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Why all online PSU calculators are wrong and is total bogus

4K views 53 replies 18 participants last post by  ASUSfreak 
#1 ·
This is something which have bugged me for a while and have annoyed me countless times so now i am going to make a thread about it and talk about the problem at hand.
That problem is all online PSU calculators are crap and totally useless and give you bogus information if not outright misinformation.

To get to the point all of them give you the end user numbers that are much higher then what you are ever going to see in real life.

Now there are many theories as to why one of them is they are all paid off by the PSU brand/manufacturers to give numbers too high so they can make more money by selling you higher wattage PSU´s.

Another one is they are doing it do cover their own butts in case you have an el cheapo crappy PSU that cant do its rated wattage.

Now my own thinking is they have moved over to peak wattage numbers instead of continuous wattage but they are not telling anyone about this nor is it stated anywhere.
To explain what peak wattage is we need to talk about a peak rated PSU and to explain in plain english its a PSU that can do UP to its rated wattage for a short time but cant do it 24/7.

Quote

What is the difference between "continuous" and "peak" ratings?

Some power supply units are rated for continuous output while others are rated at peak. "Continuous" means that the power supply is rated to run at it's maximum capability for no pre-determined period of time, while "Peak" indicates that the power supply will only run at the specified wattage for a brief period of time, possibly only a few seconds or up to a minute. This number is typically about 100W more than the power supply's actual continuous rating.


Check out my Why the AMD and Nvidia power requirements are wrong for more info about peak wattage and how it has impacted AMD and Nvidia power requirements and why there is also so much misinformation there

Why the AMD and Nvidia power requirements are wrong

To get back on track my theory is all of these so called calculators and sites are now using peak wattage means they give you numbers that are 28% too high which actually make sense if you look at it that way.

So long story short if you are going to use one of the so called bogus broken crappy useless calculators know that the numbers most likely are in peak numbers and NOT continuous wattage.

So again dont trust the info you get from all of these sites its wrong!
If anyone has any info that could shred some light on all of this it would be welcome.
 
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#2 ·
i agree and have been against psu calculators for a long time.

easiest method to find out what you need ask TRUSTED people on ocn !
 
#3 ·
Quote:
Originally Posted by Mega Man View Post

i agree and have been against psu calculators for a long time.

easiest method to find out what you need ask TRUSTED people on ocn !
I am used to the fact they are a bunch of useless crap but i like to know why they are a a bunch of useless crap.
The extremeoutervision calculator used to be good before they decided to ruin it.
 
#5 ·
Quote:
Originally Posted by Klue22 View Post

Never used calculator. Just always summed the TDP of the graphics cards and CPU, then threw in a hundred or so for mobo + other compenents, maybe a couple hundred more if I plan to balls to the wall overclock.
TDP has nothing to do with power draws.
 
#6 ·
Quote:
Originally Posted by shilka View Post

TDP has nothing to do with power draws.
Since when? TDP is the max amount of power the chip will pull (unless you OC) so building a system off of the sum of the TDPs is a perfectly acceptable practice.
 
#7 ·
Quote:
Originally Posted by Klue22 View Post

Since when? TDP is the max amount of power the chip will pull (unless you OC) so building a system off of the sum of the TDPs is a perfectly acceptable practice.
No thats is a common misconception but TDP has in fact nothing to do with power draws.
Its the max amount of heat the card or CPU is rated for measured in watts not the actual power draw.

TDP stands for Thermal design power.

The thermal design power (TDP), sometimes called thermal design point, is the maximum amount of heat generated by the CPU that the cooling system in a computer is required to dissipate in typical operation. Rather than specifying CPU's real power dissipation, TDP serves as the nominal value for designing CPU cooling systems.

https://en.wikipedia.org/wiki/Thermal_design_power

So if you have been going by TDP you have been doing it wrong all along.
 
#8 ·
The heat is generated by the electricity flowing through the chip. 100w of electricity will always generate 100w of heat unless its doing "work" (ie a motor). The amount of work in a computer is extremely small so virtually all electricity in is converted to heat. The only thing that TDP doesn't account for vs total power draw, is the few watts of leach heat that aren't expected to be dissipated by the coolers. So yea, building strictly off the TDP would mean that you'd undershoot the total power draw by a few watts.
 
