BEST way to calculate power consumption

SENOR BURTOS

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Apr 23, 2017
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I'd like to know what formula you use to determine what PSU wattage, without overestimating a lot.

I did this but idk if I'm correct

Or is there an easier way to do it? I've heard that adding CPU and GPU TDP and adding 100W for the rest of the system is fine.

But TDP isn't power draw IIRC, but estimating wattage of the GPU based on TDP does make sense bc the TDP is the power limit set on the bios. (I was told peak power doesn't matter if it's less than 1 second)

Now how to calculate the increase of power consumption when overclocking? ofc it depends per component ans such. But how do I account for overclocking in a worst-case scenario. In other words ¿How much can power increase considering ambient overclocking and lots of overvolting under a worst-case scenario? for CPU and GPU, ofc, 30%, 50%, 100%?

Is power consumption proportional to core/memory clock and voltage? So a GPU with a 16% core overclock, 25% memory overclock and 10% voltage offset would result in a 1.63x power draw?

Or should I just assume 150% is the highest typical power target (for example) and multiply GPU TDP by that, for the CPU I have no idea

Idk if peripheral overclocking makes a significant difference, probably not I guess.

Thanks.


GPU = 250W
CPU = 61W
RAM = 7W
chipset = 6W
HDD = 9w
SSD = 6W
Mouse = 2.5W
Keyboard = 2.5W



= 344W*



If I round up the numbers that's 350W



Is that fine?*



I didn't find the gigabyte RX 580 gaming 8GB but I took this one which I think gets very high clocks

Sustained power consumption is 250W



https://www.techpowerup.com/reviews/...o_Plus/28.html



For the CPU I took the readings from the 1800X OC'd to 3.8 GHz which does 61W under a gaming load



https://www.tomshardware.com/reviews...ew,5009-8.html



For RAM 16GB of DDR4 pull 6W in average

but running at 1.2V, I bumped that up to 8W to account for the extra voltages and clocks he may push



https://www.tomshardware.com/reviews...u,3918-13.html



I didn't find any info on B350 chipset power consumption, more specificaly the asrock AB350M pro4

But Z370 chipset has a 6W TDP (I know TDP isn't power)



https://ark.intel.com/products/12590...l-Z370-Chipset



For HDD I chose a very power hungry drive, its typical load power is 9W according to this datasheet:



https://www.wdc.com/content/dam/wdc/...879-771434.pdf



I added an SSD, which does 6W



https://www.pcper.com/reviews/Storag...VMe-SSD-Review



In the case of mouse and keyboard I added the numbers that are in the back of my peripherals

which are 5V, 500mA = 2.5W each
 
Work out your draw power like you did, double it and be 100% safe
But you seem to have done some home work, and I would recommend a 600W PSU for 350W power draw.... reasons?
If you look at PSU's they offer them most efficient at 50-60% range - so you know you are not pushing it more, but if it does later down the road, then you are all good.

My system uses a HX750i - fan only spins up when gaming, on idle, not much happens at all in my system. PSU can push out good power with passive cooling.
 

SENOR BURTOS

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Yea but the PSU will be less efficient at idle anyway, and there are very silent low capacity PSUs
 
yes exactly, but it is even less efficient at higher power than it is at lower power.
And if you are running higher power more often, you are adding more pressure to the components.
I would rather my car idle at 1200 rpm than idle at 5000 rpm....
Both are inefficient, but one will wear it out quicker than the other
 

jankerson

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No there aren't.

MOST PSU's under 550W aren't that great.

You can count on one hand those that are worth buying and have fingers left over.
 

4745454b

Titan
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You are correct. TDP isn't the power consumption exactly, but it does give us a close enough for our purposes number. According to the laws of thermodynamics/conservation of energy, all we are doing in a CPU/GPU is changing the electrical input into heat from the work of the transistors. We build in buffers and calculate on the high side so everything works out. I don't find it worth it to break out each sub part like RAM chips or drives. I normally just add the TDP of the CPU, GPU, then another 50W for the RoS. (Using your numbers I added up in my head 34W, so 50W is closer than 100W.)

Now comes the part that people get upset over. The popular thing to do is to double this number. After all, 50% load is max efficiency right? Lets look at a random review from Jonnyguru.

http://www.jonnyguru.com/modules.php?name=NDReviews&op=Story4&reid=557

This is a 500W PSU, so 50% load would be test three. And indeed, the highest efficiency is there at 90.4% But what is the 500W efficiency? 88.2%. This is only 2% less. And that's 100% output. I shoot for 60-80% load which would be test four. That's only 1% difference best at 89.6% You do need to be careful with the lowest loads as test 1 is only at 84.3% This is ~6% off the best. Until you get to the 80+ titanium PSU level they simply don't need to worry about sub 20% loads. A normal system will idle at 100W or less, and if you are getting a 600 or 650W PSU that's below the 20% load level. At that point they don't need to worry about staying above 82% or whatever level they were shooting for.

