Re-purposing old Desktop PC Power Supplies

🔘The power supply units ( PSU's ), known as ATX types, inside desktop 💻computers provide multiple DC voltages ( +3.3, +5, -5, +12, & -12 V ).

Over the years I have removed several of them from 💻computers that were going to be discarded; sometimes making use of just the box and fan for construction projects ( e.g., 📅22.02.2013, 22.09.2014 & 19.12.2017 ), or perhaps removing the inductors, diodes & heatsinks for future use. But even before then (📅 26.01.2010 ) I had already modified one for use as a stand-alone DC power supply unit for use in the workshop. I have just finished the fourth which I have converted for that purpose; another one for ⚡+12V.

4 modified PC PSUs for +12 (2), +5  & +3.3V ( the latest top-right)

They all have features in common: single fixed voltage output, fan, 30Amp Anderson "Powerpole" connectors for the output voltage, indicator LEDs, 10 Ohm 3W resistor from the +5V ( red wire ) to ground ( black wire ) for improved stability/regulation and rubber feet. However the one I've just re-purposed is the first to make full use of the standby mode.

Internal view - PSU powered-up (note switch position & LED status) 

To implement 'standby mode' ( similar to the original PC ), the SB wire ( green ) is connected to ground ( black wire ) via an additional switch. When the power switch on the rear is in the 'on' position  the PSU is powered-up but there is no DC voltage present on the output and neither is the 🪭fan working. The SB ( Stand By - purple wire ) LED ( yellow ) , however, is illuminated, and the PSU is in standby. All being well, closing the SB switch illuminates the PG ( Power Good - grey wire ) LED ( green ); "Power Good" signifying that the PSU is  functioning normally. A voltage is then present on the output terminals, 🪭fan operates and both LEDs🚦 are illuminated. I chose the labels ( SB, PG ) because they match those already printed on the circuit board.

A further development could be to mount the entire PSU inside a larger case, with provision for multiple voltage output terminals and metering. 🔲