High Rated PSUs Unnecessary

Discussion in 'Power Supplies' started by Eureka, Nov 2, 2012.

  1. Eureka

    Eureka Diamond Member

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    So, I finally got my hands on a Kill-A-Watt, and I'm convinced that the "need" for high rated power supplies is a scam.

    System:
    i5-3570k, 4.5 ghz, 1.28V
    Gigabyte GA-Z77X-D3H
    Patriot Viper DDR3 1600 16GB, 1.5V (stock)
    Visiontek 7970 Ghz, 1125/1600, 1.3V (stock)
    Intel 330 160GB SSD
    Seagate Barracuda 1.5 TB Green
    2x 220mm Fans
    2x 120mm Fans
    DVD Drive
    OCZ EliteXStream 800W

    Power readings from the Kill-A-Watt:
    Idle: ~80-90W
    Normal Usage: ~130W
    Prime95: ~190W
    Heaven DX11, Full Settings: ~280-320W
    Heaven Dx11, Full Settings, 7970 @ 1.38V: ~380W

    Extrapolating from a review Anandtech did:
    [​IMG]

    That means that with it never dips below 82% efficiency at the ranges I'm running other than idle. To adjust:

    Normal Usage: ~107W
    Prime95: ~155W
    Heaven DX11, Full Settings: ~230-262.4W
    Heaven Dx11, Full Settings, 7970 @ 1.38V: ~311W

    This is a mildly overclocked system with a large card. At worst, I was delivering 311W to the components. That means a 430W would be able to handle this load, and I might even get away with xfire/sli at 500W, given enough connectors (the 7970 at load only used up another 200W at full OC, and around 100W with a normal OC).

    It seems to me like our PSUs are grossly overrated for their jobs.
     
  2. NumericalMethods

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    Yup! Pretty much.

    Although there are some things to bear in mind - The killawatt might not be totally accurate, but will provide decent ballpark figures.

    For overclocking near the limit, a steady voltage input to components is required. A PSU close to it's rated maximum load might suffer from drooping voltage and increased voltage ripple, which both effect overclocking stability. So it's not totally unreasonable to aim for matching your average max power draw to approximately 66% of the PSUs rating. You also get good efficiency figures in that area.

    I don't think there should be too many PC's using more than a 600 watt PSU. I used to run GTX260's SLI on my 700 watt PSU. When I replace it, I'll buy smaller.
     
  3. Zap

    Zap Elite Member

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    [​IMG]

    My LAN box is running a 2500K (stock speeds) and Radeon 6670 with four drives (3xSSD, ODD) on a 150W PSU. Not a typo. One hundred and fifty watts. I just got in a Radeon 7750-800 that I'm going to pop in there today.

    My new main rig (finished, but need to install my software and copy data over) has a 450W PSU running a GTX 670 and a 3570K at 4.5GHz with 3xSSD, ODD, 1xHDD.

    Wife's new rig is similar, with 3570K at 4.2GHz and GTX 660 Ti on a 450W PSU.

    In the past I've temporarily run a Core 2 Duo @4GHz and a GTX 260 on a 350W PSU.

    Long time ago I recall minds being blown when people were running their computers with 8800 GTX on the first Earthwatts EA380.

    The "need MOAR powah" myth comes from a few things.
    1) There exists PSUs which do not actually put out the power they claim on their labels, thus some are accustomed to always having to purchase higher wattage.
    2) Many people buy much more power than they need "in case of SLI/Crossfire" which of course most end up not doing.
    3) There is a quantity versus unit price discount mindset. For instance, when offered 100W for a mere $10 more, many will take the higher wattage because it represents a better value for the money.
     
  4. BFG10K

    BFG10K Lifer

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    The high PSU ratings often come from manufacturers to cover themselves in case customers use crap PSUs that can’t deliver their rated loads. This gives a reserve so that a crap 750W unit could hopefully do 500W, so the manufacturer specs for 750W even if they only need 500W (for example).

    The good PSUs (e.g. Seasonic, Super Flower) can do their full rated load at 50C and still have reserve, so you can get away with lower rated units. I know of people running a GTX480 on a fanless X-460, for example.

    My Seasonic 560W often doesn’t even turn its fan when gaming for hours. It has two 8-pin connectors, and I’d have absolutely no hesitation in using such a video card with it if I was so inclined.

    With that said, there are legitimate instances (e.g. tri/quad multi-GPU) where high wattage PSUs are a must.
     
  5. Blain

    Blain Lifer

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    From whom were you hearing the need for PS rated at high wattages?
    Another thing when considering a PS is component degradation over time. A power buffer to accommodate that degradation can also be factored in, but isn't needed for running benchmarks on brand new units.
     
