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.
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sprockkets - Saturday, July 14, 2007 - link
I've used a kill a watt device to test for pfc, seems most computers are around 0.6 to 0.64. My old Shuttle box with a replaced power supply with active pfc gets a 0.95 pfc.Phlargo - Thursday, July 12, 2007 - link
This is an excellent commitment to a quality review methodology which will not only benefit the Anandtech community, but the whole power supply industry if the message here is taken to heart by consumers. That anandtech has decided to actively create a reliable and consistent power supply review rig is just another example of exactly why I have come to this great site for so many years.Great work!
mostlyprudent - Thursday, July 12, 2007 - link
My thoughts exactly!qpwoei - Thursday, July 12, 2007 - link
How fast can you ramp the current on that rig? I'd be very interested to see how PSUs respond to sudden changes in power usage (caused by sudden changes in CPU/GPU load, HDDs spinning up/down, etc).Even if the fancy equipment can't handle it, measuring this shouldn't be too hard with a cheap digital scope and a 20W passive load. Put the probe on the 12V rail to be measured, attach one end of the load to ground, attach the trigger to the high side of the load, then connect the high side of the load to the 12V rail. Should give a nice edge to trigger on. The trick would be connecting the high side fast enough. A switch/relay would probably be too slow, though a bank of MOSFETS should do the job fine. Actually, the current to turn on the MOSFET bank itself would be a good transient test :)
Also, I think a far more interesting thing with respect to temperature is how the PSU reacts to elevated temperatures, as opposed to temperature WRT load. Since a lot of cheaper PSUs are rated at 20 deg C, I'd expect to see them struggling to supply full power at 40 deg C or so. You'd need to regulate the intake air temperature, but that shouldn't be too hard.
JonnyBlaze - Thursday, July 12, 2007 - link
looks like it can do it.
qpwoei - Friday, July 13, 2007 - link
That's the "mains" supply thing. I noticed that you can read the module number in one of the shots, and it appears that the 63103 can do dynamic load tests - 5 A/us slew with adjustable repetition rates should do the job nicely. I'd be really, really interested to see some results from this.ATWindsor - Thursday, July 12, 2007 - link
Hopefully you will be using the box for some other SPL-measurments on equipment that is not a PSU also?AtW
WW2Planes1 - Thursday, July 12, 2007 - link
Great looking setup. (I love the sound isolating box). I Finally feel like I'll actually learn something from a power supply review.I agree with BladeVenom, I really hope to see some midrange/budget PSUs as well as the higher end ones.
One other thing that would be nice to see in reviews (not just the power supply ones), is longer term reliability. Most things (and especially computer components), aren't really built with longevity in mind, and with certain critical components (power supplies, hard drives, etc) it would be nice to know if certain companies build longer lasting products than others. I understand the difficulties involved with something like that, so I don't really expect to see it, but it would be nice.
TA152H - Thursday, July 12, 2007 - link
I'm not sure midrange or budget power supplies are ever a great idea, unless they are just low power units. A couple of times I bought cases with these power supplies, and was just plopping an old motherboard in it so I didn't care too much, and found they are really problematic. They poison everything downstream from them, which is pretty much everything, and they do nothing good for the reliability of the system, and of course greatly reduce the lifespan of it.The one part of system that should never be compromised on is the power supply. A slower processor or video card might work fine for most people, and if it's not fast enough, it's not catastrophic. A poorly made power supply can have catastrophic consequences and whatever money you save on it, it can cost you later on in multiples of it. You can't make a good power supply out of bad components either, so I don't see how a low cost power supply could impress. Even if it did fairly well in their tests, I'd have serious concerns about the reliability and what will happen to it as time goes along. Low cost power supplies can't be using the same high quality parts, after all.
I'm not knocking power supplies that cost a little because they have relatively low power output. I'm saying if you see an 800 watt power supply that is costing 40% less that other quality 800 watt power supplies with the same feature set, you're asking for trouble buying it. You don't roll dice with power supplies.
Still, it might be interesting just to see the differences quantified, between low and high quality power supplies. I just hope it doesn't lead to people buying the low quality junk. That would be a terrible disservice. It's better to save money on ANY other part of the system before the power supply.
mostlyprudent - Thursday, July 12, 2007 - link
When I think of midrange PSUs, I think of lower wattage models (380-450) by reputable vendors. However, as the article mentions, there are a lot of new players popping up in this market. Hopefully that kind of competition is leading to more competative pricing. It may cease to be true that you need to spend over $100 to get a high quality PSU.My point is that there may be some real value to testing less expensive PSUs.
I get the impression from this article that AT will test a wide range of PSUs (from a wattage standpoint). I hope that is the case. There is nothing more frustrating to me than finding reputable review sites who don't have any recomended PSUs below the 700 watt level.