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.

[su_spoiler title=”Requirements” style=”fancy”]
– 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 :


[su_spoiler title=”Test your Power Supply” style=”fancy”]

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!


[su_spoiler title=”Color code Voltages” style=”fancy”]



Red +5V
Yellow +12V
Orange +3.3V
Blue -12V
Black GND



[su_spoiler title=”Always on Power Supply” style=”fancy”]

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.


[su_spoiler title=”Create your Bench Power Supply” style=”fancy”]

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


[su_spoiler title=”Extra – Powering an Arduino” style=”fancy”]

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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