Use a 18-20 gauge wire to jump the circuit (they fit well without slipping).

For those of you who have never jumped a power supply the article below is written for you. For those of you who have, just use the images for reference.

The two wires that will produce voltage are green and purple. Depending on where the circuit is jumped you can get the power supply to produce 12 volts. If the fan goes one, you have done it correctly. Always double check the voltage readings with a multimeter.


The double jump is shown since it is not as simple, The single jump works the same, without the wire on the left.

Didn’t work?… I will be more specific.

For a 24 pin it is usually a Single Jump green to black. Sometimes, different black pins work with green. For a 20 pin it is common to require a Double Jump green to black and purple to yellow. You can get a permutation of 4.8-5v and 7.6-8.4v combined to giving out ~ 11.4-12.8volts on the four pin plug used for the Printrboard. If the plug is not required for the board, you can use the black and yellow wires (single or paired) directly into the source. Remember to unplug the power supply, and let the capacitor power down, if you intend to cut the wires. (This means wait until the fan dies, and/or the LED lights go dim)

Wrap clear tape around the wires so they don’t fall out. This preserves the Power supply for other uses. The plastic sheet is taped down near the fan to show: the fan is on and producing suction, so the plastic is flush to the fan intake. (This power supply has an on switch, but no LED light)



12v DC should be produced here.






Note: Most motors in cars are 12V DC.

Junkyards are a great place to be.


This is useful for powering the boards for 3D printers. And, it can be used run any 12V DC motor, as long as the amperage is not ridiculous ie really high, or really low. A great example,  the WOOF group using a (windshield) wiper motor to test out a large extruder driver.


Hint: high torque stepper motors are usually inside the doors driving the power windows. Think about is high surface area with heavy drag, these ones have serious push.

Have fun, and see what you can hack.

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3 Comments on Jumping a Power Supply for 12 Volts DC

  1. nophead says:

    The purple to yellow jump makes no sense at all. Purple is 5V standby, so feeding 12V into is likely to damage it.

    • bowman says:

      Agreed the Purple to Yellow should not be necessary, but I have come across several power supplies that do not give 12V at 12 amps with solely green-to-black, you get some other permutation of 8V and some amps. I don’t know if this is due to lack of industry standard or janky wiring. Every now and again I come across one with a pink wire or some oddball thing, I have just tested the outputs on many permutations and these were consistent. This ATX Power supply was a 300 Watt Bestec was the first Double Jump. Gen 3 Makerbot uses a 5W30RJ resistor to by-pass this problem. Conversely one of the Dells jumps with a 20Watt 8ohm resistor in Green-to-Black and a 10Watt 10ohm resistor in the Yellow-to-Purple. I have run both on the Printrboard among other things. There is most likely a better solution on the 20-24pin problem but this kept me running for a while, I will try to expound on it in a bit.

  2. nophead says:

    All you need to do is connect green and black to turn it on and put a dummy load on 5V (red and black) to make the 12V rail the right voltage. That will work with all ATX PSUs.

    None of these other permutations make any sense.

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