Power Supply Myths

Discussion in 'Power Supplies' started by Ocellaris, Jun 3, 2008.

  1. Ocellaris

    Ocellaris Ginger @le, an alcoholic's best friend.

    Messages:
    18,780
    Joined:
    Jan 1, 2008
    I think all too often, people are really overestimating how much power a particular configuration is using. There are scattered posts in the forums recommending that people need at least 600w just to overclock or run a decent video card. Now sure, its nice to have some headroom, however its also nice to save money on a power supply and make other changes like going from 2GB to 4GB or RAM too. Here is a screen shot of how much power my Q6600 system AND a 19 inch LCD are pulling out of the outlets when running the overclocked CPU and video card at 100%:

    [​IMG]

    OK now figure my LCD is pulling in about 20 watts, so the tower is using 300w. That 300w is before power supply efficiency is factored in. Now lets just say my Corsair power supply is running 80 to 85% efficient with that load, that means the components are only using 240 to 255w of power.

    Maybe its just people having bad experiences with shitty power supplies in the past, so they overshoot everything now. I've seen people with almost the exact same configuration as mine get pretty much convinced that they needed something close to a Corsair 750TX to overclock.
     
  2. pxc

    pxc [H]ard as it Gets

    Messages:
    33,064
    Joined:
    Oct 22, 2000
    Yeah, it's partially that when going for overkill and it's also skewed here because many people are running much bigger than average power loads.

    I overestimate power consumption to be safe, but that usually makes me feel very comfortable with 380W and 430W PSUs. But now I kind of wish I had overestimated more since I'd like a pair of PSUs with 2 6-pin aux connectors to go with SLI and CF builds I'm about to make.
     
  3. lamboman

    lamboman Gawd

    Messages:
    599
    Joined:
    Jul 17, 2007
    Finally, we have a post like this. I really do get fed up, as do others, when the occasional noob comes in, insisting that they need a zillion watt power supply for their mid range graphics card. Although this is a simple thread, can we have it stickied? It would help people a lot when it comes to buying power supplies.
     
  4. ChadJarvis

    ChadJarvis n00b

    Messages:
    1
    Joined:
    Jun 1, 2008
    Don't you also want to stay around 50% of your power supplies potential for energy effiiceny? So wouldn't that mean a 500-600w power supply would be perfect for 240-250w draw (provides a little headroom too)?
     
  5. heatlesssun

    heatlesssun [H]ard as it Gets

    Messages:
    44,157
    Joined:
    Nov 5, 2005
    You make a good point, but this same type of info is in just about every GPU review in the power consumption part. All of those reviews are looking at the power draw from the wall for the rig, they perhaps don't do a good job of explaining that.

    That said, its not about the total power output, its about power output quality and stability. Great 1KW PSU's are running about $200 and the PSU is so critical that I don't mind going overboard for piece of mind. But yes, like CPU temps, people get crazy about power output from their PSU's.
     
  6. Ocellaris

    Ocellaris Ginger @le, an alcoholic's best friend.

    Messages:
    18,780
    Joined:
    Jan 1, 2008
    typically on decent power supplies, operating efficiency will not vary by more than a few percent within the useful operating range. not to mention its not very often you run a pc at 100% 24/7 unless it is doing something like folding.
     
  7. RangerSVT

    RangerSVT [H]ard|Gawd

    Messages:
    1,989
    Joined:
    Jun 7, 2007
    I agree with the original poster. I also find it funny how many people like to quickly put the blame on a power supply when a particular system is not working properly.

    I still believe that an unstable system is in result of mis-configured bios or faulty computer components, the PSU being the last thing itcould possibly be.


    "I just built a new PC and I get a BSOD on bootup, I have 4GB of ram and Vista 64"

    Response: "You have a faulty PSU, REPLACE IT. Quickly, kthnx"
     
  8. pawstar

    pawstar Limp Gawd

    Messages:
    465
    Joined:
    Jul 2, 2005
    There is some truth in getting an oversized PSU: it is party because manufacturers used to (some still do) over-rate the capacity of the power supply. The second note of concern is which lines the power is drawn on. Like in the OP, say your puter is drawing max 300W and you get a 330W PSU - you may still go over the power supply limit due to the fact that the draw is not balanced over all the voltages but concentrated on the 12V lines and 5V to some extent (really depends on your hardware & architecture) and the rest of the lines will be underutilized. You are far better off sizing the psu by adding up the amp load of all components on each voltage line.
     
