A DC power supply can be hard to find and expensive. With features that are more or less hit or miss for what you need.

In this Instructable, I will show you how to convert a computer power supply into a regular DC power supply with 12, 5 and 3.3 volt outputs. For about $10!

Why use a computer (ATX) power supply? Well, they're available everywhere, and they can output tremendous amounts of power in a small form factor. They have overload protection built right in, and even a 500W model can be reasonably priced with high efficiency. The voltage rails are incredibly stable. Giving nice, clean DC current even at high loads.

Plus, it's likely that many of you simply have an extra one lying around doing nothing. Might as well get the most value for your investment.

Step 1: Getting Started

The first order of business is that of safety. While I'm reasonably sure that there isn't enough residual energy to stop your heart, those capacitors can still bite, and that can cause significant pain and maybe even burns. So be paranoid when getting close to the internal circuitry. It would probably be a good idea to put on some insulating gloves. Also (obviously) make sure the thing is unplugged. You are responsible for your own safety!

Here are the tools/parts needed:

Needle-nose pliers
Soldering iron
3 x "Banana Jack" Insulated Binding Post sets
1 x bag of "#6" Ring Tongue Terminals (16-14 gauge)
Rubber feet
Small bit of heat shrink.
Wire strippers

Ok, let's get to voiding some warranties!
<p>Thanks I think I made it... but I just have a little problem with my 12v... it seem that I got 16v.. Is that okay?</p>
<p>Made it!</p>
I am new at this ...... i didn't understand why we can not use atx directly in our circuit when our cpu's mother board and all things work with it.....what is diffrence b/w atx and regulated power supply? <br>please someone help me....
<p>Atx is not fabricate to use it as regulated power supply, it contain IC to contol underload or overload current, see links</p><p> <a href="http://hackaday.com/2013/08/30/disabling-underover-voltage-protection-on-atx-power-supplies/" rel="nofollow">http://hackaday.com/2013/08/30/disabling-underover...</a></p><p> <a href="http://planetimming.com/atx_mod/atx_mod.html" rel="nofollow">http://planetimming.com/atx_mod/atx_mod.html</a></p><p>but you can use it, after some modification :</p><p>1. connect black with green to run it.</p><p>2.connect load (resistor 10W 5,0oms) in any red wire to stabilise all other outputs.</p>
Thanks to instuctables.
<p>Is there any way to get a higher voltage out? I would love to get 24 and higher.How do you determine which bundles connect to which rail? Could a potentiometer, mini multimeter and an ammeter be added without too much more effort? </p>
<p>Hi,</p><p>Are you using standard binding posts? The cheap ones aren't rated for the maximum amperage of the PSU. Is it OK to use any old post?</p>
<p>Could we used this PSU for car battery charging? If not, what does we need to enable that?</p>
<p>Hello</p><p>I have an old power supply from a LinotronicRIP50 that is not working.</p><p>The power outputs are 12V (6 amp) and 5.1v (20 amp) would I be able to use a modern psu?</p>
<p>If you hook the +12v too the +3.3v would that give me +15.3v ? And would it make it 41amps ?</p>
No, by connecting those wires in series you will get 17+ volts, but the amperage that can be drawn safely is the lowest of the two outputs. 23 amps, in this case.
<p>why it will give 17+ V instead of 15.3V?</p>
<p>ok, thanks for the help :)</p>
<p>Can it kill me if I touch it? Because I heard that 30 mAmps can kill you, so ...</p>
Yes. Amps kill, not voltage. So long as you don't have it plugged in while working on it you're fine. Once work is done and cover back on, these are well grounded and safe.
<p>nope not enough voltage .....i wouldnt stand and pee on it holding a cold water pipe tho either ....gettiing ur hands across a 12 v car battery makes a burning sensation at 12 v ....if u have alot of cuts on ur hands then u could have a problem ...a guy in a junk yard carrying a half dead car battery fell down both hand on the terminals they determined 6v and half an amp stopped his heart ...thats blood contact ...</p><p>but if ur at the work bench dont worry much about it ..just watch the sparks when u mess up</p>
Last one working so well I made another from a unit that came bundled with a case I bought. Lack of pci'e connectors made it useless for my pc.
<p>I made mine some time ago, using an old PC cd-rom and car amplifier and added two usb from an old motherboard, looks ugly but it does the job</p>
Made mine fron a 500W Dynex unit.
<p>I built my power supply with the similar instructions as yours using only the 12Volt output to power my Car Airpump (12V 14Amp max).I joined all 5 12V wires (Yellow) together and same for the ground connections to get the max current on the 12V rail which is rated for 17A on this supply.</p><p>With no load connected, the SMPS turns on and works fine but as soon as i connect the Car Airpump it trips (shuts itself down) not sure why ?</p><p>Now if i connect the same Power supply with a Digital Ampere meter connected in series, the Air Pump works perfectly. Could you help me understand the possible cause for this behaviour and how could i go about fixing or diagnosing it.</p>
<p>Hay I'm having the same problem with my power supply that you where. Mine just shuts off if I connect much of anything to it! Did you ever figure out what the problem is?</p>
<p>i solve my problem by connecting sensing voltage wire(brown) to 3.3v rail. </p>
<p>i got same problem ,i did't use resistor is that cosing shutdown?</p>
I think the issue some folk may be experiencing with power lines not powering up is down to lack pf the power resistors on the lines. More modern power supplies need a load resistance on the 12v, 5v and 3.3v lines. If they aren't given that load, the power supply can't stabilise the outputs. Worth a try if you're struggling to get your supply up and running.
<p>Correct, a switch-mode power supply will need a load to operate properly.</p><p>I use a 10ohm, 25watt power resistor from the 5v rail to ground. </p>
