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PSU power consumption, to install or not...

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February 19, 2013 5:48:16 PM

General question on how psu's work...

I am planning on upgrading my gpu from a 6670 to a 7850 (or an 8000 series if i can be patient for a few months). This will of course neccesitate a new psu.

I already ordered a 600w psu to replace the 380w that came with the factory built pc in anticipation of a new gpu.

If I install the 600w psu with all the other components staying the same, does that mean my pc will draw more power?

-or-

Or will it just mean I have more power available, and I won't have any noticeable difference in my power usage until I install new components that use the power?

If no difference I would install the new psu right away, otherwise, will probably wait until I need it. Thoughts?
a c 1175 ) Power supply
February 19, 2013 6:05:49 PM

What's the brand and model of the old PSU?

What is the brand and model of the new PSU?

The power draw at the AC power outlet will only be what the system needs plus the AC-to-DC conversion efficiency losses.

If the system only needs 250 Watts and the PSU has a conversion efficiency of 82% at that power draw level then you should be able to measure a power draw of 305 Watts at the power supply's AC wall plug.
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February 19, 2013 6:17:05 PM

The old one is whatever (probably) garbage Dell puts on their XPS machine, and the new on is a Corsair (don't remember model, but it's 80+ Bronze).

So what your saying is, I could theoretically install something ridiculous like a 1500w psu, and as long as my components are the same, the power drawn (and I imagine heat produced) wouldn't change, all things being equal with the original components?
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a c 1175 ) Power supply
February 19, 2013 7:48:18 PM

jcharger said:
The old one is whatever (probably) garbage Dell puts on their XPS machine, and the new on is a Corsair (don't remember model, but it's 80+ Bronze).

So what your saying is, I could theoretically install something ridiculous like a 1500w psu, and as long as my components are the same, the power drawn (and I imagine heat produced) wouldn't change, all things being equal with the original components?

The power supply with the higher efficiency at that power draw level would draw less power at the AC plug and also produce less heat.

A power supply has poor conversion efficiency at low (i.e. less than 20% of the PSU's rated capacity) power draw levels.

If we use your example of a 1500W PSU and a system power draw of 150 Watts and if the 1500W PSU's efficiency is 75% at a 10% load then the power draw at the AC plug should be 200 Watts.

The same power draw with a 600 Watt PSU if its efficiency is 83% at 25% load level would result in 181 Watts at the AC plug.
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