After being stuck with only battery and USB power for a while, the time finally came that I needed something with more juice. As workbench power supplies are generally not very cheap, I decided to convert a regular old computer PSU. However, as modifying a power supply directly renders the power supply useless for its original purpose, I decided to create this box to give me the power outputs I needed. This is also a safer option as there is always a risk involved in opening up a power supply, plus you can switch out the connected power supply in case it dies with no extra work involved in modifying a new one.
Warning: Working with electricity always comes with a risk. While voltages of 12V and less are generally considered safe, they can still be dangerous and potentially lethal in the wrong circumstances. Always take utmost care when handling live wires.
Step 1: Materials
You will need the following materials:
1. A 20 or 24 pin ATX Motherboard connector. (Can be purchased online or salvaged from a broken motherboard.)
2. A handful of binding posts. (10 red and 5 black in my instance)
3. Wires, preferably at least 5 colors.
4. A toggle switch for the power
5. A dummy load to keep the power supply happy, such as an automobile lightbulb or a 10W 10 ohm resistor.
Additional, optional materials:
A Molex connector or two if you want additional outputs or grounds.
An enclosure if you do not have a 3D printer.
A soldering iron.
3D printer for creating a custom enclosure.
A CAD or other 3D modeling program to create the enclosure plans.
A vernier caliper for measuring the dimensions of the components.
Step 2: Planning and gathering materials
It is always a good idea to get everything together before starting work on a project. Getting the 24 pin ATX connector off of the motherboard was an obnoxious task. Computer components generally use lead-free solder which melts at a much higher temperature than conventional solder, as well as radiating heat faster, making removing it very difficult. I tried using a desoldering wick, but it didn't do much good. I ended up removing as much solder as I could using a desoldering pump and then simply prying it off. Unfortunately, this resulted in a handful of pins breaking off, but luckily enough of the ground and voltage pins, as well as the on/off pin, were left intact.
Once the connector was off, I marked all the pins with a sharpie following the chart above. Next, I measured the dimensions of all the components. For this, I'd recommend a digital caliper since high accuracy is necessary if you want to avoid gaps or having to file openings where components don't fit.
Step 3: Designing and printing the enclosure
I used the student version of Inventor to put together the enclosure. It consists of 11 holes for the binding posts, a hole for the switch, a large hole on the side for a fan, a guide for a sliding lid in the bottom, and of course, the holes for one Molex and one 24 pin motherboard connector. The lid was printed separately as my printer could not accommodate both parts at once.
Unfortunately there were some issues in printing. The first layer ended up sliding a bit, printing over the holes, and one of the corners warped pretty badly, but it was still good enough to serve its purpose. I used a file to fix the holes and everything was in order.
Step 4: Putting it all together
If you are using a 24 pin motherboard connector, you may wish to only use the pins it has in common with the 20 pin connector. This way, you may use both a 24 pin and a 20 pin power supply and still have all your binding posts in working order. As I wanted two of every (positive) voltage, and a 20 pin connector only has one 12v source, I added a Molex to supply the other 12V line. Unfortunately, I did not have as many binding posts as I thought I did, so I had to leave three of the holes empty in the final product.
Next up is to solder the pins. It is a very good idea to use separate colors for each voltage, as well as a specific color for ground. I unfortunately had only a short length of black wire, so I used white for the ground and black for the reset pin signal. I then used red for 12V, blue for -12V, and yellow for both 3.3V and 5V as I lacked more color varieties. I then hooked up the 12V line to the fan I had in place to cool the load. The fan seemed to be enough to keep the power supply happy, so I left out the lightbulb.
A quick tip for soldering wires to the pins on the ATX connector: try adding solder to the pin first, then heating up the wire you want to connect and touch it to the pin and adding no extra solder. This is a lot faster and less painful than trying to tie the wire to the pin and adding solder the same way you might with two pieces of wire.
Be very careful not to leave any exposed wires touching, and be sure to disconnect the power supply from the box before working with the insides in case of a malfunction. Power supplies can retain a powerful charge even when unplugged from the wall.
Congratulations! You now have your very own workbench power supply.