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Re: [TCML] Effect of doubling the input current



Hi Phil,

If current was linear, we would have expect maybe 50% increase in spark length. But double the spark length suggests a couple things. For one, the cap is taking advantage of resonant charging. Your 10/48 was about 1.7 x Cres. With the 10/100 NST, your at 1.2 x Cres roughly. This is absolutely taking advantage of resonant charging. The closer you get to Cres, the higher the output current. I personally would not go any lower than this with NST's. I like to run about 1.3 to 1.4 x Cres, so your cutting it a little closer than I would feel comfortable doing. The coil will perform very well, but realize that a day may come when all goes quiet (but near enough that "maybe not").

The other obvious point is that the 10/48 original situation was on the edge of having difficulty in charging the cap. Unless there was some ferro resonance occurring (and probably some), the cap would have been in the 70 bps range (if a static gap). But running and rsg, simply a lower voltage and probably inconsistent voltages at break. This is why I say "on the edge". That NST size would have performed better with a smaller cap size (about 0.018uF).

But now, the high current is allowing full charge and also pumping in resonant charging current into the mix. Makes a big difference!

Bart

Phil Tuck wrote:
Hello Group.

I have a query over charging currents following an exercise on my coil of
doubling the input current.

I was originally running my old 10k/48 into a 0.02143 uF cap.
However I recently acquired two identical [new] 10K/50 's and tried these in
parallel for 100 ma.

My coil was already 'ball park' tuned for the 48m/a  NST, when I substituted
the two new 50 ma NST's.
I left all other settings on the coil alone (apart from making sure the
safety gap was still appropriately gapped - voltage outputs can vary despite
what the labels say)

I did not expect any really significant difference as it was only the
current that had increased not the voltage, nor my cap size.
The 'Freau' formula of Spark length is 1.7 x SQRT(Bang Energy x BPS). Now
the bang energy [or so I thought] depended on the value of the cap x the
voltage at the gap squared.

As I was still using my original sized CD' MMC caps of  0.02143 uF and not
the recommended size for 10/100 of 0.0477uF,  why did I get such a massive
increase in performance. I would estimate the spark lengths are double to
the 48 ma original NST.

If I had doubled the  current  and also doubled the cap size [necessary to
have charged to them the same level] I could understand why.

Is it that my tuning was less than perfect originally and with the 100ma
NST's it is nearer the mark ?

Phil

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