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Re: NST Fried?

Original poster: Mddeming@xxxxxxx In a message dated 8/11/06 8:13:45 A.M. Eastern Daylight Time, tesla@xxxxxxxxxx writes:
Original poster: "Hajdrowski, Leo T." <leo.hajdrowski@xxxxxxx>

Hello Everyone,

After switching from x-ray capacitors to MMC's my son's and my tesla
coil was running great for about 5 minutes producing beautiful long
streamers....what a sight!

Then it just stopped.  I disconnected the NST xfmr (12KV - 60MA) from
the coil, connected a pair of wires to the terminals to see if it
would produce an arc.  It did, but the wires had to be a minimum of
1/4" away before the arc would start and it would grow to only about 1".

Is my NST fried?  Can it be fixed?



Hi Leo,

    Sounds like a southern chicken dinner to me. But here's a few quick tests:

1) remove lid and look for any obvious mechanical damage:
Broken lead to either HV bushing, surface tracking on potting compound, deep cracks in potting compound, etc. cracks can sometimes be filled or compound remelted. 2) Check the terminal to terminal resistance AND each terminal to ground. Readings should be consistent. (several Kohms) A to G + B to G = A to B if grounded center tap. 3) Try to draw an arc off each terminal to ground separately. They should be comparable.
4) Check HV to LV resistance on each side. Should be infinite,

If your NST has the traditional "Tar" potting, repair in often more trouble than replacement unless you value your time at <$1/hr AND the break is very close to the surface. There are volumes in the archives on depotting transformers.

Matt D.