AnandTech Power Supply Test Methodology
by Christoph Katzer on July 12, 2007 12:00 AM EST- Posted in
- Cases/Cooling/PSUs
Why It is so Difficult to Test Power Supplies
Over the past couple of years few markets in the IT industry have grown as rapidly as the power supply sector. Faster and more powerful CPUs, GPUs, and other components have led to a need for better and more powerful PSUs. A few years ago, most would have laughed at the thought of a desktop PC with a 700W or greater PSU, and yet such designs are becoming increasingly common. Companies are sprouting out of the ground like mushrooms and everybody wants a share of this fast evolving market.
With growing interest in power supplies it is natural that websites will take an interest in reviewing and testing them. However, power supplies are not as easy to test as many other components. For example, unlike a graphics card, CPU, or motherboard it is not enough to simply plug it in and run several of the latest 3D shooters.
Unfortunately, most published reviews on the internet are done in this manner. The DC outputs are quickly measured separately with a multimeter - or even worse the motherboard's BIOS. The rails seem to be stable, it runs the test system without difficulty, and it is relatively quiet; good enough for a Gold Award! These kinds of reviews do more harm than good to the actual users.
Because of the simple test rigs that are employed, the power supplies are not even close to being fully loaded and thus the DC outputs are generally without problem. It is also difficult or impossible to find flaws in this manner which would otherwise prevent people from buying a dangerous product. A certain PSU might run in system A just fine only to break down from an overload in system B and cause damage to the whole system. In addition to this type of problem, cheaper power supplies lack security features which should have been there for a reason.
The bottom line is, a normal PC is just not enough to fully load a high-end power supply, and therefore it cannot be properly tested and surely not approved by such a configuration.
Over the past couple of years few markets in the IT industry have grown as rapidly as the power supply sector. Faster and more powerful CPUs, GPUs, and other components have led to a need for better and more powerful PSUs. A few years ago, most would have laughed at the thought of a desktop PC with a 700W or greater PSU, and yet such designs are becoming increasingly common. Companies are sprouting out of the ground like mushrooms and everybody wants a share of this fast evolving market.
With growing interest in power supplies it is natural that websites will take an interest in reviewing and testing them. However, power supplies are not as easy to test as many other components. For example, unlike a graphics card, CPU, or motherboard it is not enough to simply plug it in and run several of the latest 3D shooters.
Unfortunately, most published reviews on the internet are done in this manner. The DC outputs are quickly measured separately with a multimeter - or even worse the motherboard's BIOS. The rails seem to be stable, it runs the test system without difficulty, and it is relatively quiet; good enough for a Gold Award! These kinds of reviews do more harm than good to the actual users.
Because of the simple test rigs that are employed, the power supplies are not even close to being fully loaded and thus the DC outputs are generally without problem. It is also difficult or impossible to find flaws in this manner which would otherwise prevent people from buying a dangerous product. A certain PSU might run in system A just fine only to break down from an overload in system B and cause damage to the whole system. In addition to this type of problem, cheaper power supplies lack security features which should have been there for a reason.
The bottom line is, a normal PC is just not enough to fully load a high-end power supply, and therefore it cannot be properly tested and surely not approved by such a configuration.
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jtleon - Thursday, July 12, 2007 - link
For the most accurate sound level testing, the air temperature around the microphone and the power supply is very VERY important. The microphone must reach steady state temperature and be calibrated at that temperature. The air temperature in the anechoic chamber must be maintained as constant, otherwise the microphone measurements will be off as much as 3-4dB in my experience for a temp delta of only 15°F.Also, no one is interested in the noise PS generates inside the PC case, rather the noise emitted to the exterior of the PC. And beware the air temperature inside the PC is much much higher than the interior PC air temperature. I don't see how your test approach will address these critical issues.
jtleon - Thursday, July 12, 2007 - link
Ooops...I meant to say,And beware the air temperature inside the PC is much much higher than the exterior PC air temperature.
LTG - Thursday, July 12, 2007 - link
This is exactly the high bar I expected from AT and I'm really glad to see you guys do it right.I've always felt that other review sites were missing a lot in this area.
LTG
lsman - Thursday, July 12, 2007 - link
Thanks, looking forward for the reviews. Please don't let it delay (or MIA) like those m-atx or motherboard.It will be more interesting than all those HSF reviews...
Kensei - Thursday, July 12, 2007 - link
A small nitpick... Japan is also 120VAC (actually 100) and uses flat blade plugs. I live in Japan and everthing I brought here from the US works fine. See
http://www.kropla.com/electric2.htm
Martimus - Thursday, July 12, 2007 - link
I used to test power sources and signal sources for variaous automotive components, and I am wondering why you are using a multimeter to measure the output instead of an oscilliscope. You can measure both current and voltage and actually capture the waveform to measure the ripple voltage with a good o-scope. When it comes to analyzing signals, the oscilliscope is a far more valuable tool than a multimeter.just my 2 cents.
acronos - Thursday, July 12, 2007 - link
I'm interested in how the power supply handles electrical noise from the power company. I know most of us have battery backups, but the power supply should do power line noise suppression too. In my area we have brownouts (low voltage), spikes (lightning strikes nearby), and just general noise. I also use computers in a manufacturing environment, which causes significant noise on the power lines.LoneWolf15 - Thursday, July 12, 2007 - link
What you want then, are line conditioners, or a UPS with line-conditioning capability.The most a power supply provides is Active Power Factor Correction, which will clean up things a little, but that's not a subsitute for a UPS with line conditioning, which will solve your issues with brownouts and spikes. This kind of gear would be expensive and bulky to try and add into a power supply; I don't see it happening any time soon.
LoneWolf15 - Thursday, July 12, 2007 - link
Clarification: Not every PSU has Active PFC --a better explanation can be found here:http://www.dansdata.com/gz028.htm">http://www.dansdata.com/gz028.htm
sprockkets - Saturday, July 14, 2007 - link
Yeah very good explanation. Another way of looking at it is I found a site sometime ago that showed the pfc as a 90 triangle to show the relationship.I'm looking for a good test of those fanless power supplies, but again, without a fan it does put a damper in the cooling.