Re: synch with a pole pig coil (again)

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "by way of Terry Fritz <teslalist-at-qwest-dot-net>" <FutureT-at-aol-dot-com>

In a message dated 7/29/03 2:04:40 PM Eastern Daylight Time, 
tesla-at-pupman-dot-com writes:

David,

The LTR/ STR, calcs must take into account ballasting for a
current-non-limited transformer.  To decide if the set-up is LTR for
example, one must decide how much ballasting will be used, how
much current, etc.  The ballast setting will determine the LTR,
etc., cap value.

For example if you ballast the transformer so it draws 6 amps,
then the cap may be LTR.  But if you let the transformer draw
15amps, then the same cap value may be STR.  I didn't actually
calc this, just guessing the values here.  I'm just illustrating the
concept.  The cap may even run at resonant charging, again depending
on the ballasting.  Generally, I used to adjust my systems somewhat
LTR using the PT.  This is done simply by adjusting the ballast.  If
you go too far from reso, the power factor suffers using 120 bps sync.

The impedance of the pigster is very low, but the wire in the transformer
and the other wiring limits the current even using reso charging.  If
you're running STR, then the ballast limits the current during charging.

When a system is set up for resonant charging, the ballast "cancels"
the capacitors reactance, and lets the cap charge rather quickly.  The
old books from the 1920's suggest running somewhat LTR for smoother
operation at 120 bps sync.

The only way the performance at 120 bps can exceed the performance
at 300 bps, is if the cap charges to a higher voltage.  This will then give
more power thoughput.  For example if the cap charges to 20kV peak,
this will give 16 joules per bang.  The 16 joules x 120 bps = 1920 "cap-
watts".  The actual VA draw may be 20% higher or 2300 VA
(because of losses and an imperfect power factor).  Such a case
would give about a 6 foot spark.

Pigs at 120 bps like to see large-value caps and/or high charging voltages.
For example if you charge the cap to 28kV, this will give 3763 cap-watts,
or about 4500 VA.  Such a setup should give 9.5 foot sparks.  So I would
say that you may be able to equal the performance of the 300 bps setup
using your cap.

Now if you use a 0.13uF cap, then the cap watts = 6115, and the
VA would be about 7338 VA.  This should give a 12 foot spark.

Cheers,
John


>I'm in the process of replacing my lexan and brass
>ARSG with a tungsten and G-10 SRSG. My coil system
>is powered by a 14.4 kV 10 kVA pole pig ballasted thru a
>Lincoln 225 amp arc welder. My primary capacitor is 0.0825
>uFD and I was running ~ 300 - 350 bps asynch. I was wondering
>how well the 0.0825 uFD cap would perform at 120 bps synch?
>I don't think the 10 kVA transformer was able to fully charge
>the capacitor before each discharge at 300 bps (Isn't it like
>8 milliseconds to fully charge this 0.0825 uFD cap from the
>impedance of the 10 kVA transformer?) Anyway, I know the
>resonant size cap for this transformer is around 0.125 uFD
>so will it be ok to run the synched system w/ smaller-than-
>resonant (STR) primary capacitance? I know that the high
>resonant voltage surges are not as big of a concern with
>PTs or PDTs as opposed to NSTs or OBITs. Anyway, I
>would appreciate any input from some of you guys who are
>stronger in the math than myself :^) BTW, I was getting up
>to about 10 ft. sparks from the coil running it the old >300
>bps asynch way, can I expect similar or better results run-
>ning 120 bps synch using the same transformer/capacitor
>components?
>
>Sparkin' again in Memphis after a 3 day blackout,
>David Rieben
>