Formula For Calculating PSU Requirement

[BigDay]

What are your thoughts on the following formula?

 

[(cpuTdp + gpuTdp) * 2 ] + [(numberOfGpus -1) * gpuTdp]

 

Let's say that you arrive at 676w. Could you get away with a 650w psu OR should you go with a 700w+ psu?

[flibberdipper]

You know, there's a reason a PSU will be rated at a certain wattage. Going over said wattage is not a good idea.

[Oshino Shinobu]

I think it's unnecessary. You learn about how much power is needed through experience. 

[DimasRMDO]

I just use this:

http://www.extreme.outervision.com/psucalculatorlite.jsp

[werto165]

I just used this: http://www.extreme.outervision.com/psucalculatorlite.jsp 

 

Also TDP is the heat that is emitted from the part isn't it? 

 

            @DimasRMDO

[DXMember]

I just used this: http://www.extreme.outervision.com/psucalculatorlite.jsp 

 

Also TDP is the heat that is emitted from the part isn't it? 

 

            @DimasRMDO

Thermal Design Power

it's pretty much power consumption for electronics as 100% the power gets converted into heat

unless it's like blinking lights or moving fans - then some power goes to do that

but cpu and gpu pretty much convert everything into heat

[BigDay]

the problem i have with that extreme calculator is that it doesn't seem to factor in a gpu overclock. am i wrong for saying this?

[callofDEEP]

for 676 watts u should look at over 750 or even a 850w psu.. why?

efficiency plays a big part here.. good 850w psu's are rated at 80% efficiency that means any good 850w psu delivers 80% of the advertised wattage.. that means 850W-20%=680w of power without wattage fluctuation..

[BigDay]

what do you guys think of that formula i've provided above?

[DXMember]

for 676 watts u should look at over 750 or even a 850w psu.. why?

efficiency plays a big part here.. good 850w psu's are rated at 80% efficiency that means any good 850w psu delivers 80% of the advertised wattage.. that means 850W-20%=680w of power without wattage fluctuation..

what you smoke?

80% efficiency means it can convert AC to DC with no more than 20% loss in wattage

It will however deliver 750W DC if it's 750W rated, but will pull 937W of AC

[werto165]

what do you guys think of that formula i've provided above?

It's probably best finding someone with the power supplies that measure the output it's currently giving. I think it's corsair ones with corsair link but I'm not too sure. 

[Virtual01]

Why are you multiplying by two? Just add the TDP of all your parts, then add ~30% so you have OC overhead and won't be running your PSU at it's absolute limits.

[callofDEEP]

what do you guys think of that formula i've provided above?

i dont know about that but 

 

what you smoke?

80% efficiency means it can convert AC to DC with no more than 20% loss in wattage

who cares.. effectively all it gives out is 80% of advertised wattage 

[BigDay]

Why are you multiplying by two? Just add the TDP of all your parts, then add ~30% so you have OC overhead and won't be running your PSU at it's absolute limits.

 

multiplying by two to add room for overclock on the cpu and gpu as well as room for the other components

[Virtual01]

multiplying by two to add room for overclock on the cpu and gpu as well as room for the other components

 

Overclocking doesn't require double the power though. A CPU/GPU TDP of 400 watts does not mean you need an 800W PSU, that's massive overkill.

[DXMember]

i dont know about that but 

 

who cares.. effectively all it gives out is 80% of advertised wattage 

it will give exactly the "advertised" wattage and a little bit more

that's actually RATED wattage which means it can provide it sustained through out the warranty period

it can still provide above the rated wattage for short periods of time until it craps itself and shuts down on evercurrent protection

[STRMfrmXMN]

Adding the TDP together and then mutiplying is entirely the wrong idea. That gives you WAY too high of a number and that's why people end up with 1500W PSUs for two 980s...

 

An OC'd 680 (hungry) and OC'd 3770K (also hungry) use about 350W of power.

 

Computers use significantly less power than most think.

[79 Potatoes]

for 676 watts u should look at over 750 or even a 850w psu.. why?

efficiency plays a big part here.. good 850w psu's are rated at 80% efficiency that means any good 850w psu delivers 80% of the advertised wattage.. that means 850W-20%=680w of power without wattage fluctuation..

80+ ratings refer to efficiency of converting AC to DC... not the power that PSU can actually deliver

 

i dont know about that but 

 

who cares.. effectively all it gives out is 80% of advertised wattage 

 

Lots of people care, well because of power bill, you certainly don't want a PSU to draw 800 W for a 500 W system...

[Aniallation]

Let's say that you arrive at 676w. Could you get away with a 650w psu OR should you go with a 700w+ psu?

Easiest way, CPU TDP + GPU(s) TDP + 100-150W. 

 

If you get 676W obviously don't buy a 650W PSU, too many watts is always better then not enough.

 

http://linustechtips.com/main/topic/199255-how-many-watts-do-i-need-check-here/

[Chiobe]

Most if not all pc parts these days tells you the number of watt they will be drawing, so as long as you know what parts you are going to be using, so can you figure out how many watt you need. Its just good old plus math.

For overclock just add 50% more of power that part uses, as only extreme overclocks will go past that, so you will have a buffer available.