Step 4: Connecting front-panel items

Here, I am connecting the appropriate wires to the binding posts, power switch, fuse holder, and LED's.

In an ATX power supply, there should be a wire that is used to turn on the power supply. You can see this wire (It's green) in the second picture; it is the green wire in the middle, where it says "ON/OFF" on the PCB. I connected this to the switch, and the other pole of the switch went to ground. The +5, +12, and -12 are connected right to their wires on the PCB. The ground wire is connected through the fuse holder before the binding post.

Initially, I was going to use green LED's, but I realized I had many more red LED's than green LED's, so I switched them over to reds. In the first picture, you can see the holders I installed into the front. I connected the LED's through a common resistor to ground. The LED on the left (from the front view) is a standby LED. It is lit whenever I have the power supply plugged into the wall. It is connected to the +5V standby wire on the PCB. In my PS, it's purple. The other LED is the "Power On" LED, and it is lit when I have the power supply turned on. It's connected to the "Power OK" signal wire, which goes to +5V when the power supply detects that it has stabilized the voltages. In my PS, it's the gray wire.
<p>Hello Matherbeckler,<br>Thank your for posting it. I like it a lot when you not only show the step, but also explain it. <br>One beginner question though, Can you add this kind switch to this project, I do see you add resisters to power up LED for indication. If possible, can you teach me how ? Thank you in advance. I just happen to have one and want to implement it into this project. </p><p>http://www.thebookyard.com/product.php?products_id=4498</p>
<p>I have connect that button with motor test to see if it &quot;works&quot;. connected as pic. however, in order to have motor running continuously. I have to hold the button firm. <br><br>On the other hand, I found another switch button. (see pic) connecting the motor as same as the Mac mini one. it works great with the motor. <br><br>My question is: Can can use this tiny switch button to connect the Power On(green) and Ground(black) ? Do we need to as some resisters?<br>Does anyone know how to implement the Mac mini one ? Thank you so much!</p>
The Power On (green) and Ground (black) wires need to be continuously connected to keep the power supply turned on. Most computers (even a mac mini) have a &quot;momentary pushbutton&quot; for the power button. The computer motherboard detects that momentary button press and then connects the green and black wires to turn on the power supply. You'll need to do the same, by holding the green and black wires connected for as long as you want the power supply turned on. I don't think the mac mini button will work very well for your power supply, unless you add some extra electronics. You could possibly use some sort of latch to turn the momentary pushbutton into a push-on/push-off sort of button, you know? https://en.wikipedia.org/wiki/Flip-flop_(electronics)<br><br>It is not possibly to know how a switch works based on a photograph. You need to experiment to determine how the connections work. Are there only two connection points for that switch? Do you push the blue part directly in or does it slide or rotate in two directions? You don't need any resistors for the power supply on connection.
