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Jacobs ladder fail?

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magnet18

Thu Jul 28 2011, 04:28PM

Registered Member #3766 Joined: Sun Mar 20 2011, 05:39AM
Location:

Posts: 624

Alright, I just got my NST in the mail, 12KV 30mA (supposedly)-http://cgi.ebay.com/ws/eBayISAPI.dll? ViewItem&item=300577329164&ssPageName=STRK:MEWAX: IT#ht_1583wt_1144
Being me I immediately found a power cord (a really really old one) and hooked it up as a jacobs ladder using some thick copper wire for the secondary connection.
I plugged it in, expecting a jacobs ladder like this-http://www.youtube.com/watch?v=w_jxIUeUED4
or this-http://www.teravolt.org/jladder.php? style=dark
with nice white arcs that rise dramatically.

But instead all that happened was I got a tiny little purple arc at the bottom that kinda turned yellow as it rose, IF it rose.

Did I do something wrong? Should I have grounded the case? Is this just what NST's do?
I am disappoint. :(

Ash Small

Thu Jul 28 2011, 05:04PM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

NST's have a unique rating system. The label 'should' read 12kV 'or' 30mA.

The open circuit voltage is 12kV, and the short circuit current is 30mA.

Neon signs require a high voltage to get them going, then more current at a lower voltage once they are lit.

The arc probably turns from purple to yellow as the current increases, but I've never used an NST for a Jacob's ladder, so I don't really know.

(EDIT: just niticed this is my 1,000th post here.)

Herr Zapp

Thu Jul 28 2011, 06:35PM

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

Ash Small wrote:

"NST's have a unique rating system. The label 'should' read 12kV 'or' 30mA"

Not correct. An NST nameplate will ALWAYS specify the output voltage and current, along with input voltage, input frequency, input current, and sometimes the VA rating, and identify if the transformer is a "normal" or high power-factor unit. (High power-factor NSTs have an internal power factor correction capacitor to minimize "apparent" current draw.)

magnet18:

The output arc from a 12/30 NST is not very impressive, at least not compared with higher current sources. To get the best "climbing-arc" effect of a Jacob's ladder, the angle between your electrodes must be quite shallow, or the arc will just remain fixed at the point of minimum electrode spacing. The "climbing arc" effect is driven by air heated by the arc, and a 30ma arc isn't going to provide a lot of hot air, unless it is operated in dead-still air. To maximize the effect of the small amount of hot air your arc is generating, you'll need to enclose the electrodes in a 2.5" - 3" diameter acrylic tube or clear plastic box to create a "chimney".

You might also want to verify that each side of your NST is actually generating full output. Fasten a small piece of stiff bare wire to each HV bushing, and bend it so the free end is close to the case. Adjust the distance to get the maximum arc length from wire to case, and compare the arc length at each bushing. The arc lengths should be very close to identical. (Obviously, perform all adjustments with the transformer powered OFF.)

Herr Zapp

magnet18

Thu Jul 28 2011, 08:39PM

Registered Member #3766 Joined: Sun Mar 20 2011, 05:39AM
Location:

Posts: 624

Thanks, I'll try that.
What's the easiest/best way to make a kilovolt meter?

Ash Small

Thu Jul 28 2011, 09:00PM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

Herr Zapp wrote ...

Ash Small wrote:

"NST's have a unique rating system. The label 'should' read 12kV 'or' 30mA"

Not correct. An NST nameplate will ALWAYS specify the output voltage and current, along with input voltage, input frequency, input current, and sometimes the VA rating, and identify if the transformer is a "normal" or high power-factor unit. (High power-factor NSTs have an internal power factor correction capacitor to minimize "apparent" current draw.)

.
Herr Zapp

I was repeating what I was told (and what is repeated frequently) on another site. There they insist that an NST will not put out 12kV at 30mA. They do talk quite a lot of crap on there sometimes, especially regarding HV power supplies, and I was eventually banned from posting on that site because I repeatedly proved the people who run it were wrong.

I'm not going to mention the site, because I like to think that I'm 'above' flaming on the internet.

I understand from recent posts here that NST's limit current by way of 'saturation' and 'magnetic shunts', but I still don't fully understand the mechanism.

(I'm learning a lot on this site)

magnet18

Thu Jul 28 2011, 09:49PM

Registered Member #3766 Joined: Sun Mar 20 2011, 05:39AM
Location:

Posts: 624

So... kilovolt meter...
google is not helping me...

Dr. ISOTOP

Thu Jul 28 2011, 11:16PM

Registered Member #2919 Joined: Fri Jun 11 2010, 06:30PM
Location: Cambridge, MA
Posts: 652

magnet18 wrote ...

So... kilovolt meter...
google is not helping me...

A doublepost in spirit, but not body.
Also, voltage divider?

Tetris

Sat Jul 30 2011, 08:58AM

Registered Member #4016 Joined: Thu Jul 21 2011, 01:52AM
Location: Gainesville, FL
Posts: 660

try making the wires more of a tighter V and the base, a little further apart. Your V shape might be too wide.

Sulaiman

Sat Jul 30 2011, 04:18PM

Registered Member #162 Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3141

Ash,
Ideally a 12 kV 30 mA NST gives 12 kV @ 0 mA and 30 mA @ 0 kV
12 kV x 30 mA = 360 VAR, you're doing well if you can 'use' 1/2 of that.

Killa-X

Sat Jul 30 2011, 04:54PM

Registered Member #1643 Joined: Mon Aug 18 2008, 06:10PM
Location:
Posts: 1039

I know from personal play, when you use a wire and a stick, and connect it to the Left peg, and arc to the right peg, you should be about to get a 2" white arc, roughly. My teacher owned a GFCI protected 12KV 30mA NST, and we were able to get 2-3" arcs from it, and we had a jacobs ladder for it that started at maybe 5mm, and went 3" apart.

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