Does a bigger PSU = More power usage?

DTN107

DTN107

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So two of my friends are debating about power supplies.

One guy says if someone upgrades from a 500W PSU to a (lets say) 750W PSU his power bill would go up since it uses more power.

The other guy says it doesn't even touch the extra power so its power usage shouldn't go up.

I never really thought about this so I couldn't answer their questions.

But lets say if someone had a decent computer with an Antec 500 earthwatt and upgrades or a 750 earthwatt version. Would that person's power usage go up? Or would they have just extra head room?

Also a question for myself. Would the 750 earthwatt run cooler than the 500 earthwatt version when powering the exact system. I like to think so but would like someone to confirm me.
 
Efficiency is the only thing that makes a difference in power usage. If a 500w and 1kw power supply have the same efficiency at a given load, then the power usage will be the same. It's possible for a higher wattage power supply to draw less power from the wall than a lower wattage one actually.
 
Power usage depends on what the system actually uses combined with the efficiency of the PSU in question. For a modern APFC PSU efficiency is between 80-90%, which doesn't mean a huge difference in power usage at the outlet.

How warm a PSU runs depends mostly on how the fan cooling profile is configured. Some have the fan hardly spinning until the PSU hits 50-60C, others have a more gradual curve. You can see this in good PSU reviews, like here at [H]ardOCP, or JonnyGuru.com.
 
Blue Fox said:
Efficiency is the only thing that makes a difference in power usage. If a 500w and 1kw power supply have the same efficiency at a given load, then the power usage will be the same. It's possible for a higher wattage power supply to draw less power from the wall than a lower wattage one actually.
Click to expand...

I compleatly agree that the power usage and efficiency makes a difference. And Power usage of the PC is not affected by PSU wattage, so it will not matter which PSU one uses. If PC uses 200W then it will not matter which PSU. Efficincy on the other hand will determine the final power draw form the wall socket. More effiencient PSU it will need to take less from wall to achieve the system's required 200W.
 
The components in your PC draw a certain amount of power which is irrelevant of the PSU. The PSU then has an efficiency of converting the current from the wall to usable current for the PC. Basically blue fox is right, and the efficiency is really determined by the quality of the kit, that doesn't necessarily scale with wattage.
 
yeah I mean, in the way your friend is implying the bill wont change: a 750W PSU is going to draw ~ as much current at a given load as a 500W PSU, assuming their both of the same efficiency.

But pretty well all power supplies adhere to this curve peaking at somewhere between 30% and 60%, meaning by changing power supplies you might be pushing your efficiency up or down depending on where you were on that bell curve in the first place --certainly with a more powerful power supply, when that system is putting a big load on the PSU (eg gaming), the bigger the PSU, the closer you are to its peak efficiency.
 
Everything said here is correct, but remember that PSUs do not have the same efficiency at all loads. So let's say your rig draws 400W and you have a 500W psu and a 750W psu. The 500W psu is operating at 80% of maximum load and the 750W is operating at 53% load. It is entirely possible (and likely if comparing two PSUs of the same brand/model) that the 750W is more efficient (and draws less power) at 53% load than the 500W is at 80% load.

You want to do the research on how much power your rig draws and then find a quality made psu that will be operating at its highest efficiency point given the load your computer will put on it.

OR you could just not worry about it because we're probably talking $1-3 difference over the course of a year.
 
your pc will only draw what it needs from the psu irrespective if your psu is rated 500 or 750 watts, but efficiency does come into play.80%+ rated models have various levels and mostly the difference from highest to lowest is not very significant in terms of totals saved during the usual ownership life cycle
 
ryken said:
Everything said here is correct, but remember that PSUs do not have the same efficiency at all loads. So let's say your rig draws 400W and you have a 500W psu and a 750W psu. The 500W psu is operating at 80% of maximum load and the 750W is operating at 53% load. It is entirely possible (and likely if comparing two PSUs of the same brand/model) that the 750W is more efficient (and draws less power) at 53% load than the 500W is at 80% load.

You want to do the research on how much power your rig draws and then find a quality made psu that will be operating at its highest efficiency point given the load your computer will put on it.

OR you could just not worry about it because we're probably talking $1-3 difference over the course of a year.
Click to expand...

Very good points here :D
 
Get a UPS with a display that shows load and you can see what it uses. I watch mine go from 270 watts idle to 600 watts load. I went for an 850 watt power supply and a 900 watt UPS.
 
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