Introduction: Bench Power From ATX PSU Thanks to Matthew
"Please Note! There are several large capacitors in ATX power supplies, that will store a dangerous charge for a long time. Please let your power supply discharge, completely unplugged from the wall outlet, for a few days before opening it up. You can probably be seriously hurt, so please be very careful."
That being said, on with the build…
Every builder, inventor or just tinkerer needs a power supply at some time but simple lab power supplies can run you $100 or more! In this instructable I will show how to make one for about $20 or less depending on where you get your parts.
In addition to the PSU (power supply unit) you will need the following parts in this mod.
5 way binding post (6)
LED assembly from Radio Shack (these have the resistor and LED holder as one unit and only cost a couple of bucks)
10 watt 10 ohm power resistor
SPDT mini switch
Spare Molex connector
Tools you need will vary depending on your build. Here is what I used:
Needle nose pliers
Soldering Iron and solder
Drill and center punch
Small parts brush
Printer and Label paper
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Step 1: Choose Your Power Supply
ATX power supplies that can be found in most discarded computers, or you can purchase one from $20 on up. You can get a great bench top power supply with several current outputs, short circuit protection, and reasonably tight voltage regulation on the 5V line.
On most PSU's the other lines are unregulated.
I started with a power supply that I harvested from an old e-Machine. I liked this unit because of its size. My work space is limited so the smaller the better. Once you have your chosen supply proceed to open it up. Look for 2 screws on 2 opposite sides of the unit. When you open the unit you may be in for a shock! Just see the next step...
Step 2: Cleaning Up
When I opened up the power supply, I could not believe how dirty this thing was, it was filthy! Even with all the dirt, this thing still worked, but the fan ran about 1/2 speed. Computer cleaning is probably the most overlooked chore on the spring cleaning list. The box gets shoved in a corner or desk compartment and gets forgotten about. As dust builds up the temperature goes up as well. Eventually the heat kills the chips and the system fails. I have 20 year old puters that run just fine and get a cleaning every 6 months. It's not a hard job, a soft brush and a can of air is all that is needed to get it cleaned up. In my case the PSU really cleaned up well. Yes that is the same fan! Be sure to lock the fan in place, or better yet, disconnect it from the circuit board, before blowing it off with air.
Bonus DYI: How to clean your computer
Dirty computers run hot. You can check your temps with a free program called Speed Fan. SpeedFan monitors voltages, fan speeds and temperatures. SpeedFan can even show hard disk temperatures. SpeedFan does many other things as well but I use it to monitor temps. SpeedFan works with Windows 9x, ME, NT, 2000, 2003, XP, Vista, Windows 7, 2008, Windows 8 and Windows Server 2012. It works with Windows 64 bit too.
You will need a small parts bush and a can of compressed air.
Cleaning your computer is simple just takes a little care and time. Start by shutting down your system then, once it has shut down, switch of the power supply. This is usually a rocker switch on the back of the power supply. Next you will unplug all the cables connected to the back of your system. If you are not sure were each one goes, you can label them with tape, take a picture, or draw a diagram. Just use the one that works for you. Now take your box outside, this will be messy, find a nice clean spot, like a pic-nic table. Start by opening your case. This I cannot tell you how to do, as this varies from case to case. If you don't know how to open your case try a Google search or ask your local computer dealer, most will tell you how to open it for free. Now that you have the case open the next step is lock your fans so they do not turn when you blow them with the air. Look for them on the CPU (central processing unit), GPU (graphics processing unit), rear of the case, front of the case, and don't forget the PSU. I use tooth picks for this. Even with your system off the spinning fans can produce a voltage and current that could be harmful to your system. The next level of cleaning depends on your own computer know how. If you are savvy enough, remove all cards, cables, and hard drives. If you are not comfortable doing this, don't worry, any cleaning is better than none. Now using your compressed air, blow out the inside of the computer, the PSU, video card, or anything else left in the case. If there is stubborn dust, brush it away with your brush and blow it off again. Pay particular attention to the heat sink on your CPU, GPU, and any other heat sinks on the motherboard. If you have a tower type case, the front may come off, if so, there may be a front mounted fan there. Once you have everything clean, replace all your cards, hard drives, or anything else you removed from the system. Don't forget to remove whatever you used to lock your fans. Close the case up and reconnect all cables to the back of your system. Turn the power switch on the PSU and boot up your system.
Fire up Speed Fan and enjoy your lower temps.
Safety Note: Do not use your home vacuum or shop vac to clean any part of your computer. These can produce an ESD (electro-static discarge) or static electricity that can damage your computer. If you want to vacuum your system look for vac's that are made specifically for that purpose. Do a Google search for "Data-vac" to find one.
The following is a suggested cleaning schedule:
User who does not smoke and has no pets -Clean every five months.
User who does not smoke and has pets -Clean every four months.
User who smokes but has no pets -Clean every three months.
User who smokes and has pets -Clean every two months.
Business with clean office environment -Clean every five months.
Business that is pet friendly or allows smoking -Clean every month.
Business with clean office environment; however, multiple users use each computer -Clean every three months.
Business that is a factory environment -Clean every two months.
School computers with young adult users -Clean every three months.
Step 3: Sorting Out the Wires
After I thought I had this thing clean, I bundled all wires together according to color. Of all of these wires I only needed a few and it would be a lot easier to cut the extras off with the circuit board out. After bundling the wires I removed the circuit board from the case so I could cut off the excess wires, and guess what I found, yep, more dirt! After cleaning the rest of the mess I then counted the connections I needed and removed the unneeded wires. Not only would this simplify wiring, but would also make a lot more room in the case. It is easiest to remove the wires with the circuit board removed, but, if in doubt about cutting any wires, you can always wait and cut unused ones after all the others are connected.
