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First PC Build - Power Supply Wattage?

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January 24, 2013 2:41:33 AM

Hello all! I'm getting ready for my first PC build. I have already picked out my components and am almost ready to purchase. I just have a few questions regarding power supply wattage. I used some of those PS calculator websites to determine what size PSU to get. I got my results, so here are my questions:

1. How accurate are those power supply calculator websites? Can I trust the results? (I used some from actual PSU manufacturer's websites)

2. My results averaged out to about 720W. What size PSU should I go with? Is 750 enough, or should I move up to an 850? (I have already figured for adding on later; SLI; extra HDDs; another optical drive, etc.)

3. Will it hurt your system having a PSU much larger than you actually need?

I appreciate any and all input. Thank you for your time. :) 
a c 1194 ) Power supply
January 24, 2013 3:20:02 AM

If you're expecting an accurate answer please provide your system configuration.
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a b ) Power supply
January 24, 2013 11:35:01 AM

The estimate of 600W is quite reasonable though I would go with about 750W with that system - the 850W you've picked won't be a problem for sure.
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a c 1194 ) Power supply
January 24, 2013 4:14:58 PM

For a system using two GeForce GTX 680 graphics cards in 2-way SLI mode NVIDIA specifies a minimum of a 750 Watt or greater power supply that has a maximum combined +12 Volt continuous current rating of 53 Amps or greater and that has at least four 6-pin PCI Express supplementary power connectors.

Total Power Supply Wattage is NOT the crucial factor in power supply selection!!! Total Combined Continuous Power/Current Available on the +12V Rail(s) rated @ 45°C - 50°C ambient temperature, is the most important factor.

Overclocking of the CPU and/or GPU(s) will require an additional increase to the combined +12 Volt continuous current ratings, recommended above, to meet the increase in power required for the overclock. The additional amount required will depend on the magnitude of the overclock you are trying to achieve.

The Corsair Professional Series HX850W (SKU# CMPSU-850HX), with its maximum combined +12 Volt continuous current rating of 70 Amps and with six (6+2)-pin PCI Express supplementary power connectors, is way more than sufficient to power your system configuration with two GeForce GTX 680 graphics cards in 2-way SLI mode. This model is now discontinued and has been replaced by the Corsair HX Series HX850 (SKU# CP-9020032).

The HX Series HX750 ( SKU# 75-001218 / CP-9020031 ), with its maximum combined +12 Volt continuous current rating of 62 Amps and with four (6+2)-pin PCI Express supplementary power connectors, is more than sufficient to power your system configuration with two GeForce GTX 680 graphics cards in 2-way SLI mode.

The power supply will only provide as much power as the system needs. Using the CMPSU-850HX as an example:

System power draw: 428 Watts

PSU AC Input at wall outlet: 474 Watts based on 90% AC to DC conversion efficiency at that power draw level.
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January 24, 2013 4:43:04 PM

Best answer selected by sewerslider.
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January 24, 2013 4:45:06 PM

ko888 said:
For a system using two GeForce GTX 680 graphics cards in 2-way SLI mode NVIDIA specifies a minimum of a 750 Watt or greater power supply that has a maximum combined +12 Volt continuous current rating of 53 Amps or greater and that has at least four 6-pin PCI Express supplementary power connectors.

Total Power Supply Wattage is NOT the crucial factor in power supply selection!!! Total Combined Continuous Power/Current Available on the +12V Rail(s) rated @ 45°C - 50°C ambient temperature, is the most important factor.

Overclocking of the CPU and/or GPU(s) will require an additional increase to the combined +12 Volt continuous current ratings, recommended above, to meet the increase in power required for the overclock. The additional amount required will depend on the magnitude of the overclock you are trying to achieve.

The Corsair Professional Series HX850W (SKU# CMPSU-850HX), with its maximum combined +12 Volt continuous current rating of 70 Amps and with six (6+2)-pin PCI Express supplementary power connectors, is way more than sufficient to power your system configuration with two GeForce GTX 680 graphics cards in 2-way SLI mode. This model is now discontinued and has been replaced by the Corsair HX Series HX850 (SKU# CP-9020032).

The HX Series HX750 ( SKU# 75-001218 / CP-9020031 ), with its maximum combined +12 Volt continuous current rating of 62 Amps and with four (6+2)-pin PCI Express supplementary power connectors, is more than sufficient to power your system configuration with two GeForce GTX 680 graphics cards in 2-way SLI mode.

The power supply will only provide as much power as the system needs. Using the CMPSU-850HX as an example:

System power draw: 428 Watts

PSU AC Input at wall outlet: 474 Watts based on 90% AC to DC conversion efficiency at that power draw level.




Thank you for the abundance of information you provided. I appreciate you taking the time to help answer my questions.
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