Step 1: Harvesting & Preping the Power Supply


Capacitors can bite and if not give a painful shock kill you. Please discharge the power supply by letting it sit unconnected for a few days or connecting a 10ohm resistor between the red and black wires.

If you hear buzzing when you turn on the power supply it means there is a short or another serious problem. If you hear buzzing (that not coming from the soldering iron) when soldiering it mean your power supply is on. There is still power flowing through the PSU if it plugged in but not switched on

OK lets get straight into it remove the computer case and take out the screws (usually 4) at the back of the computer to release the power supply. Now take out the 4 screws on top of the case and take the wires out of the hole then group wires of the same colour together and snip off the ends.

Just To tell you , you've just void your warranty
<p>I made it, but made some modifications. Thank you</p>
<p>Looks nice, my dude!</p>
<p>Hi, I really wonder what -12V is? If I want to get 12V, I get wires connected to +12 and ground. In which circumstances should i use -12? Thanks in advance</p>
<p>If you connect your positive wire to +12V and your negative wire to -12V, you will get 24V. It is like AC mains power: it doesn't alternate between +230V and 0V 50 times a second (Europe) but it alternates between +115V and -115V 50 times a second. The final voltage will be your positive voltage minus your negative voltage: if you have 12V on one wire and 0V on the other, then 12-0=12V and if you have +6V on one wire and -6V on the other, then +6-(-6)=6+6=12.</p>
<p>Just for safety's sake your AC maths need to be corrected. 230 V 50 Hz AC means that the voltage is alternating between the peaks of +325 V and -325 V.</p><p>The negative DC voltages are useful for op-amps and other applications where you need a -12 - 0 - 12 V supply. The power capacity of the -12 V output does not make it very useful for creating a general purpose 24 V. Also you would potentially enter into trouble with separate earth levels if you use that kind of 24 V in the same circuit as for example 5 V from the same supply.</p>
<p>Thank for enlighting me Ivang. Have a great day.</p>
<p>By the way, as other people have said, don't try to connect big loads when using the -12V cable, as it supports very small currents (around 500mA or less, depending on the power supply).</p>
<p>hi there can i use to power 2 peltier module for aquarium chiller??</p>
<p>What can I add to be able to regulate current as well?</p>
<p>-12v line on modern PSUs is VERY low output. First random PSU I just<br> looked at was 800mA. Second was only 500mA. And these are older PSUs. <br>Since -12v is rarely used now, the outputs have been dropping off.<br>And remember, when you start putting a load close to the max rated output, the voltage may drop somewhat.<br></p><p>Do not rely on the -12v line for power! It's OK for small loads, but even a small fan may overload it.</p>
<p>avoid to connect the regulator to the psu metal body</p>
Hello, I need 12v 5 amp current from a pc smps. What I need to do?
<p>Nothing just use 3 or more yellow(+12V) and 3 or more black(GND) wires</p><p>don't forget the resistor 10 ohm 10W between black(GND) and red(+5V)</p>
<p>i just built it and all my multimeter is showing is a variability from 0.3 volts to 1.5 volts what did i do wrong</p>
<p>Hi, I made this project. I also added a 2 port usb i hacked from the same old computer. I simply connected green (power on) to GND (black) to make the original switch work. This case I don't have the above mentioned 5V when plugged in but not switched on. I consider working on that to i order to power the usb port.</p><p>My observations:</p><p>The PSU itself gives only 23V. After adding the variable circuit with the LM317T it dropped another 1V, so the schematics states correctly (in my case), that output is 22V. </p><p>Problems to clarify:</p><p>I observed a .1 to .3 variation on the voltage output. I have a suspicion that it could come from my digital multimeter, so I made the following steps to verify:</p><p>1. I wired a 1K load on the output. </p><p>Result: around .5 volt dropped but still varying .1 to .3.</p><p>2. I measured with an analogue display multimeter. </p><p>Result: stable.</p><p>3. I wired a 24V 50W halogen bulb to it. (This was at hand). </p><p>Result: visually stable. Ampmeter showed steady 1.5A.</p><p>4. I took measurement on 5V (red) and GND (black) on the PSU itself. </p><p>Result: variation.</p><p>I'm still concerned with this variation. I will test it with other multimeters when I have the chance, to determine whether it is a measurement error or not.</p>