<p>I almost done. Amph I have a few question. The ATX PSU I used have 5v with 20amp and 3v with 20amp where should I connect the 10wtt10k sand bar power resistor, in 5v or 3v? and about the fuse, is that necessary? or if yes, what is the specifcation?</p><p>Lastly, is it possible to lower the amper or 3v, from 20amp to 1amp?</p>
Hello, good questions!<br><br>1. Placement of the power resistor is somewhat of an experimental process. Some power supplies don't need one at all, some need it on 5v, some need it on 3.3v. You will probably need to experiment to see where it is needed. If you turn on the added switch and the fan doesn't turn, or the fan turns off after a few turns, then you likely need to add a power resistor somewhere. I'd try 5v first, and then 3.3v, and if it still doesn't stay turned-on, maybe try both 5v and 3.3v? Good luck, and let us know what you find!<br><br>2. The fuse is there to protect your circuit from a mistake, not to protect the power supply. I would expect most power supplies to have built-in over-current protection, either in the voltage regulators or even in a fuse inside the socket where you plug it into the wall outlet. If you make a mistake in your circuit, such as an accidental short-circuit, this kind of big power supply will be able to provide amps and amps of current through that little wire, likely melting or causing other damage to your circuit. If you know your circuit will only need a few hundred milliamps (less than one amp in total) then adding a 1 amp fuse to the +5 or +3.3 or +12 line (which ever you are using) will help protect your circuit by having the fuse blow instead of dumping tons of current through your circuit. I would estimate the largest expected current use, then use a fuse with double the current.<br><br>3. This is a very common (and very good) question, and the short answer is that you don't have to worry about the PSU having too many amps of current.<br><br>This kind of power supply is more accurately described as a &quot;voltage supply&quot;. It tries to supply a fixed voltage (like +5v or +12v) no matter the amount of current drawn. If you draw too much current (more than the rating) then the power supply will be unable to keep the voltage at the right level and the voltage supplied will droop down. If you draw less current than the rating, then everything should just work, there's no worry about it providing too much current.<br><br>By way of analogy, the municipal water supply in your town probably supplies water at, say, 100 psi. A small bathroom sink will only draw a little bit of flow, while a garden hose will draw a lot of flow. Both are tapping into that 100 psi supply, but only draws as much flow as it needs. If you turned on all the faucets and hoses and taps in your house, you might draw so much flow that you exceed the flow capacity of your water supply, and so the provided pressure would drop a bit. I hope that makes sense.
<p>I have to turn it on and of 4 times and quikly to make it run, but hey, it is working!</p>
<p>nice dmm, u an eev blog fan? if you havent heard of it check it out. I ask because your choice in meter is one of his recomended ones</p>
<p>Just an idea, but if you need a load to draw a small current on each voltage rail, could you not use an LED and an appropriate resistor to drop the voltage instead of these power resistors? It would act as a status light to prove each voltage rail is powered up. </p><p>Or would it not work due to the current being too low?</p>
A &quot;power good&quot; status LED for each voltage rail is an excellent idea in and of itself, and they might even draw enough current. The whole &quot;small minimum load&quot; stuff is really black magic, nobody really knows anything except &quot;this worked for my power supply&quot;, and really takes a bit of experimentation with your specific power supply in your specific use case. Some people use their PSU as a battery charger, so there is always a large load and no power resistor is needed. Most LEDs only draw a max of a few dozen milliamps, so that might not be be enough current draw to keep the mystery &quot;minimum load&quot; circuits happy :-) Good luck!
<p>I would bet one could take the &quot;black magic&quot; out of it if they read the markings on the DC-DC converters and used google to find the data sheets. </p>
<p>Thanks for the instructable it helped me a lot with my PSU. One thing you forgot to mention, or it didn't apply to you, was that you have to connect the 3.3V brown sense wire to the 3.3V rail or else the unit wont turn on. Idk if this apply's to everyone but my unit would only turn on for a second then turn off when it wasn't connected. Also added a LM2596 buck converter in my unit so I can have a adjustable voltage output. I also used 5x 15Ohm 1 Watt resistors in parrell to get a comparable 5W resistor then I used another bundle of those 15Ohm 1Watt resistors and added it in series to have a total of around 10W at about 6Ohms. </p>
Nice work, I like the blue light and the 7-segment displays. My PSU was so old it didn't have a 3.3v sense wire, so you make a good point that newer PSU will need that.
Lol my power supply is anything but new, I think. When I bought it the fan grill was completely covered in dust and I mean like a thick layer of it. But yeah I guess it varys with PSU. Also those aren't 7 segment displays its just a cheap 3 digit voltage meter, you can buy them in ebay.