  9. mystykmax

    mystykmax Limp Gawd

    Messages:
    473
    Joined:
    Feb 4, 2005
    I'd be curious to see the same test with an 8800 GTX or the like. I'd also be curious what the draw is on boot-up as well...drives going from stopped to spin-up. Also I'd be curious of what typical water cooling solutions draw from the PSU as well. Good post.
     
  10. Ocellaris

    Ocellaris Ginger @le, an alcoholic's best friend.

    Messages:
    18,780
    Joined:
    Jan 1, 2008
    ill hook the ups into a laptop and check bootup draw. also ill post up some idle and sleep numbers for the curious.
     
  11. ryan_975

    ryan_975 [H]ardForum Junkie

    Messages:
    14,003
    Joined:
    Feb 6, 2006
    While I agree with the sentiment of this thread, a power supply doesn't provide all it's power at the same voltage, yet it's rated as the combined power the unit can output. Telling someone all they need is a 400watt supply when they're drawing 30amps on the 12v rail is going to cause them problems. We really need to move away from wattages and start worrying about amperage.
     
  12. SudburyOntario

    SudburyOntario Gawd

    Messages:
    575
    Joined:
    May 5, 2008
    I agree .. Amperage is the main concern when I build computers. 48amps on my sig comp.. but I hear musical sine sounds from the psu - not the fan :confused: ..
     
  13. Paul_Johnson

    Paul_Johnson [H] Admin Staff Member

    Messages:
    15,527
    Joined:
    Aug 29, 2004
    No.

    I beg to differ ;)

    And a large number of APFC power supplies are NOT read correctly by your Kill-A-Watt's and cheap home power meters, so guesstimating off them is not accurate
     
  14. Chombo

    Chombo 2[H]4U

    Messages:
    3,320
    Joined:
    Jan 10, 2008
    My sentiments exactly.
     
  15. leetskeet

    leetskeet Limp Gawd

    Messages:
    493
    Joined:
    Sep 23, 2007
    your icons seem huge to me.
     
  16. Ocellaris

    Ocellaris Ginger @le, an alcoholic's best friend.

    Messages:
    18,780
    Joined:
    Jan 1, 2008
    Why thank you! :D

    Anyway when I was talking about shitty power supplies in the first post, I was referring to "500w" drivers where 200w is allocated to the almost useless 3v and 5v rails, along with power supplies that just fail to provide anything close to their rated power reliably.

    I definitely think a lot of the oversize recommendations are from people (myself included) who were used to power supplies in the past not delivering a lot of power on the 12v rail(s). Now almost all of the commonly recommended units can provide a very significant amount of their max power to 12v, its not as much of an issue.
     
  17. heatlesssun

    heatlesssun [H]ard as it Gets

    Messages:
    44,157
    Joined:
    Nov 5, 2005
    Don't know if you use Vista, but you can actually resize these in Vista with CTRL and the mouse scroll wheel. Pretty cool.
     
  18. Ocellaris

    Ocellaris Ginger @le, an alcoholic's best friend.

    Messages:
    18,780
    Joined:
    Jan 1, 2008
    I'll be honest, these icons are way to big, and it drives me nuts however I never knew that would change it. I am figuring out what software I do and do not want on my PC so I can nuke it all, start fresh, then make a clean OS image.
     
  19. heatlesssun

    heatlesssun [H]ard as it Gets

    Messages:
    44,157
    Joined:
    Nov 5, 2005
    Yeah, your icons looked bigger than the default to me so I assumed that you had enlarged them. Having a clean OS image is a good thing for recovery purposes.
     
  20. ryan_975

    ryan_975 [H]ardForum Junkie

    Messages:
    14,003
    Joined:
    Feb 6, 2006
    They're the same size as my icons on a fresh install of Vista.

    [​IMG]
     
  21. heatlesssun

    heatlesssun [H]ard as it Gets

    Messages:
    44,157
    Joined:
    Nov 5, 2005
    Didn't realize they were that big, I resize them right out of gate so I never noticed. Good thing I'm not a homicide detective.
     
  22. ryan_975

    ryan_975 [H]ardForum Junkie

    Messages:
    14,003
    Joined:
    Feb 6, 2006
    Homicide detective?
     
