12V UV Germicidal Light Bulb

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A while ago I bought a pair of these 12V 3W UV-C light bulbs to use to
build an EPROM eraser:
https://www.aliexpress.com/item/3W-E17-UV-Germicidal-Light-Bulb-Intermediate-3-Watt-UV-C-Replacement-Bulb-for-GG1000-1100/32665735988.html
- http://tinyurl.com/h45emmj

There are more details in this listing:
https://www.aliexpress.com/item/3-Watt-UV-E17-Replacement-bulb-UV-C-Replacement-Bulb-for-GG1000-1100-Air-Sanitizers/32665910312.html
- http://tinyurl.com/m5rqmg9

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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Re: 12V UV Germicidal Light Bulb
On 6/5/17 9:31 am, Computer Nerd Kev wrote:
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Well the top url states 10-12vdc, did you try reversing the polarity ?

Re: 12V UV Germicidal Light Bulb
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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.

Quoted text here. Click to load it

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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Re: 12V UV Germicidal Light Bulb
Computer Nerd Kev wrote:
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  could someone get one working and see if it will cure loca glue?

Re: 12V UV Germicidal Light Bulb
On 06 May 2017, FMurtz wrote:

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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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Re: 12V UV Germicidal Light Bulb
On 6/05/2017 9:31 AM, Computer Nerd Kev wrote:
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<snip long short story>

long for the small device I had in mind).
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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.

Re: 12V UV Germicidal Light Bulb
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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).

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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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Re: 12V UV Germicidal Light Bulb
On 9/05/2017 6:39 AM, Computer Nerd Kev wrote:
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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
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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.

Re: 12V UV Germicidal Light Bulb
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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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