Desktop computer power supply "ATX"
I modified the desktop computer power supply "ATX" type for getting +12 VDC to run my solid state gears. I got the unit from my son’s computer which is relatively new. There are two kinds of power supply units for desktop computers generally, "ATX" and "AT" type and it is simple to modify the power supply for ham radio use getting +12VDC for both types.
(1)How to identify "ATX" and "AT" type.
You need to check the label on the box. "ATX" power supply unit has the output of +12DCV, +5DCV and +3.3DCV. When you see +3.3DCV, it is the "ATX" type. Also read what amperes the +12DCV can be generated. This amperes will tell you how big transceiver you can run with this unit on +12DCV.
(2)Take a look at the inside.
Remove the top cover. The cover is normally tightly closed and you need to exercise very careful handling to remove the top cover. BE CAREFUL NOT TO CUT YOUR FINGERS AND DO NOT HURT YOURSELF. The way to remove the cover defers from a manufacture to manufacture and the design is deferent from the manufacture to manufacture also.
(3)Check if the unit is working order or not.
Look at carefully on the printed circuit board inside and find on the board "PS-ON" where a green wire is soldered in my case. The wire color defers again from a manufacture to manufacture. Then find "GRD" on the board where normally black wires are soldered. Connect the power cable for 115V AC to the unit and then connect those green wire and black wire momentarily. If the unit is working order, the fun will start running.
If nothing happened, the unit seems ” out of order” and you need to get hold of a working order unit.
(4)Wiring for modification:
Check the color wire sizes used and normally 18AWG wire is used. The 18AWG wire can carry about 2.5 amperes per wire.
Firstly you provide a switch and you need to be installed on the box (you figure out the location) and then connect the green wire(PS-ON) and one black wire(GRD) so that the unit can be switched on and off to run.
Secondly check the amperes on +12DCV on label that the unit can handle. Identify +12DCV on the board. The 18AWG wire can handle about 2.5 amperes per wire so you need to figure out the number of wires required for the unit for the output of the unit that you are modifying. For example 5 ampere unit requires two wires, that is, 5 amperes divided by 2.5 ampere per wire is equal to 2 wires needed. Also the same number of wires for the GRD is needed. So for this modification you need two +12DCV wires and three GRD wires (one wire for the switch on-off and two wires for +12DCV circuit.) are required in total in this example. I used a block terminal for the power of +12DCV or two alligator clips for power take-off.
(5) The wires for 115ACV and the cooling fan.
Keep the wires for 115ACV and the wires being connected to the cooling fan to run. Do not cut those wires at all.
(6) The rest of wires:
Remove and cut the rest of wires (that is the wires for -12DCV, +5DCV, -5DCV, +3.3DCV and etc). You need the wires to run the unit and +12DCV output. Make sure the edges of those cut wires NOT TOUCHING ANY THING AND ANYWHERE.
I looked at the shape of produced DC current on my oscilloscope. It looked to be straight line indicating high quality DC current. I am using mine to run QRP transmitters and 2M transceivers and am happy for the performance of the unit.