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Hold Up Time, Overload And Short Circuit Test, Temperature

Soon At Tom's Hardware: Full-Scale Power Supply Testing
By , Patrick Afschar

Hold Up Time

Although modern power grids are stable and of fairly high quality, there are always some power fluctuations. Modern power supplies have capacitor banks to handle such power fluctuations for a certain period, called the hold up time. The ATX standard for hold up time is a minimum of 16 milliseconds.

Tom's Hardware measures this by permanently monitoring the PSU's output voltages. After cutting off the power supply, the oscilloscope records the voltage curves in order to accurately measure how much time passes before the voltages drop. These measurements are carried out both at 115V and 230V.

Overload Test

A PSU's power rating normally describes the maximum amount of power it can supply over an extended period of time without being damaged. Here, the total is the sum of the individual 3.3V, 5V, 12V, -12V, and 5V standby rails combined. To check whether a PSU operating at its maximum specified load is truly at its limit or whether the manufacturer has left the PSU with some headroom, we perform an overload test. The load on the 12V rails are set to 110% of its specified maximum. If the PSU can run the test for five minutes without dropping voltage below the ATX specification's 11.4V (a maximum 5% deviation), the test passes.

Short Circuit Test

A critical short circuit doesn't happen very often, but it's not inconceivable, and the result is often a dead PSU. Today, however, many PSUs have circuits to protect them from short circuit damage. To test the protection circuit, Tom's Hardware manually triggers a short circuit on a 12V rail. The power supply should turn off immediately so it doesn't overheat and becomes permanently damaged. If the PSU can be used normally again after deactivating the short circuit, the test passes.

Temperature

Like any electrical appliance, a PSU operates at a certain efficiency. The energy not used for powering the computer and its peripherals is released as heat into the environment. Tom's Hardware continuously monitors the temperatures of the inflowing and exiting air to track the warming effect, and the biggest difference measured between these two values is reported as the test result.

Accessories and Ergonomics

In addition to the results of the numerous performance tests mentioned above, the PSU's accessories and ergonomics are also taken into account in our final results. The testers turn their attention to details, such as included mounting solutions, housing construction quality, cable modularity, and cable lengths. Anything else making the user's life harder or easier gets mentioned as well.

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Top Comments
  • 33 Hide
    Gamer-girl , June 22, 2010 6:24 AM
    Is it possible to include sound levels in decibels?
  • 27 Hide
    JonnyDough , June 22, 2010 6:34 AM
    I second what gamer-girl said, and although this is exciting I'm still awaiting the Graphics Comparison Charts! I realize this is more of an IT website, but these days everyone's a gamer of some type! Long live PC gaming!
  • 17 Hide
    baracubra , June 22, 2010 6:37 AM
    Wow, great idea and article! This will be a huge help and I'm glad u guys took the time and effort to put this together! Long live TH!
Other Comments
  • 33 Hide
    Gamer-girl , June 22, 2010 6:24 AM
    Is it possible to include sound levels in decibels?
  • 27 Hide
    JonnyDough , June 22, 2010 6:34 AM
    I second what gamer-girl said, and although this is exciting I'm still awaiting the Graphics Comparison Charts! I realize this is more of an IT website, but these days everyone's a gamer of some type! Long live PC gaming!
  • 17 Hide
    baracubra , June 22, 2010 6:37 AM
    Wow, great idea and article! This will be a huge help and I'm glad u guys took the time and effort to put this together! Long live TH!
  • 13 Hide
    Anonymous , June 22, 2010 6:42 AM
    take the good ideas from some other nice psu reviewers

    http://www.jonnyguru.com/modules.php?name=NDReviews&op=Story&reid=153
  • 3 Hide
    joytech22 , June 22, 2010 6:50 AM
    I hope they do a large comparison, i want to see how my Antec TPQ 1Kw stacks up to some of the other manufactures.
  • 3 Hide
    baracubra , June 22, 2010 6:53 AM
    Btw, how much did all this eqipment cost TH??
  • 3 Hide
    Anonymous , June 22, 2010 7:15 AM
    This is great news. On a related note do you guys not do LCD monitor testing anymore?
  • 4 Hide
    gege , June 22, 2010 7:42 AM
    take the good ideas from some other nice psu reviewers [2]

    www.hardwaresecrets.com/page/power
  • 2 Hide
    liquidsnake718 , June 22, 2010 7:46 AM
    Bravo, good choice for a new section as more consumers and buyers should be aware of the power supplies and the quality/preformance that they offer us. I myself am about to change my older PSU and will be waiting to read the first comparisons. The problem is, which ones will you choose and every month will you have a power category? For example all the 500-600watts, then following the 700-800, 1000w onwards, ect.

    You might even succeed in killing off generic psu's or at least make more ppl buy 80 plus or 80plus bronze psu's....
  • 2 Hide
    Henry Chinaski , June 22, 2010 8:42 AM
    It's a very good news. Another qualified reviewer is always welcome.
  • 4 Hide
    KingArcher , June 22, 2010 9:09 AM
    This is an awesome setup. Wish I worked at TH.
  • -2 Hide
    neiroatopelcc , June 22, 2010 9:31 AM
    Article500W: Gaming PC with a high-end CPU and multiple graphics cards

    I've measured my system using 750W, and that's definetly more than 500W draw on the inside. And considering my system's only got two harddrives and air cooling, I'd say 500W doesn't qualify as high end cpu with multiple graphics! 600W at least!
  • -6 Hide
    Reynod , June 22, 2010 9:52 AM
    Great news.

    We should of course give the reviewer the nickname "Scotty" ... surely?

    The PSU is technically "engineering" and ratings should include references to "warp factor" and dilithium crystals" ...lol.

    Nice test gear there ... good looming job too.

    Looking forward to some definitive reviews now you have the gear.

    I am wondering how some of the vanilla PSU's will go against the more expensive units?

  • 1 Hide
    gustavost , June 22, 2010 10:13 AM
    I can't barely wait for the test!

    It's really nice that we as customers have real test we can rely on!
  • 0 Hide
    feeddagoat , June 22, 2010 11:08 AM
    Bit-tech/CPC already do something like this. Its by far the best way to test PSU's and its fantastic that Tom's is doing something similar. Can I suggest a comment on fan noise as well. bit-tech comment on the loudness of the fan at full load but don't actually do any sound measurments due to background noise in the offices. Better than nothing tho. Also is there anyway to "endurance test" a PSU. A few PSU's end up in secondary PC's, it would be nice if there was someway of testing long term strain on PSU's too.
  • -4 Hide
    7amood , June 22, 2010 11:19 AM
    YESSSSS PLEEEEEEEEEEEEEEASE \^_^/
  • 8 Hide
    allantang , June 22, 2010 11:56 AM
    I wish there were more info on this stuff, so this would be great!

    I think room temp should also be taken into account. It will make a huge difference if the room is 15C or 25C.
  • 0 Hide
    JohnnyLucky , June 22, 2010 12:13 PM
    Great news! Looking forward to reading power supply reviews. Glad to know you will be testing overload and short circuit protection.
  • 4 Hide
    saifallofjmr , June 22, 2010 12:19 PM
    Also please do the green series by rosewill so we can finally confirm whether or not this brand is in fact good or really bad.
  • 0 Hide
    elel , June 22, 2010 12:37 PM
    Good job. Another thing that I think would be VERY useful would be to test the current drawn from each rail by the SBM PCs. I know that you test system wattage already but I would like to see how much current of each voltage they draw, possibly taken from a custom modded high wattage PSU like the one x-bit made for similar measurements.
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