Re: [TCML] climbing sparks

[Joe Mastroianni <joe@xxxxxxxxxxxxxx>]

The experts here probably have more to say about this than me, but as I have just diagnosed this problem on my own coil - and as I have just totally burned up an old secondary with this problem, some solutions are fresh in my mind.

- first, run JavaTC on your coil and check the recommended coupling and the actual coupling.  Adjust your secondary, if necessary to reduce the coupling. Overcoupling causes racing sparks.

- Mistuning your system causes racing sparks.  You may have thought it was tuned correctly but it may have been exhibiting racing sparks all along. I had the exact same issue.  I was getting sparks on the "back side" of the secondary. I believe it was John Freau on this very mailing list who said to me, "make sure you have some people standing around  at other vantage points" when you're tuning, for exactly this reason.

- Overpowering causes racing sparks.  That is, if your cap bank & primary tuning and spark gap settings were set up for one power source, and then you increased the power , you could get racing sparks. This very thing just happened to me last weekend when I upgraded my NST bank from 15/90 to 15/150 without readjusting things. The sparks only showed up on the higher power settings though. Retuning and retiming solved the issue and only tweaks had to be done, not major changes.

As far as shorting turns -  I did this with one of my secondaries which is now officially dead as far as I'm concerned. I had measured the resistance of the secondary with my fluke meter, though the measurement wasn't accurate enough to pick up a 2 to 4 turn short.  Similarly, my inductance meter isn't accurate enough.  They said everything was normal.  Though, the coil would never again run without racing sparks, no matter what I did. And therein lies the insideous issue - that I was trying to fix coupling and timing and tuning, but I kept gettingracing sparks and I didn't realize it was because the coil was shorted. I just thought the other parameters were off. This suggests it's a good idea to have more than one secondary laying around if you are experimenting.  Lucky for me, Idid have another secondary and once I popped that on and saw there were no tuning issues, I examined the burned secondary further and saw the short.

Along those lines - there were many black spots on that secondary (due to other experiments gone awry) that looked "bad" but were not shorts, which I found during my autopsy of the secondary.  Sometimes just the top surface of the insulation burns and not the interwinding faces.  So even though you have marks you may not actually have a short.

The real short showed up as  enough burning of the insulation that I could actually drop a probe down onto it and detect it with my meter.  The real short also burned the wires so badly they delaminated from the secondary core.

One thing I have tried to do in the secondaries I have wound myself recently, is to coat them liberally with several layers of that Dolph's AC-3 varnish.  I have found that 3-5 layers of the stuff prevents racing sparks even when there should be racing sparks.  Not sure that's such a great situation, either, but at least it keeps my  secondary from becoming a pretty lawn art decoration.

Hope any of this is useful.

Cheers,
Joe





On Aug 20, 2010, at 10:58 AM, Dan Casaregola wrote:

> Just when I thought my coil was working well, I discovered climbing sparks on the back side of it!  I never ran it more than 20-30 seconds at a time, but I notice about 5 tiny burn marks about mid-way up.  Is there an accept method of repairing the problem?  The winding is still intact, but there may be a shorted turn.  Thanks / Dan
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