When you want to learn about electronics as a hobby, you will, of course, need to make alot of circuits, and you need to test them. For that you will need a power supply, but you will often find yourself needing different voltages for different projects, so any power supply wont do, and you would want something thats a bit more versatile. You can go out and buy an off-the-shelf Lab PSU with alot of different features, but these are often very expensive, and you dont need all that fancy features, when starting out with electronics, so you can make do with alot less.
So where do you find a suitable power supply for your new hobby? Thats easy. In almost any old computer theres a standard ATX power supply, which supply 3.3V, 5V, and 12V, which is the three most widely used voltages for electronics, which makes it a great powersupply for any new electronics hobbyist, and with a bit of modifications and accesories, it will be really easy to use as well.
So why not build your own Lab power supply for your new hobby? You might even learn a little about waht such a thing does, and you'll have your first electronic accomplishment to be proud of building yourself.
Step 1: Theory and Preparation
An ATX power suply from a computer has a standardised size, and a standardised wire layout, so its easy to use general information on PSUs from different manufacturers. There will be some slight differences between brands, but the general standards still apply (eg. wire coloring, size, method of turning it on etc)
in electronics the most widely used voltages for supplying a device, is 12V, 5V, and 3.3V. Theres also the lesser, but still widely used 9V, 24V, 36V, and the supplies for laptops, that provide anything from 16-20V. for a device powered by a battery, its usually any supply thats dividable by 1.5 (eg 3V, 4.5V, 6V, 7.5V, etc)
An ATX power supply outputs 12V, 5V and 3.3V, and all of high amperage. On top of that, it provides 5V SB which is always on, if thePSU is plugged into a wall socket, even when you have turned the powersupply off, and it provides negative 12V (but at a low amperage). It is usually able to measure if it outputs the correct voltage on some of the rails as well, and its an extremely stable supply on all rails, compared to a cheap power supply. It usually have two 12V rails, named 12V1 and 12V2, so if you short out one of them for good (should not come to that, because of fuses), you will still have the other to play with. this would be a rare situation, but still nice to have such a feature. All this makes the ATX power supply ideal for our project of making our own lab power supply for our electronics projects, since its so versatile.
By the way, the first two steps have alot of text, but the later steps is more down to earth. Also, sorry for any grammar mistakes. English is not my first language.
The wire colors of the PSU suplies as follows:
Black: GND/COM. (Ground/Common) also known a 0V
Yellow: 12V. You will often see yellow wires with a black line on them. these are the second 12V rail.
(White): -5V this is rarely present, so dont worry about this one. if you have it, you can connect it to the spare terminal in the 6 way terminal (more on that later), or you can just put some shrink tube on it.
Blue: -12V this is rarely used, but you might as well connect it in the case you'll need it some day.
Brown (or thin orange one): 3.3V sense. This one regulates the 3.3V line, if its not delivering the correct voltage. It is important that its connected at the end of the orange wires, since it needs to regulate the supply according to load and wire resistance. Since 3.3V is such a low voltage, it is sensitive to the amount of load thats on the rail.
Pink (or thin red one): 5v sense. Same function as Brown one, but for the 5V rail. In newer PSUs this is not always present. if its not present, dont worry about it. Mine didnt have it.
Thin yellow one: 12V sense. Again, same function as 3.3V and 5V sense, but for 12V. This one os almost never present in newer PSUs, so dont worry about it if its not present.
Green: PSU ON. when this one is connected to one of the black ones, the PSU will turn on.
Grey: POWER GOOD. inside an ATX PSU theres a system for testing its own output, and if it passes its own test, it will supply 5V to this wire, after a second or two. We can use this to light a LED, to get some indication if everything is allright. (althought it can give a false positive in rare occatiopns)
Purple: 5VSB/ 5V STANDBY. This one provides 5V even when the PSU is off, usually of a low amperage. Its originally used for supplying your computer with a little power so it can maintain sleep mode, or for peripherals such as charging your phone from the USB port when the computer is off, but we can use it in some special simulation situations, such as simulating the supply in a car for example (note, a car suplies 12V, usually not 5V). A car still holds some systems powered when the engine is off, so you can use this to test a project that needs to turn on when the car is on, but need to have some power when the car is off (eg sleep mode)
CASE: you will need a case of some sort. I made one on my 3D printer, but its not neccesary to have a 3D printer to make a case. You can make one out of some old plastic enclosures, or buy a box meant for the purpose. If you dont want to 3D print it, i would believe the best sollution might be getting some acryllic plate, and cut it into a box of the desired shape, since its non conductive, fairly simple to work with, and its not as flammable as wood.
