Does the higher wattage psu use more current when they idle?

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paulcheung

Active Member
Hi all,
I am wonder, do the higher wattage psu use more power when they idling? Said I have a 1200w psu and a 600w. when both of them using 450watts, does the 1200 use more current than the 600watt?
Thank you.
 
They only use as much as the system needs. A 1200 watt will not use any more then the 600.
 
As john said. Efficiency will play a part in actual power draw from the socket as well.

If your system needs 500W and the PSU is 80% efficient at that load, you'll be pulling 600W from the socket (if my math is correct)
 
linkin said:
As john said. Efficiency will play a part in actual power draw from the socket as well.

If your system needs 500W and the PSU is 80% efficient at that load, you'll be pulling 600W from the socket (if my math is correct)
Click to expand...

Your mathS isn't correct, it would be 625W
 
In that case we should get as high wattage PSU as possible if one can afford, but why alot times people are been advised to buy the lower wattage PSU?
Thank you.
 
You need a PSU that is matched to your system. Efficiency is important, but not worth purchasing gold over silver etc, because its false economics. The main issue is 12V rail stability and design. Consider the amps required and if the PSU can deliver it. Higer wattage means little if its not on the 12V rail and with ripple.
 
paulcheung said:
Hi all,
I am wonder, do the higher wattage psu use more power when they idling? Said I have a 1200w psu and a 600w. when both of them using 450watts, does the 1200 use more current than the 600watt?
Thank you.
Click to expand...
Simple answer NO
 
paulcheung said:
In that case we should get as high wattage PSU as possible if one can afford, but why alot times people are been advised to buy the lower wattage PSU?
Thank you.
Click to expand...
Does not make sense to buy something at higher cost and not utilizing it 100% hence people advised to buy what is actually suitable at an economical price....
 
Power supplies do have different efficiencies at different load values.

In other words, a 625W PSU may be 85% efficient at 50% load, but when running at only 20% load, its efficiency may drop to 65%.

Also, published efficiencies are calculated and testing is done under lab conditions (a PSU operating in a 10° C room will have better efficiency than the same unit running inside a 30° C computer case)

Your best bet would be to get something that monitors actual line usage and test the two power supplies in question to see which would be better.
 
MMM said:
Does not make sense to buy something at higher cost and not utilizing it 100% hence people advised to buy what is actually suitable at an economical price....
Click to expand...

True, but if the price is not to far, it is better to get something a bit more than it actual usage, atleast it will give more room to play with if upgrade is required; but if it is use more current then it will cost too much to run as power bill run continueously compare to one time initial cost.
Why I ask is because we have a very costly electricity supply.
Thank you.
 
Only very rubbish PSU's will have a 65% efficiency on any load profile nor tested at 10oC. In fact most if not all cheap PSUs are tested at 25oC as a standard. Corsair and others however will test at 40oC. Also,y ou never want to run a PSU at or near 100%.

Estimate or measure your max wattage, and then divide it by 12 to get your required amps on the 12V rail (estimate). Then buy a PSU that has 80+ efficiency on that wattage/amperage with an additional 20-30% for capacitor ageing.

For example,

Measured max power draw from the wall is 400W. Purchase a PSU with 30A or more on the 12V rail. Get yourself a 550W PSU that has the best efficiency at around 80% load. Therefore you are not paying for wattage you don't need and will be running on or around the best efficiency. Getting silver or gold is not worth the premium, even with expensive electricity unless you are running a 1KW beast.
 
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