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How much power is really needed from a PSU?

Discussion in 'General Hardware' started by doopydug, 14 Jul 2020.

  1. doopydug

    Mobster

    Joined: 18 Oct 2002

    Posts: 2,596

    Location: Fife

    I bought one of those power meters that plugs in between the wall socket and the computer to measure the current draw etc.

    I tested it on an I5 4670K system with a GTX970 gfx card and 16gb RAM with a 1TB Seagate HDD

    At idle , it pulls only about 50W and when used during benchmarking, it rises to about 150W - I remember a 500W PSU being regarded as the minimum for this combination - can that be right or is my meter not working correctly?
     
  2. jsmoke

    Sgarrista

    Joined: 17 Jun 2012

    Posts: 9,709

    Could be another conspiracy to keep the market ticking over, if people new they only need 200watts or so the market would collapse.
     
  3. Admiral Huddy

    Caporegime

    Joined: 17 Feb 2003

    Posts: 29,509

    Location: Chelmsford & Broadgate

    They quote a maximum draw for some systems but tech is drawing less power nowadays. However, the higher the PSU then the more efficient it becomes but I would say most of us have PSUs that are an overkill for sure.
     
  4. SonicSW20

    Wise Guy

    Joined: 1 Apr 2019

    Posts: 1,058

    What was your benchmarking process? A GTX970 will draw ~150W at max load, ~100W or so for the CPU assuming you've not overclocked it, and a bit on top of that for your board / storage drives etc, so your 150W figure does not add up.
     
  5. Tetras

    Mobster

    Joined: 22 Jun 2006

    Posts: 3,247

    The recommendations are taking into account that the average PSU doesn't deliver anywhere near the rated wattage to the +12v rails, so for the average 500 Watt PSU 150-200 watts is actually quite a lot. It's also not wise to run a PSU near the rated capacity, around 50% (down to about 20%) is a decent balance for efficiency, temperatures and noise. If you're talking about the kind of PSUs that enthusiasts buy, then a 350-400 watt model can power most modern systems no problem.

    With recent 8+ core systems their boosts can lead to pretty high power draw, so the requirements are higher than in the Intel quad core stagnation-era.
     
  6. Admiral Huddy

    Caporegime

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    Location: Chelmsford & Broadgate

    Agreed, run prime and some mixed stress tests, then see.
     
  7. EsaT

    Sgarrista

    Joined: 6 Jun 2008

    Posts: 8,865

    Location: Finland

    GTX 970 draws up to 180-190w.
    https://www.techpowerup.com/review/asus-gtx-970-strix-oc/23.html
    https://www.techpowerup.com/review/evga-gtx-970-sc-acx-cooler/23.html
    https://www.techpowerup.com/review/palit-geforce-gtx-970-jetstream/23.html


    7nm Ryzens aren't any more hungrier than those Intels 5+ years ago.
    It's current Intels whose true 100% load draw is like double the TDP.
     
  8. SonicSW20

    Wise Guy

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  9. doopydug

    Mobster

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    Location: Fife

    I will do a proper stress test tomorrow - it was just a userbench run so rather quick and easy
     
  10. Rroff

    Man of Honour

    Joined: 13 Oct 2006

    Posts: 71,509

    You should be seeing quite a bit more than 150 watt in something like Battlefield series games, etc. also it is worth having some overhead to deal with things like transient current spikes, etc. as well as a buffer against the PSU ageing where its output capabilities will drop.

    Additionally if you are running newer versions of Windows and/or newer nVidia drivers, etc. they have improved power management features these days which will reduce power draw quite a bit depending on settings and things like multi-monitor configurations for instance the GPU will potentially drop down a little power state wise when a game isn't so GPU heavy but it hitting the CPU instead of staying spun up 100% like it used to and so on.
     
  11. Unseul

    Wise Guy

    Joined: 18 Jun 2018

    Posts: 1,485

    Tech yes city on youtube actually did a bit of a test on this:

    https://www.youtube.com/watch?v=wg6pz7YTxyA

    Ryzen 3950x and a 2080ti, on a 450watt PSU.

    He's not suggesting you should do it, but shows that it can do it (he may have got lucky with the PSU). If you get a decent PSU, then you probably don't need to go for overkill. At the same time, if you're overclocking, that can eat up the power.
     
  12. pastymuncher

    Man of Honour

    Joined: 12 Jul 2005

    Posts: 18,711

    Location: Aberlour, NE Scotland

    Graphics card PSU recommendations are high to take into account the idiots that buy these so called 500/600/700/800/900/1000w £25 PSU's that are sold on Ebay and OCUK competitors. People see a big capacity PSU for little money and get taken in completely with all the marketing BS in the descriptions and see a way to save money for spending on other components. These PSU's are garbage and will typically have less than half of that on the all important 12v rails.

    As the others have said there is something wrong with your 150w. When I had a 4970k clocked to 4.6Ghz, 16Gb Samsung Green DDR3 running at 2133mhz and the GTX1070 I still have I could easily hit 400w at the wall when stressing both the CPU and GPU at the same time. Even some games made the system pull 322w at the wall. With the PC in my siggy I can still easily hit 360w when stress testing and 300w when gaming although most games are around the 250w mark. Try downloading OCCT and run the PSU stress test, that will well and truly load everything up.
     
  13. doopydug

    Mobster

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    Location: Fife

    Getting almost 300W usage on OCCT - thanks for the recommendation guys - at least i know my meter is working ok
     
  14. SonicSW20

    Wise Guy

    Joined: 1 Apr 2019

    Posts: 1,058

    ~300W sounds about right if you're running that processor stock.
     
  15. doopydug

    Mobster

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    Co-incidentally, just tried it on another system - Ryzen 3900, 16GB RAM, RTX 2060, X470 Mobo - 288W
     
  16. Sayso

    Mobster

    Joined: 30 Sep 2008

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    Location: Chelmsford

    I always aim for a 650W or higher PSU when building a system running at about 50% is the sweetspot. The 850W and higher are only needed for the highly overclocked dual GPU systems.
     
  17. Zefan

    Don

    Joined: 15 Jan 2006

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    Location: Tosche Station

    Is it though? I remember seeing this PSU efficiency myth busted ages ago, with the range actually being more like 50-80% and even then when on higher load it really is only a tiny difference of something like 3%, which - even if you were running 8hrs a day at full load - equates to around 70p per month!
     
  18. Tetras

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  19. EsaT

    Sgarrista

    Joined: 6 Jun 2008

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    Location: Finland

    That's the recipe for having PSU running at couple steps lower than its advertised efficiency rating most of the time typical PC is powered.
    PC running at max 50% PSU output under full load basically runs at 10% of PSU output when at desktop/websurfing etc.
    Only 80+ Titaniums can do something around advertised efficiency there.

    With 80+ Golds high efficiency can start from around 15% load with best area around 25 to 60% load.
    But decrease at higher loads is minor and below that 15% load it's all MCAS Boeing and efficiency at 100% load is better than at 10% load.

    This is what 80+ Gold's efficiency curve looks like:
    https://www.techpowerup.com/review/super-flower-leadex-iii-argb-gold-750-w-review/5.html



    That PSU was outdated low end already decade ago!
     
  20. Tetras

    Mobster

    Joined: 22 Jun 2006

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    A'ight, click the next page button on the review you linked :p