Computer power supplies typically cost around $30, while dedicated lab power supplies often come with a much higher price tag—$100 or more. However, by repurposing inexpensive or even free ATX power supplies found in discarded computers, you can create a highly capable lab power supply without breaking the bank. These units offer impressive current outputs, built-in short-circuit protection, and surprisingly stable voltage regulation, especially on the +5V rail.
This makes converted ATX power supplies an excellent choice for hobbyists, students, or anyone needing a reliable bench power source on a budget. With a bit of modification and setup, you can turn a common computer PSU into a versatile lab supply that rivals many commercial options in both performance and safety features.
Requirements
-
An old, working PC power supply unit (PSU). You can find these online, at local computer stores, or by dismantling an old computer and removing its power supply.
-
For example, I used a 420 Watt PSU for this project.
Check the Maximum Current Output
Look at the label on your PSU. It should list the maximum current (in amps, A) available for each voltage rail (e.g., +5V, +12V). This will tell you how much current you can safely draw from each output.
Test Your Power Supply
Before proceeding, make sure your PSU still works:
-
Locate the 20-pin or 24-pin ATX connector from the PSU.
-
Identify the green wire (this is the PSU power-on signal) and any black wire (ground).
-
Using a jumper wire or paperclip, short (connect) the green wire to a black wire.
-
Plug the PSU into power and switch it on.
-
Connect a fan or any small PC accessory to the PSU’s output cables.
-
If the fan spins, your PSU is functioning correctly.
Understand the Color Coding of Wires
Know what each wire color means on the ATX power supply cables:
| Color | Voltage |
|---|---|
| Red | +5V |
| Yellow | +12V |
| Orange | +3.3V |
| Blue | -12V |
| Black | Ground (GND) |
This helps you identify the correct wires to use for your bench power supply.
Keep the Power Supply Always On
To make your PSU turn on without needing a motherboard:
-
Connect or solder the green wire (power-on signal) to any black ground wire.
-
This tricks the PSU into thinking it’s connected to a motherboard and keeps it powered on continuously.
-
For safety, cover this connection with electrical tape or heat shrink tubing.
Prepare Your Bench Power Supply Outputs
-
Open your PSU casing carefully.
-
Cut or remove all zip ties and unplug connectors from inside.
-
Group wires of the same voltage color together — for example, bundle all red +5V wires, all yellow +12V wires, and so on.
-
Bring these bundled wires out of the PSU enclosure, leaving enough length to connect your projects.
-
Close and screw the PSU case back together securely.
Using Your Bench Power Supply
Now you have a powerful, reliable power supply for your electronics projects, delivering stable voltages at high current capacity.
Bonus: Powering an Arduino
If you want to power an Arduino or similar small device:
-
Use a DC barrel jack plug (available from online stores like DealExtreme).
-
Connect a black (GND) wire from the PSU to the negative (-) terminal of the plug.
-
Connect a red (+5V) wire to the positive (+) terminal.
-
Plug this into your Arduino’s power jack.
You now have a simple, versatile project power supply that can power a wide range of electronics safely and affordably.
