Power Supply Efficiency FAQ

Discussion in 'Power Supplies' started by jonnyGURU, Mar 19, 2008.

  1. jonnyGURU

    jonnyGURU Moderator <BR> Power Supplies
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    What is ?efficiency??

    Efficiency is the ratio between the useful output of an energy conversion device and the input. For example, if your computer uses 300W, but pulls 400W from the wall, then the efficiency is 300W/400W, or 75%.

    Computer power supplies are typically 75% efficient, especially those units included with computer chassis or units made more than a couple of years ago before power supply efficiency was made such a priority. The BFG GS, LS, MX and ES power supplies are typically 80% efficient or better.

    Why is efficiency important?

    Quite simply, if your power supply is more efficient, your computer will use less power. Depending on how much you pay for power from your utility company and how much power your computer typically uses, you can save anywhere from $1 to $10 per year, per computer? perhaps more! Furthermore, because any AC power that is NOT converted into DC power is exhausted as heat, a more efficient power supply inherently runs cooler. Not only does this mean your office is going to be cooler, but also allows the power supply manufacturer to use a slower, quieter fans to cool the power supply.

    Aren't higher wattage units less efficient at lower loads?

    With all things being equal, yes. But you can't always compare brand A with brand B and assume that because brand B is a higher wattage that it's going to be less efficient at lower loads.

    It is true that most power supplies are only at their most efficient when the load on them is 20% or more of their capability. So with conventional power supplies, you pretty much have to throw any kind of green initiative out the window when trying to buy a power supply that will allow for future expansion; like buying a second graphics card for SLI or adding more hard drives to run a RAID array.

    Of course, even conventional power supplies vary from unit to unit, and since the initiative to be more efficient is a relatively new concept be aware that even if a modern day computer power supply is only 80% efficient from loads of 20% and up, it may be 77% or 78% efficient at a 10% load and this may still be much more efficient than the power supply you're replacing, even at it's best efficiency!

    What is 80 Plus?

    For a fee, 80 Plus will test your company's power supply to confirm that is over 80% efficient at 20%, 50% and 100% loads. Recently, 80 Plus expanded to include bronze, silver and gold certifications for power supplies that are over 82%, 85% and 87% respectively. Naturally, because of multiple PSU companies sharing the same platform and the cost of certification, the list is not all inclusive... but it's a heck of a brilliant start: http://80plus.org/manu/psu/psu_join.aspx
     
  2. richwenzel

    richwenzel Member

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    would it make sense to list the 80plus website here, maybe a direct link to the manufactures page?
     
  3. jonnyGURU

    jonnyGURU Moderator <BR> Power Supplies
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    Great idea. I'll add it.
     
  4. StraightPipe

    StraightPipe Golden Member

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  5. jonnyGURU

    jonnyGURU Moderator <BR> Power Supplies
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  6. szalony1983

    szalony1983 Junior Member

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    I think haveing a water cooled pc with 8 fans 4 hd, blue uv lights, 2 dvd rw, mobo and cpu and video card when you ran in SLI mode i dont think you gonna save any money on the power, or your bill...

    PSU will need alot of power to give it to your components in your comptuer,
    I have 850W supply, and when i turn on the pc, my lights dimm for asecond .. so just imagine, how much power each psu needs.

    And if you cant aford a electric bill get a laptop lol


    J/K

    Mario
     
  7. Ratman6161

    Ratman6161 Senior member

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    Not really true. If you had a system that actually required 600 watts and were using an 80% efficiency PSU, the draw at the wall would be 750 watts. If you replaced the 80% efficiency PSU with one that was 85%, that would reduce your draw at the wall to 706 watts for a 44 watt savings. I don't know how much that would turn out to be in $$ on your electric bill, but I bet it would be noticeable. And, the higher the number of watts your system uses, the more watts you will save through that 5% efficiency gain. So having a high wattage system means you get greater benefit from a quality power supply, not less.

    And the higher quality units are better for a lot of other reasons besides just their efficiency.

     
  8. NiK0laI

    NiK0laI Junior Member

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    I have a question regarding efficiency. My main PC that I built a little over a year ago has a 550 watt Gigabyte Odin PSU, this PSU has USB headers that allow you to have software monitoring from within Windows. Just idling in windows seems to draw around 100 watts. My pc isn't anything special, Core 2 Duo, 4gig ram, Abit IP35-Pro, one 7200rpm hdd, Nvidia 8800gts (512). Does that reading mean that if I left my PC on all day idling it would only be pulling 100 watts from the wall? (I understand that it would be drawing significantly more when put under a load.) The reason I ask is because I setup my old PC (with a 600 watt PSU) for a server and am considering just leaving it on 24/7, however I am reluctant to do so because of the potential increase in my electric bill :) However if it is drawing only what it needs instead of the full blown 600 watts then it wouldn't be a big deal. So would somebody kindly shed some light on this?

    Thanks much!
    Nick
     
  9. HOOfan 1

    HOOfan 1 Platinum Member

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    There is no such thing as a 100% efficient PSU, and never will be....but you won't be pulling 550W from the wall. Probably more like 125W or 130W

     
  10. brblx

    brblx Diamond Member

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    mmm....ice cold 100% efficient PSU.

    nikolai- when something pulls energy from the wall, it has to go somewhere; either it gets used to do work, or it gets wasted as heat. when your PC is off, your PSU actually still has electricity running through it just being burned off as a tiny amount of heat. when your computer idles, the entire PC is powered, but it still doesn't consume a very large amount of wattage until the more power hungry components spring into action- loading up the CPU or GPU, accessing data on your hard disk. that's what causes power to spike- if there's no work to be done, it's not using much power. 600w is only a theoretical maximum put out by your PSU manufacturer, describing how much DC juice the parts they've implemented can convert from AC (wall). it's not like plugging in a 600w drain- you'll likely never ever see a number that high. as hoofan said, there will be thermal losses on the level of 15-30%. even so, during anything but gaming most PC's don't consume more than a couple hundred watts.
     
