Re: Synch for a PDT coil?

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

Original poster: "Bart Anderson by way of Terry Fritz <teslalist-at-qwest-dot-net>" <classi6-at-classictesla-dot-com>

Hi David,

When I read this, I immediately thought of Kevin Eldgridge and his Bigg 
Coil in Oklahoma. If you remember, Kevin built a 30KVA system using a
120 bps sync gap and 0.173uF cap (note, this is STR). He had good
success with it (after removing the series static gap). I'm calculating
nearly 21 ft sparks (accounting for energy per bang at 120 bps). I think
he was about 22 ft at the time. His coil might be capable of 24 to 25
foot sparks at higher bps, but it would take something in the
neighborhood of 600 bps. Of course, there are other ways to get there
(say 200A at about 48 KVA would do it). If only going to 240bps on his 
coil, it would be difficult to see a difference (and it would need to be 
the same gap quality or better). Regardless, Kevin showed that 120 bps can 
do very well at high power.

Low power NST's take advantage of LTR cap sizes when running sync mainly
to reduce stress to the transformer and cap (not sparklength advantage).
Higher power systems typically run STR, but have a cap size large
enough to not worry about stressing the cap (and the transformer is
already rubust).

There is a difference between your coil and Kevins, and it's value is
well over 100+ amps. With your 10 ft sparks previous at 300 bps, I would
expect your running between 5 and 6 KVA with the arc welder ballasting.
I personally don't think you'll gain length with 120 bps unless you
allow for more current. I'm showing with the same input, a drop of 3"
length at 120 bps on your system. In reality, should that occur, the
only change you'll notice is audible.

You are correct about the cap charge. It was at about 12.7 kVp (63%) at
300bps. At 120 bps, you will increase cap voltage to 18.6 kVp (90%).
With that info your probably thinking longer sparks, right? Well, not
necessarily.  The energy at the gap at 120 bps (eJ*bps), I show 1715,
but at 300 bps I show 2007. Increasing bps does not always indicate an
increase of bang energy because energy is defined by the cap size and
charging system. This is true for all systems (both small and large).
Note, this just pertains to very basic raw numbers. It does not consider
efficiency's involved or other spark related issues.

With all that said, you still have to build it to prove it <grin>. There
are a lot of variables involved and unless they are all accounted for,
the unexpected occurs. If your in a position of not wanting to do the
grinding on a motor (if it might not help), then I would advise to leave
it as is. The fact that your going to a G10/tungsten rsg is a nice
upgrade, and depending on the efficiency of the previsous gap, this
change might make a difference by itself.

Take care,
Bart


Tesla list wrote:

 > Original poster: "by way of Terry Fritz <teslalist-at-qwest-dot-net>"
 > <Tesla729-at-cs-dot-com>
 >
 > Hi all,
 >
 > 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 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
 >
 >
 >
 >