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Home made neon (or rather air) tubes with fridge comp.

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LAN_403

Zum Beispiel

Thu Oct 25 2007, 05:16PM

Registered Member #514 Joined: Sun Feb 11 2007, 12:27AM
Location: Somewhere in Pirkanmaa, Finland
Posts: 295

(I am posting this under gen. science because it deals with affordable vacuum pumps. If someone thinks it should be at high voltage or somewhere else, feel free to move it)

I did some cleaning around the lab and came accross this refrigerator compressor. I was going to use it as a crappy vacuum pump once, but never got round to it.

I was going to throw it away because it's damaged and makes a real loud sharp noise - one of the internal supports has fallen off. And I don't really need it anyway, as I have access to a proper vacuum pump. Here's the compressor.

I saw some clear tubing lying on the floor and then it hit me: Could a fridge compressor be used to pull a good enough vacuum to make some pretty plasma? I immediately put together a test setup. Please note all my super air tight connections :p.

Also notice the wonderful amprobe ammeter in the foreground. That thing is like 50 years old and still going strong!

So, to answer the question, yes, a fridge compressor can get a good enough vacuum to make some plasma, even in such a horribly sealed system.

Results:

And in the dark:

Power in these pictures is really low, only about 50V into the bridge. At higher powers the tube melts almost immediately.

Also, at higher powers, this happens:

Not good, at all :(

The tube was completely lit and bright but it arced just before the picture was taken :(

So, in conclusion, a fridge compressor, while usually regarded as kind of weak, can give some nice results. Not good for any serious work, but great for some plasma fun.

And the price is right too

Ps. I kinda worry about generating X-rays, though. There certainly is enough voltage to do it. The vacuum is so bad that I doubt it can generate any x-rays, but if anyone thinks different, I'd like to know!

Nik

Thu Oct 25 2007, 08:41PM

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

Thats impressive, you may have just spurred me into some fun with a VERY large glass jar I have.

uzzors2k

Thu Oct 25 2007, 08:55PM

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

Nice. Why don't you try evacuating a glass jar?

Zb wrote ...

Ps. I kinda worry about generating X-rays, though. There certainly is enough voltage to do it. The vacuum is so bad that I doubt it can generate any x-rays, but if anyone thinks different, I'd like to know!

Besides the vacuum being too low, there would need to be a target for the electrons to collide into. So no, don't worry about it. Even if it could, I doubt the x-rays would be more dangerous than normal background radiation.

Hazmatt_(The Underdog)

Thu Oct 25 2007, 11:25PM

Registered Member #135 Joined: Sat Feb 11 2006, 12:06AM
Location: Anywhere is fine
Posts: 1735

I've heard that 2 fridge compressor pumps in series can make a very effective vacuum pump.

If you do evacuate a glass jar that's not vacuum rated, make sure you take precautions againts implosion, like using wire mesh around the glass jar, staying behind plexiglass, using eye protection, etc.

Nik

Fri Oct 26 2007, 12:03AM

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

The glass i have in mind is 6 gallons and has ~1/8" - 1/4" glass at the thinest. I don't plan on taking it down into a heavy vacuum, just enough to get a good glow discharge from, a flyback or NST (rectified).

likewhat

Fri Oct 26 2007, 12:48AM

Account deactivated by user request on 6/11/2009.
Registered Member #1071 Joined: Fri Oct 19 2007, 02:13AM
Location:
Posts: 44

Here is a paschen curve for air

looks like around 200 mtorr is the easiest to break it down.

Wolfram

Fri Oct 26 2007, 09:47AM

Registered Member #33 Joined: Sat Feb 04 2006, 01:31PM
Location: Norway
Posts: 971

I've actually done the same lately, but with a dual stage rotary vane pump and glass tubing. It's quite entertaining. It's not too hard bending the glass into shapes, and I've made a few letters and short words. Right now I'm trying to get Neon, but Spectra Gases somehow don't seem to want to give me a price quote for neon.

I'll post a few pictures when I get back from England.

Dr. Slack

Fri Oct 26 2007, 11:55AM

Registered Member #72 Joined: Thu Feb 09 2006, 08:29AM
Location: UK St. Albans
Posts: 1659

The glass i have in mind is 6 gallons and has ~1/8" - 1/4" glass at the thinest. I don't plan on taking it down into a heavy vacuum, just enough to get a good glow discharge from, a flyback or NST (rectified).

As far as the strength of the glass is concerned, there is hardly any difference between a vacuum of 0.1 bar (still too soft for plasma fun) and 0bar (total (or heavy) vacuum), like 0.9bar versus 1 bar differential pressure. Even 1/4" sounds mighty thin for surrounding 6 gallons, unless it's been manufactured as a vacuum vessel. If it's been made as a liquid container, then you really need that mesh, and plexiglass shield, and the ABS glasses wouldn't go amiss as well.

Nik

Sun Dec 09 2007, 04:14PM

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

I found myself a fridge compressor and a suitable container that could stand up to the pressure in hopes that I could have some fun. The fridge compressor managed to lower the pressure enough for a 7kv(DC) source to strike an arc across a 1 1/2 inch gap which is far longer then it would be at regular pressure. I also managed to get some really good purple plasma "clouds" between the wires but they don't show in the video. The container is a steel bowl with a 1/4inch sheet of plastic over it.

(Sorry about the quality, the uncompressed version is 166mb and you can see much more detail)

*edit* I forgot to mention the powersupply is never turned off during the video only the compressor. The arc goes out when the pressure gets closer to normal.

Zum Beispiel

Sun Dec 09 2007, 05:04PM

Registered Member #514 Joined: Sun Feb 11 2007, 12:27AM
Location: Somewhere in Pirkanmaa, Finland
Posts: 295

Is the plexy just laid over the bowl with no gasket?

Try making it a bit more airtight... A good fridge comp can get pretty low... Getting to "plasma globe" pressures shouldn't be a problem.

Oh, these are fun things to play with

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