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Re: remote location of NSTs - away from coil base?



Original poster: Vardan <vardan01@xxxxxxxxxxxxxxxxxxxxxxx>

Hi,

At 10:53 AM 9/1/2006, you wrote:
....

Now we get to my question.  Someone, I think maybe Terry, told me
once that doing this (as opposed to leaving the NST that coil) can
cause resonance problems that would kill the NST secondary winding -
something about stray capacitance in the HV leads going to the coil?

I have some questions about this, and a certain amount of skepticism:

1) wouldn't the primary capacitance swamp any stray lead capacitance,
making it rather moot?

I don't think it is normally a problem. A 15/30 NST has a resonant capacitor size at 5.3nF. For neon sign installation they have to be a bit careful of the wiring so the capacitance from the leads to ground does not get near that. But that is really only if the leads get very long inside a metal cased sign. For say a 9/120 the 37.5nF resonant capacitance is so high one should never reach it no matter what the wiring is.


2) wouldn't the resistors in the NST "Terry filter" tend to kill any
resonance?

No. The impedance of a 15/30 is 500,000 ohms. The 1K resistors don't matter there. They are too small to damp anything.


3) Has anyone else used their NST remotely away from the coil and had
either problems you were able to trace to this issue, or no problems?
(either data point would be useful)

I think the only way to run into trouble is to maybe use something like a very long run of RG-8 coax where the cable capacitance becomes a big factor with a high impedance NST with a low resonant capacitance size.

Maybe others know more on this too??

Cheers,

        Terry



Thanks in advance,
 - Bill Lemieux,
        Denver, Colorado, USA