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Thread: Simple PSU question Please Help :D

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    Simple PSU question Please Help :D

    Ok, im a real dumass now.. but somehow after reading 5 long articles about PSU's it still doesnt answer my question..

    Does a 580watt PSU constantly pull out 580watts of power??? Or does it only imply that it is the maximum power it can get to and thus run at lower wattage under soft load?

    Im asking this because I fancy a PSU which is rated at 580 watts even though its a surplus to my needs. Since I want to save on my electricity bill, I dont want to have an system that sucks in too much power.

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    Offcourse, a PSU only pulls as much as you need, if your config needs 300W idle and 400W stressed, you ain't gonne pull more then 300 or 400Watts, 580Watts is just the limit

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    good good... that means i can still save on my electricity bill

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    • Hottentot's system
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    If you want to save on your electricity bill get a brand name PSU with an 80% + efficiency rating, like Seasonic.

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    i was planning on getting a hiper one.. ill look into that seasonic psu's

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    The power rating on a PSU is the maximum power it can supply the PC's components. Due to inefficiencies it will draw more than that from the mains.

    For example, an 80% efficient PSU providing your PC's components with 400W of power, will draw 500W from the mains and emit 100W of heat doing it. (Almost all of that 400W will get turned to heat by your other PC components, so the room will get 500W of heating).

    The efficiency of a PSU is not fixed. It depends on how much power it is producing, the temperature, and the quality of the power it is receiving.

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    so that means a better efficiency PSU that is enough to give your PC the power it needs is better than that with higher wattage? am i right?

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    Quote Originally Posted by Leepox View Post
    so that means a better efficiency PSU that is enough to give your PC the power it needs is better than that with higher wattage? am i right?
    A more efficient PSU is a good thing because it will be better designed and made from higher quality components. A bargain basement PSU will be inefficient, but will also be unreliable. Many low cost PSUs lie about their rated power, In the last PSU test that Hexus did, a couple of low cost ones blew up when they tried to run them at maximum power.

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    oh my gawd thats horrible... I used to have a win power one which came along with my case and I am sure that one was a cheapo... I think my current one serves the purpose, but my friend is trying to sell me his hiper type-r which is modular and has 580 watts rating.. just got me a bit more worried about the electricity bill. Anyway I think imma just get it from him anyway for £15 and see if my bills goes up lol.

    I think this is a good PSU, they say it goes around 75-80% efficiency... which is not that high but good enough i think

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    Quote Originally Posted by chrestomanci View Post
    The power rating on a PSU is the maximum power it can supply the PC's components. Due to inefficiencies it will draw more than that from the mains.

    For example, an 80% efficient PSU providing your PC's components with 400W of power, will draw 500W from the mains and emit 100W of heat doing it. (Almost all of that 400W will get turned to heat by your other PC components, so the room will get 500W of heating).

    The efficiency of a PSU is not fixed. It depends on how much power it is producing, the temperature, and the quality of the power it is receiving.
    I think everything you have said is absolutely correct. Would I be correct is saying that the efficiencies quoted are at the maximum power output of the PSU and that running a PSU at less than full load makes it significantly less efficient?

    As a example - A PC requires 300W to work correctly. I have a good quality FSP 'Green' PSU that puts out 300W@80% efficiency so it will actually draw 360W with 60W being losses.

    The equivalent FSP 80% rated 500W PSU is only 60% efficient when it's supplying 300W so it will use 420W with 120W being losses.

    Would you concur?

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    Remember this though!

    If a PSU is rated at 580W, the chance of it actually being able to do that if required is very very slim.

    Its just a peak rate for a split second...then....crash!!!!!

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    Quote Originally Posted by wja96 View Post
    I think everything you have said is absolutely correct. Would I be correct is saying that the efficiencies quoted are at the maximum power output of the PSU and that running a PSU at less than full load makes it significantly less efficient?

    As a example - A PC requires 300W to work correctly. I have a good quality FSP 'Green' PSU that puts out 300W@80% efficiency so it will actually draw 360W with 60W being losses.

    The equivalent FSP 80% rated 500W PSU is only 60% efficient when it's supplying 300W so it will use 420W with 120W being losses.

    Would you concur?
    No, I do not concur.

    The loss will not be a fixed amount but will vary with the load on the PSU. There will be some loss when there is no load at all, but in a modern switched mode power supply it should be very low. Most of the loss will be from the electrical resistance of internal components, especially the capacitors, so the loss from these will be a fixed percentage of the load. At very high power output, the components will be under stress, and will become less efficient, and produce more heat. When you exceed the rated load it is that excess heat that destroys the internal components and causes the PSU to blow. The PSU will also become less efficient under hot conditions, because it also stresses the components, and because some of the power produced has to be diverted to the cooling fan.

    Unless there is a standard, the manufacturer will have measured the efficiency under the best conditions to get a good number. That will probably be at about 70-90% of rated load, and in fairly cool conditions (around 20C)

    In answer to your implied question, I don't think your electricity consumption will increase if you fit a higher rated PSU to a system that does not need it. (unless you use it as an excuse to fit quad SLI graphics cards, and a huge RAID array of power sucking hard discs )


    Quote Originally Posted by Blitzen View Post
    Remember this though!

    If a PSU is rated at 580W, the chance of it actually being able to do that if required is very very slim.

    Its just a peak rate for a split second...then....crash!!!!!
    That depends on the quality of the PSU. Manufacturers like FSP, Targan or Corsair are perfectly capable of making PSUs that will deliver 580W continuously for as long as you want. Such PSUs will set you back £70-100. If you buy a bargain basement '580W' PSU for only £30 or so, then yes, it will blow up, or cause your computer to crash by not providing enough power.

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    Quote Originally Posted by chrestomanci View Post

    That depends on the quality of the PSU. Manufacturers like FSP, Targan or Corsair are perfectly capable of making PSUs that will deliver 580W continuously for as long as you want. Such PSUs will set you back £70-100. If you buy a bargain basement '580W' PSU for only £30 or so, then yes, it will blow up, or cause your computer to crash by not providing enough power.
    Im sorry but have you seen the output figures for the Tagans/Hipers/Lower Antecs?
    You certainly will not get the full rated wattage continously.

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