<p>have you ever attempted to count the little lines that make up the digits in your &quot;cheap 3 digit voltage meter&quot;... u might find that there are 7, matt wasnt wrong calling it a segment display. Next time try to understand some people know more than you...trust me when I say it takes a lot of effort to find something to like about your build but he did and yet, you give additude in return</p>
<p>if i want to put more binding post do add more specific current for my 5volts and 12 volts (like 1A, 2A, 5A) what should i do? thanks..</p>
Hello, good question! If you want to limit a specific binding post to only output a certain amount of current (1A, 2A, 5A, etc) then you need to use a fuse that will blow when the current limit is exceeded. Be aware that fuses are not very precise in terms of current limits, and there is usually a range where the fuse may or may not blow.<br><br>Hope that helps, let me know if you have further questions, or if I didn't understand what you were asking.<br><br>-Matthew
<p>hi Matthew<br><br>currently my ATX power supply have 12v with alot of Amps power...<br>i wonder it can charge my deep cycle battery 12v 9A or parallel connection with 12v 54Ah. <br><br>can you show us a diagrams that 12v have 1A , 2A, 5A , 10A ?<br><br>-Kokoro San</p>
<p>Hello Kokoro San. Be aware that many ATX power supplies have 12v split into 2 or more sub-supplies. Look at the sticker on the side of the ATX power supply for details. I would suggest using a battery charger to manage the charge process.</p><p>I am not sure what you're asking about for diagrams?</p>
Thx for reply Matthew Currently.. my ATX power supply on yellow color wire output is 12v 20A I wonder it able to make it 13v 3A to charge deep cycle batterie
have soldered a 25ohm 10watt resistor on my 12 volt rail since it has the most power.<br><br>but the resistor is getting too hot that i can't touch for long... is that normal? do i need to use a heatsink? or something else? please help..
Hello, good question!<br><br>Using Voltage = Current * Resistance, we know that 12 volts across a 25 ohm resistor results in 12/25=0.48 amps of current flowing through the resistor. The other important formula to use is Power = Voltage * Current, so 12 volts * 0.48 amps = 5.76 watts of power, that becomes heat in the resistor. Since the resistor is rated for 10 watts, you're not going to melt the resistor but it may get warm over time.<br><br>I wouldn't expect it to get too hot to touch, so perhaps the resistor has less resistance, and is therefore drawing more current? If I remember correctly, the wirewound resistors that can handle many watts usually have a large variance in the amount of resistance it actually has, compared to the &quot;official&quot; resistance. If you have a multimeter you can measure the resistance of the resistor by itself, or you can put the meter in current measuring mode, and insert it in series with the resistor and measure the actual current. Let me know if you need more info about how to use a multimeter for this kind of investigation.<br><br>If you could find a 100 ohm power resistor, that might work better. It would result in 0.12 amps of current instead of 0.48 amps. I really don't know how much current is needed for the minimum load, but I would guess that 0.1 amps would be enough. This would reduce the power burned as heat in the resistor down to 1.44 watts, so you could use a 5 watt power resistor instead of 10 watt.
<p>Thanks alot, here's my version. Converted from an old 250W Hipro unit from my mother's ancient Pentium 4 machine that just finally gave up last month.</p>
<p>I'm having a problem with one. I have the brown connected to the orange as it was in the plug, and the resistor on the red and grnd as it should be. But when I try to fire it up it will only spin the fan for a second and then quit. It won't stay running. Any suggestions? Much appreciated.</p>
What do you mean by &quot;the brown connected to the orange&quot;?<br><br>Perhaps try moving the power resistor to a different voltage rail, such as 12v or 3.3v? Maybe your particular power supply needs the minimum load on a different voltage line? Or it needs a minimum load on two or more of the voltage lines? I've never seen any specifications for this sort of thing, so you might need to experiment with your power supply. Let us know if you figure out what's going on.
