The Math Behind GPU Power Consumption And PSUs

Garbage in, garbage out. That's what you get if you don't spend enough time planning and testing your benchmarking methodologies. It's easy to fall victim to this golden rule, since preparation requires a lot of effort, eating into nights and weekends. It has taken me a year to find a solution that I’m really happy with. I’ve gained a lot of insights along the way, and discovered some phenomenon I really didn’t expect.

I originally set out to improve our power consumption measurements for graphics cards. I felt that the usual way of doing this via estimates based on measurements at the power plug just didn’t cut it, and I wanted a way to get more reliable and valid results with some extra effort.

Simple current clamps, multimeters and the first data loggers never quite worked for me. Something was always off, and it got really frustrating when every measurement arrived at a different result. There was some factor I was just not taking into account. But what could it be?

That's exactly what I want to diagnose over the next few pages. Unfortunately, I can’t spare you a certain minimum amount of theory. It’s exactly this knowledge that’s so important if you want to understand why the simple solutions don’t work. Never fear, though. The story won’t be boring or dry, and I’ve boiled down and simplified the subject matter as much as I could.

The measurement setup was systematically changed and improved time and time again in cooperation with our industrial partner. Entire configurations were tested, only to be scrapped again. Firmware was updated, nearly putting us back to square one. All in all, creating this platform was a lot of work on top of my already time-sensitive assignments, especially since everything had to be built in the midst of our normal operation.

All of the effort was really worthwhile, though. And, when it really comes down to it, transparency always beats secrecy. The latter might be good for business, but, in the end, you need to be able to back up your claims, especially if you publish them. This is why I’ll tell you the secret of how we get to the results produced by our measurements. Otherwise, you might just not believe them…

This thread is closed for comments
70 comments
    Your comment
  • Agera One
    Ha. Very good job for the beginners who confuse the power supply consumption.
  • Vorador2
    Man, everytime i'm truly fed up with Tom's posting news that read as press releases, and badly written opinionated pieces, a jewel of a deeply researched original article shows up.

    Thanks for reminding me of the reasons i started reading Tom's Hardware.
  • FormatC
    It is always difficult to break down the complex content to find an understandable level for all. We may lose a lot of information by this way (and some experts and nitpickers will kill me) or write boring and extra dry stories for a handful of readers without simplifications. It is always hard for us to find a good compromise.

    This equipment, shown in the review, is a good basement for a lot of other in-dept reviews in Germany, like the efficiency analysis of Nvidias GeForce GTX 970. You simply need exact numbers to do this. :D

    I've also visited PSU manufacturers in Asia this year and this VGA-PSU problem is now more in focus...

    But all this are another stories and I hope, that we get for all this more translation capacity here in US/UK. If not: it is a good reason to learn German :D
  • gofasterstripes
    Tom's Hardware delivers another piece of technical journalism at the gold standard.

    Well done to all involved, thank you.
  • s3anister
    This was an excellent read; thank you for the incredible amount of work done for this article.
  • justin2003jclc
    Hi Toms Hardware,
    Can you clarify on your rule number3 ? Do you means that most of the PC PSU in the market are linear power supply when you mention about analog? Do you mean that there is only minorities of PC PSU available in the market are using switching power supply design?
  • This is GOLD! Kudos to Igor for writing such a superb article. I hope he makes all the PSUs he reviews, undergo the same tests. Can't wait for his PSU reviews :)
  • pecul1ar
    Congratulations on finishing this year long experiment, and thank you for sharing us your findings. This must have lifted a load off your shoulders..

    Oh, so this was translated? Thank you for that as well :)
  • Novuake
    This article gives me a warm feeling inside.
  • NoShot
    So, my take away from this is my PC builder (will not name here but is one of the larger ones offering custom builds) mislead me on their configuration setups when they said a Corsair RM850 PSU would be fine for a r9 295x2 and a i7 4970k. Not surprisingly, I am having random issues with this build where the 29 295x2 would only activate one GPU after system reboot or awake from sleep mode. I was thinking it was a driver issue, but looks like I need to drop a couple hundred dollars on a replacement PSU.....great. Genuine thanks for the article though.
  • Traciatim
    554342 said:
    This article gives me a warm feeling inside.


