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A brief exploration of three styles of wiring used in common low voltage light strings.
These circuits and repairs are only for the low voltage sets of lights that run from battery, solar, USB or plug in power supplies.
Note that for the two/three wire flashing/effects strings the circuitry is similar to the 3-wire strings, but with the LEDs alternating polarity along the string. If rejoining a damaged set then the incorrect polarity of the two LED wires will cause a colour change at that point in the string during flashing effects.
The difference in recording environment is a temporary thing due to catching covid right at the start of a short trip to Glasgow, that has turned into a much longer stay to comply with self isolation times.
I recovered quickly and the lat flow tests strip line faded fast, but I decided to play safe and extend my stay for as long as possible before travelling.
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This also keeps the channel independent of YouTube's advertising algorithms allowing it to be a bit more dangerous and naughty.

One of the things i get asked a lot round about the sort of winter season. The time that all this of ornamental lights come out is how to repair them when they've been either damaged through either cutting them to length or if a pet's at a nibble or something's got damaged in the wind outside and suddenly the whole string of lights just Stopped working even though you'd think it would work up to that point now. I want to point out that this is only relating to low voltage lights. It's not relating to 120 volt or 240 volt ones.

They follow different sets of rules, but let's take a look at a couple of sets. The first one i'll look at is a very classic little battery operated, set very pretty it's literally just two wires coming from the battery pack and it loops into each led they're. All hard in parallel - and it goes from one end to other - and you probably can't see it with this - set well, partly because they're not that bright, because i'm using rechargeable batteries, but the intensity will probably vary from one end to the other. The the green at this end of it will be slightly brighter than the green, the other end.

But to be honest, it's not that bad and the reason for that is due to the resistance along the run. I shall show you that in a doodle later, but the one advantage of this simple, parallel circuit is that you can literally, if i get a pair of snips, and i should just turn the power off briefly to this, you can cut the end off that making Sure the wires can't touch the end and only low voltage again, you can turn it on again and that section i've cut off is not going to affect the rest of the string. I've just cut that off and the rest of the string is lit. That would not happen with this set.

This very attractive set comes from a european seller called flying tiger and it's usb powered. Let me plug it in and show you it's approximately 250. I think uh does it say what it is on? It not really sure uh, but it is, i believe, 250 leds under quite a nice shade of white they're, not cold white uh, but they're, not super golden warm white they're, a fairly neutrally warmish white, it's very attractive, but the thing to know about this is that It's a very long string but they're all uniform intensity throughout the whole string. If this technique was used, where they're all just in parallel like this one, it would start off very bright at this end and it would get dimmer and dimmer as it went to the other end and the reason they are consistent is because there's a third wire.

If i unravel this third degree, let's say try and untwist a bit here, you will see that we've got the standard arrangement of the two wires looking through them all in parallel, but there's also this third wire going up to the other end. The third of our does two things: it feeds the set from the other end with one polarity. One priority is thread from this end. The other one is spread from the other.

I'll show you this in a moment how this works, but uh. It also acts effectively as a resistor. It adds to the resistance of the circuit, meaning that they kind of balance the length of the circuit to the set of five volts and the voltage drop across the leds. And it sort of averages out right say what i'm going to get a notepad and show you how this works.

One moment please regulars to the channel will notice that there's a very distinct difference to the sound and appearance. This is because i'm kind of trapped away from my usual workshop in glasgow at the moment due to unplanned pandemic type events. So this is the circuit diagram of the little sort of dollar storage type led lights, the poundland ones and we've got the battery supply at one end. Positive and negative feeding a parallel string with the leds across it and the wire does contribute to a fairly significant resistance.