On the other hand, if you wish to 3D print it, i have included the STL files for my enclosure. if you wish to make a different layout for the front plate, i have also included the files i have made for the components mounted on the plate, so you can "punch out" the holes where you want them, in your 3D designer program. See more in the next step. The one i made is my own remix of one i found on thingiverse, made by user james_III. He did a great job on that one, so many thanks to him and his work. https://www.thingiverse.com/thing:708666
PSU: you will need a standard ATX power supply, that comes out of most desktop computers, and is in abundance in most electronics waste containers. just make sure you get a hold of one that actually works. By using one thats used, you will get it for free, and you help ensure less electronic waste, which is a good deal for our planet, along with your wallet. I used one from my old gaming computer, which was due for replacement anyway.
Accesories: You will need some extra stuff for the Lab power supply, such as voltmeters, banana blugs, fuses and holders, a switch, and so on. Heres a list of what i used:
Voltmeters: on ebay, the ones i used is called "Mini DC 0-100V Red LED 3-Digital Display Voltmeter", and if you search that, you probably will find them as the top results. i used one of each of the 4 different colors thats available.
Banana plugs: i found some on Aliexpress, since i couldnt find the exact one i wanted on ebay. They are color coded, to make it easier to distinguish, and they fortunately fit the colors of the voltmeters. The search terms are:
"20 PCS new 5 color banana"
Fuses: i used two different kinds. One type for 5x20mm glass fuses, and one type for blade fuses, normally used in cars. the search terms on ebay are
"5PCS 30A Amp Auto Blade Standard Fuse Holder Box for Car Boat Truck with Cover" and
"5pcs Chassis Panel Mount Fuse Holder Socket for 5*20 Glass Fuses 250V 10A"
LEDs: i got some assorted 5mm LEDs from ebay as well. They are the typical ones thats used in many applications general purpose situations, so you can use the rest for your other electronic projects. The search terms are:
"LED assortment 5mm"
Beware, it also exists in a 3mm variant. this will work just as fine, but you need to resize the holes in the front plate. I bought them both, so i have some options for later electronics projects, but thats not necessary for this project.
LED panel mounts: I used some panel mounter clips for the LEDs at the top. these are not strictly necessary, but you need to resize the holes if you 3D print the enclosure. The search terms are:
"100Pcs 5mm Black Plastic LED Clip Holder Case Panel Bezel Display Cup Mounting"
SMD LEDs: These are optional, and i advise you to only get them and using them for this project if you are patient, and dont mind to fiddle wtih extremely small components that are hard to work with. Chances are that you will have to redo the part where these are involved over and over again, to get them to work, since they break so easily the way they are used in this project.
i used some red 1206 LEDs for indicating that the fuses are not burned for the USB ports. i drilled a hole in the fuse holders, and put one under each of the blade fuses, so it lights up, when theres power on the USB ports. The search terms are
"1206 SMD LED Red super" and remember to buy plenty. 50 will do plentiful for this project. I used 8, since i broke 6 of them.
