SparkFun Forums 

Where electronics enthusiasts find answers.

Have questions about a SparkFun product or board? This is the place to be.
By silic0re
Hi all,

My Dad has made a really neat and simple breakout for an ATX supply to be used as a bench supply. Lots of folks use ATX supplies as bench supplies, but usually stick the binding posts for power on the supply itself. That's a great way of doing it (we do that too ;) ), but if the supply goes bad, or you just want to check the voltages, it's a bit of work. I've pasted his assembly instructions and pictures below:


ATX Supply Breakout

An ATX power supply can make a good cheap bench top power supply, and this breakout and is also good for testing ATX power supplies. This breakout provides +3.3, +5, +12, and -5 volts.

Most of the parts were salvaged from old equipment.

Parts required: 5 binding post, differant colors are best
1 single pole power switch
1 green LED
1 470 to 510 ohm resistor
1 ATX power connector ( removed from a deed motherboard )
1 plastic project box 4.5 X 2.5 X 1.25 inches

To test an old ATX power supply to see if it works and the voltages are correct, put a jumper between the green wire on the power connector and any black wire (there is a black common beside the green wire).
Now if you have an old ATX power supply you know does not work it is good for useing the wiring harness for the correct wire colors, makes it easier for wiring the male connector.

Assembly is quite easy, drill out the plastic box for the five (5) binding posts, the power switch and LED. Drill a hole in one end of the box for the wires to pass through but not to big.

Wiring colors needed are Red, White, Yellow, Green, Orange and Black. I used two (2) Black wires for the common so as to carry the current.

The male connector wiring is as follows:
Pins 3 and 7 are Black for the common
Pin 10 is Yellow for the +12 volts
Pin 11 is Orange for the +3.3 volts
Pin 14 is green for the power on switch
Pin 18 is white for the -5 volts
Pin 19 is Red for the +5 volts

I used the Red post for +3.3 volts, Blue for the +5 volts, Green for the -5 volts and a smaller red for the +12 volts and Black for the common.

TIP: If you place the male ATX connector on the power supply connector it makes it easier to keep the color code together while soldering the wires onto the connector. Place heat shrink tubbing over the wire ends after they are soldered to the connector.

For the power switch, the Green wire will go to one side of the switch and the other side of the switch will go to the common ( the black wire ). (Note: the power on the green wire goes to ground or common to turn the power supply on).

Solder the resistor to the positive side of the LED, and put a bit of heat shrink tubbing over the resistor to protect the wires. Solder the other end of the resistor to the +12 volt binding post ( yellow wire ) and the negative side of the LED to the black binding post ( black wire ).

Once all of the wiring is completed check it before you close up the box.
Testing is easy, connect the ATX connector together, make sure your power switch is off, plug your power supply into a 120 volt outlet, ( some ATX power supplies have a power switch just above the main power connector, make sure it is in the ON position ). Connect your bench meter to common and any one of the binding post voltages and turn on your power switch.
If all went well test each voltage and you have good bench power supply.
If the ATX power supply should fail in the future just plug a new one in.

(Remember to be extremely careful when dealing with power supplies and outlet voltages -- use these instructions at your own risk!).



And here are the accompanying pictures that he's sent:



By riden
Thanks for posting the project information and the photos. Do these supplies require any sort of load on them to be stable? Normally they are connected to a motherboard which presents a load. Do they continue to function properly in situations where the supply isn't connected to anything or is some type of constant load required?
By silic0re
That's a good question, and I'm not actually sure. I remember some power supplies (and some ATX to bench conversions) would use a load resistor on one of the lines (5V, was it?), otherwise the power supply might not turn on. I personally haven't had any issues with this, but perhaps someone with more knowledge of ATX supplies can jump in?
By LyleHaze
Most power supplies require a load on the +5 volt rail. Some also require a load on the 3.3 volt supply. You can read the specs of each supply to find out how much of a load you'll need.
I took an old processor heatsink/fan and clamped the load resistors to the face, offering a nice way to work the heat off.

One other note, it would be wise to fuse each leg of the power supply. Most PC supplies can deliver enough power to melt a project (or explode it) if something goes wrong. Fuses are cheap and useful for that.
By Emon
I did something like this, turning an old power supply into a bench top supply. I drilled holes for binding posts in the front of the power supply case, and put the on/off switch and indicator LED in the space where the wire bundle used to be. I have binding posts for +12, +7, +5, +3.3, 0, -3.3, -5. -7 and -12. I put a huge, low resistance power resistor on the 5v rail for load. It has a flat bottom and screw mounts, so I just mounted it to the cover for heat dissipation (which isn't much).
By riden
Emon wrote:I put a huge, low resistance power resistor on the 5v rail for load.
What was the value and wattage rating?
By gussy
I think the one I put in the last one I made was a 10W ceramic (big white rectangle thing) 10R resistor on the 5V rail. I have it zip tied to the side of the case so it keeps cool.
By riden
gussy wrote:I think the one I put in the last one I made was a 10W ceramic (big white rectangle thing) 10R resistor on the 5V rail. I have it zip tied to the side of the case so it keeps cool.
Thanks for the info. I was looking for a starting point for the resistor. It looks like we'd be dissipating around 2.5 watts with a 10 ohm resistor, so that's doable.
By krphop
1157 automotive bulbs are really cheap (MUCH cheaper than high power sand resistors) and generally provide enough load on each of the rails to bring them to the correct voltages. Putting a 'shield' near them to prevent them from being so bright is a good idea, just remember to leave enough room for some airflow for cooling of the bulbs.