Our First Foray Into ATX 3.0 PSU Testing: A High Hurdle to Clear

In light of the new ATX 3.0 standard, we took a shot at adding power excursion compliance testing into our articles. Given that this is the big addition to the ATX 3.0 specification– and indeed its very reason for being – it's where we would like to see if PSUs are truly living up to the very high standards set by the new specification.

Unfortunately, the testing requirements of the new standard have proven too high for our equipment - and that of the majority of small laboratories - to meet. The power excursion specifications suggest electrical current-to-time figures that are extremely short. For example, taking the MEG Ai1300P of this review into consideration, for the single case of the 200% power excursion testing, we would need to test that it can handle 2600 Watts for 0.1 ms. Assuming a starting load of about 800 Watts and 65 A on the 12 V rail, the 12 V load would have to get up to 215 A and back down to 65 A within 0.1 ms. Furthermore, according to Intel's testing guide, this would have to continue for at least a minute, which means at least five hundred cycles in this scenario.

In an ideal world, we would just enter the current and time figures into the software and our electronic loads would run the test, instantly getting the load up to 215 A for 0.1 ms and then immediately back down to 65 A for 1.9 ms, according to the guide's requirements.

In the real world, however, there is no such thing as "instantly". Electronic loads, like any other device that is bound by the laws of physics, require time to react. The speed at which an electronic load can increase its amperage is called Ramp (or Slew) Rate and our larger loads have an ideal Slew Rate of 0.5 A/μS. Assuming that they operate linearly and exactly as specified, which no electronic load does for a variety of reasons, our two primary electronic loads in parallel would require at least 0.15 ms (150 μS) just to get the load up at 215 A. They would also require time, albeit less than half of it, to get the load back down to 65 A. When the test dictates a test time of 0.1 ms and the testing equipment requires at least twice that much time just to react, it goes without saying that testing results are highly unreliable.

Nevertheless, we took a shot at testing the power excursion capabilities of the MSI MEG Ai1300P PCIE and of the few ATX 3.0 compliant units that we currently have available. We took two approaches: one by assuming that our electronic loads are "ideal" and programmed the exact duty cycle figures that Intel dictates in their guide, and one by trying to take into account the real slew rate times of our loads and calculate the RMS equivalent duty cycle.

Both of our approaches ultimately failed, as all of the PSUs we currently have available would shut down at most tests above 120% power excursion - therefore we need not worry about our loads being insufficient to test the MEG Ai1300P at 200% excursion (we are also currently limited to 2400 Watts on the 12V line). Theoretically, testing with the RMS-equivalent duty cycle times should work and the PSUs should not be shutting down, yet we cannot claim that the units are not technically capable of meeting their specifications when our equipment is not meant to be running such tests.

Intel requires the PSUs to have a slew rate of at least 5 A/μS, so an electronic load must be at least as fast as that figure to be able to perform ATX 3.0 compliance testing. From a professional's point of view, proper testing would require the testing equipment to be at least 30% faster than the absolute minimum required. This requires a highly advanced (and expensive) electronic load with multiple modules, like the Chroma Mainframe and High-Speed modules Intel themselves is using, which has a total slew rate of 8 A/μS and it would need only 0.02 ms to get the load from 65 A all the way up to 215 A - and that still is 20% of the test's required 0.1 ms time in our example, a figure that many experts would find far too great for precise measurements.

The MSI MEG Ai1300P PCIE5 1300W : Inside & Out Cold Test Results (~22°C Ambient)
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  • sorten - Thursday, December 8, 2022 - link

    Another reminder of why it's good to stick with mid-range gaming and computing. My 1660Ti draws 120W and my Ryzen 3600 draws 65W. No need for a $350 PSU.
  • TheinsanegamerN - Thursday, December 8, 2022 - link

    How odd, my 5800x3d and 6800xt dont push over 450 watt combined, I dont need a $350 PSU either.
  • Eliadbu - Friday, December 9, 2022 - link

    Even if you had i9-13900k and rtx 4090 you would not need 350$ PSU. At that point it's more a gimmick.
    a good 150-180$ PSU will do the trick.
  • powerarmour - Friday, December 9, 2022 - link

    'New Era' and '1300W' should never go together in the same sentence, folks shouldn't even need these ludicrously overpowered PSU's if the hardware manufacturers gave a damn about the environment.
  • PeachNCream - Friday, December 9, 2022 - link

    They can't talk about that. An entire industry revolves around producing overpriced PC hardware and then using journalism as a supporting strut to add hype and build up demand. It's a necessity to sustain the paychecks of a LOT of people at OEMs, retail chains, reviewer websites, and so forth so you will always get unified messaging hocking the benefits rather than encouraging you to be more sensible. It happens in lots of other industries as well and is a HUGE contributor to why we're burning wrecking our own little proverbial cage through horrific wastefulness without having the ability to leave it for other potentially livable places.
  • GeoffreyA - Saturday, December 10, 2022 - link

    Well, as long as money is man's "unit of energy" on Earth, everything else will be subordinated to filling the coffers. I reckon even worrying about the planet ("we use green, vegan manufacturing processes throughout our business because we care") is of a token nature and only important when it can add more dollars to the corporation's bank balance or social prestige. If ever a time comes when damaging the environment is held to be popular, they'll do that too.
  • Dorkaman - Thursday, December 8, 2022 - link

    Did you try bending the 12VHPWR cable by the end that plugs into the graphics card? I guess many PC builders would like to do that to get a tidier cable routing.

    What I read is that 12VHPWR cables are not meant to be bent by the plug. Or is this just the case with NVIDIA supplied pcie-12VHPWR cable adapters?
  • edzieba - Thursday, December 8, 2022 - link

    The various theories of bent plugs or solder joints or etc all turned out to be incorrect: only plugs that were not fully inserted into the socket were able to actually reproduce the overheating issue (even plugs butchered to disconnect half the pins but inserted fully did not fail at all). Plug it all the way in and there is no issue.
  • crimsonson - Thursday, December 8, 2022 - link

    And try not to put pressure on the cable after installation - mainly for the chassis side cover bending the cable.
  • WaltC - Thursday, December 8, 2022 - link

    So why didn't nVidia ship idiot-proof plugs, then? You know, plugs that latch into place with a satisfying "click" when properly inserted? Lots of differing connectors are made that way.

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