Switch: I used one of the MTS type, but any toggle switch will do. You will just have to resize the hole in ht front plate, if you 3D print the enclosure. The search terms are:
USB port: its always nice to have some USB ports for testing your projects, since so many things use USB today. it only suplies the voltage needed, so theres no data connection on it, but thats not necessary when starting out anyway. The search term are:
"0.5m Dual USB 2.0 A Female panel mount to10 pin female header Motherboard Cable"
6 way terminal: i also put a 6 way terminal usually used for speakers on it. this one is of course not used for speakers in this case, but it serves as a more compact terminal for the lesser used 5V SB and -12V, along with a terminal thats not connedted, in case you later want to expand your PSU with another connection. You could just as easily use a 4 way terminal if you wish, you wil again, just need to resize the hole in the front plate. The search terms are:
"6 Way Speaker Terminal"
Resistors: you will need a handful of the typical 1/4W resistors, ranging in between 100-150ohms. In my project i used 2 150 ohm and 1 120 ohm, but you might need to use different amounts and sizes, so i advise you to get an assorted kit of resistors. They are extremely cheap, and you will probably need them for other projects as well. The search terms are
Load resistors: An ATX power supply is a switch mode power supply, which most often need a minimum load to function properly. Otherwise it might not turn on, or it could be unstable, but more on this in the next step. If you need to put load on the 5V rail, you will need 2,5 ohms at 10W, and if you neeed to put load on the 12V rail, you will need 15 ohm at 10W. i got some from a friend, and he only had some 6.8 ohm 5W resistors, so i put 3 of them in parallel for a total of 2.26 ohm at 11W, with 3.7W over each of them.
They come in many shapes and sizes, and any of them will do. they will get quite hot, so beware of this when installing them. The search terms are:
"10W power resistor" or "5W power resistor" but remember you will need to find the correct Ohm for your use. You might benefit of putting some in parallel and/or serial connection, but you need to do the math (ohms law). See the next step for more info in this.
Shrink tube: You will also need some shrink tube in different sizes as well. i had some laying around, but its also cheap in most hardware stores and on ebay. The search term are
I suggest you buy some of the rolls where you cut off the lengths you need, instead of the precut kits, but the precuts works just as well. I only had black, but different colors can come in handy in later projects.
Tools: You will need a soldering iron, and some solder, along with a couple of acrewdrivers, pliers for cutting and de-insulate wires, and a needlenose plier to grab the wires in dificult places. in other words; besides the soldering iron, you will only need some basic tools to make this project. Also, you'll need a multi tester for measuring currents, voltages, resistance, and so on, but if you wish to work with electronics, you'll need one of those anyway.
optional tools: i found good use for electronic tweezers, and of course i used a 3D printer to make the enclosure. if you wish to make the enclosure in a different way, you will need tools to make it the way you want it, obviously.
Step 2: Load Resistor/power Resistor Theory
Most ATX PSUs need a minimum of about 5-10 Watts to function properly. That is no problem in an ordinary computer, but in our case, we wont have any load on the rails at all times. Therefore we need a load resistor to make up for the missing load.
The load should always be on the rail with the highest amperage. In my case there's the same amperage on the 3.3V and the 5V rail, so it doesent matter which one of those two i put the load on.
Now heres the confusing theory for a beginner about ohms law. theres alot more to ohms law, but heres the par we need:
(If you dont want the confusing theory behind it, jump to the bottom. There's the resistor values you'll need for this project)
The two formulas we need is U=I*R and P=U*I, where
R=Resistance (Ohm or the greek symbol omega)
We need to load the 5V rail with 10W total, so we need to find the correct resistance. for that we need to find the amperage of the resistor. that we can do by rearrange the P=U*I so well get I=P/U which gives us I=10W/5V=2A
Then we can find R with rearanging the U=I*R formula, so we get R=U/I=5V/2A=2.5Ohm.
We now have the tolat resistance of the system, but in my case i could only get hold of resistors that can manage a load of 5W each, and not 10W. We can get around this by making a circuit with 2 resistors in parallel, so they will evenly distribute the load between them, making it 5W each for the resistors. In a parralel circuit the total resistance will allways be lower than the lowest single resistor in the parallel system.
A parallel system is a amperage divider, meaning theres the same voltage over all the resistors, but the total amperage is divided between the resistors. the amperage over each resistor is dependent of the specific resistor value of that resistor. In our case we want to divide it evenly between the two resistors, meaning we will have 1A over each resistor, together with 5V over each resistor, meaning with the R=U/I formula, er get R=5V/1A=5Ohm, meaning each resistor in the paralel system should be 5 Ohms each, for a total of 2.5 ohms.
Alot of people find it confusing that two 5Ohm resistors make a total of 2.5Ohm, but you have to remember that its divided between them. thonk of it as water pipes. When two waterpipes are connected in paralel, and merged together again, they will distribute the water between them evenly, depending on the thickness of the pipe.
