The Ultimate ATX Power Supply Mod With USB Charging Ports




About: I enjoy building electronics & robots. I like building computers as well as writing programs & web sites. I like to build and launch rockets. I especially like to play with high voltage power suppli...

I know there is already a bunch of these on here, but I didn't see any quite like this so I thought I would post it, so here it is.

This power supply has 3 12v lines, 3 5v lines, 3 3.3v lines, 1 -12v line, & 2 USB ports.
It uses a 480 Watt ATX power supply and puts out enough power to run most projects.
It cost about $35 for everything including the ATX power supply.
This is also a good way to make those ATX power supplys that most people have sitting around gathering dust useful again.


This project involves electricity and sharp tools.
however this power supply only puts out 24v max You should not open the case, when plugged in there is a deadly amount of power inside and the capacitors inside will store a large amount of power for days even when unplugged.
This power supply puts out enough current to start a fire. Make sure to use wire that is heavy enough to handle the current and make sure that there are no shorts.
I am not responsible if you electrocute yourself or anyone else, if you blow something up, or if you burn your house down so be careful.

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Step 1: Parts & Tools


  • ATX Power Supply
  • Binding Posts With Banana Jacks
  • Butt Splices
  • Eye Connectors
  • Type A USB Jacks
  • 12 Way Terminal Block
  • Small Piece Of Strip board
  • Miniature SPST Toggle Switch
  • NC Momentary Pushbutton Switch
  • Panel Mount Indicator LED (Mine has a built in resistor for 12v use)
  • High Power Resistors
  • Heat sinks For Resistors
  • Wire For Connecting Everything
  • Super Glue
  • Electrical Tape
  • Zip Ties
  • Craft Plywood Or Other Material To Make Case Out Of


  • Wire Strippers
  • Wire Cutters
  • Crimpers
  • Utility Knife
  • Pliers
  • Hot Glue Gun
  • Soldering Iron & Solder
  • Drill & Drill Bits
  • Screw Driver
  • Volt Meter

Step 2: Mount Binding Posts

I Mounted 7 Pairs of binding posts on the front panel.
The horizontal spacing is 3/4" and the vertical spacing is 1".
I drilled my holes slightly small so that I could screw the posts in tightly.
I added the LED & the switches off to the side of the panel.

Step 3: Add the USB Ports

The pair of USB ports are soldered on a small piece of strip board.
They are mounted to the top panel. The holes were drilled out then cut to fit with an exacto knife.
The jacks are connected to the 5v standby line so they always have power even when the main power supply is off.
Pin 1 on the USB port is +5v and pin 4 is ground.
Make sure that the USB ports are wired correctly
The voltage on the usb ports must be between 4.75 & 5.25 volts

Step 4: Wire the Panel

Wire Colors For The ATX Power Supply
Color Signal
Black Ground
Yellow +12v
Red +5v
Orange +3.3v
Blue -12v
White -5v (Not used as of ATX 1.3)
Purple +5v Standby (Has power even when power supply is turned off)
Green Power On (Short to ground to turn on the power supply)
Gray Power OK (Not used in this project)
Brown 3.3v Sense (Leave connected to 3.3v line)

I used a 12 way terminal block to make connecting everything easier.
My terminal block was only rated for 25 amps so I used 2 sections for the 3.3 & 5v lines with the front jacks split between them.
I used 12 AWG wire for the 3.3 & 5v lines and 16 AWG wire for the rest of them.
The indicator led is connected to the -12v line. (Note: the led used here has a resistor built in normally a red led would need a 500-700 ohm resistor to use it with 12v)
The toggle switch is SPST and the pushbutton switch is a NC momentary. They are wired in series; one side goes to ground the other to the green power line.

Step 5: Wire Up the Power Supply

The old connectors need to be removed and replaced with some butt splices. Because the wires are thin and it will put out a lot of current we need to bunch up several wires so it will handle the current. I left the 4 pin molex connectors on so i could use them to test old computer drives.
ATX power supplys have a minimum load which should be listed on the power supply. Mine requires .3A on the 3.3v line, 1A on the 5v line, and 1A on the 12v line. I used resistors for the 3.3 & 5v lines and a mini fridge for the 12v line.
The formula to calculate the the resistor size is Resistance = Volts / Amps.
I needed 11 Ohms for the 3.3v line and the closest resistor avalable was 10 Ohms which gives .33A and a 5 Ohm resistor was needed for the 5v line.
The formula to calculate the wattage is Watts = Volts * Amps which gives just over 1W for the 3.3v line & 5W for the 5v line.
You should use a resistor that is twice the wattage you need to help keep the temp down. I used 10W resistors for both lines. They are mounted between two large TO-220 heatsinks which was then superglued to the case which keeps the resistors below 110o F.

Step 6: Finish It Up

Tighten down the connections, add labels, and double check the wiring. Flip the switch and if everything is done right it should come on.
Check the voltages with a volt meter and if the minimum loads have been met the voltages should be very close to what they are rated at.

If one of the lines is over loaded or shorted the power supply will shut down, pressing the reset button or turning the power off and back on will restart it.
If it overheats it should shut down if that happens turn it off and let it cool down and make sure nothing is overloaded and that the power supply has plenty of ventilation and that its not packed with dust.