<p>There was a brown wire piggybacked onto an orange in the 20 pin plug so I after removing the plug I tied the brown wire to an orange. Also, I've tried the resistor on the 3.3v, the 12v, and the 5 volt. Also tried two resistors. One on 3.3v and one on the 5v at the same time. I've set this one aside for now pending a solution. If I can figure it out I'll post my results.</p><p>Thanx!</p>
<p>TheLonesometoad, I was having the very same problem you were, but I was able to resolve it using two 10&Omega; resistors in parallel, on the 5v line. This gives me an equivalent resistance of 5&Omega;, and it seems that is enough for my power supply. I got the idea for this from matthewbeckler's reply to harshesh below. Hope this helps!</p>
<p>Why the extra fuses? I am sure I read that the reason converting psu's into desktop lab psu's is because of the built in protection they already have. I Am trying to convert a modern 535 watt into a desktop psu. I don't know how many wires I should join together being that my psu is much larger then all the examples I can find. I think if I joined them all together it would be far too much power possibly far to much wattage but my memory on the subject is very cloudly. Can anyone tell me how many 12 v wires I can safely join together?</p>
<p>Also, at least for me, the reason people convert PSUs into a bench PSU is because there are many old and cheap (usually free) PSUs that aren't powerful enough for a new computer, but still work perfectly fine and provide more than enough power for hobbyist needs.</p>
Hello, sorry if this results in double-posting, but my first reply seems to have disappeared. The extra fuses are added to protect your load from over-current situations, and are not intended to protect the power supply itself (the built-in protection is to protect the power supply, not to protect your circuit).<br><br>A power supply like this is known as a &quot;voltage supply&quot;. It creates the rated voltage (5v or 12v for example) and tries to provide as much current as needed by the load circuits. It can provide up to the rated load current (listed on the label on the side of the PSU). There's no danger of providing &quot;too much&quot; current, as the load will only draw as much current as it needs. If you join too-few wires, then you draw a lot of current, the individual wires might start to heat up, so I would connect as many wires as you can. It's sort of like how in your city's water supply, they provide water at a certain pressure, no matter if you use a little bit of water, or use a ton of water.<br><br>One thing that complicates the answer is that modern power supplies seem to have split their 12v rails into two or more &quot;domains&quot;. Presumably this is because it's easier and cheaper to include several smaller 12v regulators than to include one giant 12v regulator. For example, take a look at the attached image, showing this power supply has three 12v regulators each capable of providing 18 amps of current. I'm not sure if the PSU would like having all three 12v domains connected together (they might fight each other). I'm not sure how to tell which domain a certain yellow wire belongs to, but you might be able to look at the circuit board in the PSU, and maybe the yellow wires are grouped together into two or three groups? Of so, I would feel somewhat confident in combining <br><br>Hope that helps, let me know if you still have questions.
<p>Is a 10 Ohm 10W Resistor really needed ? </p><p>And what fuse have u used and why ?</p>
Some power supplies won't run if there is nothing connected, and need a minimum small load to keep it from doing an auto-shutdown. It really depends on your specific power supply, so you must do some experiments to determine what your power supply needs. If you will always have some load connected, then you don't need the power resistor.<br><br>This original design used a single fuse on the ground wire, but that is a really bad idea. The better way is to put no fuse on the ground wire, and put a fuse on each non-ground wire (like 5v and 12v). I would use a fuse that can handle just a bit more current than you expect to use in your project. This way if something goes wrong and your project starts to draw much more current, the fuse will blow and prevent a fire or other dangerous situation.
<p>maybe a stupid question, but wouldn't it be sufficient to use the cooler fan for the required minimum load? </p><p>Nice project though!</p>
Thanks gungajin, that's a good suggestion. There are a million different power supplies out there, and many require a minimum load separate from the case fan, and many don't require an additional load. Your mileage may vary, and these things require a little experimentation to see what it needs. Good luck!