If you are more of the mathematical guy, maybe this will clear it up:
The way you calculate a parallel resistor system is by taking the reciprocal value of the resistor and adding them together, to get the total reciprocal resistr. thats a lot of mumbo jumbo, but it might clear up for you when put into mathematics:
1/Rtotal=(1/R1)+(1/R2)+..+(1/Rn) (n meaning the last resistor in the system. if you have 6 resistor, set n to 6 and plus everything in between together)
So in our case its 1/Rtot=(1/5Ohm)+(1/5Ohm)=2/5Ohm. Remember that this is not Rtot, this number is 1/Rtot, meaning we will have to put this number under a fraction line once again:
I could not get some 5 Ohm resistors, meaning i had to do the calculations all over again with a system containing 3 paralel resistors, instead of two. Long calculations short, it meant that i needed to find 3 resistors as close to, but under 7.5Ohm each. I could get hold of some 6.8Ohm 5W resistors, and these will be fine, because there will be 3.67W over each resistor (they can hadle 5W each), totalling at 11.02W (and we wanted a minimum of 10W)
There's different values if you need to load the 12V or the 5V rail.
1 resistor of 14.4Ohm at 10 watt
2 resistors at 28.8Ohm at 5 watt each
3 resistors as close to, but under 43.2Ohm at 5W
1 resistor of 2.5Ohm at 10 watt
2 resistors at 5Ohm at 5 watt each
3 resistors as close to, but under 7.5Ohm at 5W
Where to put it?
Well, the load resistors get really hot, so its important to put them somewhere they can get proper cooling. In my case, i opened up the PSU and put tied them to the back end exhaust grid.
How to connect them:
Its important that you dont make a shortcircuit inside the PSU, so remember to use plenty of shrink tube. I put shrink tube on each of the resistors pins, leaving about 4 millimeters for soldering them together, and connected them together with the 5V and GND (red and black wires).
I unfortunately cut some of the 5V wires too short, so i had to extend them with some thick wire i had laying around. When you connect them, use 3-4 red and 3-4 black wires, and solder them to each side of the resistors.
Step 3: Print and Assemble Enclosure
If you decide to print your own case on a 3D printer, you probably best know yourself what settings you need for the printer, and how to print it, since every printer is different from one another.
If you get a friend to print them for you, let him worry about how to print them.
In any case, i have included the files needed for the project here.
If you wish to make modifications, i have included a "clean slate" front plate, so you can place the components where you desire, or add and remove the components as you wish. I found that its a good idea to draw the components out, as they are completely, and not just the part where the hole needs to be. When done like that, you can lock the components in place on the front place, and assemble it with the rest of the case, to see if theres enough room for the components where you want them, before printing the front plate. I originally had a different layout on the front plate, but it turned out there wasnt enough room for the USB and fuses to fit inside the case.
If you wish to make the exact same build as i did, i have of course included the front plate with the holes as i have made them.
You need to put the case together in a specific order, since it wont be possible to install the black front, after the PSU is inserted into the red casing. Also, it could turn out to be more difficult to install the handle later on, but it wont be impossible.
Unfortunately i dont have pictures of step one and step four, but its fairly simple.
All screws are 3mm of different lengths. you will have to asses the length of each one required.
REMEMBER to be careful with the screws. Its easy to break the female threads in the plasic casing. perhaps drill out the holes beforehand with a 2.5mm drill, and maybe heat up the screws before screwing them in. Heating up the screws will make it a bit harder to work with, but will make a stroger connection. It wont be necessary though, if you are careful.
Step one: Assembe two of the side bars, with the handle.
Step two: Assemble step one with the red front frame, and the front frame with the remaining tho side bars. beware that theres a difference between the red front frame and the red back frame. the front frame has 6 additional holes to mount the black front case to the assembly.
Step three: Mount the black front case with the rest of the assembly.
Step four: Put the ATX PSU in place.
Step five: Mount the back frame to the assembly.
On the last picture, you can also see a bit of the next step. Assembling the front plate.