Double and triple check the wiring on the USB ports before plugging in an mp3 player or camera and test it with a USB keyboard light if you can.
Make sure that the voltage going to the USB ports is between 4.75 & 5.25v

Step 7: Update 9-22-2009

  • I have redesigned the layout on the power supply.
  • I moved the binding posts further apart so its easier to connect wires to them.
  • And I made a nice labels for the front and top.

The power supply label in the zip archive was made in adobe fireworks and can be edited.

In order for the pdf to print at 100% size make sure to set page scaling to none in adobe reader.

The full sized label is 200dpi and should print out to be 7 1/8th inches wide.
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    116 Discussions


    Question 1 year ago on Step 6

    Can you please explain how the automatic power cut-off during accidental short-circuit is working here?

    1 answer

    Answer 1 year ago

    ATX power supplies have a protection circuit that will trip if too much current is drawn. It is reset by turning the supply off and back on again.

    They will typically use a current shunt and comparator to detect over current and a latch to keep the power supply shut down until the supply is reset. It can be built into the controller chip or separate depending on the power supply.


    1 year ago

    Question: Can I combine the yellow and orange wire to get an output voltage of 15V?

    3 replies

    Reply 1 year ago

    No, You would get 8.7 volts and many power supplies will trip out if you try that.
    You can use the -12v and the 3.3v rails to get 15.3v, but the -12v is typically rated for less than 1 amp.


    Reply 1 year ago

    thanks for the reply. I'm trying to use my atx power supply to charge a sealed lead-acid battery which came from a UPS. After 7 hours of charging i only get 10.8V from the battery. Any ideas?


    Reply 1 year ago

    Is the battery drawing any current when you charge it?
    It may have a bad cell if it doesn't draw much current.


    2 years ago

    Hi there. Im building a bartop arcade based on rPI3. I bought a 500W PSU (this one: to feed the raspberry pi 3 VIA MicroUSB port and an 2.5" USB HardDrive.

    Connected to the rpi is the xiaomi controllers encoder, and the USB Drive. My first attempt one month ago was to solder 2 usb ports to the MOLEX connectors from 5V rail but rpi3 keeps showing low current sign (low AMPS) and its boot is too slow. So, im asking you guys (as im a noob on this stuff) to help me. What do i need to do? Ive already stripped the PSU cable connectors but i dont know which kind of high power resistors should i use to keep a stable current AMPS both on rpi3 and on the USB drive.

    Thanks in advance :)

    4 replies

    Reply 2 years ago

    The power supply should provide plenty of power for the raspberry pi (it could run 10 of them). The 5V rail might be running at a lower voltage if you don't have enough load on the 12V rail though.

    Did you measure the voltage on the 5V rail while the raspberry pi is connected?
    It should be between 4.75 and 5.25 volts. If it's good, the USB cable might not use heavy enough wire.


    Reply 2 years ago

    Yes, with the rPI connect im getting about 5.15v. The problem is the current... Im only having a maximum of 530mA. I've installed a POWER_OK led to the grey + GND wires and it keeps on as soon as i power the PSU on. The problem is that im not having enough AMPS to keep both rpi and HD working properly... by the way, tried dummy loads on all rails


    Reply 2 years ago

    You need a better USB cable. Try to find one that is as short as possible and that has heavy gauge power wires. You can try measuring the 5V pin on the raspberry pi. I believe the low voltage warning shows up if it's below 4.65 volts.

    Since your power supply doesn't list the minimum loads, you will have to experiment to see what works well. The 5V and 12V rail loads are most important since they can't be controlled individually. If one rail doesn't have enough load, the voltage on the other will drop. A minimum load of 1 to 2 amps is pretty typical though.


    Reply 2 years ago

    my PSU dont have any info about min load required on each rail... is there a way to find out those values?


    3 years ago

    Mine out puts 26 amps wont it break my phone?

    2 replies

    Reply 2 years ago

    As rocketman221 said, the 5v Stand by (which is on even if the PS is switched off, which is nice for the charging ports) is current limited already by the PS - check the label, it will likely tell you the current limits per rail. For example, mine 300w PS says "+5VSB / 2A", so it's limited perhaps a little light for modern phones / tablets - hopefully charging off it won't trip the PS.


    Reply 3 years ago

    The phone will only draw the current it needs. If you are going to use the main 5V rail, I would suggest putting a 2-3 amp fuse in series with it. I used the 5V standby rail for the charging port on mine. Those are current limited to a couple of amps.


    3 years ago

    Won't 2 amps be too much for your phone or other usb devices?? I read that usb outputs .5 amps.

    Could this damage anything? What about more amps? At what point is it unsafe if this is safe? Thank you for your time.

    5 replies

    Reply 2 years ago

    The thing with current (amps), is that it's not "pushed out" of the power supply, it's more a case of having the amperage available. It's the device that draws the current, so if you have a deveice that uses, say, 5V at 0.5A, and you plug it into a 5V, 40A power supply, it will only draw that 0.5A.


    Reply 2 years ago

    It takes 2a for fast charge to happen in modern devices


    Reply 3 years ago

    The device will only use as much current as it needs. A typical charger for a phone or tablet is around 2 amps.


    Reply 3 years ago

    Oh, thank you, I've been planning to make something like this for a short while. Now I think I'll implement your usb charger port in my plans :)