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Moving arc with magnet

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big5824

Wed Jan 07 2009, 09:16PM

Registered Member #1687 Joined: Tue Sept 09 2008, 08:47PM
Location: UK, Darlington
Posts: 240

I just randomly started wondering if it would be possible to move an arc with a magnet, and iv been searching through google with no luck.....there seems to be a lot of material contradicting other material, as TVs use magnets to guide an electron beam (similar to an arc?), and mass spectrometers use magnets to deflect ions....but I cant find a single attempt to deflect an arc, and a lot of sites plainly state that electrons and ions can only be attracted by other electrostatic forces. I was wondering if i could use one or two electromagnets to oscilate an arc back and forth to produce sound.

Arcstarter

Wed Jan 07 2009, 09:30PM

Registered Member #1225 Joined: Sat Jan 12 2008, 01:24AM
Location: Beaumont, Texas, USA
Posts: 2253

I am sure you can move an arc with magnets, yes. But think about it, if you move and arc back and forth, it either wouldn't make much sound, or none at all, because arcs have no mass. I know for a fact that you can move an arc inside a xenon tube with a magnet, so i am sure you could outside of one too.

Speakers work using electromagnets to move something, which is the cone, but it has mass.

And arcs do not have mass, that is why plasma speakers sound so clear because they don't need to move any mass, so the only delay is in the circuitry.

big5824

Wed Jan 07 2009, 09:52PM

Registered Member #1687 Joined: Tue Sept 09 2008, 08:47PM
Location: UK, Darlington
Posts: 240

the ionised air has a mass though, and will create a pressure wave when oscilated wont it?

Nik

Wed Jan 07 2009, 10:03PM

Registered Member #53 Joined: Thu Feb 09 2006, 04:31AM
Location: Ontario, Canada
Posts: 638

Yes you can move an arc with a magnet. I did so about a year ago making an arc move in circles between 2 concentric rings with the magnetic field passing at right angles though the rings. Click below to see the video.

rp181

Wed Jan 07 2009, 10:16PM

Registered Member #1062 Joined: Tue Oct 16 2007, 02:01AM
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Posts: 1529

I made a video awhile back of a neodymium magnet and a MOT arc.

uzzors2k

Thu Jan 08 2009, 01:44PM

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

See the bottom of the page.

We had a discussion about it here some time ago.

Arcs consist of ionized gas which has charge, ie plasma, so magnetic fields will easily affect an arc. As to creating sound, it's the change in intensity which creates pressure waves by heating more/less air, and that's how all audio arc modulators work. I'm not sure whether moving an arc fast enough will create sound, as it isn't exactly an object so much as a state the air is in.

mikeselectricstuff

Thu Jan 08 2009, 05:03PM

Registered Member #311 Joined: Sun Mar 12 2006, 08:28PM
Location:
Posts: 253

Yes you can, but as most arcs are AC, the movement will tend to flutter between 2 directions as the polarity reverses. Using a DC arc, or an electromagnet which is driven in-phase with the arc's power source will probably be most effective.

big5824

Thu Jan 08 2009, 05:28PM

Registered Member #1687 Joined: Tue Sept 09 2008, 08:47PM
Location: UK, Darlington
Posts: 240

I think im gona give this a go when i get my hands on a flyback. Could i rectify and smooth the HV output easily enough to produce dc? (no idea what size capacitor i will need)

And i think il try using two electromagnets on either side, with one on for the rising part of the wave and one on for the falling part.

/edit

anyone know what kind of voltage a photocopier flyback can generally supply? I know a photocopier repair guy who could maybes get me some...

/edit again

About the AC fluttering thing....the air will always be ionised with the same charge, so the magnet should always have the same effect on it, it wont matter which way the electrons are moving through it

Arcstarter

Thu Jan 08 2009, 08:24PM

Registered Member #1225 Joined: Sat Jan 12 2008, 01:24AM
Location: Beaumont, Texas, USA
Posts: 2253

Most modern day flybacks are rectified, and older tv's have an external rectifier and an ac flyback. Also, some have 'cascades' which are voltage multipliers. The really old TV's that use vacuum tube, use a vacuum tube diode. That would work, but you would have o provide filament voltage, and they cannot handle much current. The ones i have had could only handle .5ma which is nowhere near high enough for a good arc to be modulated.

As for smoothing, you would not want that with high voltage. With a capacitor to act as a smoothing cap, it will just charge up and then release all energy as one discharge, if it is not a resistive load. If you put a high voltage high value resistor in series with one lead of the capacitor and the other capacitor lead as ground, it will be good and it will be a pretty much silent arc, which is what you want.

When using my large GE capacitor, charged to 2kv at 11.5uf, i would discharge it through a 32kohm resistor, and it would be a continuous silent arc, that would last a second or so.

You want a continuous arc though for this type of modulation, but to have to go through the trouble of getting the right cap and calculating the right resistor, you should just leave a dc flyback as is and use that. Either that or rectify an ac flyback with an external fast diode that should come with it.

mikeselectricstuff

Thu Jan 08 2009, 11:55PM

Registered Member #311 Joined: Sun Mar 12 2006, 08:28PM
Location:
Posts: 253

big5824 wrote ...

About the AC fluttering thing....the air will always be ionised with the same charge, so the magnet should always have the same effect on it, it wont matter which way the electrons are moving through it

The magnet is not interacting with the charge, but the current that is flowing through the ionised air. It's just like a floppy bit of wire, so the direction of the current will matter.

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