Re: NST isolation level

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

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

__________________________________
Do you Yahoo!?
Yahoo! SiteBuilder - Free, easy-to-use web site design software
http://sitebuilder.yahoo-dot-com