Author Topic: Anyone tried resonant NST?  (Read 573 times)

Offline AstRii

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Anyone tried resonant NST?
« on: August 30, 2020, 01:42:12 AM »
Hey!
I was wondering... You can see so many people making arcs with resonant MOTs, has anyone tried to do the same with NSTs?
Unlike MOTs they have very low output currents, but maybe with resonant capacitors, the arcs could be monstrous :) (maybe even try to parallel a few of those for higher currents? :D)

I have only seen very few attempts of trying resonant NST arcs, and with almost no details or information about it.
Is there any reason to why not try resonance with NSTs?

Offline Mads Barnkob

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Re: Anyone tried resonant NST?
« Reply #1 on: August 30, 2020, 01:15:46 PM »
You will see from SGTC builders that sizing of the MMC for such a Tesla Coil is aimed at a term called Larger-Than-Resonant and is a term to design the MMC to NOT resonate with the NST secondary inductance, as it will destroy the transformer from over-voltage.

The MOT only has about 2 kVAC output whereas the MST has 9-15 kVAC, but with wire with about the same voltage rating, the MOT is much more robust against over-voltage than the NST is.
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Offline AstRii

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Re: Anyone tried resonant NST?
« Reply #2 on: August 30, 2020, 01:21:21 PM »
Oh, is the voltage really rising so high?
Because MOT capacitors are rated ~2.1kVAC, yet people very often use only 1 series capacitor (and 2-3 in parallel) for MOT resonance.
Why is it that the capacitors survive?

Offline davekni

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Re: Anyone tried resonant NST?
« Reply #3 on: August 30, 2020, 06:36:53 PM »
There are smaller NSTs for small signs with lower voltage, down to 3kV.  Those are usually lower current too (for smaller neon tube diameter), so not of much interest for SGTC or arcs.

Especially with AC use, capacitor failure isn't typically instantaneous,.  Failure occurs with localized corona or similar dielectric breakdown at field concentration points within the capacitor.  This breakdown doesn't initially extend all the way to the opposite plate, just very locally at the sharp edge or corner.  Over use time, the insulation degrades and spreads until failure.  So, capacitor lifetime is more of an exponential function of voltage than an abrupt function.

Most MOT arc experiments last no more than a few seconds or minutes.  The caps would not survive long-term use in such over-voltage conditions.
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Offline AstRii

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Re: Anyone tried resonant NST?
« Reply #4 on: August 30, 2020, 10:59:51 PM »
Interesting..
When i find some spare time, i will measure the voltage of resonant MOT.
I'm curious :D

Offline DashApple

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Re: Anyone tried resonant NST?
« Reply #5 on: August 31, 2020, 03:02:16 PM »
I have tried it , Three 6.3Kv NST's with a 200nF resonant capacitor ( 5 MOT caps in series ) All three get warm rather quickly   

« Last Edit: August 31, 2020, 03:07:14 PM by DashApple »

Offline AstRii

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Re: Anyone tried resonant NST?
« Reply #6 on: August 31, 2020, 07:33:55 PM »
That's so sick!
Thank you for sharing.


Offline klugesmith

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Re: Anyone tried resonant NST?
« Reply #7 on: September 01, 2020, 02:36:45 AM »
Thank you.  Reminds me how making arcs with high voltage transformers could be fun. But take it easy with the arcs if you intend to use the transformer for something more productive. :-)

How did you choose the capacitance value?

Did you happen to measure the primary current while making those arcs?   
That might benefit someone here, who recently wondered how a NST could ever draw more current than it would with short circuit on output.

« Last Edit: September 01, 2020, 02:51:02 AM by klugesmith »

Offline DashApple

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Re: Anyone tried resonant NST?
« Reply #8 on: September 06, 2020, 04:16:45 PM »
Thanks

I never measured the primary current when i tried this as it was just a quick setup and for sizing the capacitor it was just trial and error for the most part : )


Offline johnf

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Re: Anyone tried resonant NST?
« Reply #9 on: September 07, 2020, 11:31:27 AM »
Series resonant circuits can be scary
I did a job for a startup that was making a superconducting magnet for a beam scanning system.
upshot was that an audio amp of 1kW was used to sinewave drive the magnet at approx 100Hz.
the amp was connected by a 25:1 turns ratio transformer to the series tuned circuit. The capacitors required were 20kV rated Plastic capacitors inc units. yep you guessed it we did puncture a few expensive caps due to voltage over excursion.
This is the extreme case with very high Q but similar can be expected with trying to resonate NSTs albeit with much lower Q and higher drive voltage.

Offline Mads Barnkob

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Re: Anyone tried resonant NST?
« Reply #10 on: September 07, 2020, 09:22:53 PM »
Oh, is the voltage really rising so high?
Because MOT capacitors are rated ~2.1kVAC, yet people very often use only 1 series capacitor (and 2-3 in parallel) for MOT resonance.
Why is it that the capacitors survive?

MOT capacitors are designed for abuse. I do not have a datasheet at hand, but got a copied table of specifications on my article on a MOT capacitor bank here: http://kaizerpowerelectronics.dk/pulse-power/333-joule-moc-capacitor-bank/

They are tested with 9030 VDC for 60 seconds between terminals.

I have tried it , Three 6.3Kv NST's with a 200nF resonant capacitor ( 5 MOT caps in series ) All three get warm rather quickly   

/>

I would argue that these do NOT count as regular NSTs :) Very nice arcs, but those huge iron cores with separated windings is a whole other level from the small casted resin units seen outside on buildings.
« Last Edit: September 07, 2020, 09:24:58 PM by Mads Barnkob »
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Offline johnnyzoo

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Re: Anyone tried resonant NST?
« Reply #11 on: September 09, 2020, 11:25:39 AM »
 
Series resonant circuits can be scary
I did a job for a startup that was making a superconducting magnet for a beam scanning system.
upshot was that an audio amp of 1kW was used to sinewave drive the magnet at approx 100Hz.
the amp was connected by a 25:1 turns ratio transformer to the series tuned circuit. The capacitors required were 20kV rated Plastic capacitors inc units. yep you guessed it we did puncture a few expensive caps due to voltage over excursion.
This is the extreme case with very high Q but similar can be expected with trying to resonate NSTs albeit with much lower Q and higher drive voltage.

Hmmm... superconducting tesla coil, anyone? :o

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Re: Anyone tried resonant NST?
« Reply #11 on: September 09, 2020, 11:25:39 AM »

 


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