Electronics

Activate PC Desktop Computer Power Supply

Use a desktop personal computer ATX-style PC desktop switching power supply anywhere you need 12 or 5 volts DC. These power supply units (PSU) offer fairly well-regulated, well-filtered, and high current sources. ATX PSUs make a decent bench supply. So here, we give directions to activate a PC desktop computer power supply, even while it’s separate from a PC. These show which color wires on the PSU to short together to start the supply.

Activate PC Desktop Computer Power Supply: The Problem

But the issue is: How do you turn on the power supply? Unfortunately, you can’t just plug it in to an AC outlet and go. In fact, inside the computer, power up is done via the motherboard. It sends an activation signal to the supply whenever you press the Power button on and off. So how do you create such a signal yourself without a computer? We cover that below.

Activate PC Desktop Computer Power Supply: The Solution

For most of these PC supplies on the market today, the motherboard communicates with the power supply module via the 20- or 24-pin cable that connects the two together. To activate the full-current capable part of the power supply, the motherboard connects the pin with the green wire on it to ground. You can do the same by manually connecting this green wire to any one of the black (ground) wires in the same connector.

How to Tell that the PC Desktop Computer Power Supply Is Activated

Most of these units contain at least one internal fan that will spin up when the high-current portion is energized. If no fan, or the fan does not work, measure the voltage with a multimeter. Indeed, you can read across any of the red, yellow, or orange wires and ground (black wires) for 5 and 12 volts. A few supplies may even have a lamp to show that they’re running.

Verify that You Have an Adequately Sized Load

But before that, consider that unlike linear PSUs, many switching supplies need a minimal load to work well. A load that draws one or two amps is often sufficient. You can get this lost by connecting a computer fan to the 12-volt output. The red and black wires of any of the accessory plugs offer 12 volts DC. An incandescent lamp also does the loading job nicely. But if you use the supply under constant load, then don’t worry about meeting these minimal load needs. Your constant load does that automatically. E.g. We powered a 5-volt WiFi router with an ATX PSU. It indeed worked quite well, without adding any minimal load.

I’ve also powered radios and iPods with said power supplies, and charged batteries as well. Since computer power modules cost little these days, they make great DC voltage sources. That is, they do as long as the load you put on them draws enough current, but not too much.

Activate PC Desktop Computer Power Supply: Cautions and Warnings

We advise against plugging any expensive ham radio gear or sensitive electronics into these PSUs for long. Especially true if your PSU makes lots of RF hash noise on its output lines. This is a common trait of switching power supplies, particularly those of cheap design. While we use computer PSUs in a pinch, these adapters work best with computers and other IT equipment. But not so much other non-IT equipment, especially when powering these devices indefinitely.

So connect up an ATX PSU at your own risk. But honestly, if you do it right, the risks of damage to load devices is pretty low. We’ve yet to destroy any 12 or 5 volt devices.