Re: Resonant MOT arcs
uzzors2k, Fri Jan 25 2008, 03:40PM

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.

Re: Resonant MOT arcs
Dr. Dark Current, Fri Jan 25 2008, 03:51PM

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?

Re: Resonant MOT arcs
Dr. Slack, Fri Jan 25 2008, 04:51PM

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.

Re: Resonant MOT arcs
Dr. Dark Current, Fri Jan 25 2008, 05:06PM

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.

Re: Resonant MOT arcs
Kolas, Fri Jan 25 2008, 05:13PM

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

Re: Resonant MOT arcs
Dr. Dark Current, Sat Jan 26 2008, 04:39PM

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...)

Re: Resonant MOT arcs
Kizmo, Sat Jan 26 2008, 05:09PM


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

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

Re: Resonant MOT arcs
Dr. Dark Current, Sat Jan 26 2008, 05:19PM

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)

Re: Resonant MOT arcs
guich, Sat Jan 26 2008, 10:49PM

hi i´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 wouldn´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:

Re: Resonant MOT arcs
c4r0, Fri Feb 01 2008, 09:49PM

Hi! This is cool It's great idea to use these caps. I have some MO parts laying around so afrer reading this topic I tried it too. Here's my results on youtube: ,
and some photos :)







What about aukro? I bought a few broken MOs on our polish internet auction service allegro (looks like we have a bit more MO's than aukro ) for equivalence of 300-400Kc each. It's a good deal becouse I can take out the magnetron and easily sell it for the same price. Then I have rest of the parts for free

Re: Resonant MOT arcs
Nik, Sat Feb 02 2008, 01:32AM

I took a shot at this resonant mot stuff as well.

More pics in the random chat forum.

Re: Resonant MOT arcs
Marko, Sat Feb 02 2008, 02:26AM

C4r0 these are awesome pics. How do you get these colors.

What camera is that.

Re: Resonant MOT arcs
c4r0, Sat Feb 02 2008, 10:05AM

Just set white ballance for sunny day :) These pics was not edited, only resized. I use sony dsc-f707 (drawing arc pics) and my brother's pentax k100d (ladder pics). For movies i use praktica dcz 5.8 :)

Re: Resonant MOT arcs
uzzors2k, Tue Mar 25 2008, 05:43PM

W00t, I tried this and the arcs are amazing! I love that crackling sound of mains in the arcs. I made a video which I can't seem to upload and took some screenshots from it.

Jan, I tried a primary shorted MOT as a ballast on the secondary and it seems to work fine. No extra caps required, although they might make an improvement like you say. I haven't got enough to test it. The breaker does trip on start-up sometimes, but I think that could be fixed with something as ghetto as a NTC. Or the power resistors which come with most MOTs in the mains filter section.

Re: Resonant MOT arcs
Dr. Dark Current, Tue Mar 25 2008, 05:50PM

I can see some serious arcing there Uzzors

Btw. I will try soon with 3+3 caps, the arcs should increase ~30-50% in length

Re: Resonant MOT arcs
Marko, Tue Mar 25 2008, 05:59PM

W00t, I tried this and the arcs are amazing! I love that crackling sound of mains in the arcs. I made a video which I can't seem to upload and took some screenshots from it.

Jan, I tried a primary shorted MOT as a ballast on the secondary and it seems to work fine. No extra caps required, although they might make an improvement like you say. I haven't got enough to test it. The breaker does trip on start-up sometimes, but I think that could be fixed with something as ghetto as a NTC. Or the power resistors which come with most MOTs in the mains filter section.

Uhh Uzzors would you *please* use a longer chicken stick? Something like meter and half at least, that looks very hazardous. Mot's look so small near those arcs.

To prevent breaker from tripping at startup use a 100..1000ohm resistor in series to run up the magnetizing current, and then short it out by a switch or relay.


Who here said that he has done this with a pole pig and got 2 meter arcs?

I'd *really* want to see some pictures or videos of that.

Re: Resonant MOT arcs
Shaun, Tue Mar 25 2008, 06:57PM

This has to be THE most dangerous thing done on these forums, even up there with some of the closed threads in the Chemistry section...

...which is exactly why its so much FUN!!

Re: Resonant MOT arcs
uzzors2k, Tue Mar 25 2008, 08:27PM

Video->

Yeah, I was having second thoughts about it too. But the voltage it so low that as long as I don't get an arc wrapped around my arm I'll be ok. I will look for a longer chicken stick, so you can rest easy tonight.

I can't wait.

Re: Resonant MOT arcs
Kizmo, Tue Mar 25 2008, 08:31PM



Pretty good resonance but i was limited by 16A fuse


Im hoping that some day i can afford electrician to install 100A outlets (i have 250A main breakers but no more than 16A outlets)

Re: Resonant MOT arcs
Nik, Tue Mar 25 2008, 11:26PM

What country are you in, it might be possible for you to do it yourself. In canada you can legally do some electrical work yourself and it might be the same where you live.

