Fanless PSU Torture Test Roundup

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D. SILVERSTONE ST40NF

The ST40NF looks very similar to the ST45NF, a sample of which was reviewed less than two years ago. These fanless PSUs are made by Etasis Electronics. The much earlier 300W ST30NF was reviewed back in 2004. Like the Silentmaxx, the ST40NF appears to be a re-named version of the earlier ST45NF — but in this case, the product has been de-rated instead of up-rated.

ERRATA, 23 Aug 2010 —

Sharp-eyed SPCR forum members questioned whether the ST40NF isn't another rebadged variant of the FSP Zen 400W, and more careful visual examination of the two sample suggested this might indeed be the case. A query to Silverstone confirmed the ST40NF's manufacturer to be FSP.


The specs of the Silverstone ST40NF.

The ST40NF is a modern 80 Plus Bronze approved PSU. It has two PCIe power connectors, one with 6-pins, and another with 6/8 pins. At over 6 lbs, it is the heaviest of the PSUs tested here. Unlike the earlier Silverstone fanless PSUs, the ST40NF does not features an extra indicator LED that changes color to show when thermal overload protection is engaged.


The big Silverstone box screams ZERO dBA but is otherwise tastefully silver in color.

The ST40NF is well packaged and presented, with a nice manual, Ac cable, zap straps and velcro ties for cable management. The top panel of the PSU is the only one without vent holes. All five other sides are vented.

The bottom is a heavy aluminum extrusion with large vents that show big internal heatsinks. This is a heavy PSU, weighing over 6 lbs. Ignore color and the similarity to the Silentmaxx is striking.


The open vents enable cooling airflow through the PSU, especially if there is an exhaust fan on the back panel of the computer case; it will tend to suck air from the outside through the PSU.

TORTURE TEST SUMMARY
Silentmaxx MX-560PEL01
400W Rated Output
Duration
Output (W)
Efficiency
Hotbox °C
Power Factor
10~20 min
22.0
62.7%
24
0.93
42.3
74.1%
25
0.96
65.1
78.9%
27
0.98
91.0
81.9%
31
0.99
150.6
83.9%
36
0.99
201.0
87.9%
37
1.0
15 hrs
251.8
87.7~85.9%
40~43
1.0
15 hrs (w/ fan)
400.2
86.6~84.8%
<40
1.0
+12V Ripple (peak-to-peak): <15mV @ <250W ~ 48mv @ 400W
Voltage Regulation during 1 hr test:
250W -
11.97V, 5.05V, 3.30V
400W - 11.95V, 5.05V, 3.26V
AC Power in Standby: 0.5W / 0.08 PF
AC Power with No Load, PSU power On: 10.4W / 0.57 PF
OTP Shutdown: Occurred several times at full load when hotbox reached >41°C. No-fuss recovery. Repeated several times without any side-effect.

ANALYSIS

The Silverstone had good performance in the short-term testing, with excellent voltage regulation, high PF, and good 80 Plus Bronze level efficiency. Unlike the ST45NF, the ST40NF has low standby and no-load power consumption. There were no anomalies, and electronic noise was very low. Our impression was much the same as with the ST45NF sample we tested two years ago and continue to use in the lab: An efficient, silent workhorse.

Our sample passed the 15-hour 250W torture test without any problems. Only about 10-15 minutes into the 400W test, OTP shutdown occurred, at only a bit over 40°C. After a couple minutes of accelerated cool-down with a small room fan, the unit started up and ran at full power. There was no sign of damage. However, thermal shutdown recurred in the same way. The usual Nexus 120 fan was installed and run at 12V as an exhaust fan for the hotbox to see if reducing the temperature would keep the unit running at full power. OTP shutdown happened again, this time about 20 minutes into the test when the internal temperature of the hotbox exceeded 41~42°C.

Finally, the Scythe Gentle Typhoon 120mm fan was installed as the exhaust fan and run at full speed (~1500 RPM). The increased airflow kept the hotbox temperature under 40°C, and the ST40NF successfully ran at full power for 15 hours.

Although the conservatively set OTP circuit worked well and protected the PSU from damage, the torture test findings suggest that the ST40NF must be well isolated thermally from other components and well ventilated to work in a system which demands 400W. It's probably not possible to do this without a fan that has substantial airflow near the PSU.



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