HowTo: Electronics – Build waterproof 12V fairy lights yourself

For a camping trip I was looking for a cheap and bright fairy light.

This should be waterproof and bright enough to illuminate the tent properly. It would be perfect if the brightness could be adjusted.

Since I didn’t find any of the existing fairy lights really fitting, I started to “develop” my own fairy lights. This consists of 12V LED strips and can be set up so that the individual elements are waterproof. Its brightness can also be adjusted with a suitable adapter. In addition, magnets are built into the LED elements so that they can be attached to metallic surfaces.

Everything you need to know to build your own fairy lights is described in the following article.

Safety instructions

I know the following hints are always a bit annoying and seem unnecessary. But unfortunately, many people who knew it "better" from carelessness lost their eyes, fingers or other things or hurt themselves. In comparison, a loss of data is almost not worth mentioning, but even these can be really annoying. Therefore, please take five minutes to read the safety instructions. Even the coolest project is worth no injury or other annoyance.

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For the build you have to master soldering tasks. The following articles provide tips on how to do this.

Required tools:

Required material:

Collect the parts you need

Before you can start with the construction, you should collect the required parts. The parts listed below are required to assemble one LED element. So remember to multiply the parts by the number of LED elements you want.

For example, I used ten LED elements for my light chain.

To build an LED element you need the following parts.

  • Two pieces of twin line e.g. 50cm long (the length of the pieces corresponds to the distance between the LED elements)
  • two neodymium magnetic disks with 8mm diameter and 3mm height
  • the two 3D printed housing parts of the LED element
  • 2x M3x8mm countersunk head screw
  • 2x M3 nut
  • 1x LED strip 12V 20cm long

The required STL files can be found under the following link in the Nerdiy-Git

How you can download files from a Git repository is described in the article GitHub – How to copy files from a Git repository to my computer

It is important that you pay attention to the following criteria when choosing the connection cable.

  • The cross-section or diameter should be as large as possible, but at the same time no more than 2mm (diameter).
  • It is best to use a twin line, i.e. a line that contains two lines. So the “cable clutter” is limited later. 🙂

The diameter of a single line should be a maximum of 2mm.

Prepare the LED element

To make soldering the LED strip easier later, you should first make a few preparations.

To make threading in the cables easier, it is helpful to drill the corresponding holes in the 3D printed housing parts with a 2.0 or 2.1mm drill.

The lines should then be easier to thread in.

Then insert the cables of the first piece of twin cable into the holes you just drilled out as shown.

And repeat this step for the other side with the other piece of twin line.

If the individual lines are color-coded, make sure that you have drawn the same line into the holes opposite each other.

Once you have inserted both ends of the line, it should look something like this.

Connection of the LED strip

You now have to fold the maximum 20cm long LED strip …

… in the middle.

The fold should go exactly through the contact areas.

You can now tin these contact surfaces with some solder as shown. This makes it easier to solder the connection cables later.

Repeat this too …

… for the opposite contact points.

Soldering the LED strip

The prepared LED strips are now soldered to the already prepared lines in the housing of the LED element.

To do this, bend the inserted cables slightly outwards. So you have more space later to solder the lines to the LED strips.

You can now strip the wires approx. 5mm and tin them with some solder.

Repeat this for the cable ends on the opposite side.

For the next step you now need the previously prepared LED strip.

Now you can solder the prepared wire ends to the contacts of the LED strip.

Make sure that any color coding on both sides of the LED strip is assigned to the same contact.

In the example shown, one of the lines is marked with a red stripe. This line is connected to the “positive pole” on both sides of the LED strip. You should keep this assignment for the entire chain of lights.

Another view of the soldered LED strip.

As soon as both sides of the LED strip are soldered to the cable ends, you can move the LED strip into position by gently pulling the cable ends out of the housing.

Inserting the magnets

Recesses in which small magnets can be inserted are integrated in the housing of the LED element. Each LED element can be attached to a metal surface.

The recesses are on both …

… ends available.

They are perfect for cylindrical magnets with a diameter of 8mm and a height of 3mm.

For installation, place the magnets in the corresponding recesses on the left …

… and right side of the LED element.

So that the magnets are (temporarily) held in their recesses, you can attach another magnet to the other side. This holds the magnets in position in the recesses.

View of the LED element with the inserted magnets.

Tip: It is best to orient the magnets in such a way that neighboring LED elements can be attached to one another. You can find an example of this in the section “Connecting the individual LED elements”.

Potting the LED element waterproof with epoxy

If you also want to use your fairy lights in a wet environment, it is advisable to encapsulate the individual elements in a waterproof manner with epoxy. You can find information about this in the article Electronics – potting electronics waterproof with epoxy.

Closing the lid

The last step on the way to a finished LED element is the closure with the cover cap. If you have potted the fairy lights with epoxy, I recommend doing this before the epoxy has hardened. Otherwise it can happen that the lid cannot be closed properly later.

To do this, insert the M3 countersunk screws through the base of the housing from behind – as shown – and attach the cover from the front.

Now you can screw the M3 countersunk screws with the M3 nuts on the front.

Another view of the screwed LED element.

Another view of the screwed LED element.

Connect the individual LED elements

The easiest way to connect the individually manufactured LED elements with each other is that two LED elements share the connecting line.

So you solder one end of the twin line to the first LED strip.

You then solder the other end of this twin line to the next LED strip.

Another practical feature of the magnet is that you can attach the individual LED magnets to each other for transport. Before casting with epoxy, make sure that the magnets are appropriately oriented.

Energy supply of the fairy lights

In order to be able to supply the light chain with energy during a camping trip, I was of course still faced with the problem that I had to somehow supply the light chain with energy.

Supply via the 12V connection of a car

One solution is to supply the light chain via the 12V connection of a car. The adapter cable shown is suitable for this purpose, for example.

So you can easily connect the light chain to the car’s electrical system.

Supply via a power bank

Admittedly, the possibility of power supply via the 12V connection of a car is not really mobile and independent.

It is better if you have one of these power banks available. There are now many different versions, some of which also have a 12V connection.

This power bank delivers, for example, 15A on the 12V connection. This means that some fairy lights can also be operated in parallel. 🙂

Construction completed

Once assembled, your fairy lights should look something like this.

It is much brighter than the usual fairy lights and can also be manufactured relatively cheaply.

Have fun with the project

I hope everything worked as described. If not or you have any other questions or suggestions, please let me know in the comments. Also, ideas for new projects are always welcome. 🙂

P.S. Many of these projects - especially the hardware projects - cost a lot of time and money. Of course I do this because I enjoy it, but if you appreciate it that I share these information with you, I would be happy about a small donation to the coffee box. 🙂

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