Re: Resonant MOT arcs
Zum Beispiel, Wed Mar 26 2008, 12:37PM

It's Finland and here you are only allowed to do minor electrical work, like making an extension cord or stuff like that. No messing with the fuse box!

But damn, those are some impressive arcs

Hmm, I've got some mots and caps, might have to try this some time...

Re: Resonant MOT arcs
c4r0, Wed Mar 26 2008, 01:29PM

Why not to parallel two or more outlets? And how many MOCs have you used on that photo?

Re: Resonant MOT arcs
GluD, Wed Mar 26 2008, 01:45PM

*gasp* this is teh sex! :P
But does the caps have to be the same type/ratings or is it fine if theyre just from a MO?
'cause ive got around 7 MOC's but not 2 of the same type/ratings although theyre all 2100v and around 1µF.

cheers

Re: Resonant MOT arcs
uzzors2k, Wed Mar 26 2008, 02:42PM

My caps are odds and ends, and they've held up fine. MOCs can withstand the voltage with a slight margin, and the resonance action doesn't seem to require fine tuning.

Re: Resonant MOT arcs
GluD, Wed Mar 26 2008, 03:11PM

Cool, i might try it someday then :o
Got all the stuff but im just abit scared, those arcs looks really crazy O__O
..gonna need one hell of a chicken stick before i even dare puttin the stuff together.

Re: Resonant MOT arcs
Dr. Dark Current, Wed Mar 26 2008, 05:19PM

Today i bought another 2 MO caps, and as promised here are some captures and a video:












enjoy



J.M.

Re: Resonant MOT arcs
uzzors2k, Wed Mar 26 2008, 07:00PM

Madness! They must be approaching a meter by now. I have to look for some caps too, this is more fun than I thought.

Re: Resonant MOT arcs
c4r0, Wed Mar 26 2008, 08:43PM

I have 12 of them at the moment. How do you think how many should be the best for this circuit (what capacity)?

Steve has checked it and he writes that they fails at about 10kV DC. He has been charging them up to 8kV in his can crusher -

Re: Resonant MOT arcs
Dr. Dark Current, Wed Mar 26 2008, 09:12PM

I think three parallel caps for each MOT are best for big arcs. With four you may get a bit thicker and marginally longer arcs but the resonance starts to fall away and the MOTs get darn hot.

I would put 3 mots in series (if you have) and use 9 caps in 3x3 configuration... You might need to disconnect the MOTs from their cores and put them under oil to avoid flashovers, I have no idea how well would they stand it (remember the resonant voltage is ~3kV per MOT) and of course you would need a storng breaker (~25A at 230V)

Re: Resonant MOT arcs
Ken M., Wed Mar 26 2008, 09:27PM

Very nice, but if you get any more powerful MOts your gonna be needing a crane or several individual trips to set up the system in different areas, but yes This is making me very interedted in entertaining the idea of making one of these and just for "Flaming line" fun everynow and then.

Re: Resonant MOT arcs
Dr. Dark Current, Tue Apr 08 2008, 07:14PM

[Edit- I didnt realise I have posted this already, sorry]

But someone here did resonant arcs with a NST!

Re: Resonant MOT arcs
Kizmo, Thu Apr 17 2008, 09:02PM



Some resonant stuff with very crappy camera. But only 6kV

Re: Resonant MOT arcs
Kristian, Wed Apr 30 2008, 11:34PM

OK I had a go at this. Posted a video. Here it is These are not current limited. Each mot is on its own 20A circuit. I put the caps in a bucket just in case of a catastrophic failure.

I will be trying 4 mots and 4 strings of 4 caps this weekend. I'll post a vid next week.

Re: Resonant MOT arcs
Spedy, Sun May 04 2008, 01:30AM

I hope this thread isn;t "dead" and me posting here is against the rules...


All I can say is "Wow." Makes me feel like doing the work required to ram 10 feet of copper pipe into the ground..

(arg! I hope that's not a requirement for grounding!)

Now then, all I need to do is inconspicuously break my microwave, then I'm 1/3 of the way there... *evil genius laugh*

Re: Resonant MOT arcs
Backyard Skunkworks, Sun May 04 2008, 03:03AM


"I swear the directions said wrap in aluminum foil and drive a spike through the rear housing..."

I donno if anyone ever thought of this but... It might be possible to extract an MOT without killing the microwave.

The one MOT I got came from a trashed microwave I found curbside the night before garbage pickup. The door was missing (the obvious reason it was discarded) however getting the MOT out was not a very destructive process, it just involved un-bolting it and pulling a couple connectors. Maybe you could "borrow" an MOT out of a working microwave?

