Become a fan of Slashdot on Facebook

 



Forgot your password?
typodupeerror
Power Hardware

Is It Worth Investing In a High-Efficiency Power Supply? 328

Posted by samzenpus
from the getting-your-money's-worth dept.
MrSeb writes "If you've gone shopping for a power supply any time over the last few years, you've probably noticed the explosive proliferation of various 80 Plus ratings. As initially conceived, an 80 Plus certification was a way for PSU manufacturers to validate that their power supply units were at least 80% efficient at 25%, 50%, 75%, and 100% of full load. In the pre-80 Plus days, PSU prices normally clustered around a given wattage output. The advent of the various 80 Plus levels has created a second variable that can have a significant impact on unit price. This leads us to three important questions: How much power can you save by moving to a higher-efficiency supply, what's the premium of doing so, and how long does it take to make back your initial investment?"
This discussion has been archived. No new comments can be posted.

Is It Worth Investing In a High-Efficiency Power Supply?

Comments Filter:
  • The Maths (Score:5, Informative)

    by Press2ToContinue (2424598) * on Thursday December 13, 2012 @07:00PM (#42282227)

    new efficiency @ load % - old efficiency @ load % = delta%
    integrate over time (delta%*cost kw/hr) until result = new unit cost (solve for t)

    • Or don't: it comes out at several tens of years in any realistic scenario.
      • Re:The Maths (Score:5, Informative)

        by Carnildo (712617) on Thursday December 13, 2012 @07:21PM (#42282461) Homepage Journal

        Or don't: it comes out at several tens of years in any realistic scenario.

        Scenario 1: an always-on computer running near-idle for four years.

        Idle power draw, 85% efficient PSU: 66 watts
        Idle power draw, 80% efficient PSU: 70 watts
        Delta: 4 watts
        Total power difference over the four-year life of the computer: 140 kilowatt-hours.
        At 5.5 cents per kilowatt-hour (cheapest power in the US), building with a more-efficient power supply makes sense if it costs no more than $7.70 beyond what the less-efficient power supply does.

        Scenario 2: an always-on computer running Folding@Home for four years using both CPU and GPU.

        Power draw, 90% efficient PSU: 215 watts
        Power draw, 80% efficient PSU: 245 watts
        Delta: 30 watts
        Total power difference over the four-year life of the computer: 1.05 megawatt-hours.
        At 36 cents per kilowatt-hour (most expensive power in the US), building with a more-efficient power supply makes sense if it costs no more than $378 beyond what a less-efficient power supply does.

        The second scenario represents someone running F@H on a modern high-end computer in Hawaii -- not exactly "unrealistic".

        • Re: (Score:2, Troll)

          by Platinumrat (1166135)

          I'd like to add to the above. It truly depends on circumstances.

          If you're trying to be energy neutral or positive in your living (e.g you want to be off the grid with a wind/solar setup) then every efficiency gain will more than offset the cost of producing / storing the power required).

          If you're just wanting to view movies / ebay / email an live in a McMansion, with the full home theater setup, then there's no point because the rest of your lifestyle says "Fuck the planet, I'm all right"

        • by ultranova (717540)

          Scenario 1: an always-on computer running near-idle for four years.

          Given that a more efficient power supply generates less heat, does it last longer? And does it generate less noise, since it doesn't need as fast a fan? Which gets kinda importat at the wee hours of the morning.

      • by Hadlock (143607)

        The big factor for me is: how much heat does it put out? Texas in the summer can be brutal, and anything to keep my office half a degree cooler helps tremendously, especially in the era of multiple monitors. Higher efficiency = less waste heat.