  6. pandemonium

    pandemonium Golden Member

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    As with mentioned above, it's also generalized from an engineering stand-point: always, always overstate requirements.

    Another reason why things are overstated is the fact that most power supplies are most efficient at 50% load.

    Slightly off-topic, but a while back I broke down power supply value per rating between 650-750W and between Bronze and up to Gold (bottom of original post). At the time there weren't many Gold+ rated PSUs below 650W, so I didn't bother comparing them. Perhaps I should update that since I see a lot more available on Newegg now.
     
  7. Meghan54

    Meghan54 Diamond Member

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    Yeah? FYI....they all are. And this has no bearing upon why gpu manufacturers overestimate "recommended minimum" wattages from power supplies. Rather, as was stated previously, it's much more about cheap junk in people's computers----like Deer, Allied, Diablotek---that pass themselves off as being to output XXX watts from the unit while in reality can only deliver half rated output on the +12V rail.
     
  8. Smoblikat

    Smoblikat Diamond Member

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    Ive done a pair of HEAVILY overclocked GTX 275's, 2v DDR3 and a 4ghz Ph2 X4 @ 1.55v plus lights, fans, HDD's all on a 650w with no signs of stress.
     
  9. wirednuts

    wirednuts Diamond Member

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    i have also found that people very much enjoy gaming in over heated rooms and paying a lot of money on their power bills, just as long as they can say "hell yeah, i have a 1000w power supply in my computer!"
     
  10. magomago

    magomago Lifer

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    Actually I disagree that you generalizing things from an engineering standpoint; I could imagine you designing a product that would be running DV failures left and right even if the system was actually fine, because what was REQUIRED to be met simply isn't paired appropriately with the intended use of the system.

    I would say that your requirement should be the minimum of what you need - i.e. a REQUIREMENT that is going to act as a constrain on the design.

    The actual specification/implementation that is selected can be overkill relative to the requirement (considering factors like time to implement, cost, complexity, etc etc)

    That way you can pass your requirement, which is based on the reality of what is needed, and your actual design exceeds that requirement by quite a bit.

    Videocard manufacturers pushing ridiculous 'Requirements' (ie: these are not engineering requirements in the same fashion) are responding to factors outside their control: i.e. the power supply. And this response, while being engineering in nature, is being driven much more from the marketing/legal position.
     
  11. blastingcap

    blastingcap Diamond Member

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    I got crucified for saying this a while back, but as electronics miniaturize, power draw drops, and most hardware makers are paying a lot more attention to efficiency and perf/watt.

    Combine this with our much better info on who makes good (and bad) PSUs and you should be able to right-size your PSU rather than buy a ton of overcapacity and suffer efficiency penalties for it, not to mention potentially suffer higher prices. And some of the dubious PSUs can't hit their rated wattage continuously anyway.

    Also, 12v rail is all-important. I've seen units with mediocre 12v rail ratings but high wattage... that is of limited use.

    For instance, if you know you won't be overvolting much and will be using modern CPU and GPU (and not dual GPU), you could probably get away with a high-quality 80+ Gold/Platinum PSU at 450W with 444W on the 12v rail (Capstone Gold). That is plenty of punch for a modern CPU + GPU, mobo, fans, drives, etc. Hell, I was even running a 1055T (stock) with a heavily oc'd 7970 on it perfectly. As node sizes keep falling and drag down TDPs with them, you will have plenty of reserve 12v rail wattage, too.
     
  12. Zap

    Zap Elite Member

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    Not necessarily marketing/legal, but more customer service. When someone buys a new graphics card and start having problems, first thing they'll "blame" is the new card.
     
  13. wirednuts

    wirednuts Diamond Member

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    reminds me of the other day when i was trying to decide what old junky psu i could tear apart for parts. once i found the 350w cogden i had, i noticed it said "5vusb=500ma" i knew i had the one i wouldnt be using in a computer build :D
     
  14. magomago

    magomago Lifer

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    Thank you, I was trying to think what the proper word to say that...clearly my english sucks :thumbsup: :D
     
  15. Red Squirrel

    Red Squirrel Lifer

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    Video cards are bad for having crazy requirements and they don't even use half of what they require. When I recently built a new PC I went with two video cards and they were rated at 400w, so naturally, I got a 1000w psu. I can get my PC to use 300w or so at very most when I'm doing a benchmark to push the video cards and cpu to it's max. Well I don't have a proper watt meter so I measured amperage and times by voltage, so if my power factor is off maybe it was not the most accurate way of going.
     
  16. TemjinGold

    TemjinGold Platinum Member

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    Err that's because the "400w" is for the whole system, not the card.
     
