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Ground Fault Protection Circuit

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oucivileng

Tue Oct 21 2008, 12:18PM

Registered Member #1772 Joined: Tue Oct 21 2008, 05:23AM
Location: Athens, OH
Posts: 71

I'm just about finished building my first coil and have run into a major problem with my 6kV neon light transformer. It has a "Secondary Ground Fault Protection Circuit" that shuts it off a fraction of a second after I turn it on. Is there a way to disable this or fool it into not shutting off?

By the way, I'm very new to all this stuff so I'm trying to keep it all very simple. My primary circuit is 12 beer bottles in a tub of saltwater and the primary coil in parallel to a spark gap I made from two long screws going through each side of a small piece of carpet tube that I got out of a dumpster. A larger piece of that tube is what I wound the secondary on. If you have any other suggestions that are cheap that would help out my project, I'd love to hear them. Thanks!

Bamacoiler

Tue Oct 21 2008, 03:48PM

Registered Member #1628 Joined: Wed Aug 06 2008, 08:48PM
Location: Huntsville, AL USA
Posts: 95

Can you easily open the nst? you should be able to disable the gfci if it is not potted into the nst. A picture would really help if you can get the case off the nst.

oucivileng

Tue Oct 21 2008, 04:37PM

Registered Member #1772 Joined: Tue Oct 21 2008, 05:23AM
Location: Athens, OH
Posts: 71

yeah, I can open it easily but almost everything is covered in that white glue-like stuff. What should the gfci look like? (i'll see if I can get a picture up later today)

oucivileng

Tue Oct 21 2008, 11:10PM

Registered Member #1772 Joined: Tue Oct 21 2008, 05:23AM
Location: Athens, OH
Posts: 71

I spoke with some electrical engineering students and they tell me that the transformer is kicking itself off because I'm filling the capacitors to fast or something and it thinks there's a short. (I'm pretty sure that's what they said). Does that sound right to anybody? They told me I need a resistor in series with my capacitors. Any thoughts? This sounds more plausible than what I was thinking.

Billybobjoe

Tue Oct 21 2008, 11:32PM

Registered Member #396 Joined: Wed Apr 19 2006, 12:55AM
Location: Pittsburgh, PA
Posts: 176

Does it look like this ?

NSST

I bought two a while ago and traded one with Simon Barsinister. I'd like to know if he ever found any use for it . . .
I still have one here and I know it will only draw arcs if you turn it on with the electrodes positioned so they are close enough for an arc to be immediately established (ie. no striking an arc). Unfortunately that white stuff (probably an epoxy) is very tough and resistant to solvents.

oucivileng

Wed Oct 22 2008, 12:46AM

Registered Member #1772 Joined: Tue Oct 21 2008, 05:23AM
Location: Athens, OH
Posts: 71

Yes, it's almost identical. Any idea what to do about it?

Bamacoiler

Wed Oct 22 2008, 01:03AM

Registered Member #1628 Joined: Wed Aug 06 2008, 08:48PM
Location: Huntsville, AL USA
Posts: 95

Well, you'll need a schematic to bypass the gfci if that is even possible. If that's not an option you'll have to dissolve/remove the epoxy type potting. If that can be accomplished you may or may not be able to bypass it by rewiring. Genererally it's not a good idea to use a gfci nst in this type hv circuit. Btw the gfci circuit is to prevent electrocution to the user in case of fault.

Herr Zapp

Wed Oct 22 2008, 01:07AM

Registered Member #480 Joined: Thu Jul 06 2006, 07:08PM
Location: North America
Posts: 644

oucivleng -

Two comments:

1. Dealing with an NST with a potted (encapsulated) GFI may not be worth the effort for a first-time Tesla coil builder, especially if it is potted in epoxy. It would be much simpler to hunt for a conventional iron-core transformer NST without the GFI.

2. You mentioned that you have your "primary coil in parallel to a spark gap". This is not a correct connection for a primary circuit. The primary coil, tank capacitor, and spark gap are all connected in series, with the HV input from your NST connected across the spark gap. Think of the spark gap as a switch. You want the energy stored in the capacitor to be dumped into the primary coil when the spark gap fires ("switch closes"). If your primary coil is actually connected across the spark gap, then the spark gap is being directly shorted by the primary, and can never "fire".

Regards,
Herr Zapp

oucivileng

Wed Oct 22 2008, 01:48AM

Registered Member #1772 Joined: Tue Oct 21 2008, 05:23AM
Location: Athens, OH
Posts: 71

Herr Zapp

Comment #2: I was basically using this schematic

as a basic guide. Is this a bad example?

Comment #1: Is there an easy way to tell if I'm getting the right kind of transformer (no GFI) if I'm shopping on ebay or something?

Bamacoiler

Wed Oct 22 2008, 11:42AM

Registered Member #1628 Joined: Wed Aug 06 2008, 08:48PM
Location: Huntsville, AL USA
Posts: 95

Comment #1: Is there an easy way to tell if I'm getting the right kind of transformer (no GFI) if I'm shopping on ebay or something?

The only way to know for sure is if it says NO GFCI!

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