How a PSU reacts to such a low load does depend on the platform that's used. It's possible to get a platform that handles lower loads well. 6% difference is quite a bit. But one shouldn't assume that doubling the number that's needed is best. It could be a really bad idea. As long as you get a good PSU it's ok to load it up a bit. For me personally ~80% is the sweet spot. But this is a personal choice.

Edit: OCing has so many variables that I don't even talk about it. It's up to the chip and how far you want to push it. If you are super aggressive with the Vcore then the chip can use lots more power. Think of the FX 9xxx series from AMD. They are the same chips as the FX 8xxx, but juiced way more. So the TDP goes from 125W to 220W. That's nearly "double". If you want to get super aggressive you can certainly draw WAY more power then the stock settings. As such I simply tell people to OC at your own risk.
 

jankerson

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It all depends on the power draw and the actual PSU in the end.

50% is on the low side, but it's safe generally.

I like to do around 70% personally to give 30% overhead, but then I personally buy high quality PSU's that are quiet.

It's not just efficiently, it's also heat and noise so depending on the PSU they can get loud at over 50% load.

I don't care for the 120mm fan models as they do tend to be noisy.
 

jankerson

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Normally yeah.

The problem(s) are when MOST people cheap out they tend to cheap out on everything and end up with a pile of crap in the end.

Or they buy a high end MB, CPU and GPU and cheap out on everything else and again end up with the above. They end up with a junk case, CPU cooler and PSU and generic ram and HD's. Then they end up here asking why they are having all those issues. :sarcastic:

MOST do cheap out on PSU's though, and that's never good, every time I see it I just shake my head at the stupidity (ignorance).

Even worse is when it gets recommended here on the forums, gives me a headache.

 
u cant run your PSU at 100% 24/7, it will overheat and burn, they should handle 80% load fine with few spikes above

mobo doesnt have only chipset, there are some other things like, number of power phases, type of voltage regulator, integrated chipsets and modules (e.g. on-board sound, on-board Wi-Fi/1Gbit NIC, add-on USB connectors, add-on SATA connectors etc.) so u can expect on mid range mobo something like 25~45watts from only mobo, based on what u use/bios or OS saving features

another example would be mine r5 1600x, it can hit 180watts while overclocked doing stress test
under gaming it doesnt eat much watts, as games doesnt fully use cpu, but some background apps can help utilize it a bit more

 


quality PSUs, especially 550/650W models, are designed to withstand way more than their rating. that's the reason, they offer you 10-12 years warranty when you buy a Seasonic PSU for example. "wearing a PSU out" isn't something one should be too concerned about in 2018 as the decent PSUs (and I wouldn't advise anyone to buy a cheap junk one) has made significant steps forward in the past decade.
also, if you don't accelerate your engine to 5000rpm once in a while your engine can clog with carbon-particulate and other particles - less relevant for PSUs though.

furthermore at max load a PSU is required to be (almost) as efficient as at 20% load to meed 80+ certification. below 20% however efficiency is drastically worse. in idle, a typical PC will probably use less than 60W. doesn't really matter whether you run a 1200W or a 550W PSU (the 550W will be a bit more efficient, won't really matter though). in addition, the difference between 50% load and 90% load is - depending on your power draw and the PSUs you're using - often so little, that over a course of the unit's warranty you can't save in power what you have spend extra for a wattage-oversized PSU.

TPD indicates the amount of heat generated by the power of the CPU. Watts are a unit of power. power consumption is something different. It's like saying a car with 87HP will draw 87l fuel/h (not exactly, but simplified). If you look at the test of the i5-8600k here on Tom's you can see that the i5 draws way more power when stressed (122W) than what the TPD specifies - because they're not directly related.

as for overclocking,it depends a bit on the chip. AMD's 2990WX uses twice as much power while not doubling clockrates.
when you look at the i5 linked before, power draw when overclocking behaves a bit differently. generally it can be said that it doesn't accumulate linear but the further you overclock, the more power you need to throw at the chip.
luckily many sites include overclocking results by now for power draw to give you an estimate.

your estimates seem fine. generally, CPU & GPU is the only things that are truly interesting. my rule of thuimb is to take CPU&GPU power draw, and slap around 100W on top for everything else and a little overclocking. if the result is below 400W, I get a 450W PSU (there are a few decent ones, like the Bitfenix Formula or the Seasonic Focus, however if you want a fully modular one you gotta go for 550W). if it's below 50W, I get a 550W. If I end up with 520W, I double check and look for overclocking benchmarks and all that stuff just to be sure.

generally any gaming setup with a single GPU and an Intel CPU (not enthusiast line) runs fine on 550W. if you got a topline AMD CPU and a 1080Ti, you might wanna consider 650W.
 

