Seasonic X-400 Fanless PSU

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For a fuller understanding of ATX power supplies, please read the reference article Power Supply Fundamentals. Those who seek source materials can find Intel's various PSU design guides at Form Factors.

For a complete rundown of standard testing equipment and procedures, please refer to SPCR's PSU Test Platform V4.1. The testing system is a close simulation of a moderate airflow mid-tower PC optimized for low noise.

Acoustic measurements are now performed in our anechoic chamber with ambient level of 11 dBA or lower, with a PC-based spectrum analyzer comprised of SpectraPLUS software with ACO Pacific microphone and M-Audio digital audio interfaces.

In the test rig, the ambient temperature of the PSU varies proportionately with its output load, which is exactly the way it is in a real PC environment. But there is the added benefit of a high power load tester which allows incremental load testing all the way to full power for any non-industrial PC power supply. Both fan noise and voltage are measured at various standard loads. It is, in general, a very demanding test, as the operating ambient temperature of the PSU often reaches >40¬įC at full power. This is impossible to achieve with an open test bench setup.


Normally, a 120mm fan is responsible for "case airflow" of our PSU test hotbox, and run at a steady slow speed (~800 RPM, ~13 dBA@1m) at low loads. With the X-400 Fanless, we chose to run the tests without any exhaust fan, the point of the exercise being to determine whether the X-400 can keep running in ridiculously hot conditions when pressed really hard. This test with no exhaust fan in the hotbox would represent the most extreme thermal conditions in a poorly designed fanless DIY system... which probably happens more than most fanless PSU sellers would like.

No exhaust fan for testing the X-400.

The Seasonic's vented-side-up installation gives it a big advantage in our test rig: Since there is no top cover over the PSU, the heat from the X-400 can vent freely into the room by convection. But keep in mind that this advantage also holds for all other PSUs we've tested in the past, including the fanless ones. You could say that the heat in the hotbox is excessively high, higher than in any real PC... and this is somewhat offset by the open top over the PSU.

If an exhaust fan was used, the vents in the X-400 would act as intake vents for the fan, which would draw air from the outside through the PSU. This is the air flow pattern we've see with other openly vented fanless PSUs like the FSP Zen; the closest vents in the case with the least impedance become intakes for the back panel exhaust fan.

The PSU load tester was not run fanless. There is no way 400W can be dissipated safely in our load tester without some forced airflow. This is provided by four slow-spinning 80mm fans that exhuast the heat from the DBS-2100 load test device into our hotbox, whose resistor banks take about half the load at 400W. The only escape paths for the hot air is through the PSU and the "back panel" vent where the exhuast fan usually goes.

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