I have built an anachronism. Of course, the very concept of the coil is
anachronistic, but through the tutelage and mentoring of Dave Leddon, I
have acquired and assembled the components necessary for a pole pig
driven srsg coil.
Yes, I know this is the day of the DRSSTC. Yes, I know pole pigs are
oh-so-90's.
Still, to me there feels like there's a progression of history that must
be followed to earn one's coiling stripes, and it seemed that going from
NST static gap, to SRSG, to higher power and larger diameters, larger
toroids, different style primaries, it's sort of a college major in
coiling and if you skip the steps, perhaps you'll wind up in a tough
spot later that you can't intuit yourself out of.
I got a 5KVA pig from Dave some months ago, and since then he's been
supplying me with various wisdoms though schematics, e-mails, and his
surplus parts. I have been beavering away diligently in my garage,
assembling the various components I get from Dave and a seemingly
endless stream of eBay auctions. No doubt I have assembled for a couple
hundred American dollars what would have cost thousands had I bought
everything retail (if that was even possible).
The specs - I will upload the detailed JavaTC results (as soon as I find
the file - don't have it on this computer). Once again I will say that
the JavaTC program is pure gold to the coil builder. My pig coil ran
perfectly the first time to JavaTC spec.
I'm running a 6.5" secondary, wound to 24" with 26ga, roughly 1680
turns, if memory serves.
The primary is 6.6 turns of spring bronze weather stripping wound around
a 12" core of UHMW, and spaced 1/4" with weather stripping, a-la Terry
Blake's Huge coil. In addition, the primary is sandwiched between 2
wheels of polycarbonate. There is a strike ring about 4" above the
primary made from 1/2" copper pipe. No primary strikes yet.
I have experimented with 2 tank cap sizes - one at 0.06uf (2 Maxwell
0.03uf/35Kv bricks) and one at 0.09uf (3 maxwell caps) with similar
results.
The spark gap is an SRSG propeller gap rotating at 1800rpm inside 8
stationary electrodes for 240bps. I am using a John Freau phaser on the
SRSG.
The power supply has 4 corcom-style 30A line filters in serial/parallel
arrangement. Using the guts from a cheepo adjustable 100AMP arc welder
as a current choke. An ABB EH175 serves as my contactor and I have a
2-phase superior electric 1296 powerstat for the main power Variac.
Results so far are promising. The resonator seems much more sensitive to
tuning than with the NSTs. I originally miscounted my turns and set my
tuning one turn off from the JavaTC recommendations. The arc production
was disappointing, but the SRSG became hypnotic. I began to notice a red
circle forming, following the spinning propeller rotor, which began
smoking as the gap began to burn itself into oblivion. Thank ye gods G10
and UHMW doesn't burn well.
Also, I had my safety gap set too wide (obviously). With the tuning and
the gap set "correctly" or as close as I could get I was able to achieve
several runs, most of which at only 2/3 max on the current shunt. Spark
production was better than with my NSTs, as we would expect. The
propeller gap was brighter than ever, to the point I began to worry
about how quickly the electrodes would erode.
I also noticed that the max-output power occurred at about 80% power on
the variac output. Increasing the output past 80% actually DECREASED the
power output a perceptible amount.
I have come to expect that there is an issue with one of 2 things -
either 1) I have wired the variac wrong (though I have reviewed the
connections and I can't see how I did) , or 2) the inductance of the
variac is interacting with the primary windings and affecting f0.
And since writing the above, I am noting that I have connected my
current shunt to appear in the circuit in series between the power
source and the variac, instead of between the variac and the primary.
Perhaps that has something to do with it. I need to experiment to find out.
Other things I have noticed - even at 15/240 my primary connections
never got hot (except when mistuned). Now they seem to get warm all the
time, which I suspect is just an expected artifact of the higher
currents. I do think I may have to reconsider the spring bronze and my
connection methodology for fear they present too high a resistance and
will eventually heat to the point of melting the polycarbonate supports.
The beauty of this system is that it can be a source of endless tweakage
and experimentation, which is what I adore most about coiling.
I do have an 8.5" form and a spool of 20GA which I will use to wind my
next secondary. This secondary will be used not only for the pig, but
also for my next coiling project...
For a DRSSTC controller board is stashed in my sock drawer, along with 2
CM300s, which await the day when Mouser decides to deliver the parts I
have ordered. Then I will have gone through a more logical progression
of coiling steps (except for DC resonant charging). I do have a bank of
music synthesizers, including a retro full analog synth I expect to
press into service the day I have a large DRSSTC waiting to play tunes.
Cheers,
Joe
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