## Step 2: The Diagram

The diagram at right shows the main output connector of the power supply when viewed from the end. The colors represent the different colored wires going into it. Common colors represent common functions, ie all red wires are +5 volts, all black wires are common and so on. The connections most useful to us as haunters are the +5V (red wires) , +12V (yellow wire) and the Common or ground (black wires). Both 5 and 12 volt lines normally deliver ample current for our needs.

Of the other voltages available, the +3.3V connection delivers ample current, it's just not a very useful voltage. The +5VSB (5 volts, always on), -12V and -5V are normally very low current lines and are of little use to us.

The green wire, pin 14, is the on/off switching line. To turn the power supply on, the green line needs to be shorted to a Common line. An easy way to do this is to insert a jumper between pin 14 and pin 13.

Most power supplies require a load across one or more of the outputs to operate. The link I give above shows how to add a resistor across the 5 volt side of the supply to act as a load.

The smaller connectors coming out of the power supply use the same color codes. As an example, a connector with a yellow, a red and two black wires will have +12 volts (yellow), +5 volts (red) and two commons.

To use the power supply, for 12 volts, you'd connect a yellow wire to the + input of your project and a black wire to the - input. For 5 volts, you connect a red wire to the + and a black wire to the -.
Very good information, utile. <br> <br> <br>Thanks.
Thank you !
I am curious, on most supplies, there needs to be at least a minimum load across the +5V (Not the +5vSB) to maintain the switching activity, otherwise the supply will shut-down. I've run into a few supplies, where there was a soldered-in 33-Ohm, 5W resistor across the connections on the board inside, but many others have had to add an external load, sacrificing one of the +5V (Red) &amp; GND (Black) wires to a 10-Ohm, 10-Watt 'sandbox' (sand/epoxy filled ceramic block, with a wire-wound resistive element inside.) (I've still used 33-Ohm-5Watt versions) to maintain the load. Yes, these are a great way to recycle supplies from machines which have been scrapped down.. I've made 3 myself. <br> <br>One side note, try this, it's real interesting! start-up a supply, then connect a volt meter across the various voltages, but skip the GND (Black) wires.. Yes, as example,on a supply with -5V, you can generate: <br> <br> +8.3V (+3.3V, using -5V as GND) <br> +10V (+5V, using -5V as GND) <br> +15.3V (+3.3, using -12V as GND) <br> +18V (either +5V, or +12V and -12V or -5V as GND) <br> And the highest: +24V (+12V, using -12V as GND) <br>(the object, Not connecting the GND/Common/Black wires to anything.) <br> <br>
<p>Terrific tip! Thanks. Now i can do even more with my \$3 ATX PS from the second hand store. Just mind the current draw when stacking pins. Never ask more than the least capable supply can provide.</p>
There are a few more, odd-ball, but going from some of the +5 to +12, does generate a voltage, but not sure if if it registers exact +7V, or not.. Likewise, +3.3 to +5, would generate +2.8.. But, a volt meter, is better than sacrificing a project.. (at least the volt meter will say if it's good, or not, and not fry unless set tot eh wrong maximum.) <br>
One small comment: Somewhere in the Arduino specs it mentions that if the supplied input voltage is less than 7V, then they cannot guarantee 5V at the output pins, also if the supply voltage goes over 12V then you may start to cook the onboard voltage regulator. If you do need to be sure of getting 5V to the output pins on the Arduino you could either, simply splice an old USB A connector into one of the disk drive power connectors and use that for power, or supply 8.3V, 10V or even 12V directly to the power input. Other than that, thumbs up, I love hacking old pc power supplies for my little projects ... :-)
<p>Understandable for the input voltage, But I'm pretty sure the regulator they use will cover from +5.5V up to +20V.. Though, with the Parallax BOE (Board Of Education) Board (socket for the Parallax Basic Stamp-2, breadboard, etc.) they used a 7805 to drop Vin to +5V. (reference <a href="http://www.parallax.com/sites/default/files/styles/full-size-product/public/28850.png?itok=JIdkExWl" rel="nofollow"> http://www.parallax.com/sites/default/files/style...</a> ) and the base BOE-Bot only had a voltage running of +6V (Vin... If you powered the robot with 4x NiCad batteries, you had to change the jumper between sockets X4 &amp; X5 to allow the full 4.8V to reach the servos, by changing the jumper from Vdd to Vin)</p><p>One suggestion I've always made, when I've modified these supplies, If you have a dead TEAC 3.5&quot; floppy drive handy, Don't chop-off the Molex &amp; Mini-Molex drive supply connectors! unsolder the power plug from the dead floppy drive, clip off the wings at the back, and straighten the pins that were in the board.. Now, plug it onto the mini-Molex connector, and plug the old soldered ends into your breadboard. Now, you have +5V, 2 GND, and +12V on 4 pins each.</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; https://www.instructables.com/id/Encyclopedia-of-ATX-to-Bench-Power-Supply-Conversi/<br>Take a look at about 70 different approaches to this project.</p>
