Question about Power supplies and power consumption

[kman79]

I have three computers in my Condo, and for the most part, the Box on my sig is always on. I'm wondering, does my 400 watt PSU always consume that much power, or does it only consume that much when it's at full load or when it needs it? Trying to cut down on the electricity bill. Sorry for the noob question, but any help on this is greatly appreciated.

 

[DaveSimmons]

The 400 watt rating is the max it can deliver not what it typically uses. It uses only as much as the PC parts draw (plus some waste heat), and the PC parts draw less when they aren't doing much work.

Hard drives spin down, video cards use much less in 2D, CPU uses less if you run cool-n-quiet, some case & PSU fans slow down when there is less heat.

Of course turning it off will use much less power, but (guessing) 100 watts at idle only means 2.4 KwH per day or 72 a month.

 

[kman79]

I appreciate the response, thanks for the help.

 

[Zepper]

PSU efficiencies run between 65 and nearly 90% (some tests show 90 and over % but I really doubt those results). The eff. (efficiency) tells you how much extra power the PSU is drawing from the wall over what it is delivering to the load (dumped as waste heat). And the eff. of each PSU varies over the actual output range of the PSU. A "high eff." PSU will vary from around 80 to maybe 90% at it's sweet spot - older, low-efficiency PSUs may vary from 65% to 85% at the sweet spot. The sweet spot for most PSUs is at around 80% of max output. There is now a rating service for PSUs - if a PSU has the 80+ logo, then its minimum eff. is supposed to be 80% over the entire range from 20% of rated output up. It will also have a PowerFactor of 0.90 and up across the range - so 80+ PSUs will also have active Power Factor Correction. This means that the PSU presents a 'friendly' load to the power grid.

.bh.