I've worked on a lot of the old incandescent christmas light sets and they are pretty straight forward in how they work, even if the series wiring can be a big PITA to find the bad bulb.
In 2009 I bought a christmas display (after christmas), which was a costly display, but they had it marked down after Christmas. I used it in 2010, for a couple weeks. This year I put it on the lawn last week and it worked fine.
Today I noticed that half the display is not lighting. Of course this is after dark so it's kind of hard to see what is going on with the wiring. However, I noticed that there are just two wires to each socket, thus telling me they are wired in series.
I have a good understanding of electronics, but this is the first string of LEDs that has failed on me. All of a sudden I'm looking at this light string and wondering how they work.
I know LEDs are run on DC and each LED requires a resistor. Well, this set is plugged into an AC 120v outlet. The plug has fuses, but since half the string works, I know the fuses are ok. But this is where I get confused. If this string is DC, where the heck are the diodes to convert the AC to DC. I doubt they are in the small plug which barely has the room for those fuses. Plus, a regular AC to DC power supply has filter capacitors. Maybe these LEDs dont need the capacitor?????
Then, where are the resistors for each bulb? Or are they built right into the LEDs on these christmas lights? On top of that, I never knew they were series wired, so one bad bulb knocks out half or the whole string. [that sucks]. (I proved that on a spare string I have, by pulling out one LED, half the string went off).
Also on this display I notice there are molded sections about 3/8" thick and 2 inches long in a few places in the string. What are these? Are they fusible links (which cant be replaced), are they the location of the diodes to convert the AC to DC, or simply connections to connect the different segments of the string? A schematic sure would be nice right about now!!!
This display is a bit to large to bring in the house and I did not feel like being outdoors in the dark and cold trying to trace the wiring. I had no idea that they were wired so when one bulb died a whole segment of the string went out. Nor did I expect that a string of LEDs would burn out after only 3 weeks to total use, knowing LEDs are supposed to last for many thousands of hours. (Of course anything can fail, and christmas lights are mass produced as cheaply as possible).
I'm suspecting there is one bad LED, but I have no spares, so I'll have to buy some tomorrow. I could take a bulb out of my spare string, but that brings up a whole other question.
My display has white LEDs, whereas my spare string is multicolor. I know that white LEDs operate at a higher voltage than red yellow, etc. and blue and green are slightly higher in voltage. Thus none of the multicolor bulbs would be suitable as replacements for the white LEDs on my display.
Yet, this still brings up more of a puzzle. My multicolor spare string has red, yellow, green, and blue LEDs. Since these different colors require different voltages, how can they all be run on the same string?
A string of LEDs seems so simple, or so I thought until I began to try to fix this one.....
Now I wish I could find one single socket to make a LED bulb tester to hook to the ohm scale on my multimeter. I sure hate to cut up a whole working set to get one socket.....
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Totally off the topic, but worth a laugh. I saw a set of christmas lights in a store that said on the box "FOR INDOOR OR OUTDOOR USE ONLY" Ummmmmmm, why is the word "ONLY" used? Is there a third option? :)