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Why am I getting no streamers?

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Tenicus

Sun Oct 21 2007, 06:43PM

Registered Member #864 Joined: Tue Jun 26 2007, 07:26PM
Location:
Posts: 22

Here are some specs on the Tesla Coil:
20 inch secondary
primary made of 9 turns of 3/8 inch aluminum tubing, 1/2 inch spacing
15 Cornell Doubier caps in series (the most popular one, dont remember the full name (CD-902 something?))
spark gap made of 3 threaded brass balls
NST 10.5/30

I "completed" this in August, but have yet to get any streamers or anything. So I guess I never really completed it.

I have 2 different toploads I can use. Both are spherical, one is 5 in diameter, the other is about 1 foot in diameter.
Without the topload on, I tap the primary at about 6 turns. I get the purple sparks coming along the wire coming off the secondary.

But with whatever topload I use, I get nothing no matter where I tap the primary. I even added 2 more turns of copper tubing, still nothing. The spark gap still fires though.

I know this may not be enough information, but does anybody have any ideas whats wrong?

Dalus

Sun Oct 21 2007, 07:48PM

Registered Member #639 Joined: Wed Apr 11 2007, 09:09PM
Location: The Netherlands, Herkenbosch
Posts: 512

Tuning?

Tenicus

Tue Oct 23 2007, 01:10AM

Registered Member #864 Joined: Tue Jun 26 2007, 07:26PM
Location:
Posts: 22

Even w/ poor tuning, shouldn't I get at least miniscule sparks?
I mean, I get nothing at all.

Tetrafluoroethane

Tue Oct 23 2007, 02:50AM

Registered Member #127 Joined: Fri Feb 10 2006, 03:36PM
Location: Cincinnati, OH - USA
Posts: 44

If you are enough out of tune you won't get anything. Or you may get something. Something bad. Like racing arcs. It took me several tries to get even thin wispy streamers from my first spark-gap coil. As long as you are sure the coil you built *can* be tuned, just play around with your primary taps.

If you have a chicken stick, try bringing it close to the topload and see if you can get an arc to jump to ground. I did this with a screwdriver the first time. I figured I wasn't getting anything so it couldn't have that much HV. I was wrong. Don't do that.

Tenicus

Tue Oct 23 2007, 10:40PM

Registered Member #864 Joined: Tue Jun 26 2007, 07:26PM
Location:
Posts: 22

I already dressed up like a Medieval knight and turned it on, are you telling me it is not OK?

Tenicus

Wed Oct 24 2007, 03:24AM

Registered Member #864 Joined: Tue Jun 26 2007, 07:26PM
Location:
Posts: 22

Alright, I did as you said with a 5 iron, and got some arcs. I could not get anything father than ~2 inches though, no matter where I tapped the primary.
A note of concern: The electrodes of the spark gap must be put EXTREMELY CLOSE TOGETHER, or it doesnt work.
I mean REALLY close.
Less that 1 mm. So close that they sometimes touch and it stops working.
This doesnt seem normal? Shouldnt they be a good 3-4 mm apart?

Sulaiman

Wed Oct 24 2007, 08:30AM

Registered Member #162 Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140

That sounds wrong,

test just the NST with the spark gap (no capacitors etc)
adjust the spark gap for the largest gap that will arc over
10.5 kV rms is about 15 kV peak which should mean about 5mm air gap

If not then your NST is internally shorted (quite common in TC service

)

Tenicus

Wed Oct 24 2007, 10:48AM

Registered Member #864 Joined: Tue Jun 26 2007, 07:26PM
Location:
Posts: 22

I can do it from 5 mm w/ just the spark gap
Its shorted then?
Damn

Tetrafluoroethane

Wed Oct 24 2007, 01:03PM

Registered Member #127 Joined: Fri Feb 10 2006, 03:36PM
Location: Cincinnati, OH - USA
Posts: 44

If the NST will arc across your spark gap (at 5mm or so) with nothing else attached, then the NST is okay. You have a problem somewhere else in your primary circuit.

First, what is the configuration of your primary circuit? Did you put the capacitor parallel with the NST or the spark gap parallel with the NST? Are you using any filters to protect your transformer (Terry Filter, etc). What size wire are you running from your NST to your primary circuit?

What are the values of the CDE caps you are using? You said 15 in a string, but no overall values. While I doubt this would be the case, but if if your cap it too large it might not charge to a high enough voltage per line frequency half-cycle. This would cause a very low voltage to present itself at the spark gap (and thus require a very small gap). Did you use any tools (software) when you were designing your coil to calculate the cap for your transformer?

Tenicus

Wed Oct 24 2007, 07:49PM

Registered Member #864 Joined: Tue Jun 26 2007, 07:26PM
Location:
Posts: 22

I believe the spark gap is in parallel with the NST.
No filters.
The wiring is the standard wires you find in extension cords
The caps are 15 uF each, 2000V (

I used the chart for the 942C caps floating around here, Im pretty sure 15 caps is correct. But correct me if Im wrong.

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