#9 ·
Other then the fact that a CPU and GPU will almost never run at 100% load and if it does its only for a short time which means the power draw is going to be lower then max.
And since TDP is the max amount of heat this means that just like with the useless calculators you are way overshooting.

Then add in the fact that most throw in 100 watts or more of the already way overshot wattage numbers and we the get the same only tired problem of everyone buying massive amount of wattage they dont need.
If you are fine with throwing away money on wattage you are never going to need thats fine but this thread is not for you then.

Think you would be surprised by how little power most computers actually draws.
 
#10 ·
Not surprised in the slightest. Every computer I have runs full load 24/7 for folding@home and I am very aware of my power bill.

Most people on OCN overclock their CPUs which results in significantly higher draw than TDP.

For instance, a 2600k (tdp: 95w) OCed to 4.6 will pull around 200w full system load. Maxwell cards are notorious for hitting power limits so you should always take full TDP into account for them as well. If you unlock voltage/power limitations on maxwell cards you can easily blow 300w per card.

I remember years ago an EVGA rep told me I needed 1000w to run two 285s. Those cards had a TDP of 187w. I had to stifle laughing at him over the phone since I was trying to get an RMA.
biggrin.gif
 
#11 ·
Well if you calculate by TDP it's at least not overshooting horribly like PSU wattage calculators right?
 
#13 ·
It's best to just look up professional reviews of the video card. However, doing this presents another possible problem: misinterpretation of their data. Too many people don't understand that most professional reviewers are showing you the wattage they saw on a meter that was plugged into the wall outlet - with the PSU plugged into the meter. So, most professional reviewers are showing you what their PSU pulled from the wall in order to deliver X amount of power to the entire computer (which is always a lower amount than what's pulled at the wall due to the fact that PSU's aren't 100% efficient - some power is lost as heat). You will know that you're looking at such data if they say "Total System Power Draw" or "Total System Power Consumption". The key words here are "Total System".

So it's really best to just ask us. I'm serious. I would much rather have everyone in the world come ask us than do any guessing - or end up misinformed, etc.
 
#14 ·
Quote:
Originally Posted by Klue22 View Post

Calculate based off tdp usually gets you pretty close but may be a bit low if you are overlooking and/or running everything at 100%.
Made that mistake before. Had to replace 700W with 850W or higher.
 
#15 ·
I usually overshoot the wattage I need, just to be safe. Not by an enormous amount mind you, but enough to ensure that my psu will be good for a few years.
My current psu is 900 watts I think. Not sure if it needs to be replaced any time soon either, had it for about five years maybe, and I have definitely overclocked several components on it, namely CPU and gpu's for extended amounts of time.
What do you think @TwoCables, am I still good for a bit, or should I start looking for another psu?
 
#16 ·
I take all the guessing out.

I find the most power thirsty equip. Buy 4 of the gpus and one cpu.

Oc the crap outta them. And know I need a 2kw ceiling for it.
problem solved

One of my builds has 3.2kws of power supply. Not that I need it. But I wanted them to match

Add in my hdds and spin up and my 40 (min no of fans in my builds ) 1.5a fans.... easy Peasy 2kw it is
 
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#17 ·
Quote:
Originally Posted by JTHMfreak View Post

I usually overshoot the wattage I need, just to be safe. Not by an enormous amount mind you, but enough to ensure that my psu will be good for a few years.
My current psu is 900 watts I think. Not sure if it needs to be replaced any time soon either, had it for about five years maybe, and I have definitely overclocked several components on it, namely CPU and gpu's for extended amounts of time.
What do you think @TwoCables, am I still good for a bit, or should I start looking for another psu?
I'd buy one and stick it in your closet so that you have a nice new one waiting for you, but that's me. :) You have a pretty old PSU there. Fortunately, it's a true PC Power & Cooling PSU.
 
#18 ·
Quote:
Originally Posted by Mega Man View Post

I take all the guessing out.

I find the most power thirsty equip. Buy 4 of the gpus and one cpu.

