RE: NST protection filter

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: "Lau, Gary" <Gary.Lau@xxxxxx>

The benefit of the R-C filter has little to do with attenuation of the
coil's resonant frequency.  It turns out that when the gap is firing, it
(the gap) does a splendid job of keeping the coil's resonant frequency
out of the NST, since it's essentially a short circuit at that point in
time.  The real benefit is in attenuating high voltage, high frequency
(multi-megahertz range) parasitic oscillations that occur at each
zero-current crossing of the resonant frequency, when the gap briefly
ceases conduction.  This is why having an R-C cutoff frequency in the
neighborhood of the resonant frequency is not a problem - it's actually
orders of magnitude lower than the frequencies of interest!

This is a topic that receives scant attention on this List, even though
it was Terry who first observed these transients, so I've described the
underlying mechanisms on my web site.  Please refer to
http://www.laushaus.com/tesla/protection.htm

Regards, Gary Lau
MA, USA


> Original poster: "C. Sibley" <a37chevy@xxxxxxxxx>
>
> I've learned my lesson and am in the proscess of
> adding a "Terry Filter" to my coil, along the lines of
> the one at
>
> http://www.hot-streamer.com/temp/NSTFilt.jpg
>
> If I did the math correctly, it has a cut-off
> frequency of approximately 290KHz.  I assume that the
> frequency response is adjusted up or down based upon
> the resonant frequencey of the coil?  Is there a
> discusstion/web page somewhere along these lines?
> Doing a web search find a lot of hits but none
> specifically describing the filter and it's
> application for different frequencies.
>
> Seeking advice...
>
> Thanks,
>
> Curt.
>