  23. RangerSVT

    RangerSVT [H]ard|Gawd

    Messages:
    1,989
    Joined:
    Jun 7, 2007
    He was being funny...
     
  24. Met-AL

    Met-AL [H]ardness Supreme

    Messages:
    7,875
    Joined:
    Apr 9, 2002
    I share the same opinion. I have a Coolermaster ACLY Realpower 425 with a built in power meter, and with my new e8400 and my 8800GTS, it barely breaks 300 watts. But when I mention that, I get the "your meter is inaccurate", which it is and both Toms and SPC have shown it to read HIGHER than what is actually being used due to it reading the mains and the PSU not being 100% efficient.

    1000watt PSU.... LOL.
     
  25. RangerSVT

    RangerSVT [H]ard|Gawd

    Messages:
    1,989
    Joined:
    Jun 7, 2007
    Oh no you didn't, may I recommend the Corsair HX620 PSU, it's a solid PSU, seriously, it's solid...
     
  26. bob

    bob 2[H]4U

    Messages:
    2,971
    Joined:
    Feb 13, 2002
    Which of the respectable PSU manufacturers used to, and still do, over-rate their PSUs?

    The only examples I can think of are from the late 1990s, PSUs were more toward the 5V line as the main power source. 15,20... hell 70A @ 5v on my compaq proliant psu, with less than 10A @ 12v. Nearly everything but cdrom/hard drive was off the 5v line back then. Most PSUs had the sticker with "XXX Watts", with the current and voltages below. Now, im getting to my point... The only example I can think of, was with this era of PSU, where the high current/wattage was mostly based off the 5v line.. People would see the "oh my, 300W wow this one is cool", completley ignoring that the PSU is worthless for much off the 12v line.

    Over-rated, Under-rated... Rubbish. Read the specifications, and usually even the flimsiest powmax or enermax will hold up. I have a FSPG (same as sparkle) 150W in my 1U server, its sticker has some fine print about the 5v line and 12v line, in regards to what the watt rating was based off. With mine, you cannot load the 5v line and 12v line to what the sticker says for amperes, it has to be one or the other. I would hardly call it a flaw, as this thing has been running nearly perfectly for 10 years. Its one PSU, where if someone did not read the specifications, they could have burned it up after a month and bitched/moaned/whined that it was grossly over-rated, and how they should have bought a 250w instead of the 150w. Its a small, *small* 1U PSU that doesnt even use heatsinks inside, all transistors are glued to the steel case. It has a small, single transformer for providing 5v and 12v, and a second transformer for the 3.3v. Load down the 5v line, *or* the 12v line and its fine. Compleley load down both 5v and 12v, it wont hold out.

    Not ranting at anyone, its just an example. Even the absolute best of the PSUs can be turned into paperweights, and possibly magic-smoke generators by someone ignoring specifications. Maximum Ampere draw doesnt mean "General guidelines". Maximum = maximum.

    QFT

    Though its not easy, especially if a component only specifies watts.
     
  27. ryan_975

    ryan_975 [H]ardForum Junkie

    Messages:
    14,003
    Joined:
    Feb 6, 2006
    You should read some of the reviews [H] and JonnyGuru have on Powmax, Apevia, or Allied junk. They never even made it to their rated amperages before failing. There are even a couple cases where the failure of the PSU was so bad that it damaged test equipment. There's no way in hell you're getting a 500 watt PSU for $20.

    If a component specifies watts, you can generally figure out how many amps you need. You just take the wattage and divide it by the voltage used. Of course, if the component uses multiple voltages even that goes out the window.
     
  28. SamuraiInBlack

    SamuraiInBlack [H]ardness Supreme

    Messages:
    5,677
    Joined:
    Oct 10, 2003
    I look at it like this:

    You spend $200+ for a motherboard, you spend $200-1000 on a processor, dump at least half that on RAM, and then go balls out on a video card, and then take out a second mortgage for the case, heatsink, soundcard, modded cables (i.e. braided SATA cables, UV lighted ones, etc.) and lighting kits....

    And then you're going to turn around to the bargain bin for a power supply? No. Apply for an AmEx/Mastercard/Visa/whatever card you don't have yet and call it a day, foo'.

