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Carbon Arc Lamp

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GluD

Thu Dec 30 2010, 10:38PM

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

Hello

In the chat I was encouraged to post of this old project of mine, I hope you guys wont be disapointed, its really not that impressive. I did not upload this in the first place because Im somewhat embarased how ugly it is, although it was great amusement to see it work.

First I want to say that it does not work anymore and I have somewhat taken it apart, mainly to have a look at the electrodes. Aperantly they have slightly evarporated due to the extremely high tempertures.

As you can see its a very crude and simpel construction, mostly made of what could be considered as "trash".

The three first pictures are a series I posted on a chemistry forum some time after I made it, first we see a general view up the set-up. Vacuum pump, the device itself, and the PSU. On the far left outside the picture was a large argon bottle of the kind welders use, which serves as my gas supply.

Then we have a look at the electrodes "warming" up, it starts as a short circuit and then I pull the switch from "ned" (down) to "op" (up), thus lowering or raising the upper electrode by means of a electromagnet.

Raising the electrode, obivously translate to drawing an arc. Which is exactly what happens. Its only a milimeter or two long, although it must have increased abit due to evaporation of electrode material.

Now a series of new pictures I just took:

A better view of the PSU, two rewound mots, a rectifier brick under the CPU cooling fan, two rifa caps rated for about 1000ÂµF at 500Volts, and an ampere meter from 0-100. The PSU can supply 80 volts open circuit, it drops to about 20 volts under load, and supply over a 100 amps (it went off the scale a few times). In use there is a clamp over each mot but I took them off and used elsewhere as the PSU is no longer in service.

Then we have a picture of the stationary electrode, not a very good picture but my camera wont take a better one. As you will notice the carbon stick is covered in "something", I think it is vaporized material from the insulator (made from nylon 66 if i remeber correctly).

And last we have a picture of the next and better (hopefully) version, it has unfortunately stalled because im awaiting some parts from my dad but hes too busy to make them. There will be alot of improvements on the new version.

I can provide a few more detials if there really is any interest. Most people seem to be interested in long relatively cold sparks. This project concerns very short and extremely hot arcs.

Ash Small

Thu Dec 30 2010, 11:22PM

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

It may not be 'High Voltage', GluD, but it is still 'High Power' (2kW).

This is, after all, how Buckyballs and Nanotubes were invented.

My particular reasons for being on this forum are related to power supplies for plasma/particle physics experiments.

I'm in the process of setting up a forum devoted to this, and I'd like to take this opportunity to point out that vacuum systems and HV isn't just about 'tubes'.

(I'm actually quite excited that super-conducting magnets are starting to become available on the 'surplus' market.)

Personally, I think the whole 'Itra-webby thing' is evolving and will grow to encompass new technologies as a matter of course.

(Maybe I shouldn't post after I've been drinking

)

GluD

Thu Dec 30 2010, 11:44PM

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

Be sure to give me a hint when you get that forum up.

Also I should point out this device was only thought as an experiment to see if I could actually do it, everyone I spoke to said it couldnt possiably work, and I had no degree and only a very modest knowledge of electronics, so obivously I didnt want to invest too much in it before I knew it would work and to know that required an experiment. Obivously its no where near the "quality" that some of the other members here make, but it did what I wanted and expected it to do. What else can one demand of his constructions.

The second version will be much more exciting and I'll probably make a better PSU for it too.
Just have to wait and see when my dad have time to make the last bits and pieces, I checked the market and I cant find anything similar so I dont really have any other options than to wait.

Mycologist

Fri Jan 21 2011, 11:16PM

Registered Member #2413 Joined: Sat Oct 03 2009, 08:27PM
Location: Essex, UK
Posts: 22

Well I think it's cool! You say you used argon gas in the chamber, but what kind of pressure did you need to keep the arc going?

GluD

Sat Jan 22 2011, 12:22AM

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

Hello Mycologist

I varied the pressure alot, it didnt really seem to matter much what the pressure was.
I tried to keep it in the lower end though as some of the construction is just glued together and I was afraid to blow some of the parts out if I applied too much pressure.

Most commonly I think it was about 0.6bar or 0.7bar.

I see I forgot to mention it above but I could actually only run it for very short periods of time because the big iron tube heated up rapidly, once I measured a temperature of ~60C on its outside surface and that was only after something like 10seconds of operation.

Mycologist

Sat Jan 22 2011, 07:54PM

Registered Member #2413 Joined: Sat Oct 03 2009, 08:27PM
Location: Essex, UK
Posts: 22

Oh right, that's pretty interesting see, I was always under the impression that the gas pressure would need to be really low, so I've put off ever trying to make anything like this because I don't have any kind of equipment to create a really strong vacuum. 0.6bar however would be feasible with something like a hand pump and a decent valve right?

GluD

Sat Jan 22 2011, 10:22PM

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

I have no experience with hand pumps, but 0.6bar is a pretty high pressure so I guess a simpel pump could do it.

You might get into trouble if you dont replace most of the air with something inert, like argon or other noble gasses, so I'd suggest you obtain a good pump.
If you just use air you'll probably get all sort of oxides, most would probably be gassous if you use carbon electrodes like I did. If you use metal electrodes, you'll get a huge nasty cloud of metal oxides.

If you dont care about the oxides and dont have a good pump, but have a way to get a higher voltage and still maintain a decent current, you could probably sustain an arc under a much higher pressure than my lousy re-wound mots could

Mycologist

Mon Jan 24 2011, 11:52PM

Registered Member #2413 Joined: Sat Oct 03 2009, 08:27PM
Location: Essex, UK
Posts: 22

Good point that, the argon may not need a very low pressure, but you need to get as much air out as you can first! D'oh! Time to go a hunting for a cheap vacuum pump...

Ash Small

Tue Jan 25 2011, 01:57AM

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

You can always purge with argon, as long as you have plenty to waste, although some form of vacuum pump would help. If it is not a very high vacuum pump you can always pump down as far as you can and then purge with argon, repeating the process a few times to flush out all the air.

steve516

Fri Apr 15 2011, 01:20AM

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

Not sure if this is useful info for anybody, but I loved this project post- I work in the film industry, and for the better part of film history, this is how films were lit on location and even in studio. You'd have a guy who's job it was to stand behind the light and move the electrodes together as they evaporated more and more. You would need significant ventilation at all locations, and heat was also a big issue. Following a realization that using these things to light red carpet events was just plain inefficient, they developed HMI's as a suitable replacement to carbon arcs- far more efficient, beautiful daylight- balance, and loads motet control. Also being an arc lamp the traditional magnetic ballasts for these things can be monsters- a 24kw HMI ballast can weigh over a hundred pounds. But the ballasts are absolutely the most robust electronic devices I've ever seen. I have a buddy who repairs the things and such and would love to get my hands on one some day to open up and play with.

Sorry, long first post- but I have to ask- what inspired you to build a carbon arc lamp?
Steve

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