how wattage and power consumption relates with hiend power supply

[bkzed]

my question is simple
lets say i have 850w 80 plus certified psu and my systems overall power requirment is max 400 watt.in full load now will that remaining 450 watt wil effect my electric bill?

 

[IGemini]

Short answer: Not that significantly.

The power supply rating doesn't mean it uses that amount of power all the time, that's the maximum amount of power it's designed to deliver to the computer components. It won't supply more than the system should require, but because they aren't 100% efficient, the power draw will always be higher than what your system actually uses. If your computer needs 400W, a PSU that's 80% efficient will draw 500W.

Assuming this same computer runs 24/7, the waste itself will add 2.4 kWh/day to your electric bill.

 

[Zap]

A power supply's rated wattage is its capacity, not what it always uses.

 

[Blain]

Why worry about the electric bill?

One way to think of it is, if the PS did indeed put out 200W even when running a 40W computer, the extra 160W would have to go somewhere and would eventually fry the PS.

 

[Zap]

EDIT: Nevermind. Don't want to be called to task for calling out a member, no matter how misguided he is.

 

[TemjinGold]

OP: What is true though is that the percent of your total capacity you are using affects how much power your PSU needs to draw to give you that 400watt. All other things equal, a 500watt PSU will need to draw less power from the wall to deliver 400 watts than say a 1200watt PSU.

 

[DeathRayLoveMachine]

OP: What is true though is that the percent of your total capacity you are using affects how much power your PSU needs to draw to give you that 400watt. All other things equal, a 500watt PSU will need to draw less power from the wall to deliver 400 watts than say a 1200watt PSU.

That's incorrect. A power supply at 33% load is more efficient than a comparable design running at 80% load.

Usually you get maximum efficiency at 40-60% load and minimum efficiency at less than 20% or more than 80% load.

Assuming both PSUs minimally meet the 80+ Bronze standards, the 1200 watt PSU would save about 20 watts at the wall compared to the 500 watt PSU in your example.

 

[IGemini]

A power supply at 33% load is more efficient than a comparable design running at 80% load.

Not really. The general trend is the power efficiency of different loads is negatively skewed. This depends on the PSU quality, but at low loads (<25%) the efficiency can drop by 10% or more, while high loads are ~3% from optimal.

You also have to remember that power load varies based on what amount of work the computer is doing. A computer may demand 400W at most, but if it is running idle it could drop by half or more, making that 1200W unit work harder to supply less power than the 500W.

The 40-60% is the best guideline for what PSU to use though.