Introduction: Combining Three Strings of Ikea Skina LED Lights Into One Long String

By shrad.org (a general blog)
About: I'm an engineer and biologist in LA. I'm pretty chill.

My husband and I bought some Ikea string lights of the Skina variety, but found that each was too short on its own. The lights are adorable little dragonflies, but each string is only about 3 m. To drape from one end of our balcony to another I decided I wanted three times that. Unlike with most Christmas lights, these don't have a plug on the far end to daisy-chain them, but I suspected it wouldn't be hard to wire.

In truth, it was a bit trickier than I expected, but that still wasn't too bad. Ultimately, it took about two hours, and would be faster if I were following this guide.

The tricky part is that you can't wire the lights end-to-end: you need to splice them together about half way.

Why? we'll cover that in the next step.

Supplies

Materials

  • Skina LED light strings, 3x
  • Solder
  • Flux
  • Hot glue

Tools

  • Soldering iron
  • Craft knife
  • Third hand
  • Twist ties
  • LED, 1x
  • Multimeter (Optional)

Step 1: Arrange Your Light Strings

The first step is to arrange two light strings together in the orientation you want them. Untangle your lights and line them up the floor.

Once the two LED strings are laid out on the floor so that the first LED of the second string is appropriately spaced after the last of the first string, you'll need to find the point in the first string where you're going to splice in the second. Where? It might surprise you!

Step 2: Understand Where You Need to Splice

My first thought was that I could just splice one string to the end of the second. If we look at the circuit diagram, though, we can see why that's not possible.

Each string of 16 lights actually consists of two separate mini-strings of eight. Each mini-string of eight is wired in series, and contains eight LEDs that are powered by ~3 V. If these were all in series, the total required voltage across the full string of 16 would be ~48 V. Instead, by using two mini-strings of eight, the power supply just needs to supply 24 V.

This is why we can't splice to the end of the string: if we did, the whole second string would be in series with eight LEDs. This would split the voltage across eight LEDs before it reached the next full set. I didn't test this, but I suspect if I had, the first eight LEDs would be lit up and then the next eight and the 16 after would all be dark because they'd each only get ~2 V.

Fortunately, the solution is simple: just connect the second string up-stream of any LEDs in the first so that you have FOUR sets of eight in parallel. In the diagram above, if you connect the black wire of the second string anywhere along the black wire in the first and the red wire in the second string anywhere along the red in the first, then they should work.

Step 3: Finding the Physical Splice Point

So we understand that we need to wire in the very beginning of the second string up-stream of any lights in the first string. We could splice in near the power supply, or near the start of the lights. But we can actually reduce the amount of wires a bit by spicing between the eighth and ninth light.

It sounds a bit crazy until you look again at the diagram and compare it to the actual lights in real life.

If you look at each full string, it starts with two wires coming out of the power supply. We'll call this length that comes before the lights the extension wires. The two extension wires are a positive and a ground. Then, when it reaches the first light it separates into three. If you follow these to the second light, you'll see that one goes into the light and two bypass it. The wire going into the light is the wire that is connecting LEDs one and two in series. One of the wires bypassing is the ground. And the third wire is the positive wire that will bypass the first eight.

Once we get to the eighth LED, the diagram really starts to make sense. Only two wires continue on. Just like the two coming out of the power supply, one is a positive 24 V supply and the other is ground. The positive wire will go into the ninth LED and the ground will bypass it. The wire coming out of the ninth LED is connecting the anode of the ninth LED to the cathode of the tenth.

So this is why I made the splice between LEDs eight and nine: the circuit is the same here as if we connected right before the first LED or right at the base of the power supply. Anywhere along the red wire is the same, and anywhere along the black wire is the same.

So find the eighth LED in the first string. If the two strings are lined up how you want to attach them, this eighth LED is where you want to cut the extension wire of the second string. Then, twist the extension string around the LED wires of the first string and you'll be ready to strip the wires and splice the extension wires you just cut between LEDs eight and nine of the first string. I recommend using a twist tie to hold these wires together between the ninth and tenth lights.

You're now ready to strip the wires and join them.

Step 4: Strip Insulation and Match Wires

Before you strip, consider these two challenges:

  1. We don't want our splices to touch and short out the circuit.
  2. We need to make sure the positive wire from the second string is spliced to the positive of the first, and the negative of the second to the negative of the first.

Good news: this is very, very, easy.

To solve the first problem, splice at different positions so the two don't match up in length.

To solve the second, just strip each of the four wires, plug in the first string, and guess. There's only two possible combinations, so if the second string doesn't light, try it the other way. Now you know which wire goes to which.

A tip on stripping the first string

Stripping the ends of the second string is easy, but stripping the middle of a wire on the first string is a little harder. You have two options.

One option is to cut, strip the ends, and then solder in a little extension. This isn't hard, but I went with option two.

Option two is to secure each wire with a third hand, cut around the insulation without cutting the wires inside, and then cut along the length and use a pair of tweeters to pull the insulation off. This sounds harder than it is. I recommend this option.

Once all four wires are exposed move on to step five: twist, solder, and insulate.

Step 5: Twist Wire, Solder, and Insulate With Hot Glue

At this step, you should have two exposed wires between LEDs eight and nine of the first string, and the exposed ends of the extension wires of the second. You should plug in the first string and test that the second one lights up when you touch the positive to positive, negative to negative. If so, wrap the wires nice and tight. They shouldn't be able to contact if there is distance between the splice points.

Now solder them.

Once they were soldered I coated each splice in hot glue. I removed the wires from the third hand while the glue was still hot, and I twisted it all together. The hot glue insulated the wires all around (because I want this to stay weatherproof) and also firmly bound the two wires, making a very tidy splice.

Step 6: Conclusion

That's it. This instructional might sound like "Who's On First" if you're reading it without the Skina in front of you, but I think it makes sense when put into practice. You don't really even need to understand why this works if you follow the steps precisely. I did this twice to get a triple-length string, and it worked like a charm. That's it! Enjoy!

Also, if I'm way off on something, please comment and I'll fix it. Thanks.