PSU Effiency, Power Consumption and Overestimation

Hello

I'm just wondering, when a power supply is 80+ certified, and 80% + efficient, does that mean for example, a 500W PSU on average delivers 450W? (80% of 500W)

Or does it instead need to take 600W from the wall to deliver 500W?
If so, how is efficiency measured?
E.g., in my example, 100% of 500W PSU = 600W or is it instead 80% of 600W = 480W PSU,

What is the easiest way to determine the total system wattage consumption? At first I thought T.D.P. measured how much energy a component uses, but it's related to heat dissipation isn't it?

With power consumption and PSU efficiency in mind, does this mean that many people tend to overestimate their PSU requirements? I bought an 850W PSU for an i7, a DVD drive, an HDD + a relatively power-efficient graphics card. I'm pretty sure 850W was overkill, but just to make sure just incase I'd be SLI-ing or CFX-ing, or adding more drives.

Also, I tend to see PSUs only having 80+ efficiency between 20% - 100% load. Does that mean that if you buy a 1000W PSU, and only use say 150W while idling, it wouldn't be as efficient had you bought a 500W PSU?

Thanks :)
4 answers Last reply
More about effiency power consumption overestimation
  1. Lmeow said:
    Hello

    I'm just wondering, when a power supply is 80+ certified, and 80% + efficient, does that mean for example, a 500W PSU on average delivers 450W? (80% of 500W)

    Or does it instead need to take 600W from the wall to deliver 500W?
    If so, how is efficiency measured?
    E.g., in my example, 100% of 500W PSU = 600W or is it instead 80% of 600W = 480W PSU,

    What is the easiest way to determine the total system wattage consumption? At first I thought T.D.P. measured how much energy a component uses, but it's related to heat dissipation isn't it?

    With power consumption and PSU efficiency in mind, does this mean that many people tend to overestimate their PSU requirements? I bought an 850W PSU for an i7, a DVD drive, an HDD + a relatively power-efficient graphics card. I'm pretty sure 850W was overkill, but just to make sure just incase I'd be SLI-ing or CFX-ing, or adding more drives.

    Also, I tend to see PSUs only having 80+ efficiency between 20% - 100% load. Does that mean that if you buy a 1000W PSU, and only use say 150W while idling, it wouldn't be as efficient had you bought a 500W PSU?

    Thanks :)

    http://www.hardwaresecrets.com/article/181/9
  2. Well thanks a lot, that pretty much explained all I needed to know about efficiency, but how about tools to measure system watt consumption?
  3. Are you wanting to physically measure your PC powerdraw at the socket..

    http://www.maplin.co.uk/Module.aspx?ModuleNo=38343&C=SO&U=strat15

    Or do you want to know your PC power requirements

    http://extreme.outervision.com/psucalculatorlite.jsp

    If this answer helps, please select best answer
  4. You can use something like the Kill-a-watt to measure power at the wall, then use the efficiency curve to calculate how much power the system uses.
    http://www.newegg.com/product/product.aspx?Item=N82E16882715001
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