rocks.
Operation is very smooth, with virtually no kickback, no quenching
problems, and very impressive operation.  Of course, it means setting
the ballast to one point and leaving it set there, but as my ballast is
a PITA to set, it's no big deal.

 > 2) Someone said that bang energies of 50J were out of
 > the league of garage coilers. That was before the
 > DRSSTC, which can generate bang energies several times
 > bigger than the energy storage capacity of its tank
 > cap. I believe Steve Ward's big DRSSTC must run about
 > 50J bangs.
 >
50J per bang isn't out of our reach.  It just requires a mammoth tank
cap, and is nearly the exclusive domain of LTR setups.  My "dream" is to
run D&M's magnifier (as seen at the FL Teslathon) with a 400nF tank cap,
in an LTR configuration at 120bps.  The limiting factor on reaching that
50J limit is the cost of the tank cap.

 > I have got over 3kW at 200bps into mine which implies
 > a bang size somewhat under 15J (allowing for about
 > 15-20% losses.) I was using a 0.1uF @ 10kV tank cap,
 > and since I was running about 400A peak at ~190kHz,
 > the tank cap voltage would have been only 3.3kV and
 > hence the stored energy would be less than 1J.
 >
Lower the breakrate, increase the tank cap size, and move to LTR.

 > I don't know how it does that, but it does. It seems
 > the primary and secondary coils are now just a
 > matching network that couples the inverter to the
 > plasma load. The lower the Q of the matching network,
 > the more efficient it is, and the less sensitive to
 > streamer loading. I was reading an article on link
 > coupled antenna tuners for ham radio and there seem to
 > be a lot of similarities.
 >
Spark gap primary resonant circuits are pretty low Q usually.  Broad
enough that the coil will operate even if mis-tuned, but the tuning
point is usually pretty sharp.  And changes depending on coupling, spark
loading, cap values drifting with heat, etc.

Hope it helps!

 > Steve Conner
 > http://www.scopeboy.com/
 >
 >