The color code for the wires and the wires you need are:
4x Red = +5V
4x Black = Ground
1x White = -5V (not all PSU's have this)
1x Yellow = +12V
1x Blue = -12V
1x Orange = +3.3V
1x Purple = +5V Standby (Always hot)
1x Gray or Brown = power is on (output)
1x Green = PS_ON (turn DC on by shorting to ground).
Step 4: Preparing the Case
Now it was time to layout and drill the holes in the front of the PSU for the LED and the binding post. There is not a lot to say about this as your layout will vary depending on your PSU and personal preference. I lined up my banana jacks across the front of the case and a power switch on the back. I mounted the fuse holder where the wires originally passed through the unit and the LED right below that. Start by marking where you to drill holes. Use a center punch to start each hole. This will keep the bit from "walking" on the face of your case. Once I had the holes drilled the next step was to scan the front of the case. This would give the layout of my holes and help me place my labels. Once my design was complete I printed it out on a full sheet label and stuck it to the front. Using an X-ato knife I cut the holes for the various components. Notice that I did not stick down the top of the label so I could insert the screws later. After every thing is stuck down and cut out, mount your banana jacks, fuse holder, LED and power switch.
Step 5: Wiring It All Up
OK…we've cleaned it up, drilled some holes in it, and gave it a new face. Now let’s give it some features and get it all juiced up! The first thing to do is slide in the circuit board and make sure everything fits. You may find, like I did, that you still need to do some modification to make it all fit. When I slid the circuit board in I found that the ground post hit one of the riser boards. If I had drilled an 1/8” higher I would not have had this problem. The solution was rather simple though. I simply notched the bottom of the post to fit over the board. Once you have everything fitting it is time to route the wires to their connection point. I’m not going to go into the wiring a whole lot because it has been done so well already. Just follow this link http://www.wikihow.com/Convert-a-Computer-ATX-Power-Supply-to-a-Lab-Power-Supply.
Basically it goes like this:
Connect one of the red wires to the power resistor
One of the black wires to the other end of the power resistor
One black wire to the LED assembly
One gray to LED assembly
One black wire to the power switch
The green wire to the power switch
One red wire to the fan and light (optional)
One black wire the fan and light (optional)
One orange wire to the brown wire
One black wire to a banana jack
One red wire to a +5V banana jack
The Yellow to the +12V banana jack
The Blue to the -12V banana jack
One Orange wire to +3V banana jack
If there is a white wire in your supply this will go to the -5V post.
Note: Some power supplies have either a gray or brown wire to sense power on. This wire should be connected to an orange wire for the power supply to stay on. Heat shrink or tape all soldered ends.
If you are really sharp you will have noticed that my second post is labeled -5v but I have the 5vsb hooked up to it, which would be the purple wire, and you would be right. After realizing that there was no -5v in this PSU I decided to go ahead and make it hot all the time. This way I could quick test LED’s and such without having to turn on the power. You could also install a USB jack in the case and have a charger for you USB devices. For the pin outs on various USB ports just go to this page http://www.usbpinout.net/. OK, now that we know where everything is going its time to get out the soldering iron. After connecting the LED and splicing the brown and orange wires I started on the post. After a couple of tries trying to solder to the post, I decided there had to be an easier way. Molex plugs to the rescue! I pulled the individual connectors from a couple of old female plugs. If you never taken these out the, there are two little ears on each connector, the trick is to push these in a little so it can slide out. They make a tool for this but you can also use anything small enough to get to the bottom of the connector. A jewelers screwdriver works great and so does the tip of your X-acto knife. Gently pull on the wire while you are pushing each ear, one at a time, until the whole thing slips right out. It turns out that, because of those “ears”, these would actually “snap” on to the ends of the post. Instead of trying to de-solder the connector I just broke it off instead. I then stuck the wire in the end of the connector and soldered them together. Before slipping on the connectors, to the back of the banana jack, I slipped on a piece of shrink wrap and sealed it all up.
Now that the banana jacks, LED and power switch are wired, all that is left to do is reconnect the fan and add the power resistor which I will cover in the next step.
Step 6: Add Some Bling
Ok we are almost done…I wanted to give my supply a little pizzazz so splurged and spent $2.00 for a lighted fan guard and mounted it to the top of the unit. The original guard was your standard concentric circles. Of course those had to go…I then mounted the cover to the top of the PSU fan and routed the fan and light wires through one of the fan mounting holes and secured them with epoxy. Next I connected them to a red wire and a black wire. After making the splice I shrunk wrapped each one and then put one more piece around them to hold it all together.Next step is to solder in the resistor. Again soldering to one red and one black wire. Also notice the red arrow in the pic. The mounting ear of the fan had to be cut off to keep it from hitting the switch.
For the last step I added some old case feet I had laying around.
Note: Since this is a heat producer it needs to have some sort of heat sink to keep it from burning up. There was not room to wire it to the back so I came up with what I think is a better way. Thermal epoxy. This is a two part epoxy with thermal properties. They carry two types, Artic Silver or Artic Alumina. The difference being of course a silver or aluminum base. I found this at my local “Computer Deli” but you can also order it online at ArticSilver.com.
This resistor does dissipate some heat, but in reality, very little. I have left the supply on for over 24 hours and the case was not even warm to the touch.
Step 7: The End Result!
With everything wired and the case closed up, all that is left to do is fire up your new bench power supply.
Here are voltages I recorded:
3 Volts +3V + Ground
5 Volts +5V + Ground
7 Volts +12V + +5V
12 Volts +12V + Ground
17 Volts +5 + -12V
24 Volts +12V + -12V
Well that’s it! I hope you have as much fun building your own bench unit as I did.
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