So, technically speaking, this led here is going to see the most current, even though they're all well matched, but the one at the end is not going to see quite as much current, but will still be quite bright. And if you just chop through that set it doesn't matter too much, i mean it will increase the intensity of those a little bit, but it doesn't really matter that much because they are just a simple parallel circuit. However, the flank tiger ones are the three wire system, so here's the standard, parallel array, but the negative is fed from one end and the positive goes up that extra wire and feeds the other end. That wire adds an element of resistance into it, which is used to help limit the current, but also because of feeding one end uh with one priority in the other end of the other priority.

It means that for any given led in that circuit for say, for instance, this one at this extreme end the resistance, the wire resistance will be equal. It's this full length of wire through that led and then this fuel length of wire back, whereas the one at the very start of the set it's the resistance of this wire, then the resistance of all this wire and through and then back so no matter where, In that circuitry, you were to measure the current of an led you'll, see it's pretty much identical, because the resistance of the wire is equal for them all. But unfortunately, the downside to this is, if you decide to cut that to length, it has lots of knock-on effects. First of all, they're all going to stop working, not just a bit you've cut off, but the bit that's left is not going to work because now you've broken the positive connection to the end of the set to get this working again.

You're going to have to bridge you're going to have to find which one is running loose. You've got the the uh double string running through the leds themselves, but you've also got that loose wire. That runs up to the end that if you bear these three wires, you're going to have to find the one that's uh loose, which is the main feed up to the round and you're just gon na have to dab it briefly onto either of these. Whichever one lights, then that's the one you hook it to and that will restore it to normal operation, except if you've cut an awful lot off it.

There is a risk that uh, the combined resistance of the wires was needed. It's going to actually be a lot higher current through the leds and it could potentially increase the load on the power supply and increase the output from the leds. So it's something you have to keep in mind. Now there is another set of lights that operates at low voltage.

I shall go and grab them and show you them they're, very good, actually, really nice. One moment please so here it is: it came from the local asda and it's extremely attractive. It's 400 leds, but it's the copper wire led strings where it's well. Three copper wires in this instance, but two of them are just run in parallel with surface mount leds.

Soldered across them, and then they dip them in resin, but in this instance they've then slipped them into a very thin tube. So it makes virtually a little rope light, but it is so thin. It's the thinnest. I've seen it's really attractive.

It makes me wonder how on earth they get them in, but this is operated at 12 volts. Let me show you the power supply, so i'm just going to unplug this brighten it up and the power supply is one of these standard. Little christmas light power supplies. This is the uk version and it puts out 12 volts.

So let me grab the notepad and i'll show you the wiring of these lights and how to kind of fix them if they get damaged, but you're not going to be able to cut these ones to length. One moment i'm just going to grab the notepad. So in this instance to adapt to that voltage because it's easier when you've got such a long run of lights to use a higher voltage, they divide the string into sections and each of these three leds, there's 400 in the set. So each of these three leds would actually represent about 100, but they've got the four parallel sections.

Each one drops roughly three volts 12 volt supply. Three plus three plus three plus three makes it 12 volts, plus that long wire going up to the end actually has enough resistance to help regulate the current through them. Everything will be so balanced, it'll be down to the uh, the voltage they apply and the sort of wire they use. So this time the positive goes up to that end, to make sure that the intensity is even along the whole run, and it goes through this parallel circuit, which then is in series with this parallel circuit, which is in series.

This parallel circuit in the series with that one back to the negative, and it means that the string can be implemented just as these four sections to make up that higher voltage. It's a very neat arrangement, but the downside is, if you try cutting it again. Oh dear, that's going to be a bit of a disaster because if you try just bridging over from there to there, that's going to turn this into roughly three sections of three volts: nine volts, which uh is going to result in a much higher current flow. And it's going to damage the leds so in this instance, if you damage a set like this you're going to have to work out how they were wired, hopefully, if depending where you broke them and you've got the one wire going all the way through and then You've got the little parallel circuit and you can work out which is which rejoin the wire going through, keep in mind that this enameled wire has well enamel on it.

