[TCML] Coil V4 fail

[Joe Mastroianni <joe@xxxxxxxxxxxxxx>]

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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