Do we (nearly) all use totally oversized power supply units ? - Hardware

This is a discussion on Do we (nearly) all use totally oversized power supply units ? - Hardware ; Recently I bought a power device for measuring the real power needed by a computer. I put this measuring device just between the computers power cable and the power plugin in the wall. After some days of measuring I was ...

+ Reply to Thread
Results 1 to 8 of 8

Thread: Do we (nearly) all use totally oversized power supply units ?

  1. Do we (nearly) all use totally oversized power supply units ?

    Recently I bought a power device for measuring the real power needed by a computer.
    I put this measuring device just between the computers power cable and the power plugin in the wall.

    After some days of measuring I was really surprised.

    My computer (AMD Athlon XP 64 + PCIexpress) need on average 82 Watt!
    Maximum during these days was 112 Watt.

    So why do I need a 350 power supply unit in my computer?
    Moreover 350W - 400W seems to be the standard.

    When one take into account that the power supply unit operates most efficently only
    when its is near to full capacity then it seems to me that all these 350W power supply units
    are completely oversized.

    150W would be sufficient.

    All these gamers which run a high level video/graphic cards could buy a 400W PSU.

    But for the "normal" office user this is bull ****.

    Am I right ? Or what is the reason for these high capacity PSU ?

    Jason


  2. Re: Do we (nearly) all use totally oversized power supply units ?

    Jason Stacy (jjstacy@yahoo.net) writes:
    > Recently I bought a power device for measuring the real power needed by a computer.
    > I put this measuring device just between the computers power cable and the power plugin in the wall.
    >
    > After some days of measuring I was really surprised.
    >
    > My computer (AMD Athlon XP 64 + PCIexpress) need on average 82 Watt!
    > Maximum during these days was 112 Watt.
    >
    > So why do I need a 350 power supply unit in my computer?
    > Moreover 350W - 400W seems to be the standard.
    >
    > When one take into account that the power supply unit operates most efficently only
    > when its is near to full capacity then it seems to me that all these 350W power supply units
    > are completely oversized.
    >
    > 150W would be sufficient.
    >
    > All these gamers which run a high level video/graphic cards could buy a 400W PSU.
    >
    > But for the "normal" office user this is bull ****.
    >
    > Am I right ? Or what is the reason for these high capacity PSU ?
    >
    > Jason
    >

    It likely costs as much to make a lower current power supply as the higher
    current ones. There is a certain amount of overhead that is needed in
    terms of parts whether no matter what the wattage, and the cost of the
    parts will be a small increment to provide that higher wattage.

    On the other hand, you aren't drawing more current just because the power
    supply can supply it. So it's not as if having a higher wattage supply
    is an ongoing cost.

    It's always easier to have backup than failure. Start with a higher
    wattage supply, and you won't have to fuss if you start adding a lot
    of boards, but if you start adding boards you may have to worry if
    you started out with a lower wattage supply.

    Michael



  3. Re: Do we (nearly) all use totally oversized power supply units ?

    jjstacy@yahoo.net (Jason Stacy) writes:

    > Recently I bought a power device for measuring the real power needed
    > by a computer. I put this measuring device just between the computers
    > power cable and the power plugin in the wall.
    >
    > After some days of measuring I was really surprised.
    >
    > My computer (AMD Athlon XP 64 + PCIexpress) need on average 82 Watt!
    > Maximum during these days was 112 Watt.
    >
    > So why do I need a 350 power supply unit in my computer? Moreover
    > 350W - 400W seems to be the standard.
    >
    > When one take into account that the power supply unit operates most
    > efficently only when its is near to full capacity then it seems to me
    > that all these 350W power supply units are completely oversized.
    >
    > 150W would be sufficient.
    >
    > All these gamers which run a high level video/graphic cards could buy
    > a 400W PSU.
    >
    > But for the "normal" office user this is bull ****.
    >
    > Am I right ? Or what is the reason for these high capacity PSU ?


    The rated power on a power supply is the total of all the outputs. It
    is quite easy to reach the limit of, say, the 3.3V output while having
    plenty to spare on -12V.

    Replacing a ~300W PSU with a 450W (I think) stopped a machine I had
    from crashing fairly reliably any time the CD drive and two or more
    hard drives were accessed at the same time.

    The peak power used any part in a computer is *much* higher than the
    average. You want some headroom in your power supply to survive if
    several parts should happen to peak at the same time. It is quite
    possible that your machine never reached its peak power usage during
    your test period.

    --
    Måns Rullgård
    mans@mansr.com

  4. Re: Do we (nearly) all use totally oversized power supply units ?

    et472@FreeNet.Carleton.CA (Michael Black) writes:

    > Jason Stacy (jjstacy@yahoo.net) writes:
    > >
    > > When one take into account that the power supply unit operates most efficently only
    > > when its is near to full capacity then it seems to me that all these 350W power supply units
    > > are completely oversized.

    >
    > On the other hand, you aren't drawing more current just because the power
    > supply can supply it. So it's not as if having a higher wattage supply
    > is an ongoing cost.


    I've snipped a lot above, to point out that the OP made a claim that
    power supplies are in fact more efficient when used near their rated
    maximum -- which I would take to mean that in fact a lower-capacity
    power supply would indeed be drawing less current than a
    higher-capacity supply (until it failed). I have no way of evaluating
    the claim, but it's important to note it.

    > It's always easier to have backup than failure. Start with a higher
    > wattage supply, and you won't have to fuss if you start adding a lot
    > of boards, but if you start adding boards you may have to worry if
    > you started out with a lower wattage supply.


    This is certainly true. I've never had a computer with a power supply
    that was too big, nor a disk drive with too much capacity, nor a car
    with an engine that was too big (and my Newport has a 400 CID V8).