    • I did things slightly different. Btw you didn't think this was a bitcoin story....BUT IT IS! lol. My bitcoin rig ran at 550W and I had these calculations down plus an actual meter and they were all spot on. But let's say it's my gaming computer instead. That's around 240W peak of actual device pull. Let's say it's used for 6 hours a day at max load. Let's say I was going to get a piece of crap 76% efficient one but I went with an 80+ bronze which happens to be 83%. That's 40.8 watts added in waste he
    • Re: (Score:2, Informative)

      by jamesh (87723)

      new efficiency @ load % - old efficiency @ load % = delta%
      integrate over time (delta%*cost kw/hr) until result = new unit cost (solve for t)

      You're missing the savings on removing that excess heat from your house too (in climates where that is relevant).

      In a cold climate where you are heating your house, unless you can get better $/unit heating out of something else, the "waste" energy is heating the house anyway so it doesn't matter much.

      In a hot climate where you are cooling your house, every unit of heat that you put into the house has to be removed. Firstly from the computer by making the fans work harder, then from the house itself by makin

      • by Kaenneth (82978)

        I'm not an electrical engineer, but I don't believe all waste energy is heat, some of it is probably RF energy that's not absorbed before it leaves your building.

        However, in my case, switching to higher efficiency power supplies meant I no longer had to run my air conditioner even while there was snow outside. That's a pretty big power savings.

        If it's worth squeezing the last 1-2% is a different question.

  • I'll bet... (Score:5, Funny)

    by msauve (701917) on Thursday December 13, 2012 @07:01PM (#42282231)
    we could probably use a computer to figure out the answers to those questions!
  • An investment is expected to bring a net positive return over time, not bring the expected loss closer to zero.
    • by AK Marc (707885)
      That may be for the subset of "financial investment" but more generically:

      an investment is something that returns more value than it costs.

      By my definition, a car that depreciates is an "investment" because with it you were able to get a job and make more than the car cost, even if the car itself was a loss. The power supply is the same. If you count the added cost of an 80% efficient supply, you may never make back the difference, unless you count the air conditioning savings, and put a price on the
      • by Darinbob (1142669) on Thursday December 13, 2012 @07:54PM (#42282783)

        If you're only factoring just the electricity bill as a factor. But there are also environmental reasons maybe and it's harder to put an unemotional price on that. This is sort of like the people who claim hybrid electric cars are a waste of money since they're only looking at the wallet and not the bigger picture. It's more than just saving a little electricity as well, there is also the slight increase in customer demand, which slightly increases the market forces towards creating more efficient products in general.

  • Bought one Antec Earthwatts long time ago. The PSU was not much more expensive than the others (good brands) so the savings are obvious. Still, the PSU is very quiet which is the main reason why I bought it.

    • by nabsltd (1313397)

      Bought one Antec Earthwatts long time ago. The PSU was not much more expensive than the others (good brands) so the savings are obvious.

      Another thing TFA doesn't take into account is that the 80-Plus certified supplies tend to have better components overall than non-certified supplies.

      Read some of the reviews at Hardware Secrets [hardwaresecrets.com] and you'll see that it's not uncommon for a well-built "350W" power supply to be able to output 450W, while a crappy 350W supply can't even handle 300W.

  • Cooler (Score:2, Informative)

    by Anonymous Coward

    One advantage of a more efficient PSU is that it runs cooler. This is nice at least if you are going for a silent system, as less fans are then required.

  • If you reduce the brightness of an LCD screen backlight it will also lower power consumption. Mine uses 40 watts full brightness and 20 watts dark. So if you shave off 10 watts it may nearly equal the savings of a good psu but for no outlay.
  • Have you looked at the price difference between different efficiencies for the same wattage? They're usually minimal. So might as well vote with your wallet and go for the highest-efficiency one. There's no telling how electricity prices will evolve over time...
  • To make the maths easier, lets assume you can improve your efficiency by 25% (that's huge) and assume you're loading it to 400 watts, (also huge) and assume you run it 8 hours a day, 5 days a week with 2 weeks off a year (running at full capacity).

    That's 100 watts of savings, 2000 hours a year... 0.1kw X 2000 = 200kWh per year.

    I pay about $0.10/kWh

    You could save up to $20/year.

    Reality? You'd probably see a lot less savings then that.

