Re: NST isolation level

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Chris Arnold" <chris_arnold-at-msn-dot-com> 

Greg,

I'm not a pro in the neon trade either, but from what I remember a neon 
sign transformer runs best at about half it's rated voltage, which is quite 
a bit above ~800V.  Granted, it is still much less than the maximum rating, 
but still appreciable.

Chris Arnold


>From: "Tesla list" <tesla-at-pupman-dot-com>
>To: tesla-at-pupman-dot-com
>Subject: Re: NST isolation level
>Date: Sat, 20 Sep 2003 08:53:07 -0600
>
>Original poster: Gregory Hunter <ghunter31014-at-yahoo-dot-com>
>
>Hi Rik,
>
>I'm not in the neon sign trade, but I'll share what I
>know. My understanding of NSTs it that their HV
>isolation is marginal. They are not really designed to
>withstand their own maximum voltage for very long,
>because they don't need to. The 15kv faceplate voltage
>is only required for the moment when the sign is first
>turned on. The high voltage ionizes the neon, which
>quickly becomes conductive. The sign goes from being
>an open to a near-short very quickly. From that point
>on, only 800vac or so is needed to keep the sign lit,
>and the NST shunts clamp the current at 30 or 60ma (or
>whatever) to prevent the NST from overloading and
>tripping the mains breaker. The NST can idle like this
>24/7, for years if neccessary, since it is only
>supplying ~800v-at-30/60ma, a small fraction of it's
>faceplate rating, into a simple resistive load. The
>NST is a transformer, but it is also valid to view it
>as a luminous tube ballast with a built-in starter.
>The bottom line? NSTs often fail in Tesla coil service
>because they are continually exposed to maximum
>voltage, dynamic reactive loads, abrupt switching, and
>RF feedback. For any application other than powering a
>neon sign, the lifespan of an NST is "iffy".
>
>Cheers,
>
>Greg
>
>--- Tesla list <tesla-at-pupman-dot-com> wrote:
> > Original poster: "Rikard Titus"
> > <rikard_titus-at-hotmail-dot-com>
> >
> >
> > Hi List,
> > What is a typical isolation level of 15 kV nst?
> > How much secondary voltage (repetitive low
> > frequency) it can tolerate
> > without putting it under a breakdown danger?
> >
> > Thanks,
> > Rik
> >
> > _
> >
> >
>
>
>=====
>Gregory R. Hunter
>
>http://hot-streamer-dot-com/greg