Re: NST failures

[Terry Fritz <twftesla-at-uswest-dot-net>]

Hi All,

There are three dangers I know of with "really long" NST wiring.  

The first is that a say 12/30 NST has a resonant capacitance of 6.63nF.
That is a fairly small capacitance.  If one were to start laying the wires
over metal and getting into many meters of length, you would begin to get
into the resonant case where the voltage and current would not be well
controlled.  Depending on how you string the wire around, you could really
"mess things up" with a very long length of wire.

second, neon tubes "flicker" at 120BPS much like our coils.  Every time
they do, they "ring", just like our coils.  The wire capacitance and
inductance of the NST can cause nasty ringing as the tube current chops.
Unlike our coils, neon signs do not have nice protection filters to stop
this noise from getting into the NST secondary windings.  RFI and general
NST destruction are increased as longer wires are used.  Interestingly, the
protection we use for coils could probably do wonders for troublesome
signs.  (Trent, maybe get rich!! :-))

Thirdly, The primary circuit is hitting maybe a thousand amps, 20,000 volts
at the fundamental frequency.  Just like you can induce current into the
secondary, you can also induce significant RF current into the NST output
wiring if you "get too close".  The tiny windings of the NST would not last
well if even a tiny bit of the primary current were coupled to the NST
wiring.  The voltage should transform lower, but the high RF current
hitting the giant inductance of the high voltage winding with stray
capacitance may blow it.

Protection circuits should "protect against" but not "fix" all these
problems.  Protection filters, short wiring, and sensible wiring routing,
should keep one's coil happy.  If you have a rotary gap, be sure the motor
wiring is kept away from the primary coil too.  This not only prevents a
possible arc in the motor but could also stop a significant source of RFI
in the AC wiring.

Cheers,

	Terry




At 08:56 PM 8/2/00 -0600, you wrote:
>Hello Brian and Dan,
>
>For whatever reason, NST failure IS DEFINITELY directly related to lead
>length.  As mentioned below, the side with the longer lead will fail first
>(if failure is inevitable).  Most installers and designers configure NST
>placement in the middle of the series loop.  One common way to avoid long
>lead length is to "mid-point ground" the NST.
>
>If you can visualize an NST placed dead center between a length of neon
>tubing, connected with short leads to the unit on each side, then the end
>unit on each side is wired directly to ground.  This setup works well with
>properly loaded NSTs and a good ground.
>
>Overall, I would recommend keeping lead lengths as short as possible for
>neon applications, but as far as Tesla applications, I doubt of any
>significant benefit.
>
>Trent Mullins
>"Bendin' Glass 'n Passin' Gas"
>
>
>
>----- Original Message -----
>From: Tesla list <tesla-at-pupman-dot-com>
>To: <tesla-at-pupman-dot-com>
>Sent: Wednesday, August 02, 2000 8:17 PM
>Subject: RE: NST failures
>
>
>> Original poster: "Basura, Brian" <brian.basura-at-unistudios-dot-com>
>>
>> Dan,
>>
>> Sounds like an Urban Legend to me. I can't see any way lead length would
>> affect the reliability of a NST. But maybe Neon Trent can shed some more
>> light on the subject (Neon light that is)...
>>
>> Regards,
>> Brian B.
>>
>> -----Original Message-----
>> From: Tesla list [mailto:tesla-at-pupman-dot-com]
>> Sent: Wednesday, August 02, 2000 5:37 PM
>> To: tesla-at-pupman-dot-com
>> Subject: NST failures
>>
>>
>> Original poster: "Dan Kunkel" <dankunkel-at-hotmail-dot-com>
>>
>> I spent a little time talking the guys at the neon shop a few days ago.
>One
>> guy told that a major cause of failure for NST is when rookie sign
>> installers use different wire lengths coming out of each terminal from the
>> secondary connecting to the neon tube. The side with the longer wire will
>> fail.
>>
>> I am wondering if this has any bearing in the world of coiling?
>>
>> dan
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>>
>>
>>
>>
>