So you're going to have to scrape that off or burn it off the lighter and twist them together or solder them and tape them up. Well, keep in mind this is low voltage again, don't do this with meaningful mains voltage sets, but then once you've done, that you've got the other two wires and they'll only work one way round, because the polarity has to be correct. So it's a sort of thing that trial and error once you've worked out, which one goes up to the end, repair that one and then the other two try them around. One way keep in mind: you'll have to remove the insulation off them, even though it's virtually invisible, it's literally just a thin layer of lacquer, but you're going to have to try either way round.

When you get it the right way, it will suddenly work, but when you're testing it just apply the power briefly because uh, if you don't do that and you're shorting things out, it can actually make the other ones lighter much higher current and if you leave it On too long it could damage them, but that's it i'm going to show you those uh, that's a rope, light again before i finish this video because it is very attractive. Asda has been doing this in warm white. I don't know sure if they didn't cold white, but they also have the color version. This is the color which actually, instead of using yellow they've, got the blue red green, but they've got the warm white instead of the yellow.

I kind of prefer this of orangey or yellow when they're actually doing that, but i wonder how they got this in here. The spacing of the leds is very close. It's very reminiscent of traditional rope, light that would use in municipal christmas lights, and but you can't cut this one to length. It is basically the 400 led section is like that's it.

You don't get to chop that or it causes problems. But it's very neat. It's a long run uh. It makes me wonder how long it well how easy it is for them to get the sort of like the circuit in this.

But if you look closely at this - and you won't really be able to see it there, but you'll see, there's three wires, there's the two wires going up among past leds and then just that extra wire that goes to other end and feeds at the other end. Right where the cap is, but it's very nice set uh very time to get more of those and they're attractive, or would that just be hoarding lights? It would be hoarding lights, wouldn't it, but there we go. That's how to fix your of your standard, low voltage, strings um some are fixable. Some are not um but uh.

I'd say something worth noting. I recommend, in these days with the availability of led strings operate. Low voltage, particularly if pets are going to have nibbles or kids are going to play with lights, always go for the low voltage lights because, ultimately, it's much safer.

14 thoughts on “How to fix your low voltage led christmas lights”
  1. Avataaar/Circle Created with python_avatars Jon [0ryn] Westgate says:

    We have a set of lights where there are 600 LEDs and they are colour changing. Each lamp can be ether warm white or a primary colour or both which gives a lovely pastel effect. You can also select fade from colour to white and back. They have 3 wires but as I can see strobing I suspect uses AC to select between white or primary colour. I tried shortening them with the result of only seeing the blue LED's light dimly. I reconnected the wires and hid the the 300 extra LED's under the sofa.

  2. Avataaar/Circle Created with python_avatars deslomeslager says:

    I have one of the original versions (with bulbs in it). Horrible: it uses 100 Watts to light about 3 meter. I replaced it with an LED version, how ever it is not as bright (by far). But it does to the fading, chasing and other flashing animations, I love those!

  3. Avataaar/Circle Created with python_avatars g max says:

    Great video again!!! I have a 100 led string where the controller box (sets different lighting patterns} which runs on 3AA batteries has failed. i would like to by pass the controller box and just run direct from the battery pack and eventually from usb psu …. only trouble is i cant figure out the polarity is the long 'resistance wire' always pos??? any tips on how i can figure out this conundrum .. Thanks in advance … be great to have them working before Christmas…

  4. Avataaar/Circle Created with python_avatars Richard Barber says:

    Not related.. but maybe.
    I have about 16 LED lights in the barn.They were installed as a power saver by our power company and an unusual design being in the conventional bulb form but divided into 3 segments. After 5 years operation the two pairs, the rest are in long strings, have decided to interfere with each other, alternately on and off. Replacing one of a pair with a conventional bulb sorts it. What are your thoughts on the issue?

