My Custom Benchtop PSU

Posted on in: My Projects.

In many of my projects I find myself in need of varying amounts of DC power. In the past I would find different power sources such as cell phone chargers, laptop power cables, & other such devices to power my creations. Over time I came to desire a singular device that could output a variable voltage in order to test my creations before I dedicated a PSU to them. I know that Bench-Top Power Supplies exist, however they tend to cost anywhere from 100 to 1k dollars for one that is of any quality. Although I could potentially buy one of these Bench-Top Power Supplies, I didn’t/don’t believe my hobbies warranted such an extravagant purchase. Thus I tried to think of anything that could do the job that I could easily get my hands on & thought of a regular Computer Desktop PSU. I had/have many of these lying around, so it was only a matter of figuring out how to “vary” the voltage. I attempted to build a circuit that incorporated a potentiometer that would give me very fine control over the voltage output of my device, however I failed at building the circuit miserably & decided to go a simpler route.

Within a Computer Desktop PSU there are many different wires that output certain voltages to the different components within the computer. Specifically there are +12.0v, +5.0v, +3.3v, Ground, -12.0v, and -5.0v wires. I figured if I could find a simple way to access these different voltages I would be able to connect my devices to certain wires to attain different voltages. Thus I removed the front casing on a smaller Computer PSU & then attached the different wires to terminals I bought for a few cents each. Then faceted these terminals to a piece of cardboard & glued everything to the front of the PSU. I then taped a reference sheet to the top to help me remember which terminals were which. Now if I need a certain voltage, I simply use a combination of black & red terminals to attain the voltages I desire. For example, if I use the +3.3v with the GND (or 0.0v) I get +3.3v [ 3.3 – 0 = 3.3 ]. If I use +3.3v with the -5.0v I get 8.3v (not -2.6v) [ 3.3 – (-5.0) = 8.3 ]. If I use the +5.0v with the -5.0v I get 10.0v (not 0.0v) [ 5.0 – (-5.0) = 10.0 ].

Thus with this device I can supply my projects with the following Voltages: 3.3, 5.0, 8.3, 10.0, 12, 15.3, 17.0, and 24 volts. Although this doesn’t always give me the exact voltages I require, it will more often than not, give me one darn close to the one I need, thus providing me with an eight in one device. It even has a power switch, which is handy when your project suddenly starts to fry & you need to cut the power. If you have any questions feel free to comment.