Oc the crap outta them. And know I need a 2kw ceiling for it.
problem solved

One of my builds has 3.2kws of power supply. Not that I need it. But I wanted them to match

Add in my hdds and spin up and my 40 (min no of fans in my builds ) 1.5a fans.... easy Peasy 2kw it is
lachen.gif

This guy understands the true meaning of being on Overclock.net.
 
#19 ·
Quote:
Originally Posted by Klue22 View Post

Quote:
Originally Posted by Mega Man View Post

I take all the guessing out.

I find the most power thirsty equip. Buy 4 of the gpus and one cpu.

Oc the crap outta them. And know I need a 2kw ceiling for it.
problem solved

One of my builds has 3.2kws of power supply. Not that I need it. But I wanted them to match

Add in my hdds and spin up and my 40 (min no of fans in my builds ) 1.5a fans.... easy Peasy 2kw it is
lachen.gif

This guy understands the true meaning of being on Overclock.net.
This is OCN, not OCD,
wink.gif
 
#20 ·
Quote:
Originally Posted by Klue22 View Post

The heat is generated by the electricity flowing through the chip. 100w of electricity will always generate 100w of heat unless its doing "work" (ie a motor). The amount of work in a computer is extremely small so virtually all electricity in is converted to heat. The only thing that TDP doesn't account for vs total power draw, is the few watts of leach heat that aren't expected to be dissipated by the coolers. So yea, building strictly off the TDP would mean that you'd undershoot the total power draw by a few watts.
100w of electricity flowing through a chip DOES NOT equal 100w of heat. 150W of electricity flowing through a chip and 50W of leakage produces 50W of heat.
 
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#21 ·
Quote:
Originally Posted by Alastair View Post

100w of electricity flowing through a chip DOES NOT equal 100w of heat. 150W of electricity flowing through a chip and 50W of leakage produces 50W of heat.
Not true. The energy has to go somewhere. There are only a few things that electricity can "do":

-generate heat: The electrons passing through a conductor cause friction which heats the conductor and you have heat
-Kinetic energy: Kinetic energy of electrons is imparted into a physical stator/rotor which turns
-Electromagnetic waves: Can be converted to x-rays/microwaves/etc

I'm sure there are a few specialized other things that physicists could point out, but the point is your CPU has no other energy outlet other than heat, thus all of the energy allowed to pass through it is converted to heat.
 
#22 ·
And all of a sudden I learn something. Just like that.
 
#23 ·
Quote:
Originally Posted by TwoCables View Post

I'd buy one and stick it in your closet so that you have a nice new one waiting for you, but that's me.
smile.gif
You have a pretty old PSU there. Fortunately, it's a true PC Power & Cooling PSU.
What wattage do think I should get when I do buy a new one, probably will buy a new one by October.
 
#24 ·
It makes sense from a "one size fits most" perspective. It isn't like the people making the calculators are there insuring that the most accurate of information is being included. It's better to overestimate and be sure it will work, then do the math to the watt and risk not having enough.

Same with GPU's. You see a GPU say min 500w PSU just in case you have a junk peak wattage PSU. I know testing my rig with a wattage meter the most I was able to pull was around 420w at the wall. I think the min suggested PSU for my 980 ti is a 600w.

What can be annoying though is when you're helping someone and suggest a reasonable wattage PSU only to have the results of a wattage calculator thrown in your face.
 
#25 ·
Quote:
Originally Posted by Chargeit View Post

It makes sense from a "one size fits most" perspective. It isn't like the people making the calculators are there insuring that the most accurate of information is being included. It's better to overestimate and be sure it will work, then do the math to the watt and risk not having enough.

Same with GPU's. You see a GPU say min 500w PSU just in case you have a junk peak wattage PSU. I know testing my rig with a wattage meter the most I was able to pull was around 420w at the wall. I think the min suggested PSU for my 980 ti is a 600w.

What can be annoying though is when you're helping someone and suggest a reasonable wattage PSU only to have the results of a wattage calculator thrown in your face.
Exactly, I would rather have it and not need it instead of needing it and not having it.
 
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