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

http://www.diybanter.com/showthread.php?t=37812

... 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.

In article ,
dstromb wrote:
.. 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.

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 London SW
To e-mail, change noise into sound.

"dstromb" schreef in bericht
...

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

http://www.diybanter.com/showthread.php?t=37812

.. 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

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

"petrus bitbyter" writes:

"dstromb" schreef in bericht
...

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

http://www.diybanter.com/showthread.php?t=37812

.. 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

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.

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

http://members.misty.com/don/bulb1.html#wbs

--- sam | Sci.Electronics.Repair FAQ Mirror: http://repairfaq.ece.drexel.edu/
Repair | Main Table of Contents: http://repairfaq.ece.drexel.edu/REPAIR/
+Lasers | Sam's Laser FAQ: http://repairfaq.ece.drexel.edu/sam/lasersam.htm
| Mirror Sites: http://repairfaq.ece.drexel.edu/REPAIR/F_mirror.html

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.

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

wrote in message
oups.com...
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


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.