why do we need 400w if it only pulls 120w video cards & psu's

Discussion in 'Power Supplies' started by multi-tasking_guy, Jan 14, 2018.

  1. multi-tasking_guy

    multi-tasking_guy [H]Lite

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    I'm learning about psu's but i am a little confused

    lets take for example a gtx 1060 6gb
    https://www.nvidia.com/en-us/geforce/products/10series/geforce-gtx-1060/

    It says:
    Graphics Card Power: 120W
    Recommended System Power: 400W


    i found out on a psu you should look at the 12v rail,

    what i don't understand, why do you need 400w if it only pulls 120w

    shouldn't the minimum requirements be 150w to 200w on the 12v rail?


    i even used my watts meter device, and the card pulls around 120w
     
  2. auntjemima

    auntjemima 2[H]4U

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    It assumes your other components.

    Board, ram, CPU, other possible cards, drives, possibly fans or pumps.

    Plus headroom.
     
  3. multi-tasking_guy

    multi-tasking_guy [H]Lite

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    so if i don't have many components, i should be ok?


    here is a picture of my computer on idle, 92watts
    20180114_085403.jpg




    and here is a picture of my gaming at max settings, 202watts
    20180114_085305.jpg
     
  4. auntjemima

    auntjemima 2[H]4U

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    Depends.. what power supply do you have?
     
  5. multi-tasking_guy

    multi-tasking_guy [H]Lite

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    cool master rs-550
    20180114_090459.jpg


    the company tricked me, it says 550, but the 12v rail is only 384, so really it's only a 384 watt power supply


    the gtx 1060 minimum requirements says 400w, but it only pulls 120w,
    since you said its including the system, then i should be ok?


    because my total watts is 202 watts 24/7 since i am using for mining



    so you see this is why i am confused
     
  6. ryan_975

    ryan_975 [H]ardForum Junkie

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    It's not a 384w powersupply, It provides several voltage rails that are used in various different ways by the systems that it powers. So the total wattage of the power supply is some combination of 3.3v, 5v, 5vsb, and the +/-12v rails. In your case it's a probably capable of supplying ~500w continuously (485 + 3.6 + 12.5), with the ability to push 550w peaks occasionally.

    As for GPU minimum power supply recommendations, when they say 400w, they mean the combined power on all rails to support the average computer. You will be perfectly fine as long as your supply is of decent quality (I don't know if it is).
     
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  7. quasar56

    quasar56 n00bie

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    The psu wattage rating means it will provide up to 550 watts to your pc components at 100% load. Efficiency is another matter. Also the unit provides 12v AND 5v so you are not being tricked.
     
  8. travm

    travm [H]Lite

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    It regularly baffles my mind how people come to conclusions like this.
    "I dont understand, therefore, someone must have tricked me!"

    Electronic power supply components arent a perfect science. Each tiny peice inside has a tolerance, and will always be a little high or a little low.

    A company that makes what people would call a "quality power supply", would be sure that even if all the components are on the low side, it will still provide the rated power. A company that is cheap, may generalize or give a "best case" rating, that means you might have a power supply that explodes in a fireball if you try draw the rated power.
    A quality power supply will also have decent overcurrent shutdown circuits. Something that you only ever use if you try to draw more power than the unit can provide. Cheap units have been known to fail with sparks and small fires.

    If you look at the picture you provided, it shows 384w on the 12v rail, and 120w on the 3v3 and 5v rails. 504W. Taking power supply efficiency into account, they arent out of line calling this a 550w psu. It would probably handle short peaks above those numbers. you should read some of the power supply reviews here on the [H], and gain some understanding of what they actually do.
     
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  9. ryan_975

    ryan_975 [H]ardForum Junkie

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    Efficiency normally doesn't factor into the supply rating. That only affects the "from the wall" consumption, not the power delivered to the components.
     
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  10. sirmonkey1985

    sirmonkey1985 [H]ard|DCer of the Month - July 2010

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    it's basically to cover their asses but at the same time there's no way for them to know everyone's system configurations.. hell just as an example between the systems in my sig, my current setup pulls 100w idle and ~170w full load on the cpu at the wall.. the system(cpu) it replaced pulled 165w idle and 255w full load at the wall. so when you consider the differences in system wattage 400w is a good suggested psu wattage.. everyone else has covered the rest in their posts.
     
  11. Speedeu4ia

    Speedeu4ia Limp Gawd

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    You guys have high idle watts, does Ryzen still not downclock/lower volts efficiently at idle?
     
  12. Tsumi

    Tsumi [H]ardForum Junkie

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    Not a trick, just another case of someone not doing their proper research. In the old days, the 5v and 3.3v rails were more heavily used. They are still used in systems today, just not to the extent of the past. Maybe 50 watts of a system's power consumption is on the 5v and 3.3v rails.

    You tried to gamble being cheap and failed. You got an older topology PSU that does not use the modern efficient DC-DC conversion, which is also the reason why modern PSUs can supply 99.9% of their rated power on the 12v rail. The 5v and 3.3v rail derives their power from the 12v rail instead of being independent like previous PSUs.

    There are many parts of the system that use 12v. The CPU, hard drives, fans, etc. all use the 12v rail. A typical high end consumer CPU is in the 150 watt range, and the rest of the system can add 50-100 watts. 120+150+100= 370. 400 gives headroom. Of course, low end consumer CPUs use far less than 150 watts, 50-100 watts peak and even less when gaming. Hard drive idling saves power, SSDs use less power than hard drives, and a barebones system with 3 fans uses far less power than a system with pumps and 15 fans.
     
  13. Zepher

    Zepher [H]ipster Replacement

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    I've got an EVGA GTX960 in this machine, they recommend at least 400watt psu.
    My system at full load in Prime95 pulls 585 watts from the wall, so you have to look at the rest of the machine to get an idea of what PSU to get.
    If I had just bought a 400watt PSU, my machine would just shut off when stressed.

    apc-powerchute-hal-9000-prime95.jpg
     
  14. sirmonkey1985

    sirmonkey1985 [H]ard|DCer of the Month - July 2010

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    it lowers the voltage.. at idle it sits at 1.04v but due to windows load balancing it constantly fluctuates between 1.04v and 1.28v. at idle the cpu it's self pulls ~25w(cpu + SOC). but again that's only one part of the power usage, you have to consider how many HDD's they have, how many fans they're running and whether or not the persons running a full WC'ing setup, AIO, or air cooled.. all those have different power requirements.
     
  15. Batboy88

    Batboy88 Limp Gawd

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    They do have higher idle watts and and in general a little more on consumption going on. That said think you should get a bigger unit for Headroom, never know when you might need it.
     
  16. stormy1

    stormy1 [H]ard|Gawd

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    Current spikes. I get a laugh about people who say my computer only draws X watts based on something like kill a watt meter.
    They are not fast enough to catch current spikes.