AC Adaptor Power Supply – Recycle

NOTE: This project was a bit of a failure … I’m redoing this project using an LM317 instead of just using a POT to try to adjust the power. If you follow this project, you will only end up with a pretty circuit that doesn’t do anything very useful.

CAUTION: Modification of AC Power Adaptors is potentially dangerous. Read the specifications on the adaptor and observe output and polarity. Mistakes with AC Power can kill you. If you are unsure of the specifications of the adaptor that you are tinkering with … throw it away and get one that you know. Do not do ANY soldering on the adaptor or it’s cable when the adaptor is plugged in. I take NO responsibility for your safety, that’s your job.

In my previous article on power supplies for electrolytic etching I made use of an old AC Adaptor (wall wart) to provide power via a switch and potentiometer to an anode and cathode used in a simple circuit to an electrolytic etching bath. The adaptor recycle can be used for other purposes, and in fact I made a polystyrene hot-wire cutter using this same circuit. Now that I’ve used the project in a couple of different “tools” I suppose that it’s time to revisit the design and see what can be improved or changed.

My new application for this project is in a tool that will be used to bend acrylic sheet. There are a couple of interesting articles that can be found on various sites scattered across the interweb. I’m not going to list any here, they change too often. You can look at sites like lifehack and instructables for some pretty good examples of polystyrene cutters. The power supply is really what I’m interested in, so I’m going to focus on that for now.

Essentially, the AC Adaptor power is passed through a circuit adding a switch to make it easier to turn the power on and off, and through a suitably resistant potentiometer to allow the user to adjust the output power, effectively controlling the heating element (or in the case of the electrolytic etcher, the copper electrolysis anode). It’s also a good idea to install a power indicator in the circuit to improve safety (a visual indicator that there is current passing through the circuits output terminals.

So, in my case, I’m using this supply for three tools and two different types.

• Heat:
  • Polystyrene Hot Cutter;
  • Acrylic Heat Bender; and
• Current:
  • Electrolytic Etcher

So there is some versatility in the simple circuit.

The circuit above has two two pin screw terminal posts. The left-hand side is where the AC Adaptor will be connected to the circuit and the right-hand side is where the power will be output.

There are 6 parts (well 7 if you include the circuit board):

• 2 x 2 pin screw terminals;
• 1 x Red LED;
• 1 x 220Ω resistor;
• 1 x SPDT switch;
• 1 x B 10kΩ potentiometer (the resistance value of the pot should be increased to 100kΩ if you are using adaptors between >9 and 16V, I’m using a 9V adaptor, so 10kΩ … larger than that and you should probably not be using the adaptor at all).

I have connected the input power to a SPDT switch. This is where we turn the power to the output off. Of course, the power to the circuit is still live, you need to turn the wall socket off to completely power the circuit off.

The 3rd leg of the SPDT connects to the power indicator LED, which is connected to ground via a 220 ohm resistor. Additionally, the 3rd leg of the SPDT connects to the Power (leg 3) of the B10K potentiometer. The Wiper (leg 2) of the B10K potentiometer connects to the positive output terminal.

The negative input terminal connects to the resistor of the power indicator LED (as mentioned previously) and to the negative output terminal.

Connecting the load anode/cathode is done via the output terminal. I have a couple of banana plug to alligator clip connectors that I use, but bare wire end to spade connectors or any other appropriate connectors should be OK.

This is a good project candidate for mounting in a project box. I’m planning on bending some acrylic sheet to make the project box for this circuit … or you could make a pretty one by adding an instrument panel like my Steam Punk themed Electrolytic Etcher panel.