Step 4: Assembling the Front Plate
So, mounting the components on the front plate, is fairly straight forward. Its basically just putting them in where they fit.
i would install the banana plugs before the voltmeters, because theres not much room for turning the nut on the banana plug, when the voltmeter is installed.
For the voltmeters, i have printed some brackets to put under the screw holes, tomake the front of the voltmeter to be flush with the surface of the plate, and i have included the file, but you can use anything thats 1mm thick, and nonconductive. They are in my case mounted with some M2.5 screws i had laying around. Also remember to put the correct color display next to the corresponding color banana plug. If you dont know the color of the display, just connect the red and black wire to a 5V source of some kind, and test it.
for the LEDs, put in the bracket in the front plate, and then insert the LED into this. To my surprise it turned out that the bracket didnt grab the LED at good as i thought it would, so i had to give it a bit of hot glue, to make sure it stayed in place. I advice you to give it a little blit of glue of any kind. Dont cut the connectors on the LED just yet.
this is one of the more tricky ones to install, if you 3D print the case as i did. I designed the switch hole the way i did, because i wanted the switch to be as flush with the surface as possible.
First you'll need to put one nut on the shaft of the switch, and then the directional washer on top of that. Next, put the second nut in the hexagonal hole in hte front plate, and insert the switch in the hole from behind, and turn it until the end of the shaft is flush with the nut in the front plate. Make sure the swith is oriented in the direction you want it, and if not either turn the switch some more, or pop out the nut from the hole, and reposition it, so the switch will be in the direction you want, when flush with the nut. Next tughten the nut on the bottom side with some needlenosed pliers, and you are done.
straigh forward, insert it in the hole, and put two screws in the holes. You might want to put a screw in one of the holes thats a little longer than it needs to be, but more on this later.
also straight forward, but remember that you will have to take them out, if you plan on installing the SMD LEDs in them. More on this later.
Also straight forward. when installing them, turn them around, so the "fuse" text is oriented the right way. Just a small detail.
6 way terminal.
Put it in from behind, and insert screws into the holes.
Step 5: Preparing the USB Connector
We need to do something about that long USB cable. We dont want such a long cable inside our case, so cut the plug and de-insulate the cable. that reveals the two screens inside the cable, and these you need to untwirl. Of course you could just unravel the woven screen, but thats a hazzle. instead, collect the whole screen, and put a small screwdriver in between, as shown on picture one. then you can easily pull the rest of the cable out of the woven screen. as shown on picture 3 and 4.
do the same with the tinfoil screen, and twist the two screens together, and put some shrinking tube over it, leaving about 5mm in hte end for soldering. also put some shringking tube over the whole thing, so you can insulate the last bit, closest to the USB connectors, as shown on picture 5.
Now you need to figure out which wire is connected to which pin in the USB, and for that, you will need a multitester. In my case i found that red and yellow is 5V, and brown and grey are GND wires, and chances are that its the same case for you, but no promises. Put one probe of the multitester in the USB so it touches one pin, and put the other at the end of a deinsulated wire, to test throughput.
I put the red and yellow through some holes in the blade fuse holders, so i know that thats the place they are going to be soldered to, and the brown and grey, i twisted together and clamped in the black terminal on the 6 way terminal, to temporarily keep track of it.
Dont cut the data wires. just twirl them up in a ring, and let them hang in hte back of the USB plug.
if you want to make a charger for your phone, you can do so by putting a specific resistor between the data pins, to tell the phone that it can draw as much current as it wants, instead of the usual 0.5A of a standard USB plug. theres plenty of guides to do this. Remeber that iphones need a different system, than android phones need, so you'll have to take that into account, when doing this trick.
Step 6: SMD LEDs (optional)
this step is difficult and optional
you dont need this step for a functioning PSU, but i found it to be a neat feature, that the small SMD LEDs ligt up the fuse, if its not broken. that way its easy in troubleshooting to see if its the fuse thats the problem, when messing with electronics.
But i found that its extremely difficult to work with these SMD LEDs, because they are designed to be soldered to the surface of a PCB board by a precise maschine. although it is possible to solder it by hand, its difficult, and in our case its even more dificult, since we are going to solder wires on it, instead of soldering it to a PCB.
