Re: [TCML] Coil V4 fail

["David Rieben" <drieben@xxxxxxxxxxx>]

Joe,

As others have already responded with some pretty good
advice, I'll keep my suggestions brief.

As far as your welder ballast, I would suggest going for the
tried and tested Lincoln 225 amp AC arc welder for your
ballast and if you're really looking for some big sparks, pa-
rallel two of them. (Ed Wingate uses two paralleled units
for ballasting his awesome magnifier) so that should tell you
the spark output potential that's obtainable with these units
as ballasts. These stick welder units are also designed for a
20% duty cycle at their highest setting (not 10%) and from
my personal experience, they seem to stay reasonable cool
for even the most demanding coiling activities.

Also, as others have already mentioned, you're going to have
to upgrade your secondary coil's physical dimensions if you
are really ready to start hurling 10 ft.+ sparks. I know that
some of the DRSSTC crowd thrives on bragging rights to
the greatest spark length vs secondary coil lenght ratio and
they sometimes do reach into the 5X terrirtory. However,
from my personal experience with spark gap coils, it would
seem that spark lengths around 3X secondary length is ob-
tainable with reasonable effort and once tuned up, the coil
can run at this stress level reliably for the long term without
the annoying flashovers and meltdowns that you are already
experienceing (assuming a properly sized topload). If you
start trying to reach into the 4X or 5X territory, I'd say that
all bets are off for the coil's long term reliability. John  Freau
also brings out a good ponit in that going with higher break
rates you can sometimes increase the spark length potential
from your coil due to the smaller individual bang size.

Hope this helps,
David


----- Original Message ----- 
From: "Joe Mastroianni" <joe@xxxxxxxxxxxxxx>
To: "Tesla Coil Mailing List" <tesla@xxxxxxxxxx>
Sent: Sunday, October 17, 2010 10:10 AM
Subject: [TCML] Coil V4 fail



Why do we love coiling when it hurts us so much?
Sounds like a country western song.

<http://yfrog.com/emmsj>

Out damned spot!
Too late now.

For the past 2 months I've been building my pole pig driven coil.   I didn't 
start it from scratch.  Rather, I planned on using the resonator from my 
last successful 15/240 coil, and completely rebuild the power supply. 
Thanks to help from a local coiler I got a pig and lots of parts, and 
immediately commenced to build a cabinet for the pig and a control 
panel/station from which I could operate the coil.

At the suggestion of people on this list I ditched my SRSG and built an 
ARSG.  <http://yfrog.com/em7cxj>
The coil specs:   6.5" X 24" secondary 26ga.   Ribbon primary made of spring 
bronze & 1/4" foam weather stripping,  a la Terry Blake's "huge coil". 
Stacked toroids.  4.5x18 over 3x12.  5kVA pig.  Arc Welder ballast.  Dual 
1296D powerstats.  See pics.  Running 0.09uf tank.

I got first light last weekend and my ARSG on line this weekend.  Though has 
been noted as much as a decade-and-a-half ago, sometimes you start up your 
pole pig coil and it's no better than your NST coil.  Thus was my fate.  So 
I had an afternoon of tweakage.

FIrst I tweaked the tuning  trial and error.  I probably spent as much time 
as if I'd done the signal generator + oscilloscope method, but I didn't have 
to take the thing apart.  Once found a tuning point  I started tweaking the 
arc welder.  Opening it up wide, did virtually  nothing for the spark 
production.  In fact, I noted the output amperage going from 20 to 30A, with 
no difference in the sparkage.   That was nerve wracking, as I could not 
tell what the heck was heating up, though I know full well the principle of 
the conservation of energy is in force on my driveway - so those amps were 
going somewhere I couldn't immediately detect.

Then I smelled smoke.   And it was coming from inside the garage.  IN fact, 
it was coming from very close to me.

My cheepo surplus salvage 100A arc welder came with a duty cycle warning - 
(only allow 10% duty cycle on full power).   I had not been heeding that 
warning because after all, I was coiling not welding.    But the insulation 
was burning off the windings, and the core was quite extremely warm.    In 
fact, it remained  very hot to the touch for 1/2 an hour, and was still warm 
when I tossed the entire unit in this week's trash.

My day would have been finished - and I would have been better off had it 
been - were it not for the simple fact that I have another arc welder.  This 
is a 160A version.  60% better had to be better, and indeed, for the rest of 
my experimentation this new welder didn't complain at all.

But my spark production still sucked, and in fact would start out looking 
like it was going to be good, then fade and increase in a sputtering fashion 
with a period of about 0.5 seconds imposed upon a 3-4 second larger "wave".

Then I remember reading here on TCML about inserting some resistance in 
series with the ballast inductor would smooth that out.  It turned out that 
the same surplus rummage sale that had netted me the crappy arc welder was 
also the source for a bag load of power resistors I got for $20, and among 
them was a 0.15ohm 300W version that I wired up.   Smoothness ensued.

Now the coil was behaving quite well, and the arcs were 5-6', but honestly, 
the delta in improvement between this pig powered coil and my NST versions 
did not warrant the 2 months of work and countless $$$ I put into it.

Then I eyed my bench and spotted a crummy Maxwell cap I'd won on eBay.  I 
got the thing for $25 thinking I'd just scored gold.  But it turned out the 
seller (alltronics) never mentioned the terminals to the thing had screws 
broken off in side them.  And as much as I tried to removed said broken off 
screws, I didn't want to apply too much in the way of power tools for fear 
of drilling straight through the thing and winding up with cap juice all 
over the place.  So I just soldered  wires to the terminals, but I never 
felt like using in a real circuit - till that moment.

I pressed some terminals onto the soldered wires and put the thing into my 
tank cap circuit, now giving me 0.12uF (provided this broken Maxwell 
actually worked - though it read 0.03uF on my trusty Fluke DMM).

I adjusted the primary tuning to account for the additional cap, went back 
to the operating point & fired it up.

The sparkage was incredibly gorgeous.  For about 3 seconds.

Then I saw the first secondary-to-primary arc over I'd ever seen with this 
combination.   And one was all it took.   Completely severed the secondary 
winding about 20% up from the bottom.

Now, I'd been warned off ribbon primaries by 2 experienced coilers.  But 
having seen it successful on TBs website, I figured, maybe his new design 
worked better.   In addition, I'd sandwiched my primary between two 
polycarbonate discs.   But I had removed the top disk in an effort to 
increase the k (just to see if that would change anything).   And that's 
where the flashover happened.

Even if the flashover hadn't happened, those coilers who advised me assured 
me that there would be a "current crowding" effect in the lower part of the 
secondary coil, and even if there was no flash, it would self destruct. 
They'd even led me to videos showing this would happen.

Ok.   Now I have learned, viscerally.   No more ribbon primaries.   Now I 
have to rebuild the whole resonator.

The question I have for the coiling community is this:   how many coils do 
you kill before you either 1) give up this sport entirely and take up 
something more socially acceptable, like whaling or chariot racing,  or 2) 
have the coil you just dial in and never tweak again?

Joe_______________________________________________
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