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Resonant MOT arcs

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Dr. Dark Current

Fri Jan 25 2008, 03:14PM

Registered Member #152 Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384

I made a MOT bank with resonant capacitors on the output (resonance is achieved between leakage inductance and the caps). It works nicely for drawing big electric arcs. Here is the schematic:

Input current from 230V mains peaks around 16A (will run on 10A breaker), max. secondary current is ~1.5A and ~6200V resonant voltage on the MOTs. The choke on the pri. side is to make the arc a bit more stable when drawn slowly and saves the breaker from tripping. Quickly drawn arcs are probably up to 0.7 meter long.

Video:PICT0289.avi

Few screenshots:

J.M.

uzzors2k

Fri Jan 25 2008, 03:40PM

Registered Member #95 Joined: Thu Feb 09 2006, 04:57PM
Location: Norway
Posts: 1308

Awesome! I saw your videos youtube and was wondering when you'd post it here. Will a MOT with it's secondary shorted work as the primary ballast? I have 5 MOTs and no use for them, so I'll try this once I finish some other projects.

Dr. Dark Current

Fri Jan 25 2008, 03:51PM

Registered Member #152 Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384

Uzzors wrote ...

Awesome! I saw your videos youtube and was wondering when you'd post it here. Will a MOT with it's secondary shorted work as the primary ballast? I have 5 MOTs and no use for them, so I'll try this once I finish some other projects.

Thanks

I think MOT with shorted secondary has too high inductance so you will get just small arcs. It would probably work if you can grind off the "I" section of the core (but watch if the primary wire does not get too hot) or put 2 sec. shorted MOTs in parallel. It will run without the choke but the arcs will not be as stable.
Maybe the 3-MOT variant as I posted previously would do good without any choke at all if you want to try it

Hmm, where did you get your MOTs?

Dr. Slack

Fri Jan 25 2008, 04:51PM

Registered Member #72 Joined: Thu Feb 09 2006, 08:29AM
Location: UK St. Albans
Posts: 1659

Not sure what you're doing here, or at least why you're doing it? You've added some series inductive reactance in the primary, then removed it in the secondary with some series capacitive reactance.

Dr. Dark Current

Fri Jan 25 2008, 05:06PM

Registered Member #152 Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384

NeilThomas wrote ...

Not sure what you're doing here, or at least why you're doing it? You've added some series inductive reactance in the primary, then removed it in the secondary with some series capacitive reactance.

The MOTs have quite large leakage inductance because of the shunts. The 4 MO caps get exactly to resonate with two MOT secondaries (measured L and C).
The choke on the primary lowers the Fres a bit, but the sec. resonant voltage still remains the same, as the MOTs will saturate with ~3kV (each) on their sec. windings and wont let the voltage resonate up higher. With the choke the saturation is a bit "softer" and the arcs are more stable.

Kolas

Fri Jan 25 2008, 05:13PM

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

I actually tried this was a pole mount transformer and a .22 uF resonant cap. The results were horrifically scary: 2 meter power arcs. Be careful though I found with a series resonant capacitor the voltage was practically doubling across the transformer, so the MOT's may not be the best choice for this type of experiment.
Kolas

Dr. Dark Current

Sat Jan 26 2008, 04:39PM

Registered Member #152 Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384

Kolas wrote ...

I actually tried this was a pole mount transformer and a .22 uF resonant cap. The results were horrifically scary: 2 meter power arcs. Be careful though I found with a series resonant capacitor the voltage was practically doubling across the transformer, so the MOT's may not be the best choice for this type of experiment.
Kolas

Here's my way to big arcs: 1) short the input to your transformer(s) (leave the ballast in place if you use one) and measure output inductance 2) get a HV capacitor of at least 3x the voltage rating of your output voltage and capacitance so it forms a more-or-less resonant circuit (bigger cap is better than smaller) 3) connect it in series with your output

Maybe someone could try this with some potential transformers and a xxx amp breaker, that should make one HELL of a power arc! (you know the video of the 500KV switch opening...)

Kizmo

Sat Jan 26 2008, 05:09PM

Registered Member #599 Joined: Thu Mar 22 2007, 07:40PM
Location: Northern Finland, Rovaniemi
Posts: 624

jmartis wrote ...

Maybe someone could try this with some potential transformers and a xxx amp breaker, that should make one HELL of a power arc! (you know the video of the 500KV switch opening...)

I could try this but i dont have LCR meter :(

6000V small distribution transformer and 250A breakers are available ;)

Dr. Dark Current

Sat Jan 26 2008, 05:19PM

Registered Member #152 Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384

Kizmo wrote ...

I could try this but i dont have LCR meter :(

6000V small distribution transformer and 250A breakers are available ;)

Thats no problem! Just connect up your secondary output to mains and measure how much current it draws (pri. input shorted) , from here you can calculate the reactance and inductance.
Of course use some inductive ballast on the pri. side otherwise your cap (and sec. current) will calculate waay too big...

If you try it, I hold no liability for fried transformers etc. as this circuit will push the sec. voltage until the xfmr saturates (sometimes up to ~2x the rated voltage, but distribution xfmr should take this as it has something like 1000% safety margin)

guich

Sat Jan 26 2008, 10:49PM

Registered Member #1269 Joined: Sat Jan 26 2008, 06:22PM
Location:
Posts: 9

hi iÂ´m new here

i also tried to make them swing in reso, the result was a 50cm arc! (~20inch)
My friend killed 3mots in a SGTC (he installed an HF filter!) so I wouldnÂ´t say that it is possible to put 3 mots in reso in series, but you could connect 2 mots in reso in series parallel to a string of 2mots in reso in series like this:

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