PSU power consumption
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From: yaro137 on 5 Feb 2010 05:58 If my PSU is 500W does it actually mean that when my computer is on it takes 500W all the time? yaro
From: SC Tom on 5 Feb 2010 07:44 "yaro137" <yaro137(a)googlemail.com> wrote in message news:1657ef93-f150-4bc3-a7be-1e54107bf8f1(a)f15g2000yqe.googlegroups.com... > If my PSU is 500W does it actually mean that when my computer is on it > takes 500W all the time? > yaro No, it means it will provide up to 500 watts if necessary. -- SC Tom
From: Paul on 5 Feb 2010 12:56 yaro137 wrote: > If my PSU is 500W does it actually mean that when my computer is on it > takes 500W all the time? > yaro The power supply *transforms* the power, so only draws as much power as is needed to power the load. If you connect a 12V 1 amp light bulb to the output of the power supply, the power supply in turn will draw 12 watts of power from the AC wall outlet. The power supply is not 100% efficient, so in the process of transforming the power, some is lost as heat. The worst ATX power supplies might be 68% efficient. For the 68% efficient supply, it will draw 12W / 0.68 = 17.6W So if the power supply powers a 12W light bulb, it draws 17.6W from the wall. As SC Tom points out, the "500W" is the overall limit, as to how much power it is capable of transforming, without damage. Above 500W loading, the power supply will shut off to protect itself. A typical modern computer now, suitable for office work, might have an internal load of 100W. With the 68% efficient supply, that computer will draw 147W from the wall. 47W of heat will be emitted by the power supply directly (which is why the power supply has a fan on it for cooling). The other 100W of heat is dissipated inside the computer cabinet, which is why the computer cabinet must have a cooling fan to help it stay cool. A good reality test of this, is to ask the question, "how much heat is pouring out of my computer". Do you feel 500W of heat coming out of the computer ? Or is the level of heat consistent with 150W of heating ? Reality tests like that, are great for confirming any theories you might have. At least "feeling the heat", doesn't cost you any money for test instruments. You can buy a meter like this, to measure the consumption of the computer. This is another way to confirm it is drawing 147W. http://www.p3international.com/products/special/P4400/P4400-CE.html The consumption of the computer changes with the activities the computer is doing. If you start rendering a DVD movie with software, the computer may draw 50W more than it would draw when idle. In the idle state, the computer may have features to help drop the power consumption. So when I give the "147W" example above, the actual power changes from moment to moment, and maybe 147W would be a long term average. Paul
From: Anteaus on 6 Feb 2010 06:33 Might be of interest that the power-consumption figures given on most consumer devices are wildly inaccurate. Usually on the high side. A few tests with a wattmeter some years ago suggested that a typical desktop system-unit might draw 150W, not including display. Laptops are typically around 50W when mains-powered and maybe 30W when in low processor-speed mode on battery. So if you want to save power, use a laptop. As for the PSU, you can only draw 500W if all outputs are fully loaded. If you drew 500W from (say) the 5V rail alone, you would cook it. At that, the 500W rating is an absolute max, and for a reasonable life expectancy you should not expect it to run at that level continuously. A 500W (max draw) PSU is suitable for an typical desktop, for a server or graphics workstation I'd look at 750W or 1kW. "yaro137" wrote: > If my PSU is 500W does it actually mean that when my computer is on it > takes 500W all the time? > yaro > . >
From: yaro137 on 8 Feb 2010 04:57
Thanks guys for the detailed explanation. That was very helpful indeed. yaro |