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Efficiency, Temperature & Noise
Our efficiency testing procedure is detailed here.
Using results from the previous page, we plotted a chart showing the ST45SF's efficiency at low loads, and loads from 10 to 110 percent of its maximum-rated capacity.
With normal loads, the ST45SF doesn't stand a chance against PSUs with higher efficiency certifications. However, under light loads, it fares well in the corresponding chart. This is because the secondary side's power losses aren't as severe.
Efficiency At Low Loads
In the following tests, we measure the ST45SF'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||1.200A||0.493A||0.472A||0.191A||19.680||70.896%||1050 RPM||17.5 dB(A)||0.920|
|2||2.427A||0.981A||0.975A||0.386A||39.757||80.149%||1050 RPM||17.5 dB(A)||0.959|
|3||3.659A||1.467A||1.482A||5.153A||59.877||83.819%||1050 RPM||17.5 dB(A)||0.974|
|4||4.876A||1.974A||1.959A||0.775A||79.770||85.319%||1050 RPM||17.5 dB(A)||0.979|
The fan's noise is inaudible, and the PSU achieves relatively high efficiency levels under light loads.
The ATX specification, along with CEC, ErP Lot 3 2014 and ErP Lot 6 2010/2013, states that 5VSB standby supply efficiency should be as high as possible, recommending 75 percent or higher with 550mA, 1A, and 1.5A of load. The PSU should also achieve higher than 75% efficiency under full load, or with 3A if its maximum current output at 5VSB is higher than 3A.
We take six measurements: one each at 100, 250, 550, 1000, and 1500mA, and one with the full load the 5VSB rail can handle.
|Test #||5VSB||DC/AC (Watts)||Efficiency||PF/AC Volts|
Although the ST45SF doesn't use high-end components, its 5VSB rail achieves good enough efficiency levels.
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).
The vampire power we measured is low with 115V. It increases notably with 230V input, but stays below 0.25W.
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 hemi-anechoic chamber. Background noise inside the chamber was below 16.6 dB(A) during testing (actually, it was much lower, but our sound meter’s microphone hit its floor), 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 30°C (86°F) to 32°C (89.6°F).
Under normal operating conditions, the ST45SF is silent up to 160W. It exceeds 30 dB(A) at loads higher than 220W. The noisy region begins above 275W, and only in some occasions the PSU's fan exceeds 40 dB(A).
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Aris Mpitziopoulos is a Contributing Editor at Tom's Hardware US, covering PSUs.
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