Covert ATX Power Supply to Bench Power Supply

A bench power supply is necessary when working with electronics, but a commercially available lab power supply can be very expensive for any beginner who wants to explore and learn electronics. But there is a cheap and reliable alternative. By converting a computer ATX power supply that can be found in any discarded computer or can be bought from scrapyard for less than a dollar, you can get a good lab power supply with huge current outputs, short circuit protection and very tight voltage regulation.

In this instructable I will show you how to quickly convert any ATX power supply to get a lab power supply with following specifications.

• An ON/OFF switch
• Indicator LEDs
• Output voltages : 12VDC, 5VDC, 3.3VDC
• Two USB ports with 5VDC output @2A

WARNING: YOU ARE WORKING WITH AC VOLTAGE!!! IF YOU ARE NOT SURE OF WHAT YOU ARE DOING - DO NOT ATTEMPT THIS.

Step 1: Get Your Tools and Supplies

Tools needed:

1) Screwdriver

2) Soldering Iron

3) Solder wire

4) Glue gun

5) Drill and Drill Bits

6) Wire cutter/stripper

7) Electric tape

8) Some heat shrink tubing

Parts needed:

1) Working ATX power supply

2) Binding Posts (RED) x 3

3) Binding Posts (BLACK) x 3

4) 1K Ohm Resistor x 2

5) 5mm RED and GREEN LED

6) SPDT Toggle Switch x1

7) USB Type A Female Connector x 2 (or more if you want more USB outlets)

Step 2: Making the Front Panel

Before opening the PSU, disconnect it from mains, locate the green wire on the connector and short it with any black wire present on the connector using a jumper wire. This will discharge the high voltage capacitors and know you can proceed to open it.

Open your power supply and clean all the dust which it has collected over years. You can now start by drilling holes directly on the metal sheet or the case where you want mount the components mentioned in the previous step. Or else you can make a layout as shown in the image to exactly know where and what you will place and drill.Drill the holes appropriate to the sizes of components and use a file to smooth the sharp edges or else you might get cuts while handing it.

Step 3: Installing the Binding Posts, Switch, LEDs and USB Port

After drilling the holes install the binding posts and the switch a fasten them.

Note: Make sure that the binding posts are isolated from the metal case.

Solder the resistors to the anode of the LEDs and insulate them with some heat shrink tubing as shown in the image. Place the LEDs and USB type A connectors in their respective holes and use hot glue to stick them.

Step 4: Preparation for Wiring

Cut the wires to a suitable length and separate the wires by color. The second image gives us the idea about the color code of the wires. Separate the black, red, yellow and orange wires. Strip the wires and solder them together by color but separate 1 Red wire, and 4 to 5 black wires from the rest. Also strip the Green and Purple wire as we will use them. The rest of the wires are not needed and can be cut or shortened. Remember to place heat shrink tubing over the cut ends of the unused wires to prevent shorts.

Step 5: Connect the Wires

The 1st image itself is enough to explain how the wiring is done. I have used a common 10 AWG wire to connect all ground binding posts, but you can separately solder black wires in bunch of 3 or 4 to the binding posts. Solder the different colored wires to their respective binding posts. The green wire goes to one terminal of the switch and the black wire goes to the other terminal. Purple wire is connected to anode of STANDBY LED and is also common to the +vcc pin of the two USB connectors. The last Red wire is connected to anode of the POWER LED. The cathodes and the ground terminal of the USB ports are connected to the black wire. Don't forget the slide the heat shrink tubing over the wires BEFORE soldering the wires or you can use electric tape to insulate the wires after soldering.

Step 6: Reassembly

Carefully arrange the wires inside the power supply and put it back together by replacing the screws.

Note: Make sure that no metal piece or bare wire is inside the power supply before putting it together.

Step 7: Testing and Conclusion

Plug the power cord into the back and into an AC socket, flip the main switch of the PSU (if present) at the back, the RED LED (STANDBY LED) will light up. Now flip the toggle switch on the front and GREEN LED should light up, also the fan will come on.Now you can use the multi-meter to check the voltage at the binding posts. Now you are ready to connect the load to the power supply.

Congratulations!!! you gave a new life to a rusty old power supply siting lonely in a scrapyard or a dead computer waiting to be crushed for recycling, but now sitting in your lab and ready to feed your power hungry projects with a output capacity of few 100 watts.