Efficiency, Temperature, And Noise
Our efficiency testing procedure is detailed here.
Using results from the previous page, we plotted a chart showing the ST1200-PT's efficiency at low loads, and loads from 10 to 110 percent of its maximum-rated capacity.
Compared to PSUs in the same class, SilverStone's ST1200-PT doesn't fare so well under normal or light loads. Enhance should probably take a second look at this platform to improve its efficiency without sacrificing performance in another area (like load regulation).
Efficiency At Low Loads
In the following tests, we measure the ST1200-PT's efficiency at loads significantly lower than 10 percent of its maximum capacity (the lowest load the 80 PLUS standard measures). The loads we dialed were 20, 40, 60, and 80W. This is important for representing when a PC is idle, with power-saving features turned on.
|Test #||12V||5V||3.3V||5VSB||DC/AC (Watts)||Efficiency||Fan Speed||Fan Noise||PF/AC Volts|
|1||1.199A||0.490A||0.477A||0.196A||19.61||56.08%||0 RPM||0 dB(A)||0.860|
|2||2.427A||0.989A||0.987A||0.395A||39.73||68.63%||0 RPM||0 dB(A)||0.899|
|3||3.656A||1.486A||1.495A||5.002A||59.85||75.21%||0 RPM||0 dB(A)||0.929|
|4||4.873A||1.994A||1.975A||0.801A||79.79||80.10%||0 RPM||0 dB(A)||0.933|
Efficiency under light loads is pretty low. We would like to see over 60% during the first test, at least 70% in the second one, and over 80% in the third test. Surely the ST1200-PT's high capacity is a huge handicap under such light loads, but this is still a Platinum-rated PSU. Then again, the 80 PLUS certification program only takes three load levels into account for all of its ratings except Titanium, allowing manufacturers to tune their platforms for high efficiency in the 20%-100% load range.
The ATX specification states that 5VSB standby supply efficiency should be as high as possible, recommending 50 percent or higher with 100mA of load, 60 percent or higher with 250mA of load, and 70 percent or higher with 1A or more of load.
We take four measurements: one each at 100, 250, and 1000mA, and one with the full load the 5VSB rail can handle.
|Test #||5VSB||DC/AC (Watts)||Efficiency||PF/AC Volts|
The 5VSB rail is highly efficient.
Power Consumption In Idle And Standby
In the table below, you'll find the power consumption and voltage values of all rails (except -12V) when the PSU is idle (powered on, but without any load on its rails), and the power consumption when the PSU is in standby mode (without any load, at 5VSB).
As usual, we observe low vampire power with both voltage inputs.
Fan RPM, Delta Temperature, And Output Noise
Our mixed noise testing is described in detail here.
The first chart below illustrates the cooling fan's speed (in RPM), and the delta between input and output temperature. The results were obtained at 37°C (98.6°F) to 46°C (114.8°F) ambient temperature.
The next chart shows the cooling fan's speed (again, in RPM) and output noise. We measured acoustics from one meter away, inside a small, custom-made anechoic chamber with internals completely covered in sound-proofing material (be quiet! Noise Absorber kit). Background noise inside the chamber was below 18 dB(A) during testing, and the results were obtained with the PSU operating at 37°C (98.6°F) to 46°C (114.8°F) ambient temperature.
The following graph illustrates the fan's output noise over the PSU's operating range. The same conditions of the above graph apply to our measurements, though the ambient temperature was between at 28°C (82.4°F) to 30°C (86°F).
Under normal ambient conditions, the PSU operates in passive mode at up to 220W load. After that, its fan spins slowly enough to keep the noise output lower than 31 dB(A) until the load reaches close to 700W. Then the fan's speed increases quickly, and under more than 1kW loads it's definitely annoying.