![]() ![]() To do this we have to connect a large resistor of 10 Ohms or less, with a standard power rating of 5W to 10W across the +5V output using just one set of the red and black wires, pins 3 and 4 will do. Next we need to provide a small load on the +5V (red wires) output to trick the PSU into thinking its attached to the motherboard and to keep the power supply in the “ON” mode. When pin 14 is momentarily or permanently connected to ground via a switch, the power supply will turn-ON. Luckily, pin 15 – Black is next to it so I connected a switch between the Pwr_On signal (pin 14) and Ground (pin 15). To start up a stand alone PSU for either testing purposes or as a bench power supply, we need to short together pin 14 – Green (Power-ON) to one of the common black wires (ground) which is how the motherboard tells the power supply to turn “ON”. Some of the other individual coloured wires we need to keep separate as detailed below. You can connect the same coloured wires together using crimp connectors or posts, is the same thing. I cut off the connector to have access to the individual wires and connected them into a screw connector strip to give me a higher amperage output for both the +5V and +12V supplies. You can keep the 20-pin Molex connector attached and connect directly into it or cut it off completely and group together the individual wires keeping the same colours together, reds to reds, blacks to blacks etc. There are a number of ways to convert a standard computer ATX power supply unit into a usable bench top power supply. The standard PC power supply unit has two safety mechanisms that prevent it from being switched “ON” without the motherboard attached. We can not just simply plug the PSU into the mains supply and expect to get the required 5 or 12 volts output. You are responsible for your own safety!. Also make sure that the metal box of the PSU is correctly earthed or grounded. This is important! as it could result in a potentially dangerous or even lethal situation due to the high voltages inside the PSU if you decide to dismantle it. The original ATX standard connector used for powering the motherboard was a single 20-pin Molex that has all the required +12VDC and +5VDC voltages with huge output currents and short circuit protection as well as a Power-ON wire that allows the PC’s software to turn “OFF” the PSU on shut down.įirstly and more importantly before you start to convert ATX PSU, make sure that the PSU is unplugged from the mains supply and discharged by letting it sit unconnected for several minutes before you start. Most computer PSU’s range from about 150W up to 500W so there is plenty of power. ![]()
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