1. Home
  2. Electronics Repair
  3. how can a light bulb become a short circuit?

how can a light bulb become a short circuit?

I was doing a search of diybanter when trying to figure out how to fix a touch lamp, and found this thread:

formatting link

.. where someone claimed it's possible for a light bulb to become a momentary short circuit while it's burning out. This sounds crazy to me, but in the lamp I'm looking at, the triac is shorted and a trace running between it and a wire that goes to the bulb is vaporized on the circuit board. Only thing I can think of to cause that would be a short on the bulb side of the trace.

So, on that basis I guess it must be possible for a light bulb to generate a short. But I can't understand it at all. Can anyone explain how it happens? A little arc as the filament opens would make sense, but that's not the same thing.

I've ordered a replacement triac and will repair the trace - I'm guessing that will fix it, I don't find anything else that tests bad.

--
dstromb
Reply to
dstromb
Loading thread data ...

Yup - it's common enough. They often have internal fuses, but will still trip an MCB or blow up a dimmer - most of which have pretty inadequate triacs anyway.

Think what happens is the filament supports are under spring tension. When the hot filament fails through burning out they move and short.

--
*I got a sweater for Christmas. I really wanted a screamer or a moaner*

    Dave Plowman        dave@davenoise.co.uk           London SW
                  To e-mail, change noise into sound.
Reply to
Dave Plowman (News)

"dstromb" schreef in bericht news: snipped-for-privacy@news.diybanter.com...

Happens most of the time with bulbs mounted in some atmospheric lighting. Bulbs that do not hang from the ceiling when they go, may have flying around some pieces of the defective wire that temporarely makes a short. Quality of the bulb is also an issue here. Ever bought four lamps that had bulbs with build in reflecting mirrors. They lived pretty short and all of them blew a

16A fuse when they went. The replacement bulbs never gave that problem. The internal wires were insulated in the glass over a much longer length. Maybe there were some other differences too.

petrus bitbyter

Reply to
petrus bitbyter

While the filament parts flying is one possibility, one that is also likely or more likely is described here:

formatting link

--- sam | Sci.Electronics.Repair FAQ Mirror:

formatting link
Repair | Main Table of Contents:
formatting link

+Lasers | Sam's Laser FAQ:
formatting link
| Mirror Sites:
formatting link

Note: These links are hopefully temporary until we can sort out the excessive traffic on Repairfaq.org.

Important: Anything sent to the email address in the message header above is ignored unless my full name is included in the subject line. Or, you can contact me via the Feedback Form in the FAQs.

Reply to
Sam Goldwasser

On top of all the other possibilities mentioned, the wires and supports all emanate from a relatively small area. The hot and nuetral are not that far. If burning base down it is quite possible for a small part of the filament to break off and directly short those outer wires.

JURB

Reply to
ZZactly

Possible yes, but in the vast majority of cases, an arc is struck in the argon fill gas, it melts the ends of the lead-in wires right off. An arc is low impedance which gets lower the hotter it gets, exactly the reason a discharge lamp requires a ballast.

Reply to
James Sweet

ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.