How to power a circuit from high voltage – Repurpose a wall adapter

Table of Contents

Repurpose a wall adapter

Most of us have wall adapters collecting dust in a box. We can crack these open and reuse the board in it. And then we integrate this into our project. We need to doe the following things

  • Extract the board
  • Add the 5V connections
  • Add the mains connection
  • Connect to the project

Extract the board

If you put the adapter in a vice, just clamp it and apply pressure until it cracks. Then use a screwdriver or spudger to properly open the device. In this case the board had two friction connections to the mains pins so the board came out with little trouble.

Add the 5V connections

I looked up the pin-out for the female USB socket, then I soldered two power wires inside the connector, this took a few attempts to get right.

With the board reinserted into its case, I could use a mains socket to test if both wires indeed delivered 5 volts, and they did.

With everything working as it should, I used hot-glue to fixate the wires in their socket.

Add the mains connection

At this point, things are getting a bit dangerous. Solder two anonymous wires to the mains friction pins, or whatever your board had to connect it to mains voltage.

Then, with the help of an old stripped appliance cord, we can hook the board up to a wall socket. Then once again, measuring if the boards still outputs 5 volts as it should.

Then if all is fine, we again apply some hot-glue to keep the wires secure to the board.

Connect to the project

Because my project uses mains power to switch other devices on-or-off with a relay, I made a splice on the main power cable. Then in the project box, some hot-glue will hold these wires apart, to not cause a short. This was not the best decision so far. If the box gets warm, the glue will get soft and wires could touch.


I think these will be better for future projects.

Or buy a power supply board

Ebay has loads of them.

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