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Thread: Power Supply Units Explained.

  1. #31
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    Lightbulb Errata and Addenda (Cont'd)

    Quote Originally Posted by semitop View Post
    Wheres all the info coming from? All seems nice but if u are going that route u need sources. Can't give this kinda info without backup.
    - Werd. Here goes:

    Discussions on other Forums - Answered by Experts
    • Tom's Hardware Forum - Singel vs. Dual Rail PSU discussion.

    • Bjorn3d Forum - Myths about Single & Dual Rail PSUs

    • Extreme Systems Forum: Single Rail Dominance - These guys go overboard on PC modding regularly. This particular topic on the issue is very interesting.

    • SLI Zone: Why Multi-Rail GPUs are not good enough - Here's another topic that bolsters my earlier points. Unless you're running a Mushkin PSU which explicitly fuses the amperage on the multiple rails when the GPU power demands it, you're loosing an average of 10amps for ever secondary rail if you choose a multi-rail PSU over a single rail flavour. Even manufacturers like AlienWare prefer single-rail PSUs for their monster rigs.



    Reference Material for this article

    These are a list of materials I used as a reference guide to compile all of the information you read on page one. I invite you to read and educate yourselves as well. I merely condensed all this mumbo-jumbo so that it is easily accessible from one point.
    • Power Supply Units - Read this reference column before you read anything else. All the basic information you need to know is here.

    • Power Ratings on the most recent high end GPUs - This is a relatively comprehensive list of the power ratings of all the GPUs currently in the market as at 2007. Expect this list to be updated as new technology comes on stream. Please note that this list includes the minium power (i.e. wattage) needed to run the GPUs. It does not specify the maximum power required. To determine the amperage from these power ratings, simply divide the wattage by 12, since all GPUs run on a 12v rail.

    • Power Supply Fundamentals: How much is Enough? - This article thoroughly explains why buying a monster PSU is not necessarily justified, and shows why manufacturers are only touting watt ratings to scare up some cash.

    • All about Power Factor Correction - Why it's important to have in a PSU and the significance it has on your power consumption.

    • Power Supply Design Specification 2.2 - This is an Adobe Document developed by Intel. It is highly technical, and specifies the relevance of Dual Rail technology in newer PSUs. This is the official document that describes 2.2 specifications for newer power supply units, circa 2005.

    • Voltage - A comprehensive write-up on electrical differentials.

    • Drift Speed of Electrical Charges - This will help you understand the significance of why watt rating in a PSU rating is almost irrelevant.

    • NewEgg's Exhaustive Power Supply Shopping Guide - Everything you need to know about the devices, what the specs mean and how to decide.

    • Common Power Supply Myths - Now here's some reading for those of you who believe that SLI certified PSUs carry enough power on a single rail to power a GPU, or that you need two power supplies to run your rig or that Multi-rail PSUs are better than single rail, or if you've heard any other myth about power supplies (maybe you don't even know that it's a myth), READ THIS ARTICLE. You'll be glad you did.


    That's a LOT of information to condense. So I'm going to stop right here until your hunger for knowledge grows. Please bear in mind that there's a 20v specification being developed for Next-next gen PSUs and GPUs. So in a year or so, all of this information will be obsolete.

    [Cont'd...]
    Last edited by Xenocrates; Nov 20, 2007 at 03:31 AM. Reason: Addenda

  2. #32
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    Question Questions, Answers & Commentary

    Quote Originally Posted by Genesis2kx View Post
    The biggest question my and others have had is regarding highend GPU's that say you need X amount of Amps on 12V rail, compared to what your PSU has or the one your planning to get. Some ppl say, that number eg, 22A is the minimum you need for your whole system + gpu to run adequately. Others say its the GPU alone. I think this just needs to be cleared up with hard evidence. I'm leaning towards the answer that 30A is needed by the full system.
    - See the reference material I've provided in the previous post. You'll see quite clearly that the requirement is not for the entire system. It is impossible for manufacturers to know this, since they only test the GPU with ONE motherboard and CPU to know what it is capable of drawing. It is important to note that requirements over 18 amps were not anticipated by Intel when they did their 2.2 spec. That's why they were revised - and later stated that single rail PSUs with all the amperage on one 12v rail are acceptable as well. Read the reference material that I've provided.

