Does a power supply wattage change with demand?

[iusr]

Hey all,

I am planning to build a computer soon and was looking at power supplies. i was just curious, if i get a 750w power supply and the system only needs 700w or less, will the consumption of power only be 700w (that's only logical, right?). I ask this because I am wondering what my electric bill is going to shoot up to.

 

[we1shcake]

the power supply will only draw what the internal components use, they will waste some power but that is normal through the conversion inefficiencies, youre actually beter off power wise with a power supply that exceeds what you need as they are more efficient at 80% utilisation than 100%, the number on the power supply is simply the maximum it can supply not what it will draw from the wall

 

[leon2006]

Check your electric bill and look at the KWH charge...

It varies from state to state. Normally the rate is graduated by the amount of consumption.. EX 10KW, 30KW, 50KW will have a different charges (just as example)

A 700W load will be 0.7KW Charge for one hour whatever that is.

For example if the rate is $0.25 per KW....For using your PC for one hour that will be

0.7KW * $0.25/KW = $0.175

Take note this is just an example. Check your electric bill

 

[leon2006]

Your PC will consume base on its load.

The 750W PSU has a capacity of 750W

If your load is 700W then your charge will be base on 700W plus the inefficiencies of your PSU..

A 80% rating PSU theoretically will provide 800W from a 1000W input... The loses will be in heat and whatever is consumed by the PSU circuitry

 

[k1114]

Just to add to we1shcake, the best efficiency is around 50-70% of the total rating and correction: the rating is what the psu can output, it will take more from the wall. Could you tell us you're specs?

 

[shanky887614]

think about it this way, look at the celing rose in your room

if you put a 100watt bulb in there it will draw more power than if you put a 60watt bulb

it is the same concept with electrics

the more electricity it needs the more it pulls excess power will flow down the neutrel

 

[obsidian86]

a psu will only provide what is needed by the psu if you pc is drawing 700 watts your psu will provide 700 watts regardless if your psu is rated at 750,850 or even 10000 watts the draw will remain 700 watts

only thing that will be affected will be efficiency but its minor issue

 

[HEXiT]

if your pc is consuming 700w then you need a 1000w psu. this will enable you to stay withing the psu's constant power rating. if your psu is 750wats and 80% efficient then you will draw from the wall about 900w ay full load but the chances are your pc will draw a maximum of around 400w from your 750w psu.
your electric bill will likely rise by $10 per quarter if it rises at all if your replacing a pc and about $30 if its a first build... due to todays parts being more power efficient at idle.

if your going from a core 2 quad to say an i5 2500k then your electric bill will come down due to added efficiency of the whole system at idle...

the reason i keep saying idle is that most pc's are sitting at idle most of the time and only really go to full power while gaming or doing some other short term activity. so idle numbers become more important...

my old amd 6000 x2/88gt setup used to run at around 150w at idle 16hours a day. but my newer build of the i7 920 and 5870 actually idles at around 80w so in real terms costs nearly half as much to run at idle and not much more to run at load. so it does work out that the new build is about 30% cheaper to run.