DIY PC PSU Bench Power supply voltages

DIY PC PSU to Bench / Project Power Supply

Computer power supplies cost around US$30, but lab power supplies can run you $100 or more! By converting the cheap (free) ATX power supplies that can be found in any discarded computer, you can get a phenomenal lab power supply with huge current outputs, short-circuit protection, and reasonably tight voltage regulation on the +5V line.

– An old working PC Power Supply, Look online, at your local computer store or dismantle an old computer and remove its Power Supply from its case.

I found an old 420 Watt Power Supply:


The maximum output(A) per voltage should be written on your Power Supply :


Test your Power Supply

If you are not sure if the Power Supply is still working you can test it by shorting the green wire to any black wire, this method works for the 20-pin and 24-pin ATX Connector :


Then plug-in some PC accessory or fan to test if it turns on


If the fan spins, your Power Supply is still OK!

Color code Voltages


Red +5V
Yellow +12V
Orange +3.3V
Blue -12V
Black GND
Always on Power Supply

First, you want your Power Supply to be on all the time… this can be done by connecting/soldering the green wire to a black wire :


For extra protection, you could wrap it in tape or shrink wire.

Create your Bench Power Supply

First, open your Power Supply and cut all the zip-ties and connectors :


Now tie all the corresponding colors together


Lead the wires back out of the enclosure and close your Power Supply


Screw your Power Supply back together and you now have a cheap very powerful Bench / Project Power Supply

Extra - Powering an Arduino

To power an Arduino, I recommend using a plug (DealExtreme)


connect a black(GND) wire to the (-) and connect a red(+5V) wire to the (+):


Connect your Arduino:


You now have a project Power Supply.


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