    • by blueg3 (192743)

      Okay, "up to" only applies if you are computing using reasonable maximums, which you aren't. $20/year is a reasonable estimate, but not "up to".

      25% efficiency improvement is pretty big. 400 W is a large load for some machines, but isn't that huge a load. $0.10/kWh is actually substantially below the US average of $0.12/kWh.

      The biggest variable factor here, though, is computer uptime. Hugely variable. My home PC probably sees 500-800 hr/yr use. My work PC probably sees your estimate of 2000 hr/yr. My HTPC is

  • Quieter and cooler (Score:4, Interesting)

    by Manfre (631065) on Thursday December 13, 2012 @07:13PM (#42282377) Homepage Journal

    Higher efficiency means less waste heat coming from the power supply, so its fan can run quieter.

  • by SplatMan_DK (1035528) on Thursday December 13, 2012 @07:16PM (#42282417) Homepage Journal
    Since the waste energy is converted to heat (which may increase the noise or temperature of the machine) it may well be worth the extra cash anyway.

    Saving a few bucks on electricity is hardly the only reason to buy a more efficient power supply.

    - Jesper
  • don't choose a cheap piece of shit just because it claims a higher '80 plus' certification level than a quality, name brand unit from a reputable company that might cost twice as much.


    • don't choose a cheap piece of shit just because it claims a higher '80 plus' certification level than a quality, name brand unit from a reputable company that might cost twice as much.

      yeah, this hits home. I just replaced my second failed Rosewill 80+ today (5-star reviews...). Visible build quality on the first two were great, but obviously the guts aren't so good. I'm gonna open it and look for mushroomed caps.

      The third one, my only spare-on-hand is of such poor build quality that the metal conductors

      • by Mashiki (184564)

        Yeah Antec is good generally, most of their stuff is made by seasonic. So is OCZ(generally), mushkin, and a few others. I'd recommend looking through here. [hardwaresecrets.com] And see who is making what it can change sometimes between revisions. And generally the reviews are quite good. And each PSU has a teardown, including what's being jammed inside the guts. So you have a fairly good idea of what components are being used.

  • These days, 80plus PSUs are very cheap. The only things cheaper are unreliable JUNK PSUs which won't last a year. Also, because of the legal terms of using the 80plus trademark, manufacturers seem to not inflate the wattage ratings on 80plus PSUs, while you can easily find $15 "2000watt" junk PSUs.

    And besides all that, I'd pay the 80plus premium just for the heat/noise reduction. Combine with a WD "Green" hard drive (or SSD), low-power CPU, and a couple low-noise fans, and you've got a very low heat and

  • by anyaristow (1448609) on Thursday December 13, 2012 @07:30PM (#42282545)

    A PSU has a power efficiency curve that looks like this [anandtech.com]. That article also explains what I'm about to summarize:

    Pick a PSU that is no more powerful than you need, to keep your system in the middle of that curve, for maximum efficiency. 100% margin is more than plenty, so if your components will use 250W max, you don't need a 900W PSU. Look for something in the 500 range, or even less if you pick a good-quality PSU.

    You probably won't be able to make a cost argument for maximizing efficiency, but you can build a quieter system focusing on efficiency, and it's quite satisfying obsessing over something different.

  • A while ago I purchased an EZ-Watt meter so see how Much power that my system was consuming. I found that my system at max CPU and GPU load consumes about 350 W of power. So my question is why would I buy a green 800 Watt power supply when my system only needs 300 W? It seems that it would be best to match the power supply to the system in order to maximize savings since the efficiency of the power supply is calculated at its maximum rating. How much power doesn't 800 Watt power supply consume when the syst
    • by tragedy (27079)

      It depends a lot on whether "about 350 W" is a maximum or an average and even more on what you've been doing with your computer while you measure. Measuring draw like that is a good idea, but it doesn't tell you everything. There very well may be usage patterns for components in your system that some software may cause that are higher than your normal usage. If you start using your computer a different way (say by running a demanding game which uses your CPU, hard drives, optical drives and gpu hard all at

    • So my question is why would I buy a green 800 Watt power supply when my system only needs 300 W?

