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.

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.
<p>Hi there. Im building a bartop arcade based on rPI3. I bought a 500W PSU (this one: <a href="http://www.tacens-anima.com/fuentes-de-alimentacion/apii500/" rel="nofollow">http://www.tacens-anima.com/fuentes-de-alimentacio...</a>) to feed the raspberry pi 3 VIA MicroUSB port and an 2.5&quot; USB HardDrive.</p><p>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.</p><p>Thanks in advance :)</p>
<p>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.</p><p>Did you measure the voltage on the 5V rail while the raspberry pi is connected?<br>It should be between 4.75 and 5.25 volts. If it's good, the USB cable might not use heavy enough wire.</p>
<p>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</p>
<p>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.</p><p>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. </p>
<p>my PSU dont have any info about min load required on each rail... is there a way to find out those values?</p>
Mine out puts 26 amps wont it break my phone?
<p>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 &quot;+5VSB / 2A&quot;, so it's limited perhaps a little light for modern phones / tablets - hopefully charging off it won't trip the PS.</p>
<p>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.</p>
Won't 2 amps be too much for your phone or other usb devices?? I read that usb outputs .5 amps.<br><br>Could this damage anything? What about more amps? At what point is it unsafe if this is safe? Thank you for your time.<br><br>
<p>The thing with current (amps), is that it's not &quot;pushed out&quot; 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.</p>
<p>It takes 2a for fast charge to happen in modern devices</p>
Thanks :)
<p>The device will only use as much current as it needs. A typical charger for a phone or tablet is around 2 amps. </p>
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 :)
<p>Hi there! I have seen several power supply mods, some using power resistors, but what has given me the very best results, is to use plain old automotive bulbs! Look for the best match of filament current. The common brake light 12V automotive bulb, when operated at 5 volts, will have a very loooong life!, and it produces enough light to be seen from far away ( which is a better pilot light!), and best of all: the bulb only requires some distance from the glass envelope to the nearest surface to keep temperatures reasonable... which is definitely NOT the case with a power resistor! Try it, I'm sure you won't return to using power resistors again! Amclaussen.</p><p>P.D.: and the cost is lower, as the socket and bulb only cost pennies, which is in accordance with the Instructables spirit.- Best Luck.</p>
<p>I had considered using lightbulbs for the load, I just didn't have any that would pull enough current from the rails.</p><p>I did end up replacing the original power resistors with a custom made one. It is a tin can with a coil of nichrome wire and is packed full of sand. The outside stays cool enough to touch.</p>
<p>Mine is a very common 1157 brake/rear light bulb, that pulls enough current from the 5V rail as to keep the supply happily running at 12V. I use it to feed an intelligent battery charger designed to recharge NiMH, LiPo and lead-acid batteries used in model airplane flying. At the required 7 Ampere demand when topping up my car battery, the small supply can barely maintain 11.8 V, which keeps the charger working, but I'm looking for a beefier supply, as other two smallish ones (about 180 watts) have failed after some use when recharging large (auto) lead-acid batteries. Have you found a particular brand or brands of Power supplies that are more reliable than the run-of-the-mill ones used by PC manufacturers? </p>
<p>I would try a 400+ watt atx12v power supply, they are designed to supply most of their power from the 12v rail. Get a good brand name one like a Corsair or Antec. Some of the cheaper ones will die if ran at their full rated power very long.</p><p>There are some really good 12v power supplies available, but they are much more expensive.</p>
<p>Thanx for the suggestions! I've traced the failure to two causes: one failed because of plain bad quality electrolytic capacitors, the other from a failing coil.</p><p>Evidently, there is a lot of GOOD engineering, but directed to produce a very well defined (limited) lifespan... designed to endure the year or so of warranty and then fail! Another possibility someone told me, was to search for a 12V power supply designed for LED lighting applications, but I haven't located any here (I live in Mexico City, and materials and devices are in short supply!</p>
<p>I have seen lots of those LED lighting power supplies on ebay, some up to 60 amps.<br>I don't have any of them, so I'm not sure about the quality. They are probably built similar to cheap atx power supplies though.</p>
Hi don't know if anyone can help I don't something similar to this, I have a USB type a port wired to a 5v supply, when an iPhone charger is plugged in it trips my psu, is this because of the current the iPhone charger tries to draw? As I now have noticed type a USB is only upto 0.5A
Ok thanks do you know why it would cause my psu to trip then? I have plugged in some computer speakers which worked fine, but when I plug in my iPhone charger the psu turns off and has to be left for a few seconds before it will turn back on
<p>Try measuring the current draw with a multimeter set to peak hold mode. If it is much higher than the rating of your power supply, even for a few milliseconds, that could cause it to trip. </p>
