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Re: Performance degrading over time
> Original Poster: "Ron West" <ronwes1-at-juno-dot-com>
>
> I am tuning a 4" coil using a 15/30 NST for power. Last night I had
> roughly tuned it in at 5 3/4 turns using a SG and a 16.8nF MMC.
> Everything was working quite well giving 12-15" sparks (not a lot but
> much better than my previous ignition coil power supply gave me) when
> tuning seemed to go out the window. I found myself having to adjust the
> gap smaller and smaller, chasing that 'sweet spot'. Something seriously
> wrong here. In the end I managed to fry one leg of the NST, probably due
> to my safety gap being set too wide (it never once fired).
>
> One thing I am wondering about is the SG, which is made of 7 gaps using
> stainless steel bolts. It doesn't get very hot, but it was blackened and
> pitted after probably no more than 15-20 minutes duty. I've ground them
> down smooth again and I'll be able to try the coil again tonight to see
> if performance is back to normal. But the question I want to ask is
> whether the oxidation of stainless steel could produce compounds which
> would impair conductivity and produce the kind of problems I'm seeing.
OK Ron, there are a couple of things that could be going on here. First,
how are you evacuating the gap during the run? Do you have a blower or
vacuum cleaner sucking the ions and vaporized metal free?
Second- are your capacitors heating up? Feel them after a run. If they are
heating, they will be changing capacitance on you and detuning the tank
quite a bit. In this case, you need less power or less-lossy caps.
-Adam
adamsmith-at-mediaone-dot-net