[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

RE: Unpotted NST



Original poster: "David Dean by way of Terry Fritz <twftesla-at-uswest-dot-net>" <deano-at-corridor-dot-net>

Hi Chris

400 mA does not sound like it would be unreasonable for a NST with no
shunts.
You have eliminated most of the current limiting ability of the transformer.
All that remains is the leakage inductance due to the separation between the
primary and secondary windings. I would think that you would need to use
some
sort of current limiting ballast in the primary circuit. The windings will
be
in danger of damage from over current.

Let me share an experience I had. I bought a new 15/60 NST that had been
dropped.
It did not last very long in TC duty due to cracks in the tar from being
dropped
that allowed for carbon tracking early on. I unpotted it and installed it in
a
container under oil www.corridor-dot-net/deano/nst_modifi.htm . I also had a
filter
network installed at first, but my safety gaps were too wide and the MOVs
failed.
I removed the filter network and everything worked OK. Then I connected to a
48nF
cap (approx. 4X reso.) and cranked it up. I was able to input 2.8KVA into
the 15/60
NST for several minuets with no apparent problems. After switching back to a
reasonable
sized capacitor, the NST failed immediately. Post Mortem revealed both
secondary windings
had the paper and insulation on the wires carbonized. Too much current had
over heated the
windings and destroyed them. As soon as the voltage went back up to a
"normal" level
the windings shorted out and failed. Nothing salvageable there, the
secondaries will
have to be rewound in order to work again.

You will need to limit the current to a reasonable level in order to get any
life
out of your NST. Good luck with your endeavor.

later,
deano


> -----Original Message-----
> From: Tesla list [mailto:tesla-at-pupman-dot-com]
> Sent: Wednesday, January 03, 2001 8:22 AM
> To: tesla-at-pupman-dot-com
> Subject: Unpotted NST
>
>
> Original poster: "Chris Dobson by way of Terry Fritz
> <twftesla-at-uswest-dot-net>" <cdobson-at-microtech-dot-com.au>
>
> Dear list,
>
> I have just unpotted another NST (my third so far!) only this
> time I removed
> ALL the magnetic shunts. It is a 15/60 tranny.
> The shorted secondary output now measures out at 400 mA - - - -
> can this be
> right? If so, are there any precautions I should take as regards
> protecting the
> windings? (I already use R-C filter protection)
> Regards
>
> Chris
>
>
>