    The problem with power supplies is that the price tends to be reflective of the quality in many cases, so as a result people end up spending more than they have to because they think that quality can't be found for less than $150 when it comes to power supplies, when that's simply not true. There are a number of names in the PSU business that put out great power supplies at virtually any range of wattage. They just aren't well known because most people see Antec or Enermax or Thermaltake and call it a day. That and factor in as its been pointed out that some brands are overrating their power supplies, and its really not a wonder as to why there's so much overkill invested.

    Friend of mine is running a Q6600 rig on a Corsair 620 that I just built for him on Sunday. Yeah it might be overkill for his setup of only one hard drive and a burner, 2 gigs of ram, a Zalman HSF, a 9600GT and three fans, but to be honest, I have -no- idea what his eventual upgrade plans are, and I honestly don't know what else he'll be adding in the future till he buys something and has me install it for him. For him, it made sense to go with the 620 because of the headroom for future upgrades, provided he doesn't decide he's going to try his hand at a Quad-SLI rig with multiple TEC units. Also, he prizes silence, and it is to my understanding that a power supply that isn't operating at full rated wattage isn't working its ass off trying to stay cool. Therefore the fan is moving slower, and thus not making as much noise. So, with that in mind, he has a nice midrange setup that is nice, cool and quiet when he's not pushing it, but it will still remain quiet and operate efficiently even when he's going batshit in a PC game.

    Truth be told, it makes sense to give yourself a bit of headroom. Otherwise if you cut it too tight you leave yourself in the position of having to buy another power supply if the setup you want in the future consumes more power than what your current one can do. And the money you'd have to invest needlessly a second time would take away from that setup. And well, who the hell is all happy happy joy joy over having to unwillingly settle for less than what they want?
     
  29. Ocellaris

    Ocellaris Ginger @le, an alcoholic's best friend.

    Messages:
    18,780
    Joined:
    Jan 1, 2008
    ...and here is a situation I was mentioning earlier where someone overbought a power supply that they *MIGHT* need eventually, and gimped the system with only 2GB of RAM. Fact is by the time he might really need that 620, he could just buy a 1000w unit anyway. That way when he is going batshit in a game, the 1000w unit (that he will be drawing 370w from) will barely make a noise. Except he will hear his hard drive thrashing away over the sound of silence, since he only has 2GB of RAM.
     
  30. SamuraiInBlack

    SamuraiInBlack [H]ardness Supreme

    Messages:
    5,677
    Joined:
    Oct 10, 2003
    He's on a DDR2 board and running XP. RAM will be relatively cheap (as if it isn't now?) for him to pick up by the time he switches to Vista or Windows 7, pending on when he does decide to upgrade. I had him pick the 620 because of the reasons I stated - the overhead is doing him good now and will still give him the room for future upgrades, depending on how high he steps up. He's already talking about upgrading to a pricedropped 9800 or maybe even the new GTX 200's when they come out. And seeing as there is a 6 and an 8 pin on that card, per the VR Zone pics posted earlier today, I would laugh if anyone told me that wasn't an indicator of its power draw.

    He needs the 620 now, and he will need it later. And in his words, the day he needs a 1000 watt power supply to power his computer better be the same day we have our own portable nuclear reactors to act as power generators for our entire house, or he has enough money to buy a small country.

    I built it. It's silent enough for him. That means he's happy. His hard drive is not thrashing away either. Thanks for assuming that would be the case though just because he has 2 gigs of RAM.
     
  31. Darth Bobo

    Darth Bobo [H]ard|Gawd

    Messages:
    1,057
    Joined:
    Jan 6, 2007
    I still think that it is easily possible to make an informed choice when you pick a PSU for your new shiny system.

    Also I agree that we should stop focusing on wattage and start focusing on amperage.

    About load and efficiency. Although todays high quality PSUs are fairly efficient over all loads barring the extreme load cases (near 0% and near 100%), that being said PSUs performs the very best around 50-60% load, so I think that it is fair to aim for that load when building systems and thus I would advice somebody with a system estimated at drawing around 300W (effectively) to get a 500W or so PSU.

    As for my own system I used various powercalcs on the web to estimate powerdraw and settled at a fictive maximum powerdraw just short of 400W thus I got a 620W PSU...
     
  32. Valset

    Valset [H]ardness Supreme

    Messages:
    6,530
    Joined:
    Apr 4, 2008
    I just bought a 800w BFG for 128 with express shipping. I have a 30 buck rebate coming from this. that leaves 100 dollars PSU with a lifetime warranty. I think that well below that 150 dollar mark and still pretty good.