  5. Avataaar/Circle Created with python_avatars ManWithBeard1990 says:

    My best guess for how the ropelight could be made is that the light string would be blown through it with compressed air. It's also possible that the tube is extruded around it and the light string is fed through a hollow mandrel. I don't think they're feeding it through by hand. That'd be too fiddly I think.

  6. Avataaar/Circle Created with python_avatars Robin Browne says:

    "Who put those horrible flashing Christmas lights outside the window.  They're keeping me awake all night."   "It's Grandpa. He got his new emergency flashers."

      \ | /
      / | \

    Merry Christmas, Big Clive
    from everyone.

    @:-)  Mother robot

    #:o]  Father robot

    &:-)  Big sister robot

    #:-]  Little brother robot

    @8-}  Grandma robot

    €:-]  Robot repair man

  7. Avataaar/Circle Created with python_avatars webchimp says:

    Getting those copper wire LED stings into some of tube is a pain.
    After many attempts using different methods, I managed to suck a thin bit of cotton trough a one meter tube. Then tried pulling them trough, the cotton snapped.
    Then I did it again and first pulled a thicker cotton trough, then the LEDs.
    Took about a month of trying things dumping them in a box for a while out of frustration.

  8. Avataaar/Circle Created with python_avatars mike hughes says:

    Bollocks to all this, I'm getting my Mum's old German Cristmas Tree 'Lights' out. They are a box of little metal Candle Holders, with a sort of 'clothes peg' thingy on the bottom. You can shorten the 'string' of lights as much as you want, without any tools or schematic. They are very practical and good for the environment, because they ensure job creation within the fire service.

  9. Avataaar/Circle Created with python_avatars William Hada says:

    I'm just guessing but I think that they get those strip LEDs into the plastic tubing by continuous extrusion. In other words the LED light strip is fed into the center of the extruder die and the plastic is extruded around it just like feeding of bare copper wire into an an extruder when putting on plastic insulation.

  10. Avataaar/Circle Created with python_avatars Paweł Baran says:

    I love converting those battery powered lights to USB. I just get an old USB cable and solder it inside the battery box with some little resistor (choose resistance calculating on how much batteries the set requiers). You can even solder to the switch (if it has two positions) so you can choose between batteries and USB dynamically. This season I added USB feature to 3 of those sets

  11. Avataaar/Circle Created with python_avatars RoterFruchtZwerg says:

    So, I have a solar powered LED string with simple parallel arrangement and interestingly it acts quite the opposite. When the battery gets low, the far end of the string is actually brighter than the near end. Guess this is due to the boost converter frequency and reflections in the string? 🤔

  12. Avataaar/Circle Created with python_avatars Ian Rolfe says:

    I was somewhat inspired by you this year to make my own string of LED lights, I used colour changing LEDs each with a 180 ohm resistor and twisted together some 7/0.2 wire to wire them all in paralell. I 3D printed a little seperator so the LED wires wouldn't short when you heat-shrinked over the connections and resistor, then 3D printed some christmassy shapes that I glued over the LEDs to make them interesting. I was going to use your LED covers you put on a video ages ago, but in the end spent some time in OpenSCAD designing Christmas trees, parcels, snowmen and Christmas Sloths (long story!) instead. I only made 24 lights in the string but may well extend them for next year, although I only have a small room 😀

  13. Avataaar/Circle Created with python_avatars gwc1410 says:

    Merry Christmas Clive.

    Glad your feeling well enough to make a video.

    I recently saw some very small LED lights on a pre-lit tree at a local store. The LEDs were the size of a small grain of rice, very nice.

  14. Avataaar/Circle Created with python_avatars Heather Nute says:

    Nice to know 🙂 i will check my new lights since I have two cats now, Want to send you at some point some golf ball bulbs with ‘Samsung’ LEDS guaranteed for 5 years -several of which failed shortly into their first year in my lamps, now looking for decent replacements e14 leds with min 470lm 3000k (as only have 4 wall lights lighting long lounge outside of Xmas :)) if you have any recommendations?

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