AnandTech Power Supply Test Methodology
by Christoph Katzer on July 12, 2007 12:00 AM EST- Posted in
- Cases/Cooling/PSUs
AnandTech Power Supply Test Methodology
The only way to test a power supply correctly is with special equipment designed for such tests. This starts with programmable loads, which allow the loading of precise amperages on the power supply. Next, a power meter will be needed to measure the exact amount of power used during testing. Power meters can be found in a variety of versions already, ranging from the simple to the complex, and it's good to see that some publications already test with this method.
To test the quality of the DC output we need an oscilloscope as well. This is important since each output has certain ripple and noise levels, and these are different with each power supply - even those from the same manufacturer. The ripple and noise are leftovers from the electric pulse, and every power supply should implement certain measures to reduce the ripple to an acceptable grade. The actual Power Supply Design Guide specifies that each +12V rail should not have any ripple over 120mV and the +3.3V and +5V rails should not have any ripple over ~50mV. Unfortunately we cannot present these tests right away since we are still working on the best methods. We will conduct those measurements soon and include them in the reviews.
It should be quite clear now that we will need some serious equipment to conduct all these tests. To assure our readers of the most professional and accurate reviews on the web, we are building our PSU test lab based on equipment from the renowned company Chroma. With the Chroma test equipment we can make clear and very accurate measurements and load power supplies controlled in ways that are impossible to achieve using only a PC. On the following pages we will introduce our equipment and the ways they will contribute to future power supply reviews.
The only way to test a power supply correctly is with special equipment designed for such tests. This starts with programmable loads, which allow the loading of precise amperages on the power supply. Next, a power meter will be needed to measure the exact amount of power used during testing. Power meters can be found in a variety of versions already, ranging from the simple to the complex, and it's good to see that some publications already test with this method.
To test the quality of the DC output we need an oscilloscope as well. This is important since each output has certain ripple and noise levels, and these are different with each power supply - even those from the same manufacturer. The ripple and noise are leftovers from the electric pulse, and every power supply should implement certain measures to reduce the ripple to an acceptable grade. The actual Power Supply Design Guide specifies that each +12V rail should not have any ripple over 120mV and the +3.3V and +5V rails should not have any ripple over ~50mV. Unfortunately we cannot present these tests right away since we are still working on the best methods. We will conduct those measurements soon and include them in the reviews.
It should be quite clear now that we will need some serious equipment to conduct all these tests. To assure our readers of the most professional and accurate reviews on the web, we are building our PSU test lab based on equipment from the renowned company Chroma. With the Chroma test equipment we can make clear and very accurate measurements and load power supplies controlled in ways that are impossible to achieve using only a PC. On the following pages we will introduce our equipment and the ways they will contribute to future power supply reviews.
Facebook
Twitter
RSS
49 Comments
View All Comments
crimson117 - Thursday, July 12, 2007 - link
Good point. Just because a certain digital camera fails when it is submerged underwater, it doesn't mean all users should stick to only buying waterproof cameras. You'd still have a great camera, provided you keep it out of the water.
crimson117 - Thursday, July 12, 2007 - link
<quote>The ambient temperature around the power supply will constantly grow with the time of the test. It will be placed in the same set of conditions it will experience in a real system, where the temperature rises over time.</quote>I'm very glad to see this highlighted in your review strategy.
It always irks me when I see temperature scores of heatsinks which don't consider the variable temperature of the cooling substance (the air) that was used!
If you blow hot 90 degree air over something, the best it can do is cool that something to 90 degrees. If you blast a heatsink with cool compressed air, you'd get much lower heatsink temperatures.
Rocket321 - Thursday, July 12, 2007 - link
About that 5 layer box...I re-read that page a couple times but don't get it. How do you connect the PS unit to the programmable load without running a cable through the wall of the box? If I'm reading it right, you are using the internal PCB to reduce the # of cables you run through the wall to a single cable...?
I'm just curious as it wasn't immediatly clear what was going on there.
Otherwise I applaud you for the new branch of quality reviews you're starting. I look forward to the first review!
nrb - Thursday, July 12, 2007 - link
I'm slightly concerned by this statement: I would urge you not to start doing PSU reviews until you have got the measurement of ripple figured out. It's one of the most important measures of PSU performance, IMNSHO.kaborka - Saturday, July 14, 2007 - link
I second that. Measuring ripple on my scope under various loads is the first thing I do when I get a new PSU. I have an old surplus Tektronix I use. I would not be interested in any reviews that don't include ripple measurements -- it would be useless.But Thank You, THANK YOU for finally doing serious PSU tests. The sites that do fluff pieces about the latest shiny boxes have always irritated me no end!
EODetroit - Thursday, July 12, 2007 - link
HardOCP pretty much is the gold standard on real, tough, power supply reviews atm. It will be interesting to see if you get the same results as they do.One thing that happens all the time in the HardOCP reviews is that a PSU will work great up to about 75% of its rating, then fail or get out of spec. My question is... will you consider that a failure or will you just recommend the PSU as long as you don't go over 75% ? No one runs a PSU fully loaded on purpose anyways.
One more thing slightly off topic... how come Anand (and everyone else in the biz) is willing to load a PSU to the max but won't review a motherboard loaded with the maximum "supported" memory? The latter is a much bigger problem imo, and with 64 bit OSes now commonplace that can make use of all the memory in a computer, the time is right to start reviewing MBs that supposedly support 8 GB of ram... while actually loaded with 8 GB of ram.
CrystalBay - Thursday, July 12, 2007 - link
So how is PCP&C's 750 Silencer gonna stack up with it's 80mm fan???End The Power Supply Myths AT........
strikeback03 - Thursday, July 12, 2007 - link
I recently bought some motherboards to build desktop systems for some of our grad students. They claim support for 16GB RAM, but since they only have 2 slots for RAM testing 16GB falls somewhere between "extremely expensive" and "impossible".Martimus - Thursday, July 12, 2007 - link
I would like to see that as well. MB's performance with a full load of RAM. (Actually I would want to know if there are any other issues when you run it like that.)strikeback03 - Thursday, July 12, 2007 - link
Nice new toys:)On the Temperature page where it says "We will start at a room temperature of 77°F (25°C)" perhaps mention should be made that the "room" is actually a sealed box, which appears to have far less air volume (and circulation) than the average room, so the air will get far warmer than it ever should in an actual case.