Efficiency

Using the efficiency results from the previous page, we plotted a chart showing the efficiency of the BWG850M at low loads and at loads equal to 20% -100% of the PSU's maximum-rated load.



Efficiency with both light and normal loads is pretty good for this category. The only Gold-certified unit that manages notably higher efficiency is the Cooler Master V850 (KM3). Based on a very good Seasonic platform, it is also significantly more expensive than the BWG850M.

Efficiency at Low Loads

In the next tests, we measured the efficiency of the BWG850M at loads much lower than 20% of its maximum-rated load (the lowest load the 80 Plus Standard measures). The loads we dialed were 40 W, 60 W, 80 W, 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 easily cracked the 80% mark in three out of the four light-load tests and is very close to doing so with 40 W. The fan could even spin slower in such low-load scenarios.

5VSB Efficiency

The ATX specification states that 5VSB standby supply 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 the 5VSB rail can handle.

The 5VSB rail's load regulation is excellent, but its efficiency is nothing to write home about. We would like to see more than 80% in at least one of these tests.

Power Consumption in Idle & Standby

In the table below, you will find the power consumption and 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).

Vampire power is only 0.14 W, which is low. Expect it to be even lower, under 0.1 W, with 115 V input.

Fan RPM, Delta Temperature & 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 35 °C - 46 °C ambient.



A chart that shows the cooling fan's speed (RPMs) and its output noise follows. We measure the fan's noise from one meter away, inside a small custom-made anechoic chamber whose internals are completely covered in specialized soundproofing material (Be Quiet! Noise Absorber Kit). Background noise inside the anechoic chamber was below 20 dBA during testing, and the results were obtained with the PSU operating at 35 °C - 46 °C ambient.



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



As you can see in the graph above, the PSU is very quiet at up to around 600 W, at least at normal ambient temperatures. You will have to push it beyond 700 W in order to make the fan spin faster, which would have it emit more than 43 dBA.