NST death? / Tesla Coils / Forums

Forums

4hv.org :: Forums :: Tesla Coils

« Previous topic | Next topic »

NST death?

previous 1 2

Move Thread

LAN_403

Ultra7

Sat Feb 28 2009, 02:17AM

Registered Member #1157 Joined: Thu Dec 06 2007, 12:11PM
Location: Houston, TX
Posts: 307

Brass balls don't break out too easily because of their shape.
Sharp things give the arc a chance to jump better.

The safety gap starts out being really close so you get an arc, then you slowly back the shafts off till it just barely doesn't break out. Remember, you don't really want it to arc unless it is needed.

You shouldn't have to get them too close to arc, but with round things, it is closer than with something like a bare wire.

How close do you have to get the balls before they arc?

oucivileng

Sat Feb 28 2009, 02:27AM

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

To get it to arc reliably and without getting it started with the nail, they have to be about a half centimeter. If I trigger it with the stick, i can spread them a couple of centimeters.

Maybe I'm having trouble because these brass balls are brand new and have such a smooth surface. The old ones weren't quite as polished.

Ultra7

Sat Feb 28 2009, 02:53AM

Registered Member #1157 Joined: Thu Dec 06 2007, 12:11PM
Location: Houston, TX
Posts: 307

oucivileng wrote ...

To get it to arc reliably and without getting it started with the nail, they have to be about a half centimeter. If I trigger it with the stick, i can spread them a couple of centimeters.

Maybe I'm having trouble because these brass balls are brand new and have such a smooth surface. The old ones weren't quite as polished.

Man, it's been a long week, I really meant millimeters when I wrote centimeters up there.
It sounds as if your gap might be working okay.
From what I know, 1 mm = 1kv as far as arc jump
I'm kinda crummy at the metric system , so I fed you the wrong info up there.

oucivileng

Sat Feb 28 2009, 03:05AM

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

no worries. I knew what you meant. So should i set my safety gap to just beyond where it will arc reliably, where it only will arc sometimes if i turn it on and off, or where i can trigger it with the nail?

Thanks for all the help by the way.

Ultra7

Sat Feb 28 2009, 03:15AM

Registered Member #1157 Joined: Thu Dec 06 2007, 12:11PM
Location: Houston, TX
Posts: 307

To where it just barely arcs, then just a little bit farther away.
That way any back feed goes into the safety gap and to ground, not back into your NST.

Herr Zapp

Sat Feb 28 2009, 07:25AM

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

oucivileng -

Two questions:

1. What is the diameter of your brass balls? The breakdown voltage of a spherical electrode spark gap is directly dependent on the radius of curvature of the electrodes. The larger the radius, the higher the breakdown voltage.

2. Are you sure that the balls are bare metal, and not protected by a thin layer of varnish as an anti-tarnish treatment? If there is any question, thoroughly clean the balls with steel wool or #400 wet-or-dry sandpaper.

Regards,
Herr Zapp

Coherent

Sat Feb 28 2009, 08:16AM

Registered Member #1886 Joined: Sun Dec 28 2008, 02:55AM
Location:
Posts: 73

Herr Zapp wrote ...

oucivileng -

Two questions:

1. What is the diameter of your brass balls? The breakdown voltage of a spherical electrode spark gap is directly dependent on the radius of curvature of the electrodes. The larger the radius, the higher the breakdown voltage.

2. Are you sure that the balls are bare metal, and not protected by a thin layer of varnish as an anti-tarnish treatment? If there is any question, thoroughly clean the balls with steel wool or #400 wet-or-dry sandpaper.

Regards,
Herr Zapp

If they had any varnish on them it would have already burned off in the first arc and you would have noticed it.

oucivileng

Sat Feb 28 2009, 06:26PM

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

The balls are 3/4" in diameter. And I think it's all bare metal. Here's where I got them:

I'll clean them with the steel wool just to be sure

Kolas

Sun Mar 01 2009, 03:39AM

Registered Member #102 Joined: Thu Feb 09 2006, 08:15PM
Location: Raleigh, NC
Posts: 169

Did you ever test the resistance of the secondary sections? I didn't see a reply for that. if not, that should be your first test...
I'm not too sure about the resistance you should have but I do know it will be lower then a few MegOhm.
If either or both secondaries has a really high resistance then it's a safe bet that you have burned the winding out.

On another note, the balls will infact have to be very close in comparison to a sharp object to get "breakdown"

Kolas

previous 1 2

Moderator(s): Chris Russell, Noelle, Alex, Tesladownunder, Dave Marshall, Dave Billington, Bjørn, Steve Conner, Wolfram, Kizmo, Mads Barnkob