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!
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>
<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>
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>
<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>
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>
<p>You have your red lead plugged into the common port on your meter.</p>
<p>PS and the copper wire connecting the graphite-coated stick to the red alligator clip keeps breaking off. There is something not right here! (louise)</p>
<p>To plate Cu you need low voltage and low pH so that the <br>water isn&rsquo;t electrolyzed instead of the Cu.2 volts and a little H2SO4, which also cleans the plating surface, prevent <br>electrolysis of water.A little HCl will <br>break the Cu+2 to Cu+1 also.You will <br>see snowflake like growth of the Cu.Add <br>a little polyethylene glycol, laxative to prevent the snow.</p>
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>it will work fine as long as the voltage is correct, the unit will only draw what amps it needs</p>
<p>My goal is to convert a PSU so that I can obtain around 55-60V ~ 10 amps. I'm assuming I can connect a few 12V rails together in series to achieve 48V and then add a 5V and 3.3V to achieve 56V. Do I just need a two rail 12V power supply so it has 2x -12V and a 2x +12V to achieve this or what should I look for?</p>
<p>The line of -12V or 3.3 volts in PSU It does not provide 10amps!!!</p><p>Only the lines +12V, or +5V can provive 10 amps.</p>
<p>1:30h to build it. Very simple and very usefull, is there when you need to use 3,3 - 5 -12VDC.</p>
Nice write up, very easy to reproduce! I went with externally routed wires, I like the look better than the on-chassis style. Shown with two 10W resistors hooked up, those things get hot!
<p>Good to see conversion to something like 30-60V DC...</p>
<p>I am going to use only the +12 V line. So is it good if I cut off the remaining wires including the orange, brown, purple and grey wires ?</p>
this worked out great.
<p>but how can i get 5v and 1a?</p>
<p>Voltage is fixed from the power supply, but the device will take as many amps as it needs. So you can use a 1Amp power supply, or a 13Amp power supply to power something that needs only half an amp. It will just take what it needs. MAKE SURE you use the right voltage though. If something needs 5V, DO NOT give it 12V.</p>
<p>Hello there, I've made all those steps, but my PSU don't turn on! Before I did all those things, it started up just hooking up the green and black wires, but when i disassembled it and soldered the green and black wires, it doesn't turn on. Can you help me mate? Thanks!</p>
thank you
<p>Brilliant. Only need 12v at the moment so shortened all the other wires and tucked them of the way for now. Built in less than an hour with bits from the man draw and a couple of terminals that cost about &pound;1 each. Easily saved myself &pound;40 - top marks to the OP. Many thanks. </p>
<p>I made it but problem is that I received 14.3 volts</p>
<p>Is there a way to run a few of these together to increase the amps/volts?</p>
No I don't believe so..each one is independent of each other... Want more power get a bigger transformer
<p>yes if you put each wire color relative to its voltage the more wires together will give you more amperage </p>
what I meant actually was running multiple power supplies together
<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="http://www.instructables.com/id/Encyclopedia-of-ATX-to-Bench-Power-Supply-Conversi/" rel="nofollow">http://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>
<p>Hi,</p><p>I have just finished converting a 400watt ATX power supply but unfortunately it does not work. When I switch on the fan turns over a couple of times and then stops. The only signs of any voltages are the lit up Green LED that I have connected between the purple wire and black ground wire. I have tried having a 10 ohm 10 watt resister between the red wire and ground but that does not help, in fact it appears to make it worse as the fan then only turns about 180 degrees and the. Stops. Any suggestions please</p>
<p>I have had the same problem with my power supply. The problem is that there is a shortage somewhere which results in the system shutting down. Try to find the shortage and everything should be allright. Mine was located at the added resistor, it touched the housing of the power supply when closing it. After having added heat shrinking tube, the problem was solved. Good luck </p>
<p>Hello,</p><p>I don't mean to butt in but if you have a newer ATX supply (that is one that has most of the current on the 12V rails or one lacking a white wire which IS found on older PSUs) then you will need to put the load resistor between the 12V (usually yellow wire) and Gnd (the black wire). Before you do that though, you might want to test if your PSU is still working. </p><p>If you've still have a purple wire, then that usually has a +5 volt continuous output even with the supply off (it's the PSU's standby good switch). Measure the voltage drop of that across a resistor (connect the purple wire to one end of a resistor, connect a black wire to the other end, and measure the voltage across the resistor). If that's about +5volts then that's working and so's your PSU. </p><p>Hope that fixes your problem.</p>
<p>You must have a load on the supply, or it will shut itself off. It's a safety feature in power supplies.</p>
I had a 10 ohm 10 watt resister between the red wire and ground. Is that not a LOAD on the supply?

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