    Let me state once more:

    The amp requirement on the box of your GPU is NOT for the entire system. It is for the GPU on MAXIMUM LOAD.

    Electrical devices, especially those which use magnetic motors (like heatsinks, fans, thermostats, compressors, etc.) and feature complex circuits with increased capacitance have VARIABLE current requirements. When those circuits are taxed heavily, the amp requirement on the box may be demanded. If any device on your motherboard draws more power from your PSU on the 12v rail than it can supply, the PSU will SHUT DOWN YOUR MACHINE.

    You have been warned.

    Quote Originally Posted by Genesis2kx View Post
    Why you may ask? (As it may seem silly that GPU makers can specify how much their card + your system components they know nothing about requires a certain Amps minimum)
    - And that's exactly my point. See my previous post. I pointed this out as well.

    Quote Originally Posted by Genesis2kx View Post
    Well I think that number they tack on the box and in their specifications is a generic number given a relatively average component setup + the amps their card needs.
    - If you want to risk it, it's your money on the line.

    Quote Originally Posted by DavidJa View Post
    thats what im trying to say it says it needs 30amps as the TOTAL system requirement AND for SLI it's NOT for a SINGLE 8800gtx.
    And again i will say that no single card will draw 22amps by itself.
    - Read the previous two posts.

    Quote Originally Posted by Malloc-X View Post
    this may explain everytime i try to turn up the graphics above low in crysis on my 8800gts i get a black screen and have to reboot. i need to check my psu when i get home. so what psu do u guys recommend?
    - This is a 12v rail failure. Based on the image you submitted, there isn't enough amperage on either 12v rail to handle your GTX when it starts to get really taxed and draws more current from the rail than it can provide. GTX cards draw 18 amp when on moderately graphics intensive games (see the reference material). They will go all the way up to 30 amps when that heat sink fan kicks into high gear to cool off that massive GPU dye on the processor core. DavidJa, I hope you're paying attention. 30 amps is the requirement for the GPU alone, not the GPU+CPU.

    Quote Originally Posted by [I.R.A]_FBi View Post
    generic or "name brand"?
    - Irrelevant. The point is that his 12v rail doesn't supply enough amperage to satiate his GPU. Malloc-X, checkout the Mushkin PSU that I recommended earlier. Even though it's multi-rail, it features rail fusion. So even if your GTX should max the power requirements on the 12v rail, the PSU will merge the rails to prevent PSU shut down. This problem is more common than most techies are willing to believe. The issue is that many of their concerns were written before a game like Crysis came about. Before Crysis, everybody thought that no GPU would ever pull more than 6 amp on a 12v rail. Everybody said that a 450 watt PSU would be able to more than handle a 8800GTX.

    Yeah, it can fire it up alright. But can it run it under serious load with all the settings turned up? Think about it guys.

    Quote Originally Posted by Malloc-X View Post

    this is what it says in the manual for my power supply. I currently have 3 sata HD, 2 dvd burners and a xfx 8800gts. it look like ma machine so burn up. oh well
    - It's not burned up. The machine shut down because one of the rails failed. Your power supply is designed to shut down in cause there are components drawing more amperage than it can supply on a specific rail. It doesn't mean that it's dead or that it will never work again - or have you verified that it is indeed a dead PSU?

    I'll check back later for responses.

  3. #33
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    i made a typo what i should have said is that it look like my machine soon burn up. i have a gts not a gtx. the mushkin looks nice, in total it has 80A total. i think i will be getting it
    ChAos AnD cOnfLicT ArE mY ParEntS

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    tis not totally irrelevant, some generic power suppplies die when they approach half their rated wattage.

