View source for Diy power supply from an old computer psu

== Introduction ==

== Theory ==

12 V and 5 V.

=== Current on Voltages ===

The possible outcomes are 24V (+12, -12), 17V (+5, -12), 12V (+12, GND), 10V (+5, -5), 7V (+12, +5), 5V (+5, GND), 3.3V which should be sufficient for most electrical testing.

=== Wire Coloring ===

* Black: Ground (0V)
* Orange: +3.3V
* White: -5V (on older ATX power supplies)
* Red: + 5V
* Blue: -12V
* Yellow: +12V
* Gray: power is on indicator
* Green: ON/OFF switch; turn DC on by shorting to ground.
* Purple: +5V standby 
* Brown: +3.3V sense (on newer power supplies)
* Pink: +5V sense (sometimes)
* Yellow (small gauge): +12V sense (rarely)

=== Safety Features ===

* Short circuit Protection?
* Over load Protection?
* Over Heat Protection?


=== Power Switch ===

This system need to reverse the GND and 12V line.
* Yellow cable (12V) on the colored terminal,
* a black wire (GND) to the pin opposite,
* the green cable (ON/OFF) to the centre pin.

Some power supplies need the grey and green to be connected together in order to run.

If there is the rear switch in the PSU, connect the green and black wires together.

In normal operation illuminated '''SPST''' switches have 3 terminals
* the centre pin: green Power ON/OFF
* one is indicated either by a different colour or labelled GND. 
* The terminal opposite would normally be wired with 12V,

=== Power-on LED ===

* The grey (Power On) wire to the anode (long end) to the red LED. 
* 330Ω resistor to the cathode.
* The black wire (GND) to the resistor.

=== Standby LED ===

* The purple (Standby) wire to the anode (long end) to the green LED. 
* 330Ω resistor to the cathode.
* The black wire (GND) to the resistor.

=== The Fake Load ===

10W 10Ω resistor between 5V (red) and GND lines. The power resistor will give off a lot of heat and should be mounted on the metal wall for proper cooling (or a heat sink mount).

Consider using a lighted 12V switch, which will act as the load necessary to turn on the power supply, or replace the 10W power resistor with the cooling fan that was originally inside the PSU, be careful with the polarity though - match the red and black wires to each other.

=== +3.3V ===

Connect the remaining orange wires to the +3.3V binding post: solder them all together and solder them to the +3.3V binding post.

* Gray/ White: Some power supplies may have either a gray or brown wire to represent "power ok". (Most PSU's have a '''smaller orange''' wire that is used for sensing and this wire is usually paired at the connector to another orange wire. Make sure this wire is connected to the other orange wires, otherwise your lab power supply won't stay on.) or a red wire (+5V) for the power supply to function. When in doubt, try the lower voltage first (+3.3V).

* If you only have two or less orange wires, you should also have a '''brown wire''' which must be connected with the orange (Some newer power supplies will have "voltage sense" wires that need to be connected to the actual voltage wires for proper operation).

=== +5V ===

Connect the remaining red wires to the +5V binding post: solder them all together and solder them to the +5V binding post.
* If there is only three red wires, another wire (sometimes pink) must be connected to them.

=== +12V ===

Connect the remaining yellow wires to the +5V binding post: solder them all together and solder them to the +12V binding post.

=== GND ===

Connect the remaining black wires to the ground binding post.

== References ==

https://www.wikihow.com/Convert-a-Computer-ATX-Power-Supply-to-a-Lab-Power-Supply