The way to do this is:
Drill a 2.5mm hole in the fuse holder, right between the connectors for the fuse, so it leaves a dent in the housing for the LED to sit in.
On the bottom side of the LED there a green T to show which way the current can go. the horisontal part of the T is the + side, and the vertical side of the T is the - side, meaning you should provise the + side to the top of the T and - to the bottom of the T
Solder some thin wires to each side of the SMD LED, (preferably black and red) and put the construct inside the drilled hole in the fuse holder, and make sure that the LED points upwards.
Mount the fuse holder in the front plate, and remember to pass the wires to the backside as well, while inserting the fuse holder.it should then look something like picture 4, but without the small piece of prototyping board.
Now, the LEDs cant withstand 5V on their own, so you need to put a resistor in the system, for the LEDs. I had a small piece of prototyping board laying in the shop, so i just cut it to shape, so i could mount it just beside the fuse holders. This is what the extra length screw on the USB is for, so if you do it like me, solder 2 150Ohm resistors to the circuit board, and solder the negative wire from the LEDs to one side of one of the resistors.
(The small piece of prototyping board is not necessary, and it will work just as fine if you solder a resistor directly on the wires, and put some shrink tube over it.)
You'll need to solder the other end of the resistor to a GND wire from the PSU, but we'll come back to that.
Now, solder the plus side of the LED to the OUTGOING end of the fuse holder (you decide yourself which that end is, because the ingoing end is just the other one)
next, you'll need to solder the 5V from the USB (in my case red an yellow) to the outgoing end as well, on the USB (one for each fuse holder)
On picture 5 and 6 you can see i have soldered the negative wire of the three top LEDs to the remaining resistor, but i will cover that in the next step, so people that dont want to do this step can just skip over it.
You should now have something that looks like picture 5 and 6.
Step 7: Connecting Indicator LEDs and Voltmeters
Solder the three GND pins of the top LEDs to some wire, and put some shrink tube on it.
Then solder the wires to a 150Ohm resistor (the remaining one from last step, if you have used the SMD LEDs)
the positive side of the LEDs will come later.
put some solder on the Banana plugs. this can be a bit tricky, and be carefull that you dont use too much force when soldering, because the plastic will get hot enough to be right around the melting point. Have patience.
Solder all of the red wires from the Voltmeters to the 5V banana plug. The voltmeters can handle anything from 4-30 volt as a supply voltage, so its not possible to solder it to the 3.3 volt line. only the sense wire should be on that post.
Solder all the black wires to their respective GND plug
Solder the yellow and white wires to their respective + post (yellow and white are the sense wires of the voltmeters)
you should now have something that looks like picture one.
Step 8: Joining the Front With the Rest
now you need to connect the front to the rest of the PSU.
To do this, begin with placing the front plate right in front of the case, so it looks like its meant to just flip up and screw in place. This way the wires wont be too long because theres not abundance of space in the case as it is already. Also its always best to use as short wires as possible, especially when working with low voltages, because of the internal resistance in the wires. hte thicker and shorter the wires, the less resistance they have.
solder 3 or 4 wires of each rail (12V1, 12V2, 5V, 3.3V) to their respective 5*20mm fuse holder, in any order you want them. i advise that you put the input voltage at the end of the fuse holder, t get the supply in the bottom of the fuse holder, instead of the top of the fuse holder. this is a bit more safe, and prevents some rare shortcircuits. use AT LEAST 3 wires to each of the Fuse holders. At least 3 because these connections are the ones with the potential for the highest amperage, and if the wires are too thin, they could get hot, and cause fire in the case.
Next solder one black GND wire to each of the GND posts on the 6 way terminal, and one on the PCB on the second side of the resistors (so you have the end of the LEDs to one end of the resistor, and the GND to the other end of the resistor.)
Solder the shield of the USB to any GND post you desire.
Solder AT LEAST 3 GND wires to each of the black GND banana connectors. at least 3 because these posts are the ones for potentially the highest amperage, and if the wires are too thin, they could get hot, and cause fire in the case.
Solder some wires from the secondary end of the fuse holders to the colored banana plugs. These doesent have to be as thick as the other ones, cause they are fused, and can of course then not draw as much power before the fuse breaks, and protecting the system.
