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Re: [TCML] MMC for 4 mot SRGTC
Hi Scot,
Well,, actually I said that there dosen't appear to be any
spark length gain by running a pig coil synch vs asynch.
The large coils that are running synch that I've seen the
data on seem to have spark length vs. power throughput
levels very similar to, if not slightly less than, that of equi-
valent asynch ran systems. Also, keep in mind that just
like Bart reminded us, you need the asynch gap to have
a variable speed control on your ARSG motor. Of course
there is a limit to the "run it faster for longer sparks" con-
cept. Eventually, assuming that the disc can withstand the
increasing G-forces, the presentation rate will reach a
point to where they are occuring too rapidly for the
power transformer to be able to sufficiently recharge
the primary cap between charge/discharge cycles. At this
point , the performance will deminish. Obviously, the BPS
"speed limit" is dictated by the primary cap size and the kVA
rating of the transformer, along with its % Z rating. Like I
previuosly stated, there will be a sweet spot BPS rate where
the output sparks are at there longest and brightest and if you
push the BPS rate beyond this, the performance will begin to
drop.
I would think 20K rpm to be extreme. My ARSG drive
motor is an "ebay special" StarTrak 2.5 HP, variable
speed DC motor with only a 3500 RPM rating. It was
originally designed for the drive motor of a large tread-
mill. I just run 8 flying electrodes on my rotory disc, so
that pretty well limits my theoretical BPS rate to 466.7
and mine seems to "like" the 350 to 400 BPS range. I
set the speed control variac around 80 to 85 on the
dial and I have it set to where the max ouptut voltage
is 120 volts, not 140 volts, with the dial maxed out at
100. Although I have seen potential BPS rates of ARSG
coils that reach >1000 BPS, it seems that the "sweet
spots" often fall under 500 BPS.
IIRC, you run your coil with a total primary C of
0.057 uFD which appears rather small for a big pig
coil, especially for synch, but I believe that you are
also actually seriesing (2) 14.4 kV pigs for over 30
kV output with an overdriven variac input. That
would have the same energy per bang as a 0.23 uFD
primary C for a 14.4 kV driven system. However,
I would assume that you are still well under Res size
with your primary C. Since your driving your coil
with a pig that is likely capable of sufficiently recharging
that .057 uFd C at a faster rate than 120 times a second,
you may see a spark length improvement by going
with an ARSG that would allow for BPS rates
considerably greater than 120.
David Rieben
----- Original Message -----
From: "bunnykiller" <bunnikillr@xxxxxxx>
To: "Tesla Coil Mailing List" <tesla@xxxxxxxxxx>
Sent: Sunday, April 06, 2008 6:15 PM
Subject: Re: [TCML] MMC for 4 mot SRGTC
Hey David...
alright Im gonna bite on this one....Ive been running a SRSG for eons on
the BIGPIG coil and you are stating that a BPS above and beyound 120
results in better streamer length?
Hmm how to approach this... a router on a variac? Any suggestions
other than phase controllers? ( I have the router and the variacs) Im
limited to 120VAC supply for the spark gap motor... sheesh 20Krpm from
a router seems harsh ...definately will put the G10 disc to the ultimate
G force test...
Scot D
David Rieben wrote:
Hi Scott, Kris, all,
I tend to agree with Scott on this issue. I've heard many of
the pro's and cons regarding synch vs. asynch and IMHO,
it comes down to a matter of preference on large, pig sized
coils although there does defonitely appear to be an advantage
to going synch with mid-sized coils driven by the limited avail-
able power from NSTs. If longer sparks are what you're after,
which is where the majority of us coilers are ;^), then the fast-
er BPS rates afforded by an asynch RSG are a definite
advantage with the much greater power throughput potential
of large non-current limited transformers, like pole pigs. Some
coilers do like to go synch with high powered coils, but from
the spark length reports of synch vs asynch with larger coils,
there doesn't really appear to be any advantage to "going synch"
with a piggy powered coil. An asynch gap is also a bit sim-
pler to construct. Also, there's the issue of securing a primary
cap of sufficient rating to run LTR with a pole pig, as an LTR
prerequisite would make for an impractically large and expen$ive
capacitor. It's a lot simpler and more practical to just go asynch
with an STR cap, utilizing a >100/120 BPS charge/dicharge cycle
of the primary cap to increase the power throughput for longer and
brighter sparks with large, high powered coil systems. Indeed, my
large coil, with a 0.1 uFd primary cap seems to like 350 to 400
BPS for the best output.
http://www.dawntreader.net/hvgroup/david/gm.html
My $.02,
David Rieben
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