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Re: Adjusting NST



Tesla List wrote:
> 
> Original Poster: AuroraOne-at-webtv-dot-net
> 
> Hi everyone.  Just wondering, would it be possible to power an NST with
> another, smaller transformer, rather than simply plugging in into the
> wall?  I am asking this because I am working on a project where I need a
> high voltage power supply that delivers it at standard alternating
> current at 60-cycle  frequency, so hence a simple step-up transformer
> like an NST suits this purpose.  However, I have some problems with the
> high current output of an NST.  I need an output of very high voltage,
> at low current, at 60 hz.  So here's what I intend to do:  Can somone
> read this and let me know if this is possible with an NST?
>     My simple arrangement calls for three parts: a transformer which
> takes direct wall outlet current and steps it down to a safer level of
> about 25 volts, 2 amperes, another transformer which then takes this 50
> watts and steps it up to approx. 300 volts at low current, and then
> finally the NST itself.  Can the NST be powered by this 300 volts,
> thereby theoretically developing very high voltage, but at a "safer" low
> current?
> Obviously, this output would most likely be useless for any sort of
> Tesla Coil, but the experiment I am working on requires a "safe" very
> high voltage alternating current, (say, 50 kv) at low amps.  Is this
> possible?
> Thanks!  Chris T.
> 
> P.S.  I hope it does work.  I can't just use a Tesla Coil for this,
> becaue the frequency is too high.  I need something at 60 Hertz!


There are two problems: the first problem will be the insulation of the
neon sign transformer which will break down at 50 kV.  The second
problem is that the core will saturate at about 170 VAC, after which you
won't get any more voltage out. 

The overall smallest and cheapest solution is to get a 50 kV transformer
made. If you have time and energy, but no cash, you could probably make
one. Low current means you don't need the absolute best in efficiency,
so you can probably do pretty well.

The other approach is to use a cascade of transformers and isolation
transformers. Imagine if you series up the outputs of 3 15 kV NST's (for
45 kV out). Then, use a 15 kV isolation transformer (110 in: 110 out) to
run the second stage. Another isolation transformer powers the third
stage from the second.  For instance, C&H Surplus has 500 VA isolation
transformers with 15 kV insulation for about $50.

If you need low current, why not make a series resonant circuit at 60 Hz
and drive it with your 15 kV NST. Then, all you have to do is wind a HV
inductor of some sort. The resonant rise will get you the voltage you
need.  These have the advantage that if you get a flashover, the voltage
drops real fast.

Or, wind a 1:4 transformer and drive it with your NST.  For low
currents, you won't need much core or many windings.