      Components degrade with time. Specifically with regards to electrolytic capacitors. As the PSU ages, the ability for them to run a peak ratings diminish. At best, you get excessive DC ripple that puts a strain on your motherboard components. *Always* purchase a PSU that at least rated for 30% more power than what you need!

      How much power doesn't 800 Watt power supply consume when the system is using only hundred t

    • by MtHuurne (602934) on Thursday December 13, 2012 @08:43PM (#42283177) Homepage

      If you look at efficiency graphs, you'll see that power supplies are typically the most efficient under moderate load: at low and high load the efficiency drops. A typical desktop or home server is idle most of the time, so idle efficiency will have a big impact on the total efficiency. If you over-dimension your power supply, your idle load might be 10% or less of the max rating, which is far from the optimum of the efficiency curve.

      I'd recommend getting a power supply that can deliver a bit more than what you need, for example 450 W if you think you need 350 W max. A bit of margin is useful since you might not have found the actual worst case or you might want to add components later. Also it avoids poor efficiency at the high side of the curve when the system is under load.

  • Betteridge strikes again.
  • by AdamHaun (43173) on Thursday December 13, 2012 @07:36PM (#42282643) Journal

    Noise is also a factor. High-efficiency supplies have fans that run more slowly under load, or not at all. If you're building a quiet system, this is a big deal.

    Note that the peak efficiency is usually at ~50% load, so be sure to size your power supply appropriately for best results. Newegg has a calculator [newegg.com] to help with this.

    • by sdguero (1112795) on Thursday December 13, 2012 @09:28PM (#42283453)
      Disagree about peak efficiency. In my experience testing PSUs, it is normally found around 90% load. Newer PSUs have gotten a lot better and enhancing efficiency at lower load levels, but PSUs still work most efficiently when running near the load they are designed for.

      Newegg's calculator is a joke. It drastically overestimates requirements so they can pimp massive PSUs with higher profit margins. I suggest adding up the various component manufacturer specifications (i.e. max power draw of the MB, GPU(s), HDD(s), DIMM(s), and CPU(s)) and throw in 10-15 W for overhead, then buy a decent PSU with a load rated as close to that number as you can get. Even with a dual GPU setup, you are VERY unlikely to exceed 400W of DC power draw. My current mid-range single GPU system draws around 200W under load (gaming).
      • by AdamHaun (43173)

        Disagree about peak efficiency. In my experience testing PSUs, it is normally found around 90% load. Newer PSUs have gotten a lot better and enhancing efficiency at lower load levels, but PSUs still work most efficiently when running near the load they are designed for.

        Thank you for the correction. I was talking based on the 80+ certification requirements and hazy memory of an article I saw once. Glad you know the efficiency picture is better than I thought.

  • Unless you really need it, then choose something more modest than a honking 1000W PSU. Not a frag-fracking gamer? A 90W DC PSU should have enough juice for your 65W CPU. As PSU efficiency is measured in percentage, even a 50% inefficient 90W PSU will beat a 95% efficient 1000W PSU.

    • by BLKMGK (34057)

      My experience is that nearly everyone overestimates their PSU needs and it becomes a game of "who's is bigger?". This is a stupid way to pick hardware. My desktop runs a 650, my ESX server with 24+ bays runs an 850. If I had a way better video card in the desktop I might move to a 750 and I wouldn't run dual cards.

      My HTPC with ion chipsets use 9-16 watts at the wall at 100% usage.