<p>I think the -12 +12 can cause some issues with sensible electronics. I connected a device that works perfectly fine with every other connection 3.3, 5 and 12V but not with this. Also it refused to show the right measurements with my multimeter. Just didn't work well at all with many things. Eventually it broke so the next time I will use a regular 24v transformer for this job. Takes a lot less space and gives off a lot of more amperage as well.</p>
<p>u mixed -12V &amp; +12V regardless current sourcing, -12V is usually so small sourcing current!</p>
<p>need help with this? can you help?</p>
I flipped my breaker!
<p>Hello All,<br><br>I have created this about 2 days ago and all went great. It was working fine and I was very happy with my project. But then I was testing some circuit with led diode and I have increased the voltage by mistake while the circuit was still connected. LED Diode of course blow up :) but also my power supply is somehow damaged. I will transfer the symptoms to you and hopefully someone will provide me with possible fix:</p><p>When I turn the switch ON it doesn't run (only the fan will try to run and at the same moment will go off. Please note that I do have 9W47ohm resistor as a fake load between GND and 5V (black and red wires). I know it was suggested to use 10ohms but I couldn't find one and this was perfectly fine. Just to exclude the resistor as a possible reason. Also please note that the issue started to happen after the incident)</p><p> If I connect some DC motor that operate with let's say 18V, and then turn ON the switch, it starts working but the minimum voltage (on the regulated outputs) is 12V and not 1.2 as before and it only goes up to about 14.6. Basically that is it, just I am not sure how to fix it. I did one mistake I didn't used PCB because I considered it to be fairly simple project, but now fixing will be real pain. I will now create PCB so if there is a need for future fixes it will be easier and faster.<br><br>I would be really thankful if someone suggest what could be damaged and how to check/test because although I do have some general knowledge, I am far from being expert in electronics. </p><p>Thank you in advance.</p>
Hi.codegen 350W. I have the resistor on 5v line and about pc. 12V yellow 12V wires connected. I only need 12V for my lipo charger. Psu gives out about 2amps now. On the side label ot states that 12V out is 15A.<br>any tips to get hihher current output ?.
hi, this is just what im looking for except one thing. I am using a PSU from a DELL XPS and its a 750W and it has both a 20 wire plug AND a 24 wire plug besides all the other little connectors with 6 or 4 wires. <br>Do I use ALL the wires? take every black wire and put them together, every red, every orange, blue (well, blue with a white stripe)... ? also, do i use a 10w, 10 ohm resistor or do i need a bigger one? thanks!
<p>i would suggest you use maybe 3 wires, at most, of each color. any more than that and it is a waste. just cut out all the lead wires, and leave only 3 of each color and you'll be good to go.</p>
Thanks for the update!
<p>The more wires of the same color you tie together...only increases the amount of amps you can pull without melting any wires.</p><p>10ohm 10W should be fine for most applications.</p>
<p>Thank you for the instructable, </p><p>I have used LM317 because I do not need high amperage. I have replaced 120 Ohm resistor with 240 Ohm and added extra diode (1N4002) to the right side of C2 (1uF capacitor) . </p><p>It works well, I get variable voltage between 1,1 v - 23 v</p><p>Regards</p>
<p>Hi, i tried building the variable voltage circuit according to what has been mentioned, however, strange thing is that, when I turn the potentiometer towards the lower end, it starts to burn the potentiometer ( i though new year just passed :-) ). Where could I be wrong? Btw, I use LM338K. Any suggestions? Thanks </p>
<p>You could be wiring it wrong somewhere. This happened to me too when I first tried to assemble this circuit. Make sure you follow not only the circuit diagram but the LM317's pinout. From the front, pin 1 is the adjust, pin 2 is Vout and pin 3 is Vin. Try assembling it on a breadboard first to make sure that everything is properly wired and working before you solder it.</p>