  17. boxleitnerb

    boxleitnerb Platinum Member

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    You have to have a certain reserve. I was running a 2600K@4 GHz and 580 SLI@stock on a 850W PSU. Usually in games the load was 400-650W at the wall depending on the situation. Enter GTA 4 with ENB mod: 750W. If you test a game where your system only draws 500W but another game demands 750W, you're screwed if you dimension your PSU after that first game.
     
  18. philipma1957

    philipma1957 Golden Member

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    I am running a bitcoin farm.

    3x 7970's can work on a seasonic x660 if underclocked.

    4x 7970's can run on a seasonic platinum 850 if underclocked.

    for 24/7 weeks on end.

    but 2x 7970 for a seasonic x660 and 3x 7970 for a seasonic platinum 850

    underclocked run cooler with less power use.

    I run the 7970's at .95 volts the 2x system pulls 365 watts

    the 3x 7970 pulls 525 watts


    I run 8 gpus in 3 systems pulling about 1400 watts my 3 psu's are rated at 2360 watts.

    all is on a 20 amp circuit breaker and the interior wire is 10 ga not 12 gauge.

    when I pushed the gpus they ran hotter and power was wasted.

    also underclocking can stop for a lot of stupid reasons. and using 3x 7970 on a 660 underclock works but using 3x 7970 with normal power on a 660 does not work.
     
  19. Zap

    Zap Elite Member

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    Your English is fine. If you want to magically sound very intelligent, start posting in Off Topic. :cool:

    Yup. I guess many don't realize that.
     
  20. MrK6

    MrK6 Diamond Member

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    I think many times people do "overbuy" wattage. Beyond spending extra money and possibly losing some efficiency, there really isn't anything terrible about it. There's a lot of great points posted here about the details of purchasing a PSU, and I think that's the bottomline problem - new or uninformed buyers look for a black and white rule for purchasing a PSU, which hardware suppliers cater too, when really it's a tad my involved. I typically buy my PSU's conservatively in that I buy a PSU that will run at ~50% to power my planned system's typical load. I have a 650W Seasonic X650 currently which pulls ~300W from the wall to power my system with the 7970 at a light overclock of 1.125GHz (stock volts). Assuming the 80 plus Gold rating is accurate for my unit, that's 270W output, or 41% load. However, some games I really crank the clocks to 1.35GHz and then the system pulls 450W from the wall, or 400W output. That's still only 61% load, but I don't like exceeding more than 70% load on my units consistently. For example, I certainly wouldn't run 7970 CF overclocked like that on this PSU, although I certainly could.

    In the end I think it pays off because it keeps the PSU healthy. I just sold my Corsair HX620 that I probably had for five years. Doing the back calculations on the wattage differences at the same loads showed that the PSU was still ~80-82% efficient, exactly what it was when I bought it. Overall I think PSU quality is becoming better overall, certainly not like it was a decade ago when I started building PC's and you really had to iron out rail setups, wattage specifications and delegations, etc. However, it's worth knowing this on any PSU you buy and the physics behind PSU's for general knowledge. :)
     
  21. Red Squirrel

    Red Squirrel Lifer

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    And that's part of the issue. How do they know what I have in the rest of the system or if I already compensated for it? The numbers are greatly exaggerated especially when you have multiple cards. I did not know this when I bought my video cards and I was almost wondering if even 1000w would be enough but it turned out to be more than enough.

    You don't see a 100w light bulb say it requires 400w because it assumes the fixture has 3 more sockets.
     
  22. Avalon

    Avalon Diamond Member

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    Yep, most people buy more than they need. However, I came across the situation once where I had less than I needed and was actually surprised by it.

    Had a good 520W Enhance w/80+ bronze, originally running an OC'd Core2 E8400 and OC'd Radeon 4850, no problem. Replaced the CPU and GPU with an i5 3570K and MSI GTX 460 Hawx, and while I was fine at stock, when both were OC'd, my system would shut off during intense gaming sessions.

    Picked up a nice Seasonic X650 Gold, and all good now :)
     
  23. IGemini

    IGemini Platinum Member

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    The most I've seen my rig pull from the wall is around 350W. My current PSU is right where it needs to be for that 50% load optimum.

    My next build will be an i5/i7 Haswell paired with no less than a Radeon 8850. Should handle nicely with a gold 400-450W PSU.
     
  24. OVerLoRDI

    OVerLoRDI Diamond Member

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    90% of the time you are right. Bitcoining has shown me how much power a GPU can really draw (that and Furmark, but that is pointless)

    If I overclock my two 7970s to 1.2ghz+ and have them mine coins I can pull around 800 watts of power. Furmark will jump up to 1100 watts and shutdown my computer. I'm using a Seasonic X-1050
     
  25. wirednuts

    wirednuts Diamond Member

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    i wouldnt want to see my power bill after running a bitcoin machine 24/7 thats drawing 1100w!