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Possibly broken NST? how can I fix it?

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Jrz126

Fri Mar 24 2006, 05:00AM

Registered Member #242 Joined: Thu Feb 23 2006, 11:37PM
Location: Erie PA
Posts: 210

I just got my NST and I think one of the secondary terminals was broken during shipping.

Its pretty loose and I can see the broken ceramic inside when I move it.
I threw my ohm meter on it and I get 17.33kohm between the two and 8.9 kohm between the broken terminal and ground. When I wiggle the terminal, the resistance goes up quite a bit.

So, Now what do I do? Is it safe to use it?

I'm pleased as punch right now.

Hazmatt_(The Underdog)

Fri Mar 24 2006, 05:25AM

Registered Member #135 Joined: Sat Feb 11 2006, 12:06AM
Location: Anywhere is fine
Posts: 1735

There are a large variety of epoxies that 'promise' to weld just about anything, and since you already have a screw present, you can use that for clamping force.

I was thinking of JB weld because I know it has some standoff voltage, I tried it before in a high voltage application and it was actuall an insulator at the voltage I was working with. HOWEVER, it may not work here! the voltage may be too HIGH. A dielectric test would be in order for this specific case.

You could also look into a 2 part resin which dires rock hard and is available from any auto repair or hardware store, as well as numerous epoxies.

vasil

Fri Mar 24 2006, 08:38AM

Registered Member #229 Joined: Tue Feb 21 2006, 07:33PM
Location: Romania
Posts: 506

You can try to use epoxy to glue the ceramic insulator, but you will not be sure that you filled all the fisures inside. There are two posibilities:

- remove completelly the ceramic insulator and insulate hard the HV terminal with epoxy

-remove the transformer encased in its resin block outside the metalic case, and give it a new home

Jrz126

Fri Mar 24 2006, 03:49PM

Registered Member #242 Joined: Thu Feb 23 2006, 11:37PM
Location: Erie PA
Posts: 210

well, now it is completely broken off. It was being held on by just the wire, which is rather tiny. I dont know how I am going to attach anything to it.
This really sucks

So now what?

1143215364 242 FT5359 Tesla Coil 039 Small

...err edit: meant to hit the preview instead of submit.

Steve Conner

Fri Mar 24 2006, 04:21PM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

As far as I know, those insulators are designed to give adequate insulation outdoors in the damp. For indoor use, they're basically just for looks since the dry creepage distance is a lot smaller. So just fix the broken wire and stick the insulator back in place with 2-part epoxy. You may have to dig around in that lump of resin sticking out of the hole, to find the end of the wire. But don't dig too much as the cylinder of resin will help boost the creepage distance.

European NSTs don't seem to have those cool looking ceramic insulators in the first place

Doesn't JB Weld have a metal filler? It looks kind of aluminium coloured IIRC.

Hazmatt_(The Underdog)

Sat Mar 25 2006, 05:24AM

Registered Member #135 Joined: Sat Feb 11 2006, 12:06AM
Location: Anywhere is fine
Posts: 1735

Yes I know JB Weld is supposed to be metallic, but I found it had very high resistance at one time and wouldn't conduct. In this case it might. That's why I would resort to it only last.

vasil

Sat Mar 25 2006, 06:31AM

Registered Member #229 Joined: Tue Feb 21 2006, 07:33PM
Location: Romania
Posts: 506

It is very unsure to dig for the wire, you can ruin it definitively.
Just take off the case, it would be easy to locate and make connections to the Hv terminals.

http://www.rtftechnologies.org/emtech/nst.htm

Jrz126

Sat Mar 25 2006, 03:35PM

Registered Member #242 Joined: Thu Feb 23 2006, 11:37PM
Location: Erie PA
Posts: 210

I found the HV terminal, there is ~0.5" sticking out from the case. The problem with removing the case is that the terminals come out through holes in the metal. So I would have to cut the metal quite a bit to get it out.
Maybe I will just cut the case around the broken terminal. How much space should I leave between teh terminal and the case? (Its a 15kV 30mA nst)

vasil

Sat Mar 25 2006, 06:09PM

Registered Member #229 Joined: Tue Feb 21 2006, 07:33PM
Location: Romania
Posts: 506

If we consider 1.1 kv/mm, I think 2 cm from the central stick would be enough.

GimpyJoe

Sun Mar 26 2006, 01:13AM

Registered Member #316 Joined: Mon Mar 13 2006, 01:30PM
Location: Marietta, GA
Posts: 212

Because of surface tracking you should probably leave at least 1 inch all around. Better to be safe, since with such thin wire if there is an arc the wire will melt.

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