DIY Power Supply !

By Nematic! in Circuits Electronics

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I recently found an ATX Power Supply which offers a quite a decent power at its output. But most importantly it offers +12v, +5V, and +3.3V at its output which is very commonly used in electronics so let's turn this into a Lab Bench Power Supply!

Warning: If you have No idea about electronics then don't try this, AC Mains Voltage is fatal! especially with high voltage capacitor.

Step 1: Watch the Video !

if you don't want to read all the stuff you can watch my video on youtube

Step 2: Disassembly and Testing

Before you start opening the case of ATX power supply first keep the power supply unplugged to discharge those high voltage capacitors.

Then open the case of ATX power supply and clean the internal electronics with a brush or blower.

Now we first need to check if the power supply is in working condition. To check that take 20-24pin connector and connect 14th pin i.e Green color wire to any of Black color wire Pin. If power supply's fan starts then it is in working condition.

Step 3: Trimming and Sorting

Now you can trim down the wires to an appropriate length because we don't need connectors. Once done Sort the wires according to color.

Red is +5 V

Yellow is +12V

Orange is +3.3V (Brown wire is voltage sense for 3.3V so connect it with orange)

Blue is -12V

White is -5V

Green is PSU On

I dont need -5V and -12V so I wont be using them.

Step 4: Drilling and Soldering !

Now drill holes for banana Connectors (Binding post) and attach them, Make sure they are tight or else they can short something in future.

Now strip all the wires and solder them in a group according to their colour. Now solder the entire bunch to the binding posts. Make sure to leave 2 Black wires,1 Red and 1 Green wire.

Step 5: Adding Dummy Load

To make sure our Power supply output is stable we need to add a dummy load, add a 5 Ohm 10w resistor to it. I don't have a 10W so I'm using two 10 Ohm 5W in parallel. Now solder Red and Black Wire across it. Don't forget to cover it with some tape, and place the resistor in the power supply case.

Now the only thing left to do is connect Green wire to Black wire so our power Supply is Always ON. You can add a Switch otherwise.

Step 6: Done !

That's it! You did it just plug it in mains and check the Output!

If you like my work

Feel free to check out my YouTube channel for more awesome stuff: https://www.youtube.com/c/Nematics_lab

You can also follow me on Facebook, Twitter etc for upcoming projects

https://www.facebook.com/NematicsLab/

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1 Person Made This Project!

sparkznsmoke made it!

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17 Comments

cathalferris

4 years ago

Note that you can get some useful voltages from working between the differing voltage rails.
Especially useful if the PSU you use has a -5V rail on pin 20, white cable, (ATX1.1 and older, optional on ATX1.2, missing on ATX1.3)
You can get these voltages:
24v from working between the +12v and -12v,
17v from the +12v and -5v
12v from the +12v rail and ground
10v from +5v and -5v
8.3v between the 3.3v and -5v
7v from +12v and +5v
5v and 3.3v between those rails and ground respectively
1.7v between the 5v and 3.3 rails

I would be a little wary of having high currents going between the negative rails and positive rails, but for most hobbyist work I've had no issues with differing "ground" planes for what I have usd it for
Those negative rails were for correct serial port use back in the day. I miss good serial ports!

Gelfling6

4 years ago

Usually most of the newer supplies won't require the dummy load, but 5=ohm? seems a wee low.. I built one, using a 33-ohm 5W sandblock and it runs fine. all of the older supplies (no 3.3V) required this load but most modern (with 3.3V) already have some form of load. on the board itself inside

hardwaylearn

4 years ago

To anyone who makes batt charger if charging flatter batt use headlight globe in series to limit current, or could burn out supply. Don,t ask! Eg 12v batt, use 12v halogen bulb in pos line(100W). Globe will glow dimly till current drops then go out- can then bypass globe.

ventifact

4 years ago on Step 6

All posative terminals should be red.

Kalebs-how2s

4 years ago

also if you connect the green wire to one of the black wires the fan will start spinning. I have just started making one of these and I didn't know what to use but now i seen you used banana clips so thanks.

hardwaylearn

4 years ago

These make top battery charger, just increase feedback resistor to regulator ic to get 14v ,7v, 13.4v out, add ammeter. Switch off before changing volts out.

rogermari

4 years ago

Thanks, Very useful and easy to follow guide

gm280

4 years ago

So many hobbyist have used the ATX type power supplies to build a bench top power supply. And for good reason, they are pretty good at supplying +12 volts and +5 volts and even +3.3 volts at pretty substantial currents. But you also need a variable output for higher voltage supplies. I always build my supplies with at least 24 volts or high for the odd electronic circuits. Add a LM317 or similar variable voltage circuit into your supply and you will love it. There are so many times I need a higher voltge as well as +12 and/or +5 at the same time. And a variable is great for testing relay drop out voltages and such. Just a suggestion. But you posted a great PS project all the Same. Here is my last one I made...