I have started to make a bench power supply from an old mini ATX power supply. The supply is really small and does not have room in the case to mount the binding posts for the outlets or the fuse holders for the voltage rails. I am going to mount the supply in to an ABS plastic case but still keep it in its own steel enclosure to restrict RF from the switch-mode.
I will be able to have +12VDC at 20A , -12VDC at 500MA, 5VDC at 30A and 3.3VDC at 18A.
Inline fuses in all the rails will be fitted to protect the supply. I have wired the Soft switch of the supply permanently on as I will have a Hard switch in the Mains AC input so that I don’t use any power while the supply is just sitting there. An ATX supply supplies 5VDC even when it is ‘off’.
I will also be fitting a variable voltage regulator based on an LM317 in to the case from the 12VDC rail to give me variable voltage, this will also have a Voltage meter (analog panel meter).
I have hooked up an 8.2Ohm 10watt resistor across the 5VDC rail to ground to load the switch mode as one of two things will happen if you don’t, first some supplies will fail to power up if not loaded and some will give stray high voltage (ie Mains) out, there is also the in built fan on the supply to load the 12 volt up.
Here is a pic showing the large ceramic 10watt resistor fitted in to the supply.
I have just been on to eBay and am going to order some banana sockets, a panel meter, fuse holders and the ABS case to mount it all in to. I already have some nice little rubber feet to mount to it.
The supply on the test bench the meter on the right is reading the +12VDC rail and I was getting 12.06 volts and the one on the left is the +5VDC rail at is at 5.14 volts.
I will be hard wiring the supply with a mains lead and get rid of the C13/C14 connection normally used on a PC supply.