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Calculating required PSU wattage.

Discussion in 'Power Supplies' started by lttlejoe, Jul 25, 2018.

  1. lttlejoe


    Joined: Jan 14, 2011

    Posts: 841

    Location: East Yorkshire

    I have a 530w Be Quiet L7 PSU which has provided the power to run my current computer and CPU ( Phenom 11 x4 955 BE @125W) flawlessly.
    I intend to add temporarily a GTX 1060 3Gb GPU (@120w) and would assume that the PSU will be able to cope without it being overloaded. I say temporarily as I intend to upgrade to a Ryzen based system in the coming weeks and will be replacing the PSU with a new good quality one and fitting the old PSU together with this mobo/CPU into a backup machine.
    I am of the opinion that the PSU is one of the most important parts in a computer and a cheapo PSU is false economy as it could cause serious damage if it fails.

    However it got me wondering ...is there an actual standard calculation for determining the minimum/ideal PSU wattage requirements needed to run both the CPU and GPU safely without overloading the PSU?
  2. Rroff

    Man of Honour

    Joined: Oct 13, 2006

    Posts: 59,019

    There isn't really a standard as such - ideally you always want some overhead to take into account PSU's performance decreases as they age and transients peaks in current draw, etc. one of the often overlooked aspects as well is how much a PSU can actually provide on the rails (and layout of the rails i.e. single or split 12V and how best to connect to that) especially the 12V rail.

    Then there is the consideration of decent overhead and the range the PSU works most efficiently in (which doesn't necessarily come to the same conclusion).

    Personally I've tended to over-spec on the PSU quite significantly as usually it gives far more buffer against ageing, better quality power delivery in terms of voltage ripple, etc. which tends to help prolong the life of components and usually less noise and potentially less heat to deal with.
  3. lttlejoe


    Joined: Jan 14, 2011

    Posts: 841

    Location: East Yorkshire

    I'm with you on over-spec, in fact I'm in agreement with everything in your post. When I built this computer 7 years ago, I could have got away with a much a lower wattage output PSU for what I needed as I only used the onboard graphics but having owned pre-built computers up until then, the only parts ever to fail except for HDDs were the PSUs so I made sure I put in a decent one and it's paid off though I can't expect it to go on forever but if the build quality is good initially, it should give good service.
    Fitting a cheapo PSU to me is a bit like buying a fast sporty car and then putting the cheapest economy tyres available on it but expecting them to perform like expensive tyres when it's driven fast.

    My next build won't be terribly demanding but I'd still be looking at a 650-700 watt minimum for reassurance.
  4. pastymuncher

    Man of Honour

    Joined: Jul 12, 2005

    Posts: 17,023

    Location: Aberlour, NE Scotland

    It is good to see somone in the right frame of mind when it comes to the psu. As you rightly say, it is one of the most important things in a pc and not the place to save money. Thumbs up to you for that. I can't beleive someone else has said that on here. Usually I feel like I am banging my head against the wall getting nowhere trying to get that point across.

    One thing to take into account though is ignore the headline wattage. Many psu's and your Bequiet L7 530w is a prime example, cannot deliver all it's power on the 12v rails where it's needed in a modern pc. Your 530w psu can only deliver 420w across a pair of 12v rails. The rest is on the minor rails. When looking at psu's to buy do some research and see what the psu is actually able to deliver. Any quality modern psu should be able to deliver all or near enough all of it's power on the 12v rail(s). I have the latest version of the Bequiet Straightpower 550w, the straightpower 11 550w and it can deliver 549.6w across it's quad 12v rails and is a very good psu. I only have it because it was a freebie in exchange for a review though. I would never buy one as it is very overpriced and has a short warranty compared to the competition.

    A 550w psu would be more than enough for you with a GTX1060. The pc in my siggy along with 12x 120mm fans, 4x 200mm fans, 2x fan controllers, 2x Temp monitors and a couple of leds for the reservoir only pulls 128-275w at the wall while gaming depending on the game and the very max I have managed to make it pull was 367w at the wall while using OCCT's psu torture test. Idling/ internet browsing is 72w at the wall. I have live power draw displayed in one of my fan controllers which is how I know what is being drawn all of the time.

    With that in mind I would be looking at the Seasonic Focus Plus series or Antec High Current Gamer series (essentially the same psu in a different case) both of which are fully modular, gold rated and have 10 year warranties. If you don't mind fixed or semi modular cables the Bitfenix Formula series (5 year warranty) and Antec Earthwatts series (7 year warranty) are very good, both gold rated and highly worthy of consideration. I see little point in paying any more as theses are all high quality psu's and spending more get's you virtually nothing extra for your money.
  5. lttlejoe


    Joined: Jan 14, 2011

    Posts: 841

    Location: East Yorkshire

    Glad you approve of my view...some would say I'm somewhat melodramatic! :D
    I realise my Be quiet 530w PSU is unable to deliver full output and the actual output I suppose equates roughly to the 80% efficiency rating of ( 424w) which hopefully should still handle the 1060 3Gb (120w TDP) at least until I get the new parts put together for the upgrade.
    I'm aiming at something like a Ryzen 5 2600 for the new system build, which should cope with anything I'd throw at it as it's to be another universal/general purpose computer and I only want to engage entry level casual gaming and the TDP of the Ryzen is only half of what my current CPU is so I'll definitely look at your suggestions about which PSU to choose for the new build when I make my choice.
    The same goes for my GPU choice. While the 1060 6Gb is obviously the best choice, the 3Gb version is only about £20 more in some outlets than a 1050 Ti and the performance from the 1060 3Gb outstrips the 1050 Ti by some margin and will do all I want for the moment and I'd rather spend any savings on a newer and better PSU.
    I've substantially upgraded the cooling on my old gaming case so with a new PSU, two new SSDs and HDDs all will be good to go when I've got all the other parts together.;)
  6. billysielu


    Joined: Aug 9, 2009

    Posts: 10,206

    Location: Oxfordshire

    PSUs do degrade over time, so buying "barely enough" isn't a good idea.
    If you can have a PSU operate at a lower percentage of its capability it'll run quieter and last longer.
    Hardware changes over time, it's pretty common for people to upgrade GPU and then find they need to upgrade PSU too.
    You get what you pay for in terms of quality, cheap PSUs are worse quality.
    When your PSU goes it can take the rest of the system with it.

    Generally there are only three types of PC anyway, so this is how I'd pick a wattage.
    - Non-gaming PC. 450W
    - Gaming PC on a budget. 650W
    - High-end Gaming PC. 750W.

    That works out somewhere around 10% of the total budget.

    It's also worth remembering that home energy prices are rising really quickly.
    You can choose a more efficient PSU. https://en.wikipedia.org/wiki/80_Plus
    You can choose energy efficient components.
    Last edited: Jul 25, 2018


    Joined: Oct 19, 2002

    Posts: 5,711

    Location: Woolyback Country