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Can a flash tube light continuously?

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LAN_403

Plasmaarc452

Sat Mar 22 2008, 04:23AM

Registered Member #1394 Joined: Sun Mar 16 2008, 06:18PM
Location:
Posts: 111

I have wanted to know this for some time, i mean they are REALLY bright when they are flashed but if they were on all the time it would be like a flashlight from hell.

I know that it takes a lot of power to light it for a millisecond but suppose i had an unlimited power source capable of providing that amount of power continuously.

It might sound like a dumb question but this it would be really cool if it is possible for projects ect...

ShawnLG

Sat Mar 22 2008, 05:44AM

Registered Member #286 Joined: Mon Mar 06 2006, 04:52AM
Location:
Posts: 399

They would explode when run continuously like that.

"I know that it takes a lot of power to light it for a millisecond"

Some of that power is dissapated as heat in the tube. Integrate that power for a longer period of time than a millisecond and you will see why it is not possible.

Nik

Sat Mar 22 2008, 05:49AM

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

I wonder if it would be possible to water cool the tube for continious use. It would make focusing the light a lot harder but just for the take of trying it would be interesting.

flannelhead

Sat Mar 22 2008, 06:27AM

Registered Member #952 Joined: Mon Aug 13 2007, 11:07AM
Location: Finland
Posts: 388

Heh...
I put a small disposable camera flash tube on my small TC. Very nice effects, but it got too hot to touch in 15 seconds. So the heating will be a big problem!

In the other hand, I managed to light one continuously with my small CW, but I used a 10M limiting resistor...

Proud Mary

Sat Mar 22 2008, 09:26AM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

Unlike conduction is metals, where resistance rises as temperature increases, resistance actually falls once an ionized gas has started to conduct, so that more current flows, heating the gas still further. Thus the ionized gas behaves as a negative resistance.

This is why ordinary mercury vapour fluorescent lights need ballast - a resistor in its simplest form, or an inductor - to keep them within their safe operating area - to prevent thermal runaway that would very quickly destroy the tube.

The camera flash tube is best considered as a switch or gas relay. When it is OFF, its resistance is very high in the gigohm range. Once the tube has been triggered ON, the gas starts conducting and heats up so its resistance falls very rapidly to a low value, perhaps 100 milliohm. A very large current is able to flow from the capacitor very quickly in a short pulse.

Bored Chemist

Sat Mar 22 2008, 09:54AM

Registered Member #193 Joined: Fri Feb 17 2006, 07:04AM
Location: sheffield
Posts: 1022

You can run these tubes continuously. I've done it, but you need a balast resistor ( as Harry said) I think there's someone on this site who uses such a tube as an avatar.

Tesladownunder

Sat Mar 22 2008, 12:43PM

Registered Member #10 Joined: Thu Feb 02 2006, 09:45AM
Location: Bunbury, Australia
Posts: 1424

I've done some pictures just for you.

Here is a strobe light tube running on DC through a 100k resistor. Self triggered at 5kV then dropped to about 240 V across it at 9 mA.

Second photo is with the camera moving to show the near constant output with only a little ripple. Third photo shows the effect of a NIB magnet like in the avatar mentioned before.

Helium Neon lasers are a bit similar with a negative resistance region. They use a 70K resistor in series to keep it in the positive range otherwise it will turn on and off like a relaxation oscillator.

TDU

1206189244 10 FT41613 Flashtubestrobedcblur

1206189244 10 FT41613 Flashtubestrobedcmagnet

lpfthings

Sat Mar 22 2008, 02:17PM

Registered Member #1361 Joined: Thu Feb 28 2008, 10:57AM
Location: Cairns, Australia
Posts: 305

I know you can send HV through them continously, like TDU has done above, but having it continously "flashing" isnt really possible without some major cooling issues.

...

Sat Mar 22 2008, 02:22PM

Registered Member #56 Joined: Thu Feb 09 2006, 05:02AM
Location: Southern Califorina, USA
Posts: 2445

Those 10w horseshoe tubes can be submerged under water (as long as you leave the electrodes exposed you do not need to worry about the normal problems associated with hv and water cooling) and be run with about 100w average power. Unfortunately at this region the efficiency of the tube is quite poor and I would estimate <10w optical power out.

Ken M.

Sat Mar 22 2008, 02:22PM

Registered Member #618 Joined: Sat Mar 31 2007, 04:15AM
Location: Us-Great Lakes
Posts: 628

If cooling is an issue with continuos operation, and since water conducts, perhaps use a container of clear oil and maybe place some AL foil on 1/2 the oil filled container.

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