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>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>
<p>Can it kill me if I touch it? Because I heard that 30 mAmps can kill you, so ...</p>
<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>
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>
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>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>
<p>&quot;if you connect 12 to -12 you'd get 24&quot; </p><p>To get 12 can I connect +12 to ground?</p>
<p>Keep in mind that the negative voltage rails (-12v and -5v) usually provide only very little current (a few hundred milliamps max in most I've seen).</p>
<p>How can we use this power supply in laser engraving where the current requirement s about 1-1.8 amps at 12 volt dc.. ? </p>
<p>Im not sure I understood your question, But most ATX power supplies can give ~15-20 amps...</p>
Just a small warning: Most ATX supplies have a minimum current on one (or two) rails below which regulation is not guaranteed. I've done this many times and I have not yet had problems, but just in case I started adding a minimum load resistor to the rails in question. It's a bit wasteful though, so for non-critical use, leave it out. I also add an LED on the POWER OK and a switch on the PSU ON, but that's not really needed.
<p>How much of a resistor would I need? I've got an old power supply which seems to put out only half the rated voltage for each unless it is plugged into the motherboard. Obviously it needs some load to kick on, but how much and where?</p>
<p>It isn't always the same - different supplies have different minimum current ratings, so you may have to experiment a bit. For an old supply, start by drawing 1/2 an amp (10 ohm) on 5V. Remember it will be dissipating a bit of power - 2.5W for my example above. Also, use a resistor with at least double the power rating that you intend to dissipate and be careful - it gets hot.</p>
I think the ATX spec states that the power supplies should reach their target voltage (and be within spec) with no load now.<br/>There may be older supplies which need a minimum load though?<br/><br/>Good work on the 'ible :-)<br/><br/><a rel="nofollow" href="http://www.pcbpolice.com/">PCBPolice</a><br/>
<p>respeced sir.</p><p>-- &gt; is this capable to give 12v 13A output (to run the peltier TEC-12706) ?</p><p>--&gt; is consist of lots of wire .then how can i find the 12v 15A wire.?</p><p>plz help.!!</p>
<p>Nice instructables!!</p><p>My power supply says 12V rail can give 16Amps, however I cant seem to get full 12V even 10Amps. Using my turnigy charger to charge a 3S Lipo at 5Amps, the voltage from the power supply drops to about 10V and the charger obviously refuses to charge anything and shuts down.</p><p>And yes, I used every yellow cable (there were 6 for the 12V line) and about 5 black wires (for ground). The psu fan doesnt even turn on so I guess that's because the charger isnt pulling too much amps.</p><p>Any hints ?</p>
You need a high amperage and high voltage resistor on one of the power outputs to have a stable output
So glad i read this. I was about to order another power supply for my kooltron 12v refrigerator for $50. The amperage requirements are about 5-6 amps. Every time I think I find a nice one on amazon, the reviews scare me off. So many reviews say voltage drops or amperage is nowhere near advertised. I took a power supply out of a junk PC. it's rated 250 watts and sticker says 12v is 14 amps. Should be more than enough for this little refrigerator. I removed red and orange cables since I only want 12v. I then attached yellows and blacks to a cigarette plug. It works awesome.
Depending on your PS, there may be &quot;Power Sensing&quot; wires that also need to be connected. You can tell because there will be two wires to a single terminal on the 2x10 or 2x12 plug. Mine had a brown wire that needed to be tied to the orange otherwise it would not run.
<p>THANK YOU!</p><p>I was freaking out why my PSU was not working - especially since it was working before!</p><p>I had kept the connectors which I had cut off, and indeed the brown wire is tied to one of the orange wires.</p>
<p>Thanks for this guide. I am getting into combat robots, and didn't realize that battery chargers didn't come with power supplies. Rather than spending $70 on one, I took a spare power supply I'd had for years, and made my own using this guide for about $8 in parts. I only did the 12v plug, partly because I figured I'd never use the others, and partly because it was already a pretty tight fit with the 12v and ground wires (I wanted to make sure I got the full 33A of the 12v rail, so I used all of the yellows).</p>
<p>Hi there, thanks for the great instructable! </p><p>A question for you... my dad and I made this according to your instructions, but with the wires connected to bolts (see photo below). We tested the voltage with our meter (photo below). Our results for the yellow wire were:</p><p>black pole on black wire &amp; red poll on yellow wire (would have thought it should be positive) = <strong><em>negative</em> 12 volts!</strong></p><p>black pole on yellow wire &amp; red pole on black wire (you would have thought this would give positive 12 volts) = <strong>positive <em>2.85 </em>volts!</strong></p><p>Neither of us understood why we got this result. Any suggestions much appreciated.</p><p>Also, now I'm using the power supply to electroform a piece of stick (coated in varnish, dried, sprayed with waterproof glue, covered with graphite powder as a conductive medium). It's been in there for more than 24 hours, but I don't see any plating happening (lots of bubbles though!).</p><p>If you have any thoughts as to what we could be doing wrong in either part of the procedure, they would be great to know!</p><p>Thanks for your help :-)</p>

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