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Electricity usage of a 1200w Power supply

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February 10, 2010 9:42:05 AM

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
February 10, 2010 9:47:16 AM

No difference. The PSU will only output whatever the system needs. In fact, if it has "80 PLUS" or anything similar, it will actually *lower* your bill, compared to a PSU without the 80 PLUS certification.
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February 10, 2010 10:17:02 AM

Gracefully is mostly right, the power output of your supply is determined by what your computer needs you give an example of 700W (which is a lot!) is the power supply is 80% efficient it will take around 875W of input to provide 700W of output.

To complicate things a little further, most power supplies vary in their efficiency depending on how hard you push them, so yours may be 80% efficient at 80% capacity, but only 70% efficient at 60% capacity. So in answer to your second question, yes, there is a difference betweeen an 850w and a 1200W supply.
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February 10, 2010 10:29:33 AM

so if my system only use 750w, is it better off buying a 850w or a 1200w? in terms of electricity usage, or theres no big difference in either?
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February 10, 2010 12:07:36 PM

PSU makers suggest that you don't max out or nearly max out your PSU load. Try to keep the load below 70% of your PSU's rating. For example, with an 850w PSU, try to keep the load below 600w. You can check out some graphs which show the efficiency of PSUs when you put them at 20, 50, and 100% load. You will see that the efficiency usually peaks at around 50%.

EDIT: For your planned setup, I suggest you go with a 1000W PSU. If you can, go get the ones with "80 PLUS Bronze/Silver/Gold" certifications, as those are the most efficient PSUs. Gold is the highest, followed by Silver, then Bronze, then simply "80 PLUS". The higher-efficiency models are more expensive, but they might pay for themselves in the long run with their power savings.
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a b ) Power supply
February 10, 2010 5:22:34 PM

Ref: (PS appears pretty accurate based on my system (I750 @ 3.2 w/5770, 2 HDDs and 2 DVD drives) as measured at my wall. Also agrees pretty close to the chart I orginally looked at, but could not relocate.
http://www.tomshardware.com/reviews/radeon-hd-5850,2433...

Alot depends on usage, that is how much time do you spend at full load vs light load, Do you power on/off or do you leave the system on 24/7

I would recommend a GOOD 850 watt supply vs the 1KW. As stated 80% min eff.

At idle you will have about 170 Watts (170/850 = 20 %) This is one of the deciding factors I use as recommended min is 20%).

At max load you will see about 560 Watts. 560/850 = 66 % - also good.

As previous posters have said, little diff, but at the end of the day the 850 will cost you less (not a lot) than a 1KW.

I would not go above the 1 KW as for the cost jumps considerablity for the SAME quality. Same applies for the jump from 850 -> 1KW, but not as great.
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a b ) Power supply
February 10, 2010 8:57:10 PM

XZR said:
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


Future proof?...as technology advanced and progress its efficiency increases making components more powerful yet using less electricity and producing less heat...you will never need a 1200watt PSU unless you have a i7 975 w/ 2 ATI 5970's and a bunch of hard drives and you overclock the juice out of everything. Your PSU will only take as much as it needs/ your system requires to power it, it doesn't matter if you have a 1000000watt psu or a 1000watt psu, if you system needs 500watts the PSU will only pull 500watts however efficiency between PSU's varies so the power can be + or - the required amount.
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a c 248 ) Power supply
February 13, 2010 9:08:52 AM

Here are the official power requirements for the ATI Radeon HD 5870 video cards.


ATI Radeon™ HD5870 System Requirements:

PCI Express® based PC is required with one X16 lane graphics slot available on the motherboard.

500 Watt or greater power supply with two, 75 watt, 6-pin, PCI Express® power connectors.

600 Watt or greater power supply with four, 75 watt, 6-pin, PCI Express® power connectors for ATI CrossFireX™ technology in dual mode.

The power supply recommendations are for an entire pc system.

There is a big push in the corporate/mainstream communities for more energy efficient pc's. ATI is developing video cards that require less power instead of more.
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October 27, 2012 7:53:35 AM

XZR said:
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


My dilemma is that I can get a 1200W psu on sale for the same price of a 850W, same brand. I figured my system only needs a little lesd than 700W so far, single gpu config.. Is it wiser to go with the 850W? It's only the 1200W which I can get on sale, so 1000W is not an option ;) 
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October 27, 2012 8:14:31 AM

deleted ..
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a c 110 ) Power supply
October 27, 2012 8:22:21 AM

2 year old thread guys..... :ange: 
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October 27, 2012 8:28:45 AM

bah, who dug this crap up ...
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August 10, 2013 11:23:43 AM

lol it is 2 years old
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