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Registered Member #2628
Joined: Fri Jan 15 2010, 12:23AM
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Posts: 627
thats neat as you may already know, some MOTs behave differently from others, my MOT in this picture is a reletivly small one, and from MOT to MOT the value of the capacitor needed to induce resonance differs. by process of trail and error I found that for 1 mot, the absolute limit on capacitors in series was 3 for me, any more and the voltage is not enough to start an arc (small tiny ball of light and no arc). but what you see in the picture is what you get, my MOT seems to work with this setup, i can put more capacitors in parallel to make the arcs thicker, but i think it will throw of resonance as the increased capacitance so i stick to a 3 capacitor bank. the mot can run for 20 seconds before the primary becomes too hot to touch, and the secondary is always cold, so no problem there. on a torture test, i found a mot like this can endure 1 minute of constant arcing before bursting into flames. so oil is a good idea for extending the life of a mot.
here is a bigger picture of the setup, you can see the end of the 3 capacitors is attached to the core and the other end is connected to the post. the arc stick is connected to the slot terminal found on the secondary winding. (click on picture for enlargment.)
Registered Member #2463
Joined: Wed Nov 11 2009, 03:49AM
Location:
Posts: 1546
The arcs are interesting. A lot of effort goes into supressing them in modern switchgear.
Here's a possible experiment. Bring an AC electromaget close to the arc running at the frequency as the arc current and see how you can move that arc around. Now if that works, power the magnet from the output of audio amplifier at about 100 watts and make the arc dance to music.
In switchgear, a magnetic blowout coil repells the arc up into an arc-shute where it is dissipated, Sounds like a cannon if it breakes a bolted fault, the same sound as when a drop-out fuse on a polepig clears a bird short circuit.
Registered Member #2628
Joined: Fri Jan 15 2010, 12:23AM
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Posts: 627
I can try that, but there is one small problem, when i tried to put magnetron magnets (the ring ones from microwave ovens) around the terminal, the arc looked like an arc welder, created earpiercing buzzing noises and was distorted to hell. as for the electromagnet, those distortions might play a song, but the electromagnet will need to be very powerfull, I think it might be easier to use a system simular to the TL494 musical flyback, but high powered for a MOT. im unsure of this method, becuase flybacks are high frequency and mots are low frequency, so probably will not effectively drive a 60hz MOT no matter what power input, I might try it one day. so I think a 100W might be too little for the electromagnet and WAY too little to directly drive the transformer
as for the arc suppressors, If i need arc suppression its seems pretty simple to use magnetic quenching, fan quenching or a blast of sulphur hexafluorate. I never worked with industrial HV switching equipment, no body will hire a high schooler to work for a substation!mistrust
the largest arc I produced was 3 feet long, 2 Modified MOTS, wiring 180 degrees out of phase with center ground, a 5 microhenry inductor on one end, and a 6kv 0.66 capacitor bank (6 mo caps).
Registered Member #2463
Joined: Wed Nov 11 2009, 03:49AM
Location:
Posts: 1546
no, the key is an AC field, that will either repell or attract depending on polarity. The magnetron causes the arc to wibrate at the current frequency.
Registered Member #2628
Joined: Fri Jan 15 2010, 12:23AM
Location:
Posts: 627
makes sence, AC switches polarity. okay, I am kinda curious as to how will the arc react if the electromagnet is "played" at bass frequencies. I might have a speaker to play the music, and install a electromagnet around the base of the terminal. but i'll need to ballast the mot, It will draw too much juice and overheat if left unballasted. I'll try it out when I have the time.
side note: before I hook this setup up to a sound system, I should try running the electromagnet on a variable frequency drive, and perhapse the arc will look more stable if I ditch the mot, and go for a high powered flyback in a vacuum tube, or a cathode ray tube.
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7 inch arcs from modified MOT - im happy
