kind of interesting power usage test

[rise]

before heading to bed i figured i'd test my apc backup and was looking at the power usage. it said it was supplying me 216w to run-

3200+ @ 2475
dfi-sli-dr
1 gig ram
3 hdd sata
2 opticals
6800gt @ stock
2 pci cards
5 case fans

threw prime on and usage went to 264w
turned on rthdribl as well, usage stayed at 264
oc'd the card slightly, 365/1050 and usage went to 300 even.

a long freakin way off the 480w dfi is "requiring" on their mobos. i guess i could see it climbing up there with ultras in sli.

 

[CrispyFried]

Most cheap power supplies dont put out anywhere near what they say as they qoute using optimum conditions, real world ps age and drop wattage as temp increases.

I think theyre just covering their bases. I have an Antec 350 and hang a rediculoius amount of stuff of it, in theory I should be running a 400 or 450.

 

[Vageetasjn]

What APC software can display this information?

 

[Zepper]

You are forgetting the efficiency factor. That 300W peak is AC power at a typical 70% efficiency, your PSU is putting about 210W of DC power into your system (even less if you forgot and left your monitor plugged into one of the backed up outlets). Very, very few use more than what a well specified 350W PSU can provide... And it costs money to have an oversized PSU as the efficiency of most switching regulators is lowest at below half power.

.bh.

 

[rise]

Originally posted by: Vageetasjn
What APC software can display this information?

it came with mine, the "parachute" i think it is


err, i meant "powerchute"

 

[imported_Kensai]

Nice! I like it.

 

[rise]

Originally posted by: Zepper
You are forgetting the efficiency factor. That 300W peak is AC power at a typical 70% efficiency, your PSU is putting about 210W of DC power into your system (even less if you forgot and left your monitor plugged into one of the backed up outlets). Very, very few use more than what a well specified 350W PSU can provide... And it costs money to have an oversized PSU as the efficiency of most switching regulators is lowest at below half power.

.bh.

granted, i haven't had my coffee yet, but i'm completely lost as to what you are saying with the efficiency and the peak from 300w to 210w i see it is 70% but how does that correlate to what the apc is saying its supplying?

 

[Zepper]

The APC is supplying AC - PSUs are rated in their DC output capacity. If the AC side is pulling 300W, the DC side is outputting about 210. So under your highest usage conditions - the PSU was operating at way less than half its power rating (assuming your PSU is rated at 480 or higher as suggested by DFI).
. Let's look at it another way - say a PSU is rated at 490W total (easier to calc in my head than 500) then at full output and 70% efficiency (meaning AC to DC power conversion and regulation efficiency where 1W AC in yielding 1WDC out would be 100% eff.) it will be needing to draw about 700W from the wall (or the battery backup as in this case).

IOW, the watts coming in from the wall or battery backup are not equal to the watts being supplied to the components inside the computer by the PSU. And efficiencies can range from about 65% to 80% or so in switching PSUs.

.bh.

 

[rise]

wow, thank you for clearing that up. as you alluded to, i still have my lcd, printer, speakers, router drawing off it as well. kinda puts things in perspective.

i did find the increase in load from idle more significant than i thought. i figured max 20% but its really closer to a 30% increase.

 

[willstay]

A quick question. If efficiency of converting AC power to DC power is generally 70%, are we losing 30% of the power in the process of conversion?

 

[Zepper]

Exactly - just be glad computing equipment isn't still using linear power supplies with much worse efficiencies... And the PSU is just the start of the losses.
. There are even further losses as there are more regulation stages on the different devices (e.g. the mobo does further regulation/reduction/filtering). Have you noticed the heatsinks on some voltage regulators on some mobos?

. Losses here, losses there, losses losses everywhere...

. And the fancy new video cards are now regulating and reducing locally from 12V rail for yet more losses.

At least in the winter we get to make use of some of the waste heat. I can redirect some of the hot air heat that would go to my computer room to some other rooms... Luckily we haven't had much in the way of summer here lately so I haven't had to run extra Air Conditioning to compensate for the waste heat.

.bh.