    That's just the small gauge wiring. :)


    As for the article, I'm not sure how useful this much detail is except for in a couple of cases where people really want to know the in and outs of power delivery. It really doesn't change the general rule of "If you are doing a single GPU then a good quality 500-550watt power supply should be just fine and last years". It's really only when you get in to very unique power usage scenarios that you really need to think about it these days, and even then it's more of a "My machine might take this much, so I add 15-20% and buy a supply that can do that".
  • Onus
    I agree that things change; and a company that used to make junk may not any more. Still, while reviewers are still faulting Samxon capacitors for early failures, fixed by recapping, I will maintain the attitude that Samxon capacitors should be avoided.

    A great deal of work went into this excellent article, and I hope this summary point does not make it seem too trivial, but once again, "you get what you pay for."

    Has it occurred to any graphics card manufacturers that they might overcome some of the potential shutdown issues by incorporating additional filter capacitors on +12V on their boards? We're talking about flagship cards, and another $10-$20 in component costs aren't going to matter.
  • anthony8989
    You must have popped a bottle of champagne after publishing this bad-boy. Excellent article.
  • FormatC
    633674 said:
    Oh, so this was translated? Thank you for that as well :)

    My English is too bad to write complete reviews in English but it is enough to order in China a beer or to have fun with KTV (or to answer in a forum). But I hope that we get more translations from German into English in the future. ;)
  • dgingeri
    All this talk about bad capacitors reminded me of a motherboard I had a while back. I had an Epox KT266 board, the EP-8KHA, that I ran for a little over a year. At just after the one year point, I was running a game, heard a loud pop and bang from my system, and it shut off. I looked down at my system, and there was a visible dent outward on the access panel, right about the middle. (Beige cases show that so much more than black cases.) I opened up the access panel and found a capacitor sitting on the bottom of the case and two pins sticking up from the middle of the board just above the AGP slot and next to the memory slots.

    The capacitor had shot off the board with such force that it dented the case. It was cheap case, but it was still rolled steel. That sucker had some force to it.

    Bad capacitors are a big problem. Be aware of what you buy, and how good the quality is. At that time, I wound up buying an Asus KT333 board to replace the Epox board, and I have stuck with Asus for the most part ever since. (The recent incident with my Z97-WS hasn't changed my overall opinion of Asus, but I am still annoyed with them over it.)
  • FormatC
    Bad caps are always a problem.

    But a lot of this marketing discussions are pure voodoo. A big Japanese primary cap is for example a perfect honey pot for the most reviewers. And nobody takes a closer look at the secondary site. Each manufacturer has good and not so good caps. To understand the difference you have to read data sheets and specs and to know the function of this cap in detail. And finally - as I wrote - a good Taiwanese cap might be better than a standard Japanese cap for the same price. Brands are mostly hot air and PR gimmicks. ;)
  • Juxu
    Excellent read, it has been a long time since I have read an article this high in quality on TH, thank you!
  • tadej petric
    This is one of THE best articles I've ever read on Tom's hardware!
    Good job Igor, the whole article is easy to understand (no matter the skill level I guess), interesting and gives quite some things I didn't know before.

    More articles like this please Tom's!
  • kittle
    Great article!
    Need to check my PSU and see if it has any of this small gauge wiring.
    And its good to know my personal mantra is true: Getting these high wattage PSUs isnt a good idea, if your not going to use it.


    Now we need a followup article that uses this info and explains how to find the PSU that fits our needs. (And probably a motherboard too).
  • Au_equus
    Very informative Igor. Many thanks!

    Aluminum hydroxide is Al(OH)3
    BTW, the aforementioned gas is hydrogen
  • FormatC
    481417 said:
    Aluminum hydroxide is Al(OH)3 BTW, the aforementioned gas is hydrogen


    Typical typo - thanks! Just wrote to the guys to fix it in English version.
  • none12345
    Love in depth articles like this. Wish there was a lot more of this. (the 2part graphics card myths one was another good one).

    At the end of the day tho. HTF do we actually know what we are getting. Its been about 5 years since i bought my last PSU, but i never saw any data on what caps are in it, or what gauge wire they use etc. And i never come across power supply reviews that go into enough depth to know what you are getting.
  • ko888
    1310218 said:
    Love in depth articles like this. Wish there was a lot more of this. (the 2part graphics card myths one was another good one). At the end of the day tho. HTF do we actually know what we are getting. Its been about 5 years since i bought my last PSU, but i never saw any data on what caps are in it, or what gauge wire they use etc. And i never come across power supply reviews that go into enough depth to know what you are getting.


    Use the review database here:

    http://www.realhardtechx.com/index_archivos/Page541.htm

    The reputable review sites do a teardown of the PSU and reveal such things as capacitor brands and wire gauges.
  • CaptainTom
    Tom's, PLEASE make more articles like this.