BTW amazing arcs! If I had more MOTs and the risk of electrocution wasn't so high I would have to try!

Re: Resonant MOT arcs
Dragon64, Sun May 04 2008, 05:50AM

Wow, Plasmaddict. Those are some impressive power arc's! I also thought that the tub was full of water O_O. When I was handling my MOT to try and set up the resonant curcuit, I forgot how much they weighed and almost dropped it.

Re: Resonant MOT arcs
Spedy, Sun May 04 2008, 05:29PM

Yah, large blocks of metal and plastic tend to be heavy =P

I wonder when the next garbage pick-up is... last time I saw an old water boiler in the street..

EDIT: Dumb question. For one MOT, would I use 2 MOC's in series or in parallel? I only have 2 MOC's so I was wondering..
Also, would a smaller MOT w/ shorted secondary on the the primary side work as ballast?

Re: Resonant MOT arcs
Mads Barnkob, Thu Jun 05 2008, 09:01AM


I did one MOT with 2 parallel MOCs in series with the MOT, no ballast and it worked like a charm. It can deliver about 20cm arcs at the top of the jacobs ladder I build for it.

Calculating the resonating frequency is like a standard LC circuit? As I am currently not home I cant measure the inductance of the secondary and give it a go.

Re: Resonant MOT arcs
Dr. Dark Current, Fri Jun 06 2008, 06:41PM

Resonant frequency is determined by capacitance and leakage inductance of your MOT. Short the MOT primary and then measure the secondary inductance.

Re: Resonant MOT arcs
Mads Barnkob, Fri Jun 06 2008, 07:41PM


unballasted it draws around 1250W, with another as ballast I will draw about twice as much right? and my only single phased circuit breaker for my appartment is at 10A / 230Vac. I would have to remove my oven to access the 3phased 16A isntallation if I want more :(

thanks about the measurement, I forgot to short the primary so the value was off the meter, turns out i accidently hit the sweet spot I guess, with a secondary inductance of 5.55H and 1.81uF capacitor bank its freq. is 50Hz, same as the primary.

Re: Resonant MOT arcs
Fraggle, Tue Jun 10 2008, 12:27AM

It will draw LESS current with the ballast.

This is my first post...Hello!

Re: Resonant MOT arcs
Dr. Dark Current, Tue Jun 10 2008, 06:14AM

Maybe it will draw a bit more, as it will probably drift off the resonance for a little. But this little "slip" will make for more stable arcs.


Hi Fraggle and welcome to 4hv
You may not be right as this resonant circuit behaves differently than just "plain" transformer. If in proper resonance, it will draw little current with output shorted and the current will go up as you draw out the arc.

Re: Resonant MOT arcs
Spedy, Tue Jun 10 2008, 06:33PM

Weee! Finaly got my 2-MOC setup working. Turns out that second MOT for ballast wasn't needed. 6" arcs are good enough for now I might be getting another microwave off of freecycle, so I'll have even more stuff to work with.
Video coming soon (found out my camera has a short video-clip option. Too bad there's no sound, the BZZZZT sounds sooo cool..

Re: Resonant MOT arcs
Dr. Dark Current, Tue Jun 10 2008, 08:00PM

I don't think 6" is that much... do you have another capacitor? If so connect it in parallel, it should increase the arc length considerably, for some lower leakage transformers it is not uncommon it can double.

Re: Resonant MOT arcs
Fraggle, Tue Jun 10 2008, 11:50PM

I agree, you ought to get longer arcs than that. I found that some ballast stopped the arcs blowing out so quickly and stopped my fuse blowing, this is why I suspect lower current draw. I think pulling out some shunts from the transformer might lower the inductance a bit and help you tune in but I`ve not tried that.


Thanks :o)

Re: Resonant MOT arcs
Spedy, Wed Jun 11 2008, 01:04AM

I'm just guessing, it could be up to 10-12". I'll hold it next to a ruler on the next run. Sorry, the two MOCS are all I have. They're in parallel w/ each other and in series with the MOT'S output. I might try prying out one of the shunt layers later.
Edit: aww, the freecycle microwave was taken. ahh well..

Edit 2: Wait, how exactly do you remove the shunts? I've used a screwdriver to pound one out of the core most of the way, but now it won't budge any more... Also, it seems pretty much impossible to remove individual shunt pieces. I assume you meant the groups on either side of the core center.

Re: Resonant MOT arcs
Dr. Dark Current, Wed Jun 11 2008, 12:29PM

Do NOT remove the shunts. You want to add inductance, not lower it.