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    Quote Originally Posted by zRo ToLeRaNcE View Post
    Didn't you see it in the Sticky from long time?
    Quote Originally Posted by Sticky
    Last edited by zRo ToLeRaNcE : Yesterday at 12:34 PM
    Yup... from long time. Now take a look at the time of my post


    I like the mushkin too. My PSU was a cheap 20USD one from the but it seems to be able to do the job perfectly at the moment.
    Last edited by Electrotechnic; Nov 20, 2007 at 10:10 AM.

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    http://techreport.com/articles.x/12379/8

    a highend 8800ultra system uses 315W under load (whole system)
    Thats 315/12 = 26.25 amps. < 30amps for the whole system by the top end GPU. And all o dat is not coming from the 12v rail(s)

    8800GTS in SLI uses 393W under load
    393/12 = 32.75 amps . finally over 30amps in sli but thats not all from the 12v rail still. And thats a system with an x6800 core 2 extreme and 4gb ram

    If u want an answer to ur how can they know unless they do a bunch of tests on all possible systems query, all they need to do is test the highest end system with one of their cards and give a number in amps. If the amps given is for the GPU alone there'd be no point. A gpu cannot be used by itself and them telling me the gpu needs 30 gives no help because i would be no better off in knowing which PSU would be adequate for my entire system.
    Last edited by semitop; Nov 20, 2007 at 11:53 AM.
    This posting is provided "AS IS" with no warranties, and confers no rights.
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  7. #37
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    Are there any PSUs with >30W on the 12V rail?

    19" LCD|Asus A8N SLI Deluxe|AMD X2 3800+ @ 2.5GHz Cooled by Zalman CNPS9500|4 x GSkill 1Gb DDR 400|2.25 TB Total storage|eVGA 256mb 8600GT DDR3 @ 640/1600MHz cooled by ZalmanVF700|Ultra X-Finity 600W PSU w/ 135mm fan|1 x 120mm|4 x 80mm|Altec Lansing AC56|Windows7 x64 : Ultimate

  8. #38
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    nuff. all 90amp on it too.
    http://www.pcpower.com/home/

    But i can't put my comp in that kinda risk. From the links in the sources provided, the "advantage" of single rail is that it can support a massively power hungry system, because they assume multiple rails are limited to the power on the seperate rails. But u putting everything on one single rail with a whole heap o current. If something messes up in that rail thats more probs than multiple rails. Not to mention that several of the higher end PSUs for multiGPU setups have several rails that can still provide ample power more safely. U will see some saying 12v1 is CPU, 12v2 CPU/PCI-e 12v3...., 12v4 PCI-e.THere is some overlap in what rails can support.

    The trend is not more power for single components now. GPUs are getting smaller dies and less power consumption. So are CPUs. just when u put in multiple of these things u raise power demands but still, is not so bad.

    Single rails are less stable.

    All this quad sli and crossfireX bull. Multiple GPUs on one PCB is the way to go if one GPU cannot handle the stress. And improvements in PCI-e Bandwidth and power output to support it is all they need. Now ppl can't even use PCI slots anymore once they decked out with GPUs.
    Last edited by semitop; Nov 20, 2007 at 11:51 AM.
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  9. #39
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    Red face

    Single rails are less stable

    Was this something you read semitop or your personal opinion... cuz a recent study was done and it was found that single rails are actually more stable thats why you have people like silverstone making extremely high end single rail PSU.


    It's like we have a two sided affair in this thread... those who know better but cant afford to do better and those who dont know better and convince themselves they know better cuz they cant afford to do better...
    Last edited by MaxFactor1; Nov 20, 2007 at 12:01 PM.
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    is not me. From the sources he provided the multi rail thing was put in place for safety reasons as well as for stability. Maybe companies can make a single rail supply more stable than a multirail supply but it makes sense that a multirail be used considering the varying devices that rely on the 12V rail.

    Would be nice if u could point out the recent study tho
    Last edited by semitop; Nov 20, 2007 at 12:22 PM.
    This posting is provided "AS IS" with no warranties, and confers no rights.
    You assume all risk for your use. © 2006 Azix Solutions.
    All rights reserved.

    Dropbox: http://db.tt/8qVS35lo

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