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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  • thestryker - Monday, December 12, 2022 - link

    The GALAX RTX 4090 HOF would like to have a word with you about that. While I think it's stupid and would never run such a thing myself it does already exist.

    I'm assuming MSI erred on the side of maximum compatibility without adapter cables which is why it only has one 12VHPWR connector. I can understand why they did it, but it is not outside the realm of possibility that power consumption is going to keep going up at the top end where this PSU also certainly sits.
  • Glock24 - Monday, December 19, 2022 - link

    And the next Intel CPU will also probably require another 12VHPWR 😂
  • Arutius - Thursday, December 8, 2022 - link

    Back in the day we had these things called "right angle" connectors. They work quite well and avoid the large loop needed for proper strain relief.
  • shabby - Saturday, December 10, 2022 - link

    Pepperidge farms remembers...
  • WaltC - Thursday, December 8, 2022 - link

    I don't see ATX 3.0 PSUs becoming the norm for a long, long time, fortunately...;)
  • TheinsanegamerN - Thursday, December 8, 2022 - link

    These are great, now when your GPU melts a plug you have to replace your PSU as well! Fantastic stuff, really.
  • Byte - Thursday, December 8, 2022 - link

    Seems like all the mobo makers wanna get in on the PS game. I just had a chance to work with an Asus Thor and it is bloody amazing with its OLED screen and pretty decent price. I used to be an EVGA Superflower lifer, but I think i will be switching to Asus with that screen and really nice cables. Now i gotta upgrade to a goddamn case that actually shows the power supply since it was banished from view 5 years ago.
  • lopri - Thursday, December 8, 2022 - link

    If you want to show that screen you have to mount the PSU fan-up, meaning it’ll suck in hot air from the video card above. Typical ASUS.
  • Leeea - Thursday, December 8, 2022 - link

    1300 watts for the next gen systems.

    . . .
    Just not feeling excited about that at the moment.
  • Samus - Friday, December 9, 2022 - link

    Your not the only one. I already have a 4" duct exhaust some air from my case out my office window in the Summer. And it's only a 500w load draw PC according to my UPS LCD. That's 500W of heat I'm removing from my office when the goal is to cool my house in the Summer, not heat it.

    It's all fine in the Winter but 1300w or even 1000w is a radical amount of heat to remove from a small space. And you will want to remove it, otherwise your air conditioning system requires AT LEAST 1000w just to offset it!

    So that's 2000w+ to keep a room the same temperature to play a game.

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