  5. Re: Do we (nearly) all use totally oversized power supply units ?

    Joe Pfeiffer wrote:
    >et472@FreeNet.Carleton.CA (Michael Black) writes:
    >
    >> Jason Stacy (jjstacy@yahoo.net) writes:
    >> >
    >> > When one take into account that the power supply unit operates most efficently only
    >> > when its is near to full capacity then it seems to me that all these 350W power supply units
    >> > are completely oversized.

    >>
    >> On the other hand, you aren't drawing more current just because the power
    >> supply can supply it. So it's not as if having a higher wattage supply
    >> is an ongoing cost.

    >
    >I've snipped a lot above, to point out that the OP made a claim that
    >power supplies are in fact more efficient when used near their rated
    >maximum -- which I would take to mean that in fact a lower-capacity
    >power supply would indeed be drawing less current than a
    >higher-capacity supply (until it failed). I have no way of evaluating
    >the claim, but it's important to note it.


    It isn't generally true to a degree that is economically
    significant. You might save $2 worth of electricity over a 5
    year lifespan... :-)

    There were a couple of basic misperceptions in the OP's
    analysis. One is that the average/peak AC power draw shown by
    his measuring equipment had any relation to the required rating
    of the power supply.

    Consider that each voltage rail has to be able to supply some
    particular maximum power on a continuous basis, and some other
    specific peak power as a surge for some specified (limited)
    amount of time. The total power rating of the supply is the sum
    of *all* of the maximum ratings for the various voltage rails.
    But it will be a very rare occurrence that any two of those
    voltage rails will be required to supply a surge at the same
    time.

    If there were only two voltages supplied, the observed AC peak
    power surge would be half the actual peak capability used by the
    supply over any given interval! And of course the supplies we
    are talking about have several different voltages and usually
    multiple rails for some voltages. Hence the measured AC peak
    power indicates the power rating required for only one or maybe
    two of the voltages. Subtract the average from the peak, and
    then multiply that by the number of individual voltage rails the
    supply provides, and add it to the average power draw to get an
    estimate of the required maximum power... (Not that it is
    accurate enough, but the example demonstrates why the OP's
    results were off by several multiples of the difference between
    average and peak power draw.)

    The point of course is that measuring the peak AC power input is
    really of no value in determining the appropriate size of the
    required supply.

    --
    Floyd L. Davidson
    Ukpeagvik (Barrow, Alaska) floyd@apaflo.com

  6. Re: Do we (nearly) all use totally oversized power supply units ?

    Jason Stacy wrote:

    >
    > Am I right ? Or what is the reason for these high capacity PSU ?
    >


    Some power units may seem over sized. But did you measure current
    drain during start-up of the machine?

    Disks may require during spin-up from 4 to 6 time the power they use
    during normal read/write operations and from 10 to 15 time the power
    they use when idle.

    The same is true for CD/DVD units. Writing requires a lot of power.

    And also the drain of the CPU itself varies in a wide range depending
    on the load.

    Ciao
    Giovanni
    --
    A computer is like an air conditioner,
    it stops working when you open Windows.
    Registered Linux user #337974 < http://giovanni.homelinux.net/ >

  7. Re: Do we (nearly) all use totally oversized power supply units ?

    jjstacy@yahoo.net (Jason Stacy) writes:
    >Recently I bought a power device for measuring the real power needed by a computer.
    >I put this measuring device just between the computers power cable and the power plugin in the wall.
    >
    >After some days of measuring I was really surprised.
    >
    >My computer (AMD Athlon XP 64 + PCIexpress) need on average 82 Watt!
    >Maximum during these days was 112 Watt.
    >
    >So why do I need a 350 power supply unit in my computer?


    Maybe you don't. But if you expand your conputer, you might.

    >When one take into account that the power supply unit operates most efficently only
    >when its is near to full capacity


    That is not generally true. Looking at the power supply test in c't
    24/2006, I see that the tested power supplies have 71%-83% efficiency
    at 20% load, 76%-86% efficiency at 50% load, and 72%-82% at full load.

    If you strive for efficiency, it's more important to get an efficient
    power supply than one that is more than 50% loaded. BTW, if you shop
    around for a new power supply (especially a tightly sized one), look
    up at which voltage your motherboard consumes the most power, and
    check how much power the PSU can deliver at that voltage.

    >150W would be sufficient.


    Maybe. A few stories:

    - We recently bought a Dual-Xeon server. Our vendor could not get it
    to boot with a 600W (IIRC) power supply, so this machine got an 800W
    PSU. The highest power consumption that we measured on this machine
    is 423W.

    - My computer has a 350W power supply, like yours. It used to consume
    up to 180W, and its PSU was sufficient for that. So for your 112W,
    you probably can use something smaller, if you can get it.

    - Several years ago a friend of mine bought a broken Elitegroup
    motherboard for an Athlon or Duron system. He's the kind of person
    who never does returns; instead, he tinkered around with various
    combinations of CPUs, RAMs, and PSUs, and he did get this board to
    run with exactly one PSU, a ridiculously small one (IIRC 125W); with
    the stronger power supplies it failed.

    Followups set to comp.os.linux.hardware

    - anton
    --
    M. Anton Ertl Some things have to be seen to be believed
    anton@mips.complang.tuwien.ac.at Most things have to be believed to be seen
    http://www.complang.tuwien.ac.at/anton/home.html

  8. Re: Do we (nearly) all use totally oversized power supply units ?


    >
    > This is certainly true. I've never had a computer with a power supply
    > that was too big, nor a disk drive with too much capacity, nor a car
    > with an engine that was too big (and my Newport has a 400 CID V8).


    I have. I recall the Studbaker Lark V8 - it WAS overpowered.


+ Reply to Thread