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Re: [TCML] No-load NST's
Hi Gary,
I believe that NSTs are designed pretty well for their _intended_ purpose,
although there seems to be a lack of quality control in the manufacturing
process. This leads to some NSTs being nearly bullet proof, while others of the
same make and kind will fail unexpectedly. I would imagine that the biggest
problem is due to the potting methods and materials used most frequently.
Anything except vacuum impregnated coils, or the whole core and coil assembly,
just won't have a consistent quality at that kind of voltage, and there's no way
to tell what you have until it fails.
The transformer manufacturer has to walk a thin line between profit and
reliability, and find an 'acceptable' failure rate THEY can live with. In other
words, it's usually cheaper to warranty a few transformers, than to make them
as reliable as possible. I suppose they are made on a continuous assembly
line, and vacuum impregnation would likely be a batch process, which would add
too much time and cost to an already expensive product. (Damn those mandatory
GFCIs!!!)
It's also interesting to note that the USA is about the only country to make
and use neon transformers with an output over 10 kV. Almost every one else
has learned that insulation breakdown, both inside the NST and the external
secondary wiring, becomes a real problem with anything over that.
I wouldn't put much faith in those purple energy angels for my NST. Accept
only "Genuine Tesla Purple Energy Discs" for your coiling protection! :)
Tony
******
In a message dated 6/26/2008 11:06:01 A.M. Central Daylight Time,
Gary.Lau@xxxxxx writes:
Hi Tony,
Thank you for chiming in and sharing your experience. The voice of
experience trumps the voice of speculation (mine) every time.
Unfortunately this does not bode well for NST's in our (coiling)
application, as spark gaps are routinely set to permit voltages well in excess of the
peak open circuit value. And there's not a thing we can do about it except to
hobble performance with very closely set gaps. Filters (even with chokes!)
can't help us. Perhaps if we all found religion and prayed to the patron
saint of NST's. There's the purple energy angels so common on eBay. That's an
untapped market - the equivalent of a St Christopher medallion for mounting
atop your NST.
Excellent point about the fence charger also.
Regards, Gary Lau
MA, USA
> -----Original Message-----
> From: tesla-bounces@xxxxxxxxxx [mailto:tesla-bounces@xxxxxxxxxx] On
> Behalf Of Sfxneon@xxxxxxx
> Sent: Thursday, June 26, 2008 1:47 AM
> To: tesla@xxxxxxxxxx
> Subject: Re: [TCML] No-load NST's
>
> >> In a message dated 6/25/2008 4:26:25 P.M. Central Daylight Time,
> _Gary.Lau@xxxxxxx (mailto:Gary.Lau@xxxxxx) writes:
>
> << Yes - I too have heard many times that running an NST with no load will
> stress its insulation beyond what it was designed for. But it does seem
> unlikely that an NST should be designed to self-destruct should its
connection to
> the load fail. So being the skeptic that I am, I have to wonder about
the
> origin of that belief. Did it come from a source in the sign or
transformer
> industry, or just a coiler who observed that an in-use NST with a sign
operates
> at well below its faceplate voltage?
>
> Gary Lau
> MA, USA >>
>
>
> Gary, all,
>
> It's common knowledge in the neon sign trade that operating a neon
> transformer for extended periods of time with no load, such as a with a
broken tube
> or
> wiring, _greatly increases_ the chances of a secondary insulation failure,
> not only inside the transformer but also in the secondary wiring itself.
>
> I have owned and operated a commercial neon sign shop and plasma art studio
> for almost 30 years, and I can say without a doubt that this is true. I'm
not
> saying that _every_ NST run open circuit will fail, just that it greatly
> increases the chance the longer it runs. In fact, this just happened to a
neon
> transformer on a border tubing installation at my own shop. I failed to
> promptly fix a bad tube, and about a week later the transformer went bad
too.
>
> So, it's not likely that you are going to kill your NST if you happen to
> hook it up without a load, unless you leave it that way for days, weeks or
> months. What really kills them in TC usage is opening up that spark gap
too wide,
> or the voltage ringing up to insane levels if the gap misfires a time or
two.
> They really, really don't like any capacitance across their output, even
> extended GTO runs or GTO in metallic conduit.
>
> >> In a message dated 6/25/2008 7:20:42 P.M. Central Daylight Time,
> _evp@xxxxxxxxxxxx (mailto:evp@xxxxxxxxxxx) writes:
>
> << I ran a "skunk zapper" electric fence for
> several years which was powered by a 9 kV, 60 ma NST. >>
>
> PS: A word of caution about using a NST for a "fence charger"! Common
> practice...but bad idea. IT'S LEATHAL, not only to small animals, but
humans too!
> Real fence chargers send out a high voltage microAmp pulse about once a
> second, which smarts like hell, but won't cause you to go into cardiac
arrest or
> become unable to let go of a 'hot' fence wire. They will also not produce
a hot
> enough or long enough duration spark to burn you or set the
grass/weeds/house
> on fire when they finally get that tall.
>
> However, your NST _WILL_ keep the skunks out!! :)
>
> Tony Greer
> Special Effects Neon
> Lubbock, Texas
> *************************
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