<p>this work very very good</p>
That is a very very low quality power supply, you would be better served by something made better. <br> <br>Also the picture of your barrel plug shows that the ground wire is not soldered on good, it's a &quot;cold&quot; solder joint which may fail eventually. All you need to do to fix that is apply some soldering flux and reflow the joint as there is already enough, even too much solder there as that large blob will interfere with putting the barrel connector jacket casing back on it. <br> <br>For that reason it is often easier overall to just solder the lead to the inside wall of the negative contact, doing that before soldering the positive wire lead so it is not in the way.
Very good!
Might not work with all power supplies.. there are a few Dell supplies, which have a different wiring scheme for the ATX connector.. (PG or the constant (standby) +5V, can't remember which.) occupy the wrong pin, and connecting them will end in a loud POP as the switching IC will blow its top. (been there, done that, everyone came running, wondering why they smelled burnt epoxy.) Also, not all supplies will start off with zero load. the Arduino is hardly enough.. Some of the older ATX supplies required a minimum load to maintain the switching circuit.. a 33-ohm, 5W 'Sandbox' resistor (ceramic block, with sand/epoxy holding a wire-wound resistor), across the +5V to GND has always worked for me. The supply will see the load, but match to maintain the voltage. One more little tip, try this.. If you have an old 3.5&quot; floppy disk drive that is fried, desolder the power connector, and keep the matching mini connector on the power supply side that matches it.. You can then, from a breadboard, run jumpers from the VCC on the arduino to +12V (Yellow), and run +5V external devices off the +5V (red).. One final tip, if the supply cooling fan draws air in, forcing it into the box, flip it around! drawing air out is more efficient for cooling.. <br> <br>I've converted two supplies like this myself, and run arduino, raw breadboard projects, and even a Raspberry Pi off them. <br> Nice thing about the ATX supply, is you have access to 3.3V, which is great if you're running projects for the Pi's GPIO bus... I still haven't put together a 3.3V&lt;--&gt;5V level handler, so been slowly learning to run things from the 3.3V level.
This is just what I needed for converting an old ATX power supply for use to power my 10M and 2M radios. Now I know how to wire up a switch to power the supply up. I'll take one of the 3.3v lines and connect a red LED and resistor for a power on light while I'm at it. <br /> <br />73 de N0YBC
I've been using a 350W atx power supply for a few years now, well when I do electronic bread boarding stuff anyway. I use a 1/2 watt resistor (don't remember the ohms) and led on one of the +5v pins to make sure there's power before I flip the on switch for whatever I'm testing.
That would be the perfect job for an old at power supply also. Still have an Amiga ps that has the power switch on the box. You just gave me an idea.
the older Non-ATX versions, generated only +5V, +12V, -5V, &amp; -12V, to GND.. Should still work with the same principle load across the +5V.. I have a few of the original IBM AT supplies lying around too.. Just applied one of my converted ATX units, +12V to -12V, to recharge a Razor mini Kart, (+24V system, two 12V gel cells.) <br>
I do to, but I also have systems than can use those old ps units.
To anyone wants to make this, be very careful because these PSU have very hight wattage (400 W and more) and this could be lethal! <br>This is really interesting as know-how, but remember that a good switching psu from the Bay is very cheap, compact, and safe!
Side note, I think you mean Lethal at 400W, because of the high output of the +5V &amp; +3.3V voltages could essentially fry the thin wires on the PC-Board in an instant (If shorting the supply.).. Or, are you referring to the working voltages of the primary input side? (the filter capacitors on the Input side usually have a working voltage of 200V-DC, so yes, THIS is Lethal too!) A good rule of thumb, ALWAYS allow the supply to sit for at least 10-15 Minutes, before opening. This should provide more than ample time for the input capacitors to discharged. (most supplies have a bleeder resistor across them.) These cannot be mistaken. they're the LARGE canisters and will say anything from 200WV to 240WV for the voltage.. Yes, this IS a serious warning! contact with the pins of these capacitors, unless they've discharged will literally kick you to the floor, and could possibly stop your heart if the voltage is allowed any path across the heart. (I.E. in one hand, to the other on the other arm.)
Good job!! Voted =D!
Hmm Thank u ! :)
This is a nicely minimalistic version of this idea, and it does work well. I use a slightly similar version of the same on my bench.