<p>I have a little problem here I keep getting double voltages on each group of cables . For example in 3.3 v i get 6.6 v on 12.v i get 24.v etc.. What is happening ?</p>
<p>Make sure you're meter is set to measure Volts DC, not Volts AC. </p>
<p>Mine doesn't have a green wire!</p>
<p>Hi ! I've done this to plug a lipo charger but i have a problem. When i plug the lipo charger, the screen light for a second and the atx cut off. On the voltmeter i have 12v showed, so no problem, but it seems that when i apply some little load (just the charger without charging anything) it goes away.</p><p>Any idea ? :/</p>
<p>Great article and great idea. I've used these PSUs in the past for various purposes, but the idea of adding the banana plugs, etc. is so much better!</p>
Hi there i tried a lot but there is no power in orange red and yellow. Only live wire is purple. Can u help me
<p>You need to short the green wire with any black wire to make the PSU power up. The purple is a constant +5v supply no matter if the PSU is on or off. Once you have shorted the green and any black wire, the PSU fan will spin up and you'll receive power on all rails.</p>
<p>I made it! Thanks for providing such an easy-to-follow Instructable -- this is something I've wanted to make for a while and was finally able to take the plunge. Thanks!</p>
<p>Great tutorial, it does a lot of help esp to the newbie like me.</p><p>I'll just ask what if I have multiple devices that required 12V DC supply and different ampere supply? </p><p>My 12V DC-requierd devices are the ff:</p><p>12V DC Arduino</p><p>12V DC DC-geared motor</p><p>12V DC Relay (2 relays)</p><p>12V DC LED Strips</p><p>I also have 5V devices like Microswitch, Honeywell water Level sensor and LCD.</p><p>Guys, please help me how to connect these devices to the 500 Watts PSU.</p><p>Thank you and you may all have a great day :)</p><p>Any response will be appreciated.</p>
<p>Can anyone tell me if one of these resistor will work ? i want to add just to be sure ? it wont blow op :D</p><p>http://www.ebay.com/itm/2x-5-10w-10-ohm-10-J-Ceramic-Cement-Power-Resistors-Flame-Resistance-Brand-New-/401045504802?hash=item5d602cc322:g:NrIAAOSwT5tWGjvK</p><p>http://www.ebay.com/itm/Chassis-Mounted-10-Watt-10-Ohm-5-Aluminum-Case-Wirewound-Resistor-/191680189623?hash=item2ca10794b7:g:WycAAOSwHnFV5mMN</p><p>Thanks :D</p>
<p>A follow-up question.. how can I use this power supply for a circuit requiring 12v and 6 amps?</p>
<p>I have a question on volts, amps and watts... Is 400w variable depending on whether 12v or 5v used? When you are using 12v, the total wattage will be 276 and with 5v, 200W. Am I understanding this correctly? What if I use both 12v and 5v at the same time?</p>
I had a little project which required 12v dc current to power it... But couldn't find a power supply/adapter powerful enough for the job.. So I decided to use my old computer PSU... This guide has been very useful.. Thank you!
I have a 12v psu how can i make that into a 14v so then i can power a 14v car head unit
12v is enough to power a car head unit... <br>Usually... Car head units can work on a voltage range from 11.2 to 14.4v..
It works so good. I had no problems during modifications. I don't know if i was lucky or good building it.
<p>I made it using an old power supply. The rails are 12 V, 5 V and 3.3 V. It can provide 15 A from each rail.</p>
<p>I have a more basic question concerning how a power supply would be used to power a device.</p><p>If I have a device that requires 12 volts@3.33 amps (40 watts) and I have a power supply that produces 12 volts@15 amps (180 watts) is it safe to use the larger power supply?</p><p>Also is there any way to figure out how a power supply with a larger voltage would impact a device that requires a smaller one?</p><p>As an example, I have a device that requires 5 volts at 1 amp, I have an 18 volt power supply rated at 0.5 amp. Is there any way to make the 18 volt power supply fit the requirements of the 5 volt device.</p><p>Thanks.</p>
<p>The power supply is actually a &quot;voltage supply&quot;. Each voltage rail will provide it's rated voltage, and the load will draw as much current as it needs (up to the voltage rail maximum). It is safe to use a device that requires 12v@3.3A with a power supply that provides 12v@15A. The device will only draw the needed 3.3A which is well-within the capabilities of the PSU.</p><p>It's not straightforward to directly use an 18v@0.5A power supply with a device that requires 5v@1A. You can use a voltage converter that will reduce the 18v down to 5v, but there are some different considerations you need to think about. Especially if your input current rating is less than the output current you need. The simplest way to reduce a voltage like this is a simple-but-inefficient linear voltage regulator chip like the 7805, which will waste ( (input_voltage - output_voltage) * current) watts worth of electricity as heat. It is also limited to the input PSU's current limit. There are other converters like switch mode converters (a buck converter) but these are usually more complex. I'd honestly suggest finding a different power supply.</p>
<p>You can buy a basic 5V buck converter on Ebay or Amazon for just a few dollars; spend a little more ($10 or so) and you get one that's adjustable with an LED voltage display. Then you can run the power from your power supply into the buck converter and it will output 5V. </p><p>However the easiest way is just to buy a 5V, 1A power supply, also available on Ebay or Amazon for a few dollars. Or scavenge a charger from an old piece of electronics.</p>
Works like a charm!
<p>What is the difference between 12v and -12v? Also can i connect more Voltages together eg 3.3v and 5v for 8.3v?</p>
<p>Hey! So, in DC we have positive and negative tension, so, -12 would represent negative 12, and 12 is positive 12V, meaning, if you connect 12 to -12 you'd get 24! The voltage is the difference between the two pins you connect, thus, for 8.3V you'd need -5V and 3.3V or 5V and -3.3V. </p>

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