4745454b

Titan
Moderator
The problem(s) are when MOST people cheap out they tend to cheap out on everything and end up with a pile of crap in the end.
Or they think because it says "600" somewhere in the model name it's a 600W. But when you check the 12V rail it has one, and it's 25A. (300W) Just because you think it has lots of watts doesn't mean it does, or that it's good for your system.
 

jankerson

Illustrious
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Yeah. LOL

Like.... "I just got this 700W PSU for $30".... ROFL

Only has 25A on the 12V.
 

4745454b

Titan
Moderator
Bingo. Those are garbage and not a real 600 or 700W PSU. And many people don't realize they are better off forgetting the garbage "700W" PSUs and getting even a mid range VS500 or CX500. More isn't always better.
 

zebarjadi.raouf

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Like.... "I just got this 700W PSU for $30".... ROFL
Bought this PSU 5 years ago for 31$ brand new (70$ now). Still working with my OC. Good deals can be found if you look around hard enough. Heck, I even found 59CFM/1.7mmH20 case fans for 2$ last year. Bought 4 instantly.

What do think? I only understand half of it. :/
--------------------
Overall we can't go too cheap on the PSU unless we know what we're getting.
 

4745454b

Titan
Moderator
It's an older group regulated PSU. EU only as it talks about the input voltage being between 180-245V. They also list High power and the OEM so it's not made by one of the better companies. They do list having 100% Japanese caps and a 105C main cap so that's good. Overall it's ok to use, but my guess is it's an older design so it could be better.
 

zebarjadi.raouf

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I think you have just been lucky.
Bought three straight (BFF + cousin too). Still working. I should sell my luck.:)
I recommend replacing it with a quality PSU since it's 5 YO.
it's an older design so it could be better
Yeah, going to do that with my next build but I'm stuck in Turkey (Istanbul) for the next 6-9 months and every friend I have recommends this manufacturer. This is their best line up for 140$. The link should have everything from standards to graphs.
http://www.green-case.com/products/power/power.php?model=GP1200B-OC_Plus
https://pasteboard.co/HBU5HmG.gif (If the link above doesn't work)
It's an older group regulated PSU. EU only as it talks about the input voltage being between 180-245V. They also list High power and the OEM so it's not made by one of the better companies. They do list having 100% Japanese caps and a 105C main cap so that's good. Overall it's ok to use
BTW, what technical stuff should I pay attention to when fishing for PSUs? Should be good info for the OP too. I understand most other components but PSU technical stuff is a mystery to me.
 

4745454b

Titan
Moderator
Technical things to know can be difficult sometimes because it's possible they lied on the label. For example, they listed that they use 100% Japanese caps with "full 105C electrolytic caps". I've read reviews where that info is on the box/label, but when opened it's only on the primary side. Just because someone claims something doesn't make it true. Because of this I tend to only believe the companies I know.

Group regulated designs are old now. You can tell it's group regulated because it only has 630W available on it's 12V rail. More modern PSUs would have the full 700W there. They do list a lot of good things there but it's hard to know if it's real.
 

zebarjadi.raouf

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I meant the newer one with more modern standards. It's 1200W. Should I get it or wait till I get back?
http://www.green-case.com/products/power/power.php?model=GP1200B-OC_Plus
https://pasteboard.co/HBU5HmG.gif
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EDIT:
That appears to be a fine PSU. But why would you get one? That's overkill for nearly all systems.
I tend to upgrade and OC a lot and my next build will have multiple stuff for a workstation. It has a 1050W version too.
Edit: This also belongs in your own thread.
I know. I was trying to keep it to two/three posts while learning helpful tips and technical stuff about PSUs. That way It would have been relevant to the thread. Two threads with one answer as I call it. (I just remember P=VI from physics 101)
 

Rexper

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Apr 12, 2017
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There’s not much we can reliably take from specifications.
Power distributuion, temperature rating, peak/continuous rating, cables, fan bearing, input voltage, dimensions, warranty, missing protections (the brand can specify non-functional protections, but if they don’t specify a protection we can assume it isn’t included), maybe efficiency rating.
The rest we can’t trust.
This is why experts spend thousands of dollars and weeks worth of time just to test and review a power supply.
As I like to say, a PSU is bad until proven otherwise.
 

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