| Submitted by: | John Goldsmith (John.Goldsmith@AMOT.com) 12/17/2007 1:22:17 AM PT |
| Location: | Bury St. Edmunds, UK |
| Occupation: | Quality Engineer |
I worked in my father''s electrical shop (in the UK) at Xmas 1971 and I am sure the Xmas strings at that time used the self-shorting bulbs. As there were often long gaps between customers I used to do little repairs for customers like fixing light strings and extracting tights from vacuum cleaner hoses. The UK method of one bulb that does not short seems enough protection, but with a 240V supply I guess we have twice as many lamps to start with, so 1 or 2 failures does not have a big effect.<br><br>
For the shop window we used to wire 2 strings in series - it looked OK but never failed. <br><br>
I think lamps that fail ''over the summer'' actually fail when handled. New filaments are tough but prolonged running at high temperature causes the filament to go brittle - something to do with the crystal structure - and minor shaking causes breakage.
| Submitted by: | Don Johnson 12/19/2006 6:48:49 AM PT |
| Location: | MI |
| Occupation: | Electrical Engineer |
I have struggled with the "find the dead bulb" many times, and as an Engineer I have a hard time throwing away something which shouldn't be that hard to fix.<br><br>
This year I tried a new tester and so far it works great! I have a non-contact voltage tester. These are available in the electrical departments of most hardware stores for less than $10. They are used to detect live voltage in a household electrical box, so they are a handy tool to have available for home electrical work. You press a button and if 60hz voltage is detected near the tip of the tester it beeps.<br><br>
By placing the detector next to each bulb in a light string, you can detect if voltage is present at each bulb. As you move down the string, when you get to the point where you switch from present to not present, you have found the (or at least a) bad bulb.<br><br>
This seems to work very fast (just swipe the tester past each bulb and listen for the beep.)<br><br>
I have only used this a few times, but so far my results have been very satisfying.
<br><br>
Don
| Submitted by: | Rod Weeks (rweeks@mceinc.com) 12/13/2006 10:24:07 AM PT |
| Location: | Sacramento CA |
| Occupation: | RnD guy |
Nice detective work.
If you want to end the madness, try an LED string. No socketed lamps, no glass, no heat, and incredible color saturation. Most strings are made with heavier wire than the incandescents, so they last for many seasons, which keeps disposable crap out of the landfills.
Happy Holidays!
| Submitted by: | Peter Jones 12/8/2006 12:22:59 AM PT |
| Location: | Gloucestershire, England |
| Occupation: | Engineer |
In the UK this type of Christmas light string has one "fuse" lamp that is designed to blow at a higher current than normal. When several "normal" lamps are shorted due to filament failure the current through the string increase thus blowing the fuse lamp. The "fuse" lamp does not have the short circuit device in thus turning off the string, saving the remaining lamps and preventing a fire through overheating. The "fuse" lamp is usually identified by a white tip and is normally included in a replacement lamp set.
| Submitted by: | Bob Duet (robert.a.duet@medtronic.com) 12/7/2006 11:08:12 AM PT |
| Location: | Tempe, AZ |
| Occupation: | Sr. Test Engineer |
About Dan Strassberg's comment on tripping a circuit breaker if the filaments all burn out and the shunts take over: I've seen strings of light with a small fuse inside the AC plug. A small lid can be slid open and the fuse can be replaces. The light set mentioned in the aritcle should include a small fuse in the AC plug that should blow long before a breaker can trip. Most breakers for outlets are rated at 15 amps. 15 amps would fry the small gauge wire in a string of Christmas lights. A fuse in the AC plug is a must for safety reasons.
| Submitted by: | Dave Bell 12/17/2004 12:43:42 PM PT |
| Location: | Engineer |
Regarding odd lighting systems, when I was a kid, in the late 50's or so, the traffic signals in a neighboring small, northern California town used 130 V clear lamps. Run at 115 V, they would last virtually forever, but were still replaced as preventive maintenance, on a regular basis. My uncle, who was a local cop there, had several 2x2x3 foot boxes full of used lamps in his garage. They may not have been "pretty" , but their household was never lacking in lamps!
| Submitted by: | Jett Field 12/16/2004 2:14:34 PM PT |
| Location: | Roanoke VA |
| Occupation: | electrical engineer |
In regards to the light bulb string, I read an article in the paper about this recently. Yes, the shunt in the bulb is supposed to short out when the voltage goes high, but this does not always work. There is on the market now a new device to fix the entire string in such a situation without removing any bulbs. I don't recall the commercial name, but it is a piezo-electric device which sends a high voltage (>>170V) pulse into the dead bulb to weld the recalcitrant shunt. It functions like the spark generator on a gas grill. By the way, I have personally run partial strings of these bulbs at low voltage, and know that the shunt in a dead bulb will often fuse at just 12VDC. Obviously there must be a lot of variation in the bulbs on the market if some fuse at 12V but others can fail to fuse at 120VAC.
| Submitted by: | William Crawford (william.crawford@emersonnetworkpower.com) 12/16/2004 10:20:17 AM PT |
| Location: | Lorain, Ohio |
| Occupation: | Ssytems Engineer |
When I was stringing the lights on the tree this year, I noticed a bad light on the new string I had just pruchased. When I touched the socket, I noticed it was rather warm. After replacing the bulb, the socket cooled down. It sounds like there is a shunt built into the socket itself to keep the string acitve. But my concernhere is could this become a fisr hazard if too many lights go out?
| Submitted by: | Paul Roth 12/16/2004 9:34:45 AM PT |
| Location: | Illinois / Kentucky |
| Occupation: | Engineer |
Hey, that question about strands failing over the summer is a good one. All 4 "icicle" sets we 1st used last year have failed over the summer. There were a couple burned out bulbs in each set when we took them down, but I figured I'd take care of it during the usual necessary pre-Christmas fixes this year. Bad figuring!
We now have two sets with about half the bulbs working, and two sets with NONE working. I figured oxidation of contacts was to blame, but so far reseating of bulbs is not helping. This is really not worth the time to try and fix, but it does irk the "fix it man" whom I suspect lies in the heart of most engineers -- otherwise why would we even be talking about this? As far as how they do it so cheaply, I think the answer is "China!" Which may also explain the reliability...
Merry Christmas!
11/26/2009 4:59:56 AM PT
That is the reason why bulb sets have a 'fuse' bulb to prevent the current escalation melting the whole string - which in itself is a fire hazard.
So always ensure you have a fuse bulb fitted!