12V UV Germicidal Light Bulb

A while ago I bought a pair of these 12V 3W UV-C light bulbs to use to build an EPROM eraser:

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SHORT STORY: ^^^^^^^^^^^^ One blew on 15VDC (did nothing on a lower voltage), the other blew on 12VAC (did nothing on 9VAC). How are you meant to power them?

LONG STORY: ^^^^^^^^^^^ In my ignorance, I assumed these would work like normal incandecent or halogen bulbs, so I mounted a bulb in a tin with a hole in one end covered in layers of hot glue to act as a hopefully eye-safe viewing window (I only view it indirectly as an added precaution). Then, unsure of whether the voltage specification was AC or DC (and frankly, assuming that it didn't matter), I slowly raised the DC voltage from my bench supply.

There was no light, and until I reached about 15VDC only a few tens of milliamps current. Then the current suddenly surged to amps (still no light) and even though I made a hasty attempt to cut the power, I found that one of the two vertically stretched filaments had blown.

DC clearly wasn't working out, so I tried AC, starting low with a 9VAC plugpack and the backup globe (multimeter in series to measure current). This gave me the same "no light, a few tens of milliamps" condition, so I moved up to a 12VAC plugpack (I don't have a variac unfortunately).

Now I finally got light and decent current (although around .6A of it, so more than 3 Watts). As it ran, the blue light got darker and apparantly less visible, seemingly as the globe warmed up. The current also slowly increased to .88A after two minutes, then dropped back to .81mA by 2m 30s with the light still looking good. But current rose again to .92A, then it seemed to go into thermal runaway at 3min 20 and rapidly spiked to over 1.2A before I could cut the power. Inspection revealed that one of the filaments had now blown in this bulb as well.

I tested one of the half blown bulbs on another 12VAC plugpack, this time only rated at 500mA instead of the 1.7A of the one I used before. I could fill a page with the weird behavior that it showed in regards to both light an current consumption, but the blue light never became very dark, and the data on two EPROMs I put in was unaffected (checksums matched) after forty minutes. Current varied between .25A and .4A during operation.

So I clearly don't know the right way to drive these bulbs. Does someone know how they're meant to be powered, or should I just give up and go with one of the flourescent UV bulbs (which are unfortunately awkwardly long for the small device I had in mind).

P.S. I know about the $20 EPROM erasers sold from China, but I have a strict policy of not buying mains powered devices direct from China. Especially devices that I'll be tempted to leave unattended during use.

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Reply to
Computer Nerd Kev
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Well the top url states 10-12vdc, did you try reversing the polarity ?

Reply to
Rheilly Phoull

I can't find it in the top link, but I notice now that when you select the "One Bulb" option on the other listing, the image that's shown does say "DC10-12V". I don't think I noticed that before.

I didn't make a note of trying that, but I tried just now with the half-blown bulb that still makes a fairly bright blue light on 12VAC (but doesn't erase EPROMS). At 11VDC there's no light with either polarity, except that I notice now a dim red glow which is presumably the filament getting hot.

The 11VDC current is now .24A, perhaps because some of the blown filament is shorting something, but the current is identical in either polarity.

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Reply to
Computer Nerd Kev

could someone get one working and see if it will cure loca glue?

Reply to
FMurtz

No LOCA glue here I'm afraid. From a breif search it looks like that glue uses longer wavelengths than the narrow UVC sort that EPROMs require. There might be easier sources of UV light that you could use (ebay listings seem to indicate that UV LEDs work).

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Reply to
Computer Nerd Kev

long for the small device I had in mind).

I've never considered how they work, I just assumed it was similar to a fluoro.

I've had one of those Chinese ones for years and it has worked flawlessly. I believe it was ex-university as it wasn't brand new but it was in excellent condition. Less than $20 at the time, so no regrets.

I bought a spare tube a few years ago but I'm still on the original one.

Reply to
Clocky

Most are, I understand that all fluorescent tubes produce UV light, but normally the white phosphorous coating on the inside of the glass blocks this (while also producing more generally useful wavelengths of light).

Halogen bulbs also produce UV, so I guessed that the bulbs in question were halogens that had been optimised for the purpose. Wrong entirely as it turns out.

I preferred them because they're smaller and looked to be simpler to rig up in a small device (and they still are, now that I know how).

Yeah, I don't doubt it (although I'm a little surprised that a university wouldn't have better standards). I just figure it's safer to have a blanket rule than try to work out exceptions.

Actually you'd have a hard time convincing me at the moment, because after getting the DIY EPROM eraser sort-of working, now my cheap Asian EPROM programmer is giving me trouble. You can't win...

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Reply to
Computer Nerd Kev

Dunno, they work well enough and it hasn't failed, that's a pretty high standard for Chinesium stuff.

I just figure it's safer

Heh ;-)

Which EPROM programmer do you have? My old faithful is an older Willem model 3.something or other. The only thing to fail was a transistor but that was probably my own fault and easily fixed.

Can't say it's great feature or quality wise, but it does the job quite reliably.

Reply to
Clocky

Well it's actually an old 80s programmer named "MEPX4" which connects to a PC ISA port. It reads fine, and I programmed a chip with it not long ago, but now it seems to just program the first byte (correctly) and then give up while claiming a verification error. The hardware looks pretty good, but the MSDOS software is pathetic (spelling errors and all). It might be that I've changed something about how I run the software (booted to real DOS from a floppy (a different floppy to before though, it just occoured to me... they're both MSDOS 5 though...)). I got it second-hand without documentation unfortunately.

I've been planning to build my own Willem programmer anyway because the software supports a lot of newer devices, in fact I've already made the PCB. The old one has the boast that it can program four chips at once though.

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Reply to
Computer Nerd Kev

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