Testing Methodology

Editor’s Note:

Because the testing methodology is constantly evolving, the following pages have been extracted and re-compiled from several different pages. Therefore, it may seem a bit disjointed. Just as the testing methodology is a work in progress, so are these pages. Please accept my apologies in advance.


For testing power supplies, a SunMoon automated power supply load tester and a Weibo PF1211 are used. The Weibo reads the Volts, Amps, Watts and Power Factor on the AC input of the power supply.

JG Testing Methodology

My dining room is now a mess. With a power supply tester, mains diagnostic machine, notepad, PC repair bible, a bunch of opened up power supplies, Black and Decker cordless screwdriver, laptop, calculator… I won’t be eating in here for some time.

The SunMoon load tester can dynamically load a power supply at the push of a button. The SM-268 model shown on this page has five memory settings and the ability to manually crank up the amperage while the power supply is already up, running and loaded.

I will actually program the loads each time I am given a different power supply to test. The loads are based on the overall capability of whatever power supply I’m looking at.

In the lower left of the SunMoon is the cluster of power connectors that I plug the power supply into.

JG Testing Methodology

Here you can see this Raid Max under a 366.8W load, but pulling 485.6W from the mains. That’s an efficiency of 75%. Notice the Comp-Nurse on top of the power supply.

JG Testing Methodology

You can see here that I’ve loaded up the 12V to 20A, the 5V to 20A and the 3.3V to 3A. The -5 and -12V are getting a half of an amp load and the 5VSB gets a 2A load. You can tell these three pictures were taken in sequence if you look at the Comp-Nurse. Notice the temps getting higher.

JG Testing Methodology

Under this load, notice how the 12V is at 11.31. Well under the 5% Intel allows for ATX specifications. In all fairness, this power supply is rated with a more capable 5V rail, since I’m loading the 12V up to 20A, it’s voltage drops. This makes it a good power supply for a Prescott with an AGP card or an AMD64 with a PCI Express card, but not a Prescott with PCI Express and certainly not SLI.

The display on the SM-268 has six fields. Each one representing a loaded rail. There’s a display for the 12V rail, 5V, 12V2 if I’m testing a dual rail power supply or -5V if I’m testing a single rail power supply, -12V, 3.3V and 5V stand by. With the press of a button, the displays will switch from load in amps, to voltage, to wattage. In wattage mode, I also get a display telling me the total wattage being loaded onto the power supply.

Now to calculate efficiency…

Let’s say we have a power supply plugged into the Sun Moon and it says it’s pushing 300W. Now I’ll take a look at the PF1211 and see how much wattage I’m getting from the mains. If it says 500W, I divide 500W by 300W and come up with 60%. This would mean the power supply is running at 60% efficiency. The PF1211 also tells me my power factor as well.

JG Testing Methodology

Busting out the old school calculator and notepad for this test.

Along the bottom of the display of the SM-268 is a number of buttons. It’s quite intimidating and sometimes to accomplish something you have to push a “shift” button and another button simultaneously. I have most of my settings pre-programmed, so all I have to do is select “memory 1,” through to “memory 5.” I then have an up and down arrow for increasing and decreasing load while the tester is running.

For the record (because someone asked me this the other day) the preset loads that I have pre-programmed into the SM-268’s memory DO NOT ramp up. The load on the PSU is immediate, so not only does the Power Good signal on the power supply have to work correctly, but the power supply also has to be able to accept a sudden, nearly crushing load, in a split second’s notice.