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Author Topic: How to tell how much Power a PSU is using?  (Read 4880 times)
bboques
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July 21, 2011, 03:06:32 PM
 #1

I have an 850W powering 2 5970s, 3 out of the 4 cores are overclocked, ones just too hot.

If my electric is billed at $0.117 KW/Hour I can find my monthly electric cost by .85 X .117 X 24 X 30 = 71.6
My KW, X electric cost, X hours in a day, X days in a month.

But if I move up to a 1250PSU I can theoretically OC more and get more use from everything, currently my computer freezes at an OC or 900/1000, but are stable at 800/1000.

I am not sure if any additional OC I can do with a 1250W is worth paying $105.3 a month.

Can an increase to a 1250 PSU from a 850 PSU generate enough OC ability to make up for $35/mo in electric?

Any thoughts?

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Xephan
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July 21, 2011, 03:23:42 PM
 #2

I have an 850W powering 2 5970s, 3 out of the 4 cores are overclocked, ones just too hot.

If my electric is billed at $0.117 KW/Hour I can find my monthly electric cost by .85 X .117 X 24 X 30 = 71.6
My KW, X electric cost, X hours in a day, X days in a month.

But if I move up to a 1250PSU I can theoretically OC more and get more use from everything, currently my computer freezes at an OC or 900/1000, but are stable at 800/1000.

I am not sure if any additional OC I can do with a 1250W is worth paying $105.3 a month.

Can an increase to a 1250 PSU from a 850 PSU generate enough OC ability to make up for $35/mo in electric?

Any thoughts?

Only if your OC limit is due to insufficient power manifesting as voltage instability or drops that causes the overclock to fail.

If the issue is with heat or just a lousy batch of GPU, upgrading your PSU won't help.

Lastly, a 850W PSU does not use 850W of power, neither does a 1250W PSU use 1250W of power. They just use whatever is needed by your system / efficiency of their design. So if they are equally efficient, they will use almost the same amount of electricity, with the 1250W actually using a bit LESS.

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CYPER
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July 21, 2011, 11:00:30 PM
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Any power supply loaded to the max will always use around 10% more electricity from the wall.

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trentzb
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July 21, 2011, 11:20:59 PM
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An 80% efficient 850W PSU delivering 850W DC to your system (full load) will draw 1020W AC from the wall and likewise a 90% efficient 850W PSU (same conditions) would draw 935W from the wall.
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July 21, 2011, 11:23:26 PM
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Yeah, any power supply will only draw what it needs to use.  If your components need 400 watts your power supply will draw 400W (Plus any loss through efficiency) from the wall regardless of whether it's a 500W, 800W or 1200W PSU.  

An 850W PSU should be more than enough to run those two cards unless you have some crazy amount of hard drives, etc.  You're likely locking the PC up because the card can't overclock any higher than that.  If you look at the Hardware Comparison Wiki, very few people are clocking those cards past 850 without messing around with the voltage.  Honestly, I suggest you just leave well enough alone and don't mess with the voltage because you can just as easily toast the card.

If you really want to figure out your power draw at the wall, pick up a Kill-A-Watt meter online or at your local hardware store.
bboques
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July 22, 2011, 01:45:34 AM
 #6

Thanks a lot, thats a lot of great feedback. Can a 400W pull additional power to cover many GPUs if needed or it doesn;t work that way?

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Meatball
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July 22, 2011, 01:59:05 AM
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The max rated wattage on a PSU is the max power it can supply to all the peripherals, so if you have 500 watts worth of peripherals a 400W supply will not cut it.  That 400 may actually draw more power from the wall, but the most it can supply is the 400W.  The extra it is drawing from the wall is lost in heat and such and that's where efficiency of power supplies come into play.

Generally it's best to try to get something with at least 10-20% more wattage than you expect you'll be using to give yourself a little bit of headroom.  So if you have 500 Watts worth of stuff you need to run, go with at least a 550-600.
Xephan
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July 22, 2011, 02:57:11 AM
 #8

Thanks a lot, thats a lot of great feedback. Can a 400W pull additional power to cover many GPUs if needed or it doesn;t work that way?

A good quality one can pull above its rated specification to deal with sudden surges. Usually it isn't designed to do that for more than say a few hours or a few minutes, depending how much more you are pulling, before dying on you. So it's NOT a good idea to try that.

A heavily loaded PSU will have a shorter lifespan, so generally it's best not to load it beyond 90%. A rule of thumb load for a decent lifespan is not more than 75%.  PSU also tend to be most efficient around 50~60% so if you push it harder, you will also waste more electricity.

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