can you reevacuate a light bulb? - Page 1
Forum section: electronics / projects

author: coppercone2
author_rank: Super Contributor
timestamp: September 28, 2024, 06:42:48 am
content: If I wanted to take the filament out of a light bulb and put it in another container, assuming I got the proper atmosphere, would it be OK?I am also wondering if its OK to put it in a thick acrylic tube that is sealed up. It says its only 0.7ATMIt would be for intermittent use, I think it would take a while for it to get hotThe idea was a 'singular' inrush current limiter that is controlled by a rotary switch kinda like a rheostat to adjust the resistance. for funtapped light bulb

author: Bryn
author_rank: Regular Contributor
timestamp: September 28, 2024, 07:11:38 am
content: The first thing you asked about isn't really advisable to do, as the filament of a light bulb is designed for a specific environment.For the second thing asked about, while this may protect it from immediate exposure to air (and reduce the likelihood of oxidisation), it would easily break because it's so fragile.So really, both things are not really practical and you shouldn't really attempt to do them...

author: coppercone2
author_rank: Super Contributor
timestamp: September 28, 2024, 07:15:14 am
content: Well I meant the whole assembly to the stem, not cutting off the spring.I think you can arrange a bunch of them in some circle shape to make a tapped light bulb for inrush limiting purposesI found a large glass tube actually, I think an indium seal can be made (low effort low cost project)its not supposed to really shine, if it glows you turn it off. I even thought a LDR can be used to turn it off if there is a high current condition so it does not melt down

author: Gyro
author_rank: Super Contributor
timestamp: September 28, 2024, 10:17:27 am
content: Modern (if you can call them modern now) filament lamps use a low pressure Argon filling, not vacuum.

author: MK14
author_rank: Super Contributor
timestamp: September 28, 2024, 10:43:06 am
content: Quote from: coppercone2 on September 28, 2024, 06:42:48 amI'd suggest, getting a (cheap) pack of perhaps x10 12 volt (or different voltage) possibly automotive, (somewhat small) bulbs, of suitable wattage.Then stringing them together, in series, so you can choose which tap you want.The raw bulb filaments, are (as I understand it, but I could be wrong), extremely weak and fragile (without the intricate supports, built into bulbs, at various points), so I doubt you would have much luck, trying to solder (or other methods) to them.If you insist on going that route, then perhaps use some kind of resistance wire. There are a number of types.You could use 1.5V, 3V, 6V, 12V, 24V, 48V, bulbs, with (binary like) switches, to enable a wide variety of voltage settings.

author: Xena E
author_rank: Frequent Contributor
timestamp: September 28, 2024, 01:12:11 pm
content: There's no real need for pumping down to vacuum, you're not making an electron tube. For your suggested method of use you just need to exclude oxygen.(OK if the filament doesn't get too hot.)That can be done by displacement with another gas, or just burning it off!For a limiter, standard mains lamps are best, chosen for the greatest cold/hot resistance variation, run in series and parallel to achieve the best effect, (leave them intact).The ultimate is the iron filament in hydrogen barretter.Good luck creating one of those!

author: Kim Christensen
author_rank: Super Contributor
timestamp: September 28, 2024, 03:53:37 pm
content: Not sure how many taps you need, but a tri-light type bulb can give you 3 series resistance values in a single bulb. (filament A, filament B, Filament A&B in parallel)Or a single tap between the two filaments if you wire it differently.For lower voltages you could use an old automotive tail light bulb with the two filaments in the same manner.But as already mentioned, if you want more taps, then simply a string of lower voltage bulbs in series makes the most practical sense.For pure interest sake, many DIY vacuum tubes have been made with repurposed lightbulb filaments. But it's finicky stuff.

author: m98
author_rank: Frequent Contributor
timestamp: September 28, 2024, 05:53:54 pm
content: Should work perfectly fine, did that quite often to create cheap cathodes in a vacuum chamber. The lifetime of the filament is quite short in vacuum, you really should evacuate the tube, fill with argon or nitrogen, do that 1-2 times to flush out the residual oxygen, and then leave it at ~700 mbar.

author: coppercone2
author_rank: Super Contributor
timestamp: September 29, 2024, 09:17:10 pm
content: I am thinking about how many taps. would be cool for a adjustable variable dim bulb limiter. A 400W one with 25 W taps might be feasible to put in this large tube I have (I think its glass pipe from a dairy factory).

author: coppercone2
author_rank: Super Contributor
timestamp: September 30, 2024, 02:16:14 am
content: and a mini one with 5W bulbs and 50W max. THen a micro one with 1W bulbs 10W max. Then you can dial a precise current limit to the watt you want. I wonder what it would do for repair of shitty circuits.

author: CatalinaWOW
author_rank: Super Contributor
timestamp: September 30, 2024, 03:58:34 am
content: Or with a similar amount of effort hook up a set of saturable transformers so you can gang them in as current needs increase.You can put the filament version in a wooden box as long as you keep bleeding in Argon during use and during a prep period (think of the prep for a deep sea dive where you purge nitrogen from your blood). A welding tank should last for years of normal troubleshooting activity.I've not actually measured it, but the heavy duty coils used in portable room heaters should have non-linear resistance also, and are robust enough to operate for long times in air.Lots of ways to kluge together something along the lines you are looking for, though your approach would give more visual effects than most.

author: MK14
author_rank: Super Contributor
timestamp: September 30, 2024, 04:14:50 am
content: Quote from: CatalinaWOW on September 30, 2024, 03:58:34 amI think they use special alloys, to give a relatively stable resistance, despite big changes in temperature. Otherwise, assuming the heater is somewhat close to the main fuse(s) ratings, wiring and socket current limits. It would tend to overload the fuses, wires and sockets, during initial heating, with corresponding risks of blowing fuses, etc.E.g. Nichrome wire, which has a relatively small change in resistance with temperature.https://en.wikipedia.org/wiki/Nichrome

author: coppercone2
author_rank: Super Contributor
timestamp: September 30, 2024, 04:39:36 am
content: well I am havin trouble attaching indium tin to anything other then the crucible it was melted in. It reminds me of aluminum soldering. I can't seem to do anything in the shop other then drill holes good lolall these processes that always fail for me have to do with "cleanlyness" I guess it means im a mega dirty bastard

author: BrianHG
author_rank: Super Contributor
timestamp: September 30, 2024, 04:52:39 am
content: Nile Red beat you to it. And you do not need a vacuum, see here:https://www.youtube.com/shorts/aFJ1ThX8XHU