Articles: Cases/PSU
 

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Temperature and Noise

Considering Scythe’s main line of business, it would be odd to encounter something other than Scythe's own fan inside.

Indeed, the PSU is cooled by a Scythe SM1425SL12PM fan. Its mounting holes correspond to those of a standard 120mm fan whereas its impeller is as large as that of 140mm fans.

What does it mean for the end-user? Well, if this nonstandard fan fails, you will be able to replace it with any 120mm one. However, the efficiency of the replacement fan will be lower due to its smaller impeller as well as to the larger cutout in the PSU case.

The fan starts out at 800 RPM and keeps this speed until a load of 270 watts. Then the speed grows up linearly, reaching 1800 RPM at full load. The PSU becomes rather noisy at loads above 400 watts.

The Scythe SM1425SL12PM is about as noisy as the above-discussed Hiper but quieter than the original Enhance which used to increase its fan speed linearly right from the start.

UPS Compatibility

The Scythe SM1425SL12PM was stable with my APC SmartUPS SC 620 at loads up to 360 watts (when powered by the mains) and 300 watts (when powered by the batteries). The pair switched to the UPS batteries without problems.

Output Voltage Stability

The cross-load diagram of this PSU doesn’t look neat. Unfortunately, it is the +12V rail's fault.

The most advanced of our reference PC configurations (marked with the number 3 in the diagram) wouldn’t work with this PSU due to the voltage sag on the +12V rail, even though the PSU should be able to power it up according to its specs. The +12V voltage depends too much on the +5V load.

The +5V voltage diagram may be frightening at first sight with its abundance of yellow and orange, but this voltage is actually close to ideal in the real-life load range. Our first two reference configurations are within the bright-green 1% zone, and the third one would also be there if it were not for the +12V rail.

There are no problems with the +3.3V voltage as it deflects no more than 3% from the face value.

Output Voltage Ripple

There is conspicuous output voltage ripple on the +5V and +12V rails but it’s within the permissible limits. There are no short-term spikes above those limits.

The same goes for the low-frequency voltage ripple.

Efficiency and Power Factor

The PSU’s power factor is somewhat lower than that of typical PSUs with active power factor correction.

The efficiency is high at low and medium loads (above 85% within the range of 70 to 400 watts) but sags at high ones (only 81% at full load). The native PSU from Enhance was somewhat better in this respect.

+5V Standby Source

The standby source copes with its task.

Summary

The cross-load test shows the reason why this model has disappeared from Scythe's product range. The +12V voltage sags too much when the +5V rail’s load is rather low and this can hardly be a defect of the particular sample. An Enhance PSU with the same circuit design as the Stronger 600 W Plug-in produced the same picture in our earlier review.

Otherwise, the PSU is good, if not perfect. But what's the use of all of its benefits if it fails to perform its main duty, which is to deliver stable power to computer components?

 
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