  • by atarione (601740) on Thursday December 13, 2012 @07:53PM (#42282773)

    so it probably for 99% of the people won't make sense to upgrade a power supply just for efficiency

    but if for some reason you need a new power-supply anyways finding a good quality (80+ gold ..etc) unit on sale is totally reasonable.... at this point most units worth trusting the rest of your gear to are probably 80+ anyways.

    in my own case i had been using a 80+ power-supply that wasn't modular and cables where a hassle to manage ... i wanted a modular power-supply and also have no intention of risking a $200 processor and $300~ video card etc to a generic / shoddy power-supply so i found the Seasonic X750 (80+ Gold ) on sale for $100~ (which if you look at newegg is cheaper than any 700-800watt fully modular power supplies currently.

    since i wanted/needed fully modular 750~ish watt power-supply finding the X750 for $99 made sense as it was cheapest meeting those requirements.... the fact is it 80+ is just bonus ... seasonic's 5year warr and generally pretty good reputation for quality power supplies drove the choice more than the 80+ gold.

  • The design choices that manufacturers make in order to meet these levels of effeciency have other impacts. Active power management, cooling fans that only run when needed, and higher quality components are all good reasons to consider a higher effeciency rated PSU. My computers often run 24x7 for years on end so I tend to choose decent PSU.

    Also, just as a data point, I have a 4U box running a Xeon, 32gig of RAM, many cooling fans, 3x SAS cards, an SSD, and at least 20x HDD. It has a gold rated PSU listed as

  • Most PSU that do not sport the 80+ badge are outright junk that does not respect environmental and security norms in the first place, and will blow up in a variety of creative ways if you were to draw half of what is written as max wattage on the sticker. The 80+ badge weeds out most of the crap (not all though).

  • I've been wanting to start a project; 'GlobalWarming@Home', with client software for people who want to contribute to the global warming effort.

    All it would do is run your CPU/GPU full tilt, using as much power as possible to 'contribute' to global warming.

  • I bought a midrange power supply (Antec Gold £150 job) for my gaming rig some years ago (it was an Athlon XP2400+), which said 750W on the box. With a 4-box RAID0 and GeForce 7600GT the power draw was something like half that. It's still running.

    I built an identical box around the same time for someone else. He didn't see the point of a beefcake PSU so he said to use a cheap (read: £20) 350W brick. His computer lasted a month before the caps blew and took the motherboard with it.

    For me, it's le

  • If people use less power through more efficient devices there needs to be less power produced. Less power production means less pollution and less greenhouse gases. Environmental issues may be a contributing factor in the selection of a more efficient power supply.

    • Not everyone is polluting by consuming electricity. Pretty much all of the power I use comes from hydro.

  • by mathimus1863 (1120437) on Thursday December 13, 2012 @10:07PM (#42283663)
    How about reliability? I require a PSU that I know is going to

    (1.) Not die within a year of running at 50-75% load
    (2.) Not take any other components of my computer with it.

    Power supply problems are the most annoying to diagnose, because the symptoms usually show up in other components (like apparent RAM corruption, HDD stuttering, etc). I would pay $50 extra for a power supply that is *not* 80-plus if it has stellar reliability, because it means I only have to build my computer exactly once. On that note, the Corsair HX [newegg.com] series power supplies have not only stellar reliability, but also pretty much silent. I refuse to buy anything else, and you can usually them 20% off if you watch slickdeals.

    Efficiency saves you money, while reliability saves you time *and* money. And time is a limited resource for some of us...
  • I have no tangible proof, but generally PSUs that have an 80+ certification are generally much better quality than those that aren't. The peace of mind knowing that your PSU is likely to out-last the rest of your components is definitely worth it. Sometimes having your computer fail costs real world money (or equatable in-game money).
  • by TeknoHog (164938) on Friday December 14, 2012 @08:09AM (#42285943) Homepage Journal
    I have built passive-cooled machines since 2004 (or very nearly passive, with some machines having a single, huge, slow fan). The only way to make a PSU fanless is less wasted heat, or better efficiency. I don't care about a few wasted watts, when I have over half a kilowatt of computation going on, but I can't stand the noise of typical computer fans. High efficiency gear also tends to be very high quality for obvious reasons, so they last long. (I still have my first passive PSU from 2004, a precursor to the PicoPSUs.)

No one gets sick on Wednesdays.

Working...