Thanks for your replys, the only exposed wire is where I have soldered onto the back of the USB connector which is reading 7.4A, also not sure if this makes a difference but it cuts out just by plugging in the apple cable, nothing on the other end of it. I was only trying this as a added feature so I may try another USB connector if that doesn't work just leave it lol great instructable btw thanks
<p>Check your cable, it probably has a short.</p>
Just tried another USB port and I have tried 3 different iPhone leads and same thing happened, il leave it for now, was mainly to power a headunit and some leds off the 12v rail which work fine, thanks again for taking the time to help me
<p>Most phones will try to pull up to 2 amps while charging if you wired the data pins for charging mode. If you leave the data pins floating, nothing should pull more than 0.5A but some devices will not charge like that.</p>
<p>very nice</p>
is this downloadable ?
Would it be wrong if I connected +5 and +12 outputs in series, to get 17V? That's because I'm trying to charge car battery using ATX, and connecting it to -12V is not the option, due to it's poor current rating.
You can't connect the outputs in series.<br> The negative connections are connected to ground so you can't connect two different power supplies in series either.<br>
It seems obvious to me now, what was I thinking :)<br>Any other suggestions how to get 17V and some decent current?
<p>-5v and 12v make 17volts. Just think of it like thermometer readings. -12v and +12v is a 24v swing</p>
<p>No!!! Be careful of this. Different power lines are rated at different amperage - so while you could use -12 and +12 for a 24 volt differential, the -12 volt line does NOT sink the same amperage as the positive one does. You would be better to use something like a LM2596S DC-DC Constant Current and Voltage Adjustable Module, which gives you something like 1.2v-30volts adjustable and up to 5 amps output with an input of between 7-15 volts I believe. There are similar products out there that allow you to get to what you want without breaking the rules. So depending on your amperage requirements, you could use it connected to the +12v line. Remember that the amperage you use for the adjustable line will reduce the available output from the +12 line.<br></p>
<br> You could look for an old laptop power supply. Some of them will be around 17 volts and the usually supply 2 - 4 amps. I have gotten them cheaply at yard sales and swap meets.<br> I have a 16v one that works well for charging batteries.<br>
Hi everyone i'am new to instructable I'm looking to build a power supply out of a computer power supply i need 12v 4amp but the power supply says 12v 12amp for a amplifier please help me thank you
<p>Your device will only use as many amps as it needs. Using a power supply that has a higher current rating is fine.</p>
Thank You
<p>how can I wire this for 24v?</p>
<p>Just a note to let you know I have added this instructable to the collection: <br>Encyclopedia of ATX to Bench Power Supply Conversion <br>&gt;&gt; <a href="https://www.instructables.com/id/Encyclopedia-of-ATX-to-Bench-Power-Supply-Conversi/" rel="nofollow">https://www.instructables.com/id/Encyclopedia-of-ATX-to-Bench-Power-Supply-Conversi/</a><br>Take a look at about 70 different approaches to this project.<br> </p>
Very nice job. The only suggestion I have is to make it have molex and motherboard connectors in the back so you can just plug in any power supply withought taking anything apart. You could put the resistors with heat sinks in the wooden case and add a fan and air vent. Then it would be completely modular.
Me to thats what i`m making
<p>how did yours go? i found attaching the ATX plug to the terminals a waste of time scrapped the idea. its only a $38 PSU</p>
I was going to do this project, but then the power supply decided to die. Some of the ground rails didn't work. In the end, I trashed the power supply, and the parts are sitting in my closet. So yeah, that comment was from four years ago. Sorry I couldn't be more useful.<br><br>-Eric
I was going to do this project, but then the power supply decided to die. Some of the ground rails didn't work. In the end, I trashed the power supply, and the parts are sitting in my closet. So yeah, that comment was from four years ago. Sorry I couldn't be more useful.<br><br>-Eric
<p>Made This: Substituted minium load resistors for cooling fans and a the LED in a light up magnifying glass that i jerry rigged </p><p>yes they are always on but so is the PSU fan, its of little consequence </p>
did you wire the atx power on switch like so: http://ubuntuone.com/p/155G/
No, I've never seen it wired like that before. The green wire (ps_on) is connected to ground.
i have had it wired like this and had no problems but when i wired another power supply with ps-on wire to the ground it burned the power supply immediately. i read about &quot;ps-on to ground&quot; on wikipedia. i figured out the right way (ps-on to pwr-ok) by my self.
i just tried ps-on to ground on two power supplies. i gues we now have two ways to turn a power supply on: ps-on to ground or ps-on to pwr-ok. i probably short circuted that other supply that burned. :)<br>

About This Instructable




Bio: I enjoy building electronics &amp; robots. I like building computers as well as writing programs &amp; web sites. I like to build and launch rockets. I especially ... More »
More by rocketman221:Strong Electromagnet From An Old Transformer LED Computer Case Lighting Dual USB Charger With Switching Regulator 
Add instructable to: