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Carbon Arc Lamp

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teravolt

Fri Apr 15 2011, 01:43AM

Registered Member #195 Joined: Fri Feb 17 2006, 08:27PM
Location: Berkeley, ca.
Posts: 1111

when I made a arc lamp I used a container of salt water with two electrodes in series with the line and my corbon rods in air. they will get hot enough to melt anyting.

GluD

Fri Apr 15 2011, 10:30AM

Registered Member #1221 Joined: Wed Jan 09 2008, 06:17PM
Location: Odense, Denmark
Posts: 196

Hello Steve and welcome to the forum

- what inspired you to build a carbon arc lamp?

First I was just playing around with a TV flyback in the "vacuum chamber" if I can even call it that, then I moved on to MOTS for more power, and then I got the idea of using moveable electrodes and very high currents. So it wasnt really just an idea that came to me out of the sky, it was more like a natural move in my series of "experiments", an increase in power and thus plasma temperature. The main interest at first was to obeserve the plasma (mot and flyback arcs) at variable pressures, but then after I'd done that it sort of developed into a quest for pumping in as much power as I could (thats about where it became a carbon arc lamp).

For the last many months I have been working on and off with the new version, it should be done in a few months hopefully. It will feature alot of improvements, although it will still just be an iron tube as I dont have the tools to manufacture a proper vacuum chamber.

When the new one is done Im hoping to play around with various lenses and other optical stuff.

steve516

Fri Apr 15 2011, 04:30PM

Registered Member #3832 Joined: Thu Apr 14 2011, 11:57PM
Location: Downtown Chicago, IL
Posts: 37

GluD wrote ...

When the new one is done Im hoping to play around with various lenses and other optical stuff.

Would definitely be interested in seeing pictures, etc. when your done with it. Look at the lenses for some modern HMI "fresnel" lights, these can really do wonders to almost any light if you know what you're doing!

I've always been sort of a light junkie- in fact, one of the coolest things I have done is take a 1.2kw HMI, run it without a lens/ diffuser, so just bare bulb at a pane of glass 20 feet away, and just watch the glass shatter. Beautiful what that amount of light can do.

I wouldn't put it past your carbon arc lamp if you can tweak it enough. It's all about getting enough "quantity" of light/ photons per unit area and amazing things will certainly ensue.

Thanks for the warm welcome as well. Look forward to spending a lot of time on this forum.
SK

James

Fri Apr 15 2011, 10:50PM

Registered Member #3610 Joined: Thu Jan 13 2011, 03:29AM
Location: Seattle, WA
Posts: 506

Most carbon arc lamps run with just air at atmospheric pressure. While HID lamps have taken over in most fields, there are still carbon arc cinema projectors and follow spots in operation. Typically the reflector has a hole in it and one electrode pokes through the hole while another sits out in front on a movable sled. Normally there is a motorized or solenoid driven mechanism to automatically feed the rod as the electrodes are consumed. The one I remember looking at up close was a Peerless Magnarc, I think they were quite common.

Ash Small

Fri Apr 15 2011, 11:19PM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

teravolt wrote ...

when I made a arc lamp I used a container of salt water with two electrodes in series with the line and my corbon rods in air. they will get hot enough to melt anyting.

If I remember correctly, some theatres used to have drums of saltwater backstage, and the lights were 'dimmed' by raising the electrodes from the drums, thus increasing resistance.

GluD

Sat Apr 16 2011, 01:13PM

Registered Member #1221 Joined: Wed Jan 09 2008, 06:17PM
Location: Odense, Denmark
Posts: 196

Look at the lenses for some modern HMI "fresnel" lights, these can really do wonders to almost any light if you know what you're doing!

I abseloutely don't know what I'm doing, but I am hoping to improve on that.

Most carbon arc lamps run with just air at atmospheric pressure.

Yes, I have read a little about arc lamps, and this really sort of suprised me. Wouldn't there be synthesized alot of carbon oxides (CO2 or CO whichever is more favourable), I would think that the actual 'burning' of the electrodes in the air would significantly speed up the rate at which the electrodes are consumed?

An inert atmosphere such as the one I attempt to sustain in my device using argon, should limit the electrode losses to only vaporization as there is no oxygen to support combustion.
Maybe the atmospherfic designs are more effecient because they give off more light as the electrodes burn with the oxygen, but I like to be able to control the pressure so I am very please with my choice although it may not be the way it is usually done.

James

Mon Apr 18 2011, 08:51PM

Registered Member #3610 Joined: Thu Jan 13 2011, 03:29AM
Location: Seattle, WA
Posts: 506

The electrodes are consumed fairly quickly, as I recall they are enough for just a couple spools of film, A large duct connected to an exhaust fan extracts the vapors and provides cooling.

There are some old manuals for various cinema and stage equipment here

The one for the Peerless lamphouse like I was looking at is here

An inert atmosphere does prolong the life of the carbons, but this can be obtained just by restricting the flow of air into the lamphouse. The oxygen already in there is consumed by the arc, leaving a mix of inert gasses. This was used in a lot of the later carbon arc light fixtures used for streetlighting and interior illumination of department stores and such until they were replaced by incandescent lamps in the early 1900s.

Nah

Wed Apr 20 2011, 12:17AM

Registered Member #3567 Joined: Mon Jan 03 2011, 10:49PM
Location: USA, 1960s
Posts: 260

I think you have to look at it from cost.

Which costs less

1. Replacing giant pencil leads every week
2. Buying a vacuum pump, buying gas, makign sure there wans't an explosion because of the low preasure, and paying to keep the pump running.

GluD

Wed Apr 20 2011, 11:55AM

Registered Member #1221 Joined: Wed Jan 09 2008, 06:17PM
Location: Odense, Denmark
Posts: 196

I think you have to look at it from cost.

This is not a comercial venture, it is just me trying to amuse myself with various(perhaps over-complicated) devices. Being able to control the pressure significantly improves that in my opinion, and it is after all I whom shall be operation this thing

I already have the Argon and the vacuum pump, so it is only the useage that will cost me anything, wear and tear on the pump and of course some electricity and some Argon, but Argon barely cost anything at all. Although the bottle is rather expensive but as I said, I already have it.

I could also ask which cost less

Watch some lame show on TV like the rest of the country
or
Build something interesting and perhaps more complicated than it may have to be.
The easiest and cheapest is not always the best choice. It depends on what the purpose is, here the purpose is to amuse myself, and for that the TV just will not do.
I could also just draw arcs with two piece of carbon in air but that wont do either.

It is sort of like asking a guy who is building a huge DRSSTC why he didnt just make a small cheap SGTC instead.

Also now I come to think about it, being able to control the pressure could prove to be a significant advantage if I get serious with my optical experiements later on. I read in some of the papers James posted eariler that, on the old theatre equipment you had to adjust some chimney thingy until the arc stabilised. In my devices here I will 'adjust' the pressure, if nessecary, until the arc too are stabilised.

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