Solder one GND wire to one end of the switch, and the green wire to the middle pin on the switch. when a connection is made between the green and a GND wire, the PSU will turn on.
Solder the grey wire to the middle LED and insulate it with some shrinking tube. this will supply 5V when the PSU has passed a self test.
solder a leftover wire to the LED next to the switch, and insulate with some shrink tube. Solder the other end to the first positive post on the 6way terminal, along with the purple wire and insulate it with some shrink tube. This is 5V always on, when connected to a wall socket. (5VSB)
Solder a leftover wire to the last LED and and insulate it with shrink tube, and solder the other end to the nearest 5V source (before any fuses) in my case i used the input side on the blade fuse holder.
Lastly solder the blue wire to the middle positive post on the 6way terminal, and insulate it wwith some shrinking tube.
in my case i had some leftover wires for one of the 12V rails, and if you find yourself in the same situation, then just cut them in the maximum length, so they can reach any side of the front plate (in cas you need them in a rebuild for example), and then put some shrink tube over the end of the wires, to insulate them as shown in the last picture, and squeeze the end to close it off. Remember dont put wires from different rails under the same piece of shrink tube.
you should now have something that looks like picture 5
Step 9: Close It Up
You are done with all the soldering now, and you can begin testing it. If theres any faults or errors, you its of course easier to troubleshoot while its open, and chances are that there is some faults in the system.
in my case the middle LED for selftest didnt work at first test, and both the SMD LEDs didnt work. It turned out that the self test LED was probably dead on delivery, because i just changed it and it worked fine again. The two SMD LEDs ihad to do over again and again, because they so easily broke, and i had to do it over 6 times in total, before both of them worked. also the fuse i originally used for the first 12V rail was broken, so that needed a change as well.
its almost impossible to predict what errors that could occur in your case, but remember to go over it step by step and rule out every possible cause. The multitester will come in very handy at this point, to measure if theres the correct voltage supplied to each component in the system.
possible errors could be something like:
Switched positive and negative wire. LEDs are especially sensitive to this, because the current can only flow in one direction, which differ from a normal lightbulb or resistor, where it doesent matter which way the current flows
Bad soldering. In some cases the soldering can be so bad that it doesent connect properly, or it could break off of the post its soldered to. whe using shrink tubing, its not always easy to spot this fault, but try to measure on each side of the post if possible, to figure it out. alternatively youll need to cut off the shrink tubing.
burned fuse. As you can see on picture 4, i had no power on the top rail at first. it turned out to be a bad fuse. to spot this, just take out the fuse and measure throughput with a multitester on the fuse.
broken wire. In rare cases, the wire can be broken internally. this is very hard to spot, and you need to measure the voltage in both ends of the wire to detect it. This is not always easy.
There can be many other errors, and these are just some of them. I will try to help you, if you have trouble, but i can of course not promise anything. write a comment to the instructible, and i will answer it as soon as i see it.
After testing, its time to clse the case. Flip the front up, and work it in place so its possible to close it up. be careful not to use too much force, and you might have to fiddle a bit with it the first time you close it up. Perhaps you should bend some of the wires in different directions, or position it in a different way, so its possible to close it.
Step 10: Done
Thats it. you have now made a power supply, perfect for learning about electronics, and chances are that you have already learned a bit about it, making this PSU, along with saving alot of money over buying a proffesional Lab PSU
i suggest only to put 2.5A fuses for the four main rails, and 1A for the two USB ports. for the main rails, you can easily put bigger fuses in, but 2.5A is plenty for most projects, and you should always go for the smallest possible fuse. The USB wires are really thin, so i dont reccomend more than 1A on those.
DONT loose faith if you run into alot of problems along the way. making mistakes and troubleshooting is the way you learn, and it only makes you better. I have found myself run into problems and errors over and over again in many electronics projects. Most of them caused by myself. So be confident and keep on learning.
Leave feedback please.
This is my first instructable, so please leave some feedback for me. if theres something i can do better or if theres something you find unclear, write a comment and i will try to correct it. I hope you enjoyed my instructable, and take care :)
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