Use a spare power supply to test fans, lights etc

Disclaimer: The information presented should not be considered a complete how to article, but merely a documentation of my conversion process. Modern PC Power Supplies can produce high output current levels that may cause internal overheating in the PS or damage to devices connected to them. Any individual attempting their own conversion is cautioned to carefully research their PS specifications and to be mindful of the associated voltages and power. DO NOT work on your opened power supply with it plugged in!!!!

How to use a PSU to test components, without connecting to a motherboard

Ever wanted just to test a fan, or a light, to see if it worked but didn’t want to dismantle a rig to do it?

Ever wanted to supply 3.3v, 5v, 12v, etc to fans to see how noisy they are?

When I’m modding I find it very helpful to have an independent power supply on the bench to do this and more, without connecting up to a motherboard

There are several guides on the net for doing this but most involve opening the PSU up. I’m the first to open up something with ‘void if opened’ but there are some big capacitors in there and you can do yourself some harm if not competent, and messing around too much could be a fire risk. So I prefer to leave the box closed and work with the lower voltages. Here’s how I did it:

Basically you need three things – a PSU, wire, and a ‘load’ to put the system on so it powers up. Switches are a refinement. An LED is a further refinement to show it is working.

There is a good write up, but it involves opening the PSU so I don’t advise it, but does give more details athttp://web2.murraystate.edu/andy.batts/ps/powersupply.htm

I altered this a little to avoid opening the PSU

PC power supplies like these are SWITCHMODE or SWITCHING MODE power supplies and must have a load to function. I bought a 10 ohm 10 watt load resistor, known as wire wound or sandbar resistors from Radio Shack for about $1. This resistor gets hot and should have some sort of heat sink. I used thermal paste, same as used for installing a CPU, and a cable tie to attach it to the piece of steel I had screwed into the wooden base

I took the thick 24 pin (or 22 pin) bundle which normally connects to the motherboard and cable tied this down onto the other end of the wooden base

I connected an old switch with two pieces of hook up cable. 22 gauge or thicker. I stripped the ends, and then folded over the exposed copper so that they would fit snuggly in the 24 pin bundle.

Connect one line to black, which is ground, or ‘zero’ and the other to the single green line. This is the power on line. If you use a switch it must be an ‘on or off’ not temporary on. This means it must keep a permanent circuit

Similar set up for the load line, I put a switch in the circuit but you don’t need one. Put the load between black and a red (5v) line.

I had a 3v yellow LED, so I connected this between a black and an orange (3.3v) line, just put it in and bent it upright. Works well to show it is on

I tucked all the other PSU cables away in a bag, except for one set of molex lines and a fan line, since this is what I usually need.

Here are the color codes

• ORANGE +3.3 V


• YELLOW +12 V


• BLUE -12 V


• RED +5 V


• BLACK GND


• GREEN POWER-ON must be shorted to ground to force power up

You can combine different combinations to make other voltages for other equipment. For example Yellow and Red would be +12v on one side and +5v on the other, making a difference of +7v; useful for undervolting a 12v fan to make it quieter yet still run

Anyway be safe with this, you can still generate a lot of heat and a decent current, but used sensibly it is a useful thing to have on the bench. You can be as professional as you want with the wiring but I’ve shown it without soldering or opening the PSU

Remember the disclaimer, although “modding” is by nature a death defying, warranty voiding, unconventional activity and we all know the joy of not quite doing what the manufacturer intended… but with electricty be careful with this, make sure you research what you are doing and be careful. And of course if you do decide to mod a power supply you do so at your own risk - if you burn the house down or lose an eyebrow, you and your first born child are liable for all and any loss, etc, etc.

Regards

Bruce