The Math Behind GPU Power Consumption And PSUs

Setting A New Standard For Power Measurement

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…

  • 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.