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15kV 30ma x2, 13.7nF, 8 series static gap, 20" max spark length.....?

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NickCesar

Sat Jan 03 2009, 03:18AM

Registered Member #1799 Joined: Thu Nov 06 2008, 02:20AM
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Posts: 23

Alright, so I got 4 awg copper wire and cut some 1/4" tubing lengthwise and flattened it to make a primary tap. Everything was soldered. All copper on copper contact. Max spark length: 20"....
Which only proves my aluma-rope wasn't necessarily a bad idea, and that aluminum oxide is a negligible resistance at 15kV.

However, I did test the coil on each NST. Non-GFI ran the coil at a well reduced output (3-4" streamers), which is expected when the capacitor is so oversized. The GFI kicks on, a spark projects it self from the breakout point and then it ceases being able to reach the gaps firing voltage. In order to allow the GFI NST to consistently fire the gap, three of the gaps had to be shorted (with aluminum foil). The Non-GFI reached full firing voltage consistently even with the gap being sucked by a vacuum cleaner motor. Something is definitely wrong with the GFI NST, and it's odd that the actual GFI unit in the transformer is not lighting and does not appear to be functioning. I am prepared though and have a heating element ready.

MOT_man

Sat Jan 03 2009, 05:18AM

Registered Member #1127 Joined: Mon Nov 19 2007, 12:08AM
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Posts: 139

I'd take that transformer a part. Heat the tar up and pour it off. Inside you'll find the GFI unit and connecting wires. Then submerge the remainder of the transformer in gasoline for a few days to clean it off.

Then you can knock some shunt plating out and submerge it in mineral oil for higher power usage. :)

Herr Zapp

Sat Jan 03 2009, 06:31AM

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

Nick -

OK, so now we have established that your GFI NST shuts down as soon as you power up the coil. This is typical of a GFI NST.

Nevertheless, a streamer output of only 3-4" when the coil is powered by your remaining conventional (non-GFI) 15/30 NST indicates that there is still something very wrong with your system. You should be getting much better performance then this, even with a "large" .013 uF tank cap value.

Even if you've already done it once, go back and verify the output of your non-GFI NST. Ideally, connect an AC milliammeter (old moving-coil type analog meter) directly across the HV bushings see if the transformer is really delivering 30ma.

If you don't have an AC milliammeter, connect a stiff piece of wire to each HV bushing, and position the free ends about 1/2" from the NST case. Power up the NST, and you should get a nice, continuous arc from each wire to the NST case. The maximum arc length obtainable from each bushing should be nearly identical.

Again, attaching a series of photos showing all the components of your coil, and the overall setup, may allow us to see some obvious deficiency.

Leave the new copper primary wiring in place until you get the coil debugged and running decently, then substitute your aluminum foil wiring for a direct comparison.

One more question: are you using wood for any part of the coil that is carrying high voltage, like primary supports, tank capacitor housing, etc? Wood (especially plywood) can be somewhat conductive at high voltages, and I've seen cases where the carbon tracking occurred along an internal glue line in a piece of plywood. It may take a long time before the wood heats up enough to any external evidence of the internal carbon tracking.

Regards,
Herr Zapp

NickCesar

Sat Jan 03 2009, 07:23AM

Registered Member #1799 Joined: Thu Nov 06 2008, 02:20AM
Location:
Posts: 23

no, the GFI one is not shutting off. When I plug it in it charges and fires the cap once or twice (transient voltage thingy) and I can hear it charging the capacitor. Then, shorting gaps just lowers firing voltage. It runs with low voltage triggered gap and cause corona formation from the breakout point although fairly small.

The coil is on a wooden table, but the legs are pvc for the purpose of insulation. Primary turn spacers are acrylic.

This leaves only the tank capacitor and maybe my secondary to ground? I dont have a "ground strap", I soldered 18awg wire to the 25awg magnet wire but there is about a good inch of mating surface. Hmm, it runs through the wood table top though.... same as the primary coil... don't Oudin resonators have the bottom of their secondary connected to the primary though? I'm going to go check this out on the coil...

Also, Microsim shows that my maximum power throughput with a 13.7nF cap and a 15kV 30mA is ~65W.

MOT_man

Sat Jan 03 2009, 08:01AM

Registered Member #1127 Joined: Mon Nov 19 2007, 12:08AM
Location:
Posts: 139

Oudin coils are really coils connected to the same ground - RF ground that is - not house ground. Primary and secondary as one unit. Now this is common among coilers who use a single bushing type transformer - like a PT or a PIG unit. This is not practical for a double bushing style transformer as in the case of a NST - like you have.

NickCesar

Sat Jan 03 2009, 08:14AM

Registered Member #1799 Joined: Thu Nov 06 2008, 02:20AM
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Posts: 23

There is a good distance of wood between the primary tubing and the secondary ground wire, but it could be connecting...
Would that cause by coil to be performing so poorly?

Herr Zapp

Sat Jan 03 2009, 04:49PM

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

Nick -

Another question about your "NST"s: these are both conventional iron-core transformers, and not solid-state "gaseous tube power supplies", correct? If they are really good old fashioned iron-core NSTs, they should weigh at least 10 lbs each. Solid-state gaseous tube power supplies will have "nameplate ratings" similar to NSTs, but will be physically much smaller and lighter, and somewhere will say "high-frequency". These power supplies are NOT suitable for driving a TC.

The reason I ask is your comment "...When I plug it in it charges and fires the cap once or twice (transient voltage thingy) and I can hear it charging the capacitor...".

This is very odd; what, exactly, are you hearing? If its a some sort of high-frequency whine, then I suspect that you have something other than a 60Hz iron core transformer.

As for your primary arcing to your secondary ground wire, of course this would severely reduce coil output. All the energy in the tank circuit needs to get coupled into the secondary for the coil to run correctly. Any losses (corona losses, HV leakage through wood components, arcing from anything in the tank circuit to any other part of the coil, etc) will kill output.

If you haven't done so, try running the coil in complete darkness and watch for corona from sharp points or edges, arcing in the tank circuit, etc. Shield the spark gap with a cardboard box or something similar so that you aren't blinded by the intense light from the gap. You need to walk all around the coil, looking at every point that is carrying HV. It helps to have an observer on the opposite side of the coil to help catch any intermittant arcing.

Regards,
Herr Zapp

MOT_man

Sat Jan 03 2009, 07:05PM

Registered Member #1127 Joined: Mon Nov 19 2007, 12:08AM
Location:
Posts: 139

I can hear it charging the capacitor .... that doesn't sound very good. I never hear my transformer charging my capacitor unless you count in the 180 db fiery blue white arc between the electrodes. If you aren't getting a loud arcing sound between the electrodes of your static gap then something is a miss.

Could you post a picture of your transformers, Nick?

NickCesar

Sat Jan 03 2009, 09:37PM

Registered Member #1799 Joined: Thu Nov 06 2008, 02:20AM
Location:
Posts: 23

They are both franceformer super mcheavy ass tar potted transformers. It's like a 60Hz hum i hear from the cap, not loud at all. There is some force generated between cap plates so it is not unlikely that they move just a little and propagate small sound waves. A similar "phenomena" is seen with magnetostriction, why you here a transformer hum. The iron core grows and shrinks (very very small amount) at 60Hz.

I'm going to make an acrylic spacer to go in the table to insulate the primary from the wood.
Then do a dark test.

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