  11. stephengillie

    stephengillie Junior Member

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    Your PC power supply, just like your car's alternator, only provides as much power as is needed.

    There's circuitry inside that determines how much is being used, and makes sure only that amount is provided. So if your system is only using 100w, the PSU will only put 100w into the wires.

    But still, there's the efficiency bit. If your system is drawing 100w and the PSU is 80% efficient, it'll take 125w from the wall plug. (100w / 80% = 125w OR 125 * 80% = 100)


    The voltage (600w) is a maximum that your PSU can put out. It can't do that much for long though. If you know how much your system uses when gaming, you should get a PSU that can provide about 30% more.
     
  12. theAnimal

    theAnimal Diamond Member

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    Bump for re-sticky.
     
  13. Emulex

    Emulex Diamond Member

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    most of the new energy star 4.0/5.0 85&#37;+ efficiency power supplies will reject a square or modified square wave (aka APC BACK-UPS). You can ask the manufacturer or APC for guidelines.

    They will recommend a pure-sine-wave model. Cyberpower makes a standby-puresine and APC makes the SMART-UPS. Expect to see many many power supplies follow suit.

    The battery backup folks are laughing this to the bank - $35 apc replaced by $235 unit.

    The symptom is when power is lost - the rejection of the modified square wave will cause the PFC circuitry to pull more watts as it believes its a brown-out. This will nosedive into a death spiral in which your power supply will shutoff or the backup unit will go into overload mode and shut down. either way you have no protection.

    The really nifty part is this is something that is one of those "walks the line" on whether it will accept or reject the square wave - the same power supply made months between each other - one may - one may not - the only "recommended" solution is a true sine wave battery backup.
     
  14. jyp007

    jyp007 Junior Member

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    Never knew about power usage. Thank you for the info.
     
  15. Dadofamunky

    Dadofamunky Platinum Member

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    This is great. If you're in the market for a power supply, you could do a lot worse than read this thread, go to Ecos PLus to check out the vendors they're painstakingly listed (hats off!) and then search 80 PLUS GOLD under power supplies in NewEgg. I have a pretty decent Corsair CS600 which is basic 80 Plus but I may make a change by and by...
     
  16. LiuKangBakinPie

    LiuKangBakinPie Diamond Member

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    A power supply runs at its max eff when its running at 50 percent of its load. Manufacturers basically say we guarentee you the max eff at the rated wattage if you run the psu at 50 percent of its load.

    Eff badges on the psus means jack coz some of them are fake and some past the test at room temps that is 23 degrees. No PC is that cold inside. When tested at 40 or 50 they falter.

    Transistors have a de rating the hooter they get the more power they loose. And yes a PSU gets hot inside. A psu loose 33 percent of its power between temps of 23 degrees and a 105. So that ECOs trick your going to walk into a trap I WARN YOU

    http://www.hardwaresecrets.com/article/Understanding-the-80-Plus-Certification/742

    Go here to see the avg requirement for your gpu
    http://www.realhardtechx.com/index_archivos/Page362.htm

    Go here to check up PSUs and respectable reviews of them done at real worl temps between 40 and 50 degrees
    http://www.realhardtechx.com/index_archivos/Page541.htm
     
    #16 LiuKangBakinPie, Feb 21, 2011
    Last edited: Feb 21, 2011
  17. pandemonium

    pandemonium Golden Member

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    Relative to this, I just posted my thread here on Anand that many of you will find useful for when you consider purchasing new components. And please vote!



    link deleted

    No crossposting, please.
    Admin allisolm
     
    #17 pandemonium, Mar 17, 2011
    Last edited by a moderator: Mar 17, 2011
  18. lehtv

    lehtv Lifer

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    Listen to this man
     
  19. buggers

    buggers Member

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    but we learned here :awe:
     
  20. velis

    velis Senior member

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    Just chiming in with some consumption data. I suppose more practical application data would be good to put perspective behind theory :D

    Anyway, I just replaced power supply in my HTPC / home file server. This HTPC also powers my router, VDSL modem, home phone system, telephone and some LED lighting.

    Used to use Corsair CX 430, replaced it with LC Power Gold LC-9450.

    Power consumption dropped from 85W typical to 63W typical.

    I need to find me some more devices to raise usage to where efficiency would be even better. On the old PSU turning on the LED lights (50W load) registered only halfway on total power consumption (85W --> 110W) because the raise of efficiency from 12% to 25% load was so high that effectively I was running half of my LED stripe for free.
     
    #20 velis, Nov 13, 2013
    Last edited: Dec 6, 2013
  21. battfast

    battfast Junior Member

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    Good writing, thanks for your share
     
  22. Cthompson281

    Cthompson281 Junior Member

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    What is 80+ gold? What does it mean?
     
  23. theAnimal

    theAnimal Diamond Member

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    It means the PSU is certified to meet minimum efficiency at 20%, 50%, and 100% load of 87, 90, 87 @115V (or 88, 92, 88 @ 230V).
     
  24. Heloperator

    Heloperator Junior Member

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    I assume you want to go over what your system spec needs to allow for upgrades and OCing anyways. Who know if you'll throw in a 2nd video card.
     
  25. Tr4nd

    Tr4nd Member

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    This is really useful, finally understand the PSU stuff even though I've been building my own PC for quite awhile. Time to get some power saving PSU then.
     
    #25 Tr4nd, Nov 6, 2014
    Last edited: Nov 15, 2014
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