<p>and use a pot with a high enough wattage rating so as not to burn the windings</p>
<p>Don't do the variable circuit this way. It'll fry your PSU. Look at the schematic; he's tying -12V to Ground. No way that will work right.</p>
<p>looks okay to me. the -12v isn't going to ground, it is floating, and acting as ground only for the purpose of his schematic. no problem</p>
<p>Are you referring to a green line on the bottom? :)</p>
<p>Hi, I've a Dell N875EF-00 PSU (825W) that I scavenged. I don't really understand the sticker, it says 18A / 12V. Does it mean I'll have 90A if I connect all the 12V together ???</p>
<p>no, you will not have 90A.</p><p>if you look closely at the circuit board, you'll notice that all the 12v lines are already connected together.</p><p>have fun.</p><p>aidan</p>
Each 12v line is usually derived from the same transformer, but I'm unaware of the internal circuitry beyond that. I don't recommend tying them together.
<p>One month ago I have made this. Everything was fine until today. I have used it in different voltage settings. But, today while I was working on project with 18.9 Volts, it suddenly blowed up. </p><p>I made no short circuit on the project. Didn't even touched the breadboard for nearly 10 mins. </p><p>I checked later on, the fuse soldered on the main board (5A L240V) has blown.</p><p>Can you please give me any idea what caused this ? </p>
<p>I think I know why and think everyone who follow this guide should too! If you read +12V on your PSU, it says about 14A, atleast on mine. But if you on the other hand read on the -12V, not the GND, then the maximum current is 1A. That means that you can pull lots of amps out of the 3.3V, 5V and 12V. But on the variable output you can never pull more than 1A from the PSU, atleast not for any extended period of time. I am puttin a 1,25A fuse onto my circuit as I write this.</p>
Anything could have. Try replacing the fuse with an equivalent type.
Hey dude please reply fast..<br>I am using 10k pot instead of 5k<br>Lm317t for lm338k<br>And 1N4007 instead of 1N4002<br>Suggest me the changes in circuit and also let me know why my pot gets red when it is in lowest positin
<p>I use a LM317T as well and a 1N4007. I used a 4,5k potentiometer and it got hot and started smoking at lowest too. Then I tried a bigger one and then I could only switch between 11 and 12 volts. Now the old one doesn't work either and I don't seem to be able to regulate at all. If I disconnect the potentiometer (connected it through a terminal block) and it sends out 12V. Is it supposed to do that?<br><br>Did you figure out your problem? </p>
Sorry bro..i didnt find any alternatives and nor i had continued on project but i will be working on it soon. Till then u can google and sort out, if u could get the solution plz tell me @ unmeshsawant55@gmail.com. I will also reply you as soon as possible. Till then good luck!!!!!???
<p>If I couldn't figure it out, I got the advice to try this instead: http://www.eleccircuit.com/wp-content/uploads/2012/09/Circuit-of-my-first-variable-dc-power-supply-1-2v-to-30v-1a-by-lm317.jpg Might be of interest to you as well.</p>
Thanks bro....me also trying to find any issue in circuit..
<p>I am trying to make this out of 100% salvaged material from my garbage room. The only thing lacking right now is the diode and a potentiometer. The latter I know I will find in a couple of days but for the 1N4001 or 1N4002 it doesn't look as promising. I've found loads and loads of 1N4007 though which seems a lot more common in new electronics. From my very much layman based research I've found out it would be just as good for the purpose, just that it's made for higher voltage. My question is, can I use a 1N4007 instead?</p>
<p>Please tell me,</p><p>Does power supply leak current from its case when it turn on.</p>
<p>how you connect the screen to show the voltage also how i can read the AMp</p>
<p>I've tried to make this but I've found a couple of problems:</p><p>What should I do with the gray wire? It's the only wire left unconnected and the supply only stay in standby mode.</p><p>And I've teste the bornes for short circuits and apparently all of them are connected (5V, 12V, GND...), what have I done wrong?</p><p>Thanks in advance.</p>
<p>Connect the gray wire to gnd (on your own risk)</p>
&nbsp;My PSU has no green wire. What should I do?<br />

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