PSU question - Noob alert

Boycie · 9 Nov 2006 at 19:46

Hey Guys,

I've built plenty of computers in my time however when it comes to general electronic knowledge i'm slightly lacking. Now my question... if the total wattage required by the components in a PC is less than the rated output of the PSU does the PSU still draw its rated wattage from the wall? i.e. if the components need 400W of power and the PSU is rated at 500W will it draw 400W or 500W from the wall?

Hope this is clear and thanks for the help

Luke

semi-pro waster · 9 Nov 2006 at 19:54

The PSU will draw what is necessary from the wall, so in your example if it needs 400w then it will draw 400w whether you have a 500w PSU or a 1000w one. Of course there are slight variations due to the efficiency of the PSU in question so some have an optimal range of power, too low and they won't be running efficiently and if it is too high then you risk damaging components.

With all that said if you think your PC will need 400w then a 500w PSU(as long as it is a decent brand) will be absolutely fine.

Boycie · 9 Nov 2006 at 19:55

Thanks SPW

Yellowbeard · 10 Nov 2006 at 21:15

Just to add a bit, efficiency will play into it as well and therefore, efficiency rating should be figured in too. It is not always a 100% indicator but it's a good sign of quality.

For example, let's say (for easy math) your PSU is 80% efficient. Your system needs to draw 80w for a given task, then the PSU will draw 100w from the wall. The other 20% lost is typically converted to heat. That's why you need to also look at what temperature a PSU is rated at. A rating at 25c is worthless as your case ambient will typically get hotter than that and the PSU internally will definitely get hotter than 25c. A 50c rating is much better.