    BTW I bought the 800 instead of the 650 for future proofing. not because I needed it to day but with the graphic cards they are coming out with....
     
  33. Mithent

    Mithent [H]ard|Gawd

    Messages:
    1,616
    Joined:
    Dec 19, 2007
    While I wouldn't like to say that a machine that appears to be drawing 300W would be a-ok with a 400W PSU, taking into account inaccuracies in measurement as well as transitory loads and efficiency, I also agree that people seem to go rather ridiculously overboard. There seems to be some group who think that having anything SLI means you need to have over 1kW. Very very few people need more than 850W, I'd say, and in most cases 500-600W is plenty.

    Having a decent PSU is a different matter of course; I don't think anyone around here would advocate buying cheap PSUs that burst into flame if you try to load them to 75%.

    I also kinda hope that power demands won't just keep increasing; I don't want to be running a machine in the future that costs $5 per day in electricity and expels 15 tonnes of CO2 daily.
     
  34. LOCO LAPTOP

    LOCO LAPTOP [H]ardForum Junkie

    Messages:
    10,182
    Joined:
    May 4, 2006
    yeah well I found out that 1600W (I knew it but still) is overkill but it saves upgrades later on. :)

    [​IMG]
     
  35. secure.boy

    secure.boy Limp Gawd

    Messages:
    474
    Joined:
    Oct 22, 2007
  36. LOCO LAPTOP

    LOCO LAPTOP [H]ardForum Junkie

    Messages:
    10,182
    Joined:
    May 4, 2006
    Back-UPS XS 1500 with LCD

    oh and that 116Volts is normal for my house... :rolleyes:
     
  37. Valnar

    Valnar 2[H]4U

    Messages:
    3,055
    Joined:
    Apr 3, 2001
    I've got the Corsair HX520W and probably only need less than 270 watts myself. I bought it because it's a top rated and silent PSU, so long as the fan does not ramp up.

    Why did I buy it if I only needed half of that power? Well, because even Corsair says that the efficiency peak is about half-way and the fan doesn't spin faster until you get to 300 watts or so. I haven't tested that, but it's nice to know. Silentpcreview.com verifies Corsairs claims.

    Yes, getting a 1000 watt PSU is stupid if you only need 300 watts. You'll be wasting both money and electricity. Getting something about twice as big as you need is okay. However, if I could do it over again, I'd probably look for something in the 450W range, but Corsair doesn't make a modular cable PSU in that range.

    Heck, if Corsair/Antec/Seasonic made a PSU that stayed quiet up until it's maximum wattage, I'd be happy with a 300W PSU!
     
  38. Spare-Flair

    Spare-Flair [H]ardness Supreme

    Messages:
    7,471
    Joined:
    Apr 4, 2003
    Indeed, running an X2 3800+ @ 2.6GHz, 8800GT overlocked with volt mod, 2GB ram, two harddrive, cd-rom, floppy, 5 slot USB expansion card, USB wifi, etc. etc. etc.

    All on a 250watt PSU. I bought an older 8800GT at Best Buy once during a good sale. The guy behind the counter said: "here you go, what kind of powersupply do you have?" and I replied "a 250watt PSU" and he was shocked and adamant that I had to buy at least a 600w or the card wouldn't work.

    Total bull****.

    I posted a thread about this exact same topic months ago but of course I didn't have the power meter to back me up. Glad to see somebody had the time to get the empircal evidence to prove the point.
     
  39. Ang

    Ang Gawd

    Messages:
    597
    Joined:
    Mar 20, 2008
    Yeah to run a Q6600 and a 8800 GT 512mb this kid I know that is a computer reseller. I asked him to purchase me a 430w PSU for my computer, and he refused to do it claiming:

    "The Q6600 needs at least 400 watts, and the 8800GT needs at least 200watts."

    And now matter how much proof I show him, he refuses to believe.
     
  40. thebeephaha

    thebeephaha 2[H]4U

    Messages:
    2,054
    Joined:
    May 27, 2007
    I kind of agree with the original poster as well after looking at my power use vs what kind of power supply I have.

    This is a huge pic I am sorry. I got lazy.

    [​IMG]

    Above is full load on my comp, only thing running off the battery backup is the computer, the monitor I turned off for the screenshot. So 640w load and I have a 900w PSU, maybe a bit overkill.