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Re: Why NST's are doomed...
At 09:14 PM 11/14/98 -0700, you wrote:
>Original Poster: Gary Lau 14-Nov-1998 2223 <lau-at-hdecad.ENET.dec-dot-com>
>
>I found some interesting commonly asked questions on the France
>transformer company's page: http://franceformer-dot-com/html/home.html
>
>Most interesting, they confirmed what has long been suggested, that the
>terminal voltage of an NST in lighting applications is normally a much
>lower voltage that the faceplate value, and that higher than normal
>running voltages will stress the insulation, leading to breakdown. It's
>a wonder that NST's work for us at all!
>
>Q:What is overloading and what affect does it have on a transformers life?
>
>A: Overloading, or the connecting of more tubing than recommended, produces
>higher secondary voltages resulting in increased stress on the insulation
>system. This stress can cause insulation failure and reduced transformer
>life. Overloading can also cause tube flicker creating high voltage
>peaks or spikes in the secondary coils, damaging the insulation system
>and again, significantly reducing transformer life.
Yes, this is quite correct. It is also worth noting that the continuous
current rating is lower than the faceplate rating on a typical NST. If more
than approximately 80% of faceplate current is drawn, the NST will suffer
from thermal stress and failure will not be far away. Hard resin potted
NST's (e.g. FART's) are especially susceptible and should be visually
checked for cracks in the resin.
I have found that even a small cooling fan (such as a 5 volt, brushless, PC
power supply fan) will significantly lengthen the serviceable life of a NST.
Safe coiling,
Gavin Hubbard