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Electricity usage of a 1200w Power supply

By XZR ยท 5 replies
Feb 10, 2010
  1. I'm planning to add a 1200W PSU, just mainly to future proof it, I don't think I would need that much, probably use only about 700w.

    I do plan on having 2x 5870 radeon cards in crossfire
    sound card
    5-1 memory card readers
    etc etc

    but I'm worried about the power bill.. Will having a 1200w power supply but only using 700w give me a huge bill?

    or it wont be any different to a lets say 850w Psu?

    Thanks guys
  2. Archean

    Archean TechSpot Paladin Posts: 5,690   +95

    Forget about the bill; why go for such an overkill? Because in few years time the PSU will degrade anyway; and you may end up having to replace it.
  3. jobeard

    jobeard TS Ambassador Posts: 10,432   +801

    The capacity of the PSU is quiet different than the 'current usage'.

    The 1200W rating only says what the limit is than can be used safely.
    The actual will be Line Voltage X Current Drawn.

    The max(1200w) would be reached with a line supply of 120v @ 10amps draw.
    Your current draw can be measured or at least estimated by adding the requirements of
    the components.
  4. captaincranky

    captaincranky TechSpot Addict Posts: 12,509   +2,300

    I would argue that if you can afford all that crap in the first place, it seems trivial to worry about the electric bill.

    As with all things PSU related, the brand of the PSU speaks to whether or not it will deliver its rated capacity, or if it's just a "fairy tale" from the marketing department.

    Other than that, jobeard is correct that the line draw would profile the cumulative draw of your components, save for the fact you would need to add another calculation to compensate for the efficiency of the PSU itself.

    Thus, if you have 300 watts of computer hardware, the PSU would draw perhaps 400 watts from the line, at the average efficiency of 75%.

    There is the fact that even if you have components requiring say 500 watts at 100% activity, the average draw would be much lower, perhaps even idling on the desktop at only 200 watts.

    Usually, it is considered "nominal" to load the PSU to about 70% of its total claimed output. Here again, a 300 watt system draw would call for a PSU of about 400 watts
  5. SNGX1275

    SNGX1275 TS Forces Special Posts: 10,729   +409

    There won't be any difference in your power bills provided the 1200 and the 850 if they are the same efficiency. As others have noted, they are only going to pull from the wall what they need for the components. So in summary a 1200W PSU isn't pulling 1200W from the wall continually, it is only capable of pulling 1200W if necessary.
  6. compdata

    compdata TechSpot Paladin Posts: 529   +7

    If you want to know your expected power bill you need to know an average watts that your system is going to pull - this is some fraction of your maximum and is dependent on your usage and if the computer is on all the time or not.

    Power bill = Average Wattage/1000 (gives you kilowatts) * 720 (hours in 30 day month) * $.10 (or your kilowatt/hour rate).

    My guess is you will average ~ 300 Watts (includes idle & off time) which would give you a monthly bill from your computer of ~$21. This is a small fraction of what you are spending on the PC in the first place.
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