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my friend asked me a questions how much kWh he would get per day around if he is going to buy a power suply that is 1200W and place in the system and system would use 950W as he said http://www.newegg.com/Product/Product.aspx?Item=N82E16817153145 his power suply I really hope you are able to help me :/

Driglou
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  • Please do try to write in a way that makes the question readable! Anyway, to get the kWh number, you multiply the power with the time period during which you'll be consuming power. – AndrejaKo Dec 20 '13 at 15:33
  • Kilowatt-hours = kilowatts * hours – John U Dec 20 '13 at 15:37
  • What does the 950W represent, is it the mains power (PSU input) or the power consumption in the output of the PSU? – alexan_e Dec 20 '13 at 17:13
  • @Chetan I disagree about this being a duplicate; this question is about calculating total power consumed in 24 hours, not selecting an appropriate power supply. That said, it would be beneficial for the OP to read the proposed duplicate target. – JYelton Dec 20 '13 at 19:22
  • @JYelton sure, that's why the words "possible duplicate". Not sure why "just flagging" creates a comment. Thanks. – Chetan Bhargava Dec 20 '13 at 20:43

2 Answers2

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You don't need to factor in the 90% efficiency. You would have to if the 950W was what the CPU, GPU, etc consumed, but here the 950W is what goes into the system, and then the power supply's efficiency is already included.

So

\$ 950W \times 24h = 22.8 kWh \$

Multiply by the cost of 1 kWh your power utility charges you, and you know what the system costs you per day.

Samuel
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flup
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    I disagree, the GPU, CPU etc consumption is on the 5v/12v power lines, the conversion efficiency comes into play for the actual PSU that has to convert the 220v mains to lower voltages , that is the point where you get about 85% efficiency. – alexan_e Dec 20 '13 at 16:58
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    @alexan_e If the system consumes 950W, then that's what it takes from the grid. If the PSU is 85% efficient, then the electronics will consume 807 watt. 807 W / 0.85 = 950 W – flup Dec 20 '13 at 17:06
  • It depends on what the OP meant when he said 950W consumption, seems to me that he meant the consumption on the low voltage power lines but if he meant 950W on the mains line then you are correct. The specification as given is not very clear. – alexan_e Dec 20 '13 at 17:10
  • @alexan_e Come on! The power consumption at the low voltage level can't even be measured easily. If they want to know that they measure the power into the supply and multiply by the PSU's efficiency, like I calculated. How on earth are you going to measure the power consumption for each component? Overmore, nobody cares about that. What people care about is their electricity bill. – flup Dec 20 '13 at 17:14
  • This is up to the OP to say, but until he says specifically where the 950W refer to it can be either way, it's as simple as that. – alexan_e Dec 20 '13 at 17:31
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The link doesn't work for me. However, the 1200W rating of the power supply tells us the maximum average power that it can supply. The psu does not continuously consume 1200W, unless required to by the system.

The average power requirement of your friend's system is 950W, so it is less than 1200W. Assuming that the power supply is 90% efficient, the system will consume, roughly: $$ \frac{950 \text{W}}{0.9} \cdot 24\text{h} = 25333\text{Wh per day} $$

Alex Pacini
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any1
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  • i updated the link – Driglou Dec 20 '13 at 16:47
  • 1200W does not necessarily tell you what the PSU can supply, it may tell you its maximum input power requirement. Internal losses may mean it outputs less than that at peak. Or, it may be that 1200W is indeed its max output, which would make its input higher than 1200W. – John U Dec 20 '13 at 20:05
  • John, due to incompleteness of the question assumptions had to be made for sake of keeping the answer short. – any1 Dec 20 '13 at 20:15