Load peaks and capping
Let’s first take a look at the flowing currents. Measurements were taken at coarser 20-ms intervals, or about 50 times per second, to simulate the load on the supervisor chip of the power supplies (shutdown). We see that ALL load peaks are capped at 33 A at the latest. The colocated gaming card should be a maximum of 2 amps above that here.
Nevertheless, we still have to take a look at the voltages, or the product of voltage and current flow. I already wrote that I measured at three different power supply connections here, even though all connections meet again somehow on the graphics card’s PCB in the end. What we can see here now as much clearer fluctuations and peaks is due to the partially a little bit overvolting power supply and thus the voltage and not the currents. This is due to technical reasons, but it’s not a big deal. However, we can also see that the few peaks at just under 450 watts are not caused by the flowing current (graphics card), but actually result from the power supply! This is also due to the topology and especially the input filters. The RX 7800XT could easily spike up to 480 watts with this topology.
It hardly looks different in the torture test as well, even though you can see the RX 7900XT’s lower TBP here. But the individual voltage spikes look rather uncool, by the way, on both cards.
If you now add the voltage again, then you see a stronger ripple, which again results from the somewhat jittery operating voltage. However, to the power supply’s credit, it has to be said that this affects all current products from all manufacturers and can hardly be avoided.
But because I still want to know exactly, I’ll resolve the whole thing even higher and take 20 ms as the total runtime. The intervals of 10 microseconds can just be measured sensibly and we also see the voltage here as a gray curve, whose average value is just over 12 volts, but which nevertheless still alternates somewhat within the scope of what is permissible. We see a real cap at around 34 amps. With the RX 7800XT, it would certainly be 35 amps or more.
If you then convert that to the power consumption in watts, you get this picture:
I also did the whole thing again for the torture loop, where we get to admire the regular drops. First, the currents again, but they still have lots of weird, sporadically recurring drops in each rise. This looks like a violent hiccup before the power is really throttled back shortly after.
And then total wattage again:
Power supply recommendation
Now we come to the point that completely reduces the expected sensation of exploding power supplies to absurdity. Even IF you hopelessly overpower the card, no one really needs ATX 3.0 power supplies over 1000 watts, unless the CPU eats more than 300 watts. This is really just a job creation measure for the struggling power supply industry and only satisfies the sick imagination of some standardization fetishists. You really have to put it so harshly. I would estimate around 400 watts for the GPU performance of the Radeon Pro W7800 and 450 watts for the RX 7800XT. Depending on the CPU and peripherals, the total system should be sufficient with 650 to 700 watts.
This is also the reason for my power supply recommendation, which is that you should be able to get by with a modern 650-Watt Gold or Platinum power supply for both models. If you want to overclock everything hardcore, you should plan another 100 watts more, which is especially true for the possible board partner cards.
- 1 - Introduction, technical data and background
- 2 - Test system in the igor'sLAB MIFCOM-PC
- 3 - Gaming performance Full-HD (1920 x 1080)
- 4 - Gaming performance QHD (2560 x 1440)
- 5 - Gaming performance UHD (3840 x 2160)
- 6 - Power consumption and load balancing
- 7 - Transients and PSU recommendation
- 8 - Summary and conclusion
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