<p>this guide has been really helpful to me as I work on my own PSU. I found this handy wire color and purpose chart, hope it helps. Heres the link to it http://www.instructables.com/id/A-Makers-Guide-to-ATX-Power-Supplies/?ALLSTEPS</p><p></p>
<p>I love this project. I have everything connected but I can only get it running if I turn on and off the switch quickly many times. It is the only way I can get it running. Any Idea why this happens?</p>
<p>Hook the load up and then turn it on. Mine stays on just fine with a load on it, but shuts off after a few minutes if I remove it. </p>
<p>Great idea. I'm building mine now. Going to one thing a bit different though since I also work on computers. I'm leaving the computer wires on the supply intact so I can use it on a motherboard or use the terminals installed on it for running my ham radios, testing things, etc. Be even more useful that way. The one I'm working with puts out 12 volts at about 17 amps. That such power an Icom IC 735 ham rig just great!</p>
<p>Thank u for this =)</p><p>One question...</p><p>Can I add a regulator on the 12v? and connect a voltmeter? So I can change between 1-12v? Please let me know :) And maybe give me a link to a regulator =)</p>
You can definitely use a regulator to convert the 12v down to a lower voltage.<br><br>The LM317 is a popular adjustable voltage regulator, but the max output voltage is about 2 volts less than the input voltage, so you'd be limited to 0-10 volts. There maybe other types of regulators that have a smaller &quot;dropout&quot; voltage. This is a &quot;linear&quot; regulator, meaning it burns excess power as heat, equal to the current * (Vin - Vout), which can waste a lot of power. Maybe you do or do not care about that, but you might need a heatsink.<br><br>There are also switch-mode buck converters that don't waste as much power, since they are more efficient.<br><br>Good luck!
<p>I connected PSU's green wire with black (ground) wire, but not with the gray wire. Should that make any problems or is it OK?</p>
The gray wire is only used to indicate if the power supply is turned on, so you don't need to do anything to it if you don't want to have an LED indicate when the power supply is turned on.
<p>Sorry, I forgot to write that I have already put LED, resistor and switch between green and black wire. When I pull the switch, the LED indicates that PSU is turned on and the fan in PSU starts spinning. Aparently, the LED indicates that PSU is turned on altough it's not connected with the gray wire.</p><p>BTW This instructable is great! :)</p>
<p>so if i use one wire from each source I can make 11 outlets on a box?? I know I couldn't USE all 11 at once, but I could use three or four as long as it didn't exceed psu amp capacity, yes??</p>
<p>Wire everything in parallel and you could have a thousand outputs on a box, provided that the total current load doesn't exceed the psu specs. You don't necessarily need to use the wires the box comes with. For instance, the molex connectors for the hard drives, floppy, optical drives etc. are daisy chained together in parallel, with more than one output on a single 5v or 12v wire. You can always extend that.<br><br>If you plan on using higher amperage, e.g. to power a car amplifier, it's better to wire all the outputs of same voltage into a single output. This mimics the effect of a thicker gauge wire, and eases the load on the psu.</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; <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.</p><p>As far as I can tell you are the first to start this madness on instructables, congrats.<br> </p>
Hi Russ, thanks for the note. That was a great idea to collect all the different approaches to this project!
<p>nice work...</p><p>I found that my power supply did not follow the standard colour coding.</p><p>i was able to look at the original ATC motoerboard connectors and the table at <a href="http://pinouts.ru/Power/atxpower_pinout.shtml" rel="nofollow">http://pinouts.ru/Power/atxpower_pinout.shtml</a> and found that the purple, blue and white were non-standard on mine. double check with a meter before trusting the colours.</p>
I need 13.6v @0.6amp from 12v rails and +5v @1.5 amp from a pc smps for my project. Please help me here. Do I need to add few turns of winding to 12v coil with additional rectifier with 12v as it is (for sensing)? Or by connrcting some dummy load to 5v, can increase voltage from 12v? So that I can get desired voltage?
5v@1.5A should be no problem for any ATX PSU. Getting 13.6 volts will be more tricky, and I would not personally mess around with anything inside the power supply. I would suggest buying a 16-20 volt power supply (you may even have one already as a wall-wart AC-DC adapter) and then add an output regulator to get the 13.6v you need. Since it's only 0.6 amps, even an inefficient linear regulator should work, such as the LM317. Good luck!
I have 20 pin ATX supply and I need 12 volts and at least 50 amperes from it for my experiment. So can a connect all yellow wires of my supply(12volts, 16amp each) to make a single 12 volt, 50 amp power supply? I have a total of 5 yellow wires in my supply...

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