Efficiency

Using the efficiency results from the previous page, we plotted a chart showing efficiency of the ST50F-ES at low loads and at loads equal to 20-110% of the PSU's maximum-rated load.



Overall efficiency, both at low and normal loads, is acceptable considering this unit carries the basic 80 Plus certification.

Efficiency at Low Loads

In the next tests, we measured the efficiency of the ST50F-ES at loads much lower than 20% of its maximum rated load (the lowest load that the 80 Plus Standard measures). The loads that we dialed were 40, 60, 80, and 100 W (for PSUs with over 500 W of capacity). This is important for settings where the PC is in idle mode with power saving turned on.

The unit achieves fairly good efficiency at low loads by managing to surpass the 80% efficiency marks in two out of four tests. It even scores over 70% and very close to 75% with a mere 40 W load.

5VSB Efficiency

The ATX spec states that the 5VSB standby supply's efficiency should be as high as possible and recommends 50% or higher efficiency with 100 mA of load, 60% or higher with 250 mA of load, and 70% or higher with 1 A or more of load.

We will take four measurements: one at 100, 250, and 1000 mA each, and one with the full load that the 5VSB rail can handle.

At 5VSB, things don't look so good, at least at lower loads where the PSU either fails or just barely passes the corresponding limits. Things get better with the last two tests since efficiency is close to 75%. We should remind you that readings close to or above the 80% mark are considered quite high for this rail.

Power Consumption in Idle & Standby

In the table below, you will find the power consumption and the voltage values of all rails (except -12V) when the PSU is in idle mode (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).

It may be a budget unit, but this doesn't prevent it from being ErP Lot 6 2013 ready with a vampire power below 0.5 W.

Fan RPM, Delta Temperature and Output Noise

The cooling fan's speed (RPMs) and the delta difference between input and output temperature are illustrated in the following chart. The following results were obtained at 38-45°C ambient.



A chart that shows the cooling fan's speed (RPMs) and the output noise follows. We measure the fan's noise from 1 meter away—inside a small custom-made anechoic chamber with internals that are completely covered in specialized soundproofing material (Be Quiet! Noise Absorber Kit). Background noise inside the anechoic chamber was below 30 dBA during testing, and the results were obtained with the PSU operating at 38-45°C ambient.



The following graph illustrates the fan's output noise throughout the entire operating range of the PSU. The same conditions of the above graph apply to our measurements, but the ambient in this case was between 28°C and 30°C.



Not the quietest PSU we have ever encountered, since low efficiency leads to increased heat dissipation and all of that heat has to be moved out of the PSU's internals somehow, so the fan operates at increased speeds, which produces a significant amount of noise.