How to Convert a Computer ATX Power Supply to a Lab Power

It is possible to make a lab power supply from the ATX power supply that you can salvage from a discarded computer. All you need is the old computer and some extra supplies. Follow these steps to convert a computer ATX power supply to a lab power.

Things You'll Need

• Discarded computer
• Drill
• Needle nose pliers
• Wire cutters
• Tape
• Supplies from Section 1
• Reamer
• Heat shrink tube
• Soldering iron
• Soldering wire
• Low wattage switch
• Current limiting resistor (330 ohms)
• Power resistor
• LED
• Binding posts

Instructions

Gather Supplies

1. Unplug the power source from the computer. Open the computer case and find the gray power supply unit box. Find all the wires that lead from the power supply to the boards and devices and disconnect them.

2. Detach the screws that attach the power supply to the computer and remove it.

3. Cut loose the connectors.

4. Eliminate the power supply by affixing a 10-ohm resistor between a red and black wire (on the output side). This only takes a few seconds. Alternatively, you can let it rest unconnected for a few days.

5. Remove the screws on the top and bottom of the power supply unit to open it.

6. Bind together the wires that are the same colors.

Assemble Components

1. Drill holes in an area of the power supply case that is free. Do this by marking the holes with a nail hit lightly with a hammer. Drill the starting holes using a rotary tool. Then, enlarge the holes with a hand reamer until they are the correct size. Determine they are the right size by test fitting the binding posts.

2. Make holes for the Power switch and the power on LED.

3. Insert the binding posts into their holes and affix the nut on the other side.

4. Fasten all the pieces together. Connect one red wire to the power resister and then the rest of the red wires to red binding posts. Attach three black wires to the opposite end of the power resistor, the DC-On switch and a resistor attached anode of the LED. Affix the rest of the black wires to the black binding post. Fasten the white wire to the -5V binding post and the blue wire to the -12V binding post. Attach the yellow wire to the +12V binding post. Finally, unite the gray wire with the LED cathode. Remember that some power supplies may have a brown or a gray wire to represent "power good" or "power ok." Connect this wire to a red wire or an orange wire for the power supply to perform. If the power supply is AT or non-ATX compliant, there is the possibility it will have its own color scheme.

5. Connect your green wire to the other terminal on the switch. Use heat shrink tubing to insulate the soldered ends. Classify the wires with zip ties or electrical tape.

6. Tug on the connections gently to ensure they aren't loose. Inspect for bare wire and cover it. Stick the LED into its hole. Replace the cover.

7. Insert the power cord into an AC socket and then into the back. Turn on the main switch on the power supply unit. If the LED light doesn't come on, power up by flipping the switch on the front.

Tips & Warnings

• For proper operation, a few power supplies will have wires that you will need to connect to the actual voltage wires. In the main power bundle (the one with 20 wires), you should have three orange wires and four red wires. If there are only two orange wires, connect a brown wire to the orange. If there are only three red wires, connect another wire (which may be pink) to them.

• Line voltage can hurt you by delivering a very painful shock. Always remove the power cord before doing anything. Remember to discharge the capacitors.

• Don't touch the lines that lead to the capacitors. They retain a charge as batteries do, but they will discharge it quickly. Avoid touching anything on the board. Before working, use a probe to connect anything that you may touch to a ground.