Re: Resonant MOT arcs
Spedy, Wed Jun 11 2008, 04:52PM

Arg! mixed signals >.<
Ok then, how do I ADD inductance? (goes to pound shunt back in)

Re: Resonant MOT arcs
Dr. Dark Current, Wed Jun 11 2008, 05:03PM

Well if it works well with the shunts in, leave it alone, otherwise you can add inductance by a ballast (sec. shorted) MOT.

How do you know when you need more inductance? If the inductance is too low, the arcs will not be stable and make funny noises before they go out. Also quickly drawn arcs will be much longer than slowly drawn ones.

On the other hand if you have too much inductance, the resonant rise will not be as apparent and the arcs will be smaller no matter what you do (and they won't make any funny noises).

Re: Resonant MOT arcs
Fraggle, Wed Jun 11 2008, 07:46PM

Yes I mispoke myself, I apologise. You will need to add inductance to lower the frequency of course.

Re: Resonant MOT arcs
Kristian, Mon Jun 16 2008, 01:45AM

This is my third attempt at a 4 mot stack with the resonant capacitor. At least I got some video before I smoked the transformers this time.

Re: Resonant MOT arcs
Nik, Mon Jun 16 2008, 01:58AM

WOW, those are huge from a 4 mot stack, too bad they burned out.

Re: Resonant MOT arcs
Myke, Mon Jun 16 2008, 06:03AM

Are the transformers under oil?

Re: Resonant MOT arcs
J. Aaron Holmes, Mon Jun 16 2008, 06:20AM

Wowzers, there must have been a three-footer in there somewhere! This thread has been fun to watch. It makes me happy to see that folks still have fun just drawing big arcs off of transformer banks I'm a big fan of that too!

Pity about losing all those MOTs, though Kristian: I really dig the nice containers you made for them with the ceramic bushings and all!

Cheers,
Aaron, N7OE

Re: Resonant MOT arcs
Kristian, Mon Jun 16 2008, 09:59AM


Yes, the second set, the ones that see double voltage where under mineral oil. They held up fine, until I ran them with the capacitors.

I had two identical mots in this position. They were insulated very well, and held up to everything I threw at it. The inside secondary lead broke off one of them right at the insulation. Every mot I've used to replace it has fried the secondary. The original, the one that didn't break, is still working fine, even after getting deep fried in mineral oil.

Re: Resonant MOT arcs
Dr. Dark Current, Mon Jun 16 2008, 02:03PM

Cool arcs. With 4 transformers you might need 0.5 to 0.75uF resonant capacitor (not 1uF), otherwise the transformers will get too hot quickly and you won't get any longer arc.

BTW where did you get such a number of microwave caps? I'm jealouos

Re: Resonant MOT arcs
..., Mon Jun 16 2008, 09:34PM

The using coolers for hv enclosures is certinly a unique idea, although I wouldn't recomend it since the thermal properties of coolers are horrible (remember they can also be used to keep hot food hot). You might even be able to keep your mots running longer if the oil bath they are in had better cooling.

Re: Resonant MOT arcs
Fraggle, Mon Jun 16 2008, 11:17PM

I think there was too much capacitance as well.
All those microwave caps make me think of induction launchers and coin crushers, not arcs!

Re: Resonant MOT arcs
..., Mon Jun 16 2008, 11:33PM

He has his cap bank arranged as 5 strings of 5 caps, which will give the same amount of capacitance as a single cap--only the voltage and current ratings will be higher. It should be just about right for the application.

Re: Resonant MOT arcs
Kristian, Mon Jun 16 2008, 11:48PM


I scrounged around Freecycle, Craig's list, the scrapyard, garage sales, etc. I got 30 microwaves over a 6 month period. I payed no more than 5 bucks and most where free. I spent maybe $30 or $40 total.



I had them in an ammo can. The connections to the insulators arced over to the case. It was loud and made a burnt pvc and carbon mess in the oil, so I decided to try the cooler.

Each failure was a learning experience. The design improved with each time I had to rewire. I really thought this was the one. Oh well, I'll just rebuild it and this time I won't put it to this kind of punishment. My original 4 stack ran at up to 3KVA on my Tesla coil for 6 months, without oil, without any trouble. As soon as I hooked up the resonant capacitor, it fried.

Re: Resonant MOT arcs
Dragon64, Tue Jun 17 2008, 12:41AM



Oh man 30 microwave? Each Microwave probably takes me a 30 minutes period to dissect them and take the MOT and MOC.

Re: Resonant MOT arcs
Fraggle, Tue Jun 17 2008, 09:04AM

I just remember my 2-mot resonant setup was optimum with 1uf. On my scavenging expeditions I`ve discovered that powerful commercial type microwaves often use a full wave doubler which is nice when you`re hoarding capacitors. I`ve also found that nearly every restaurant seems to have one or two in the back yard :o)