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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 RM850x’s efficiency at low loads, and loads from 10 to 110 percent of its maximum-rated capacity.
The PSU's efficiency is high under normal loads. Meanwhile, efficiency is satisfactory under light loads, but certainly not the best we've seen.
Efficiency At Low Loads
In the following tests, we measure the RM850x'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||PSU Noise||PF/AC Volts|
|1||1.201A||0.491A||0.481A||0.195A||19.685||66.867%||0 RPM||<6.0 dB(A)||0.878|
|2||2.424A||0.989A||0.994A||0.396A||39.801||78.444%||0 RPM||<6.0 dB(A)||0.941|
|3||3.650A||1.476A||1.504A||5.023A||59.882||83.029%||0 RPM||<6.0 dB(A)||0.966|
|4||4.861A||1.984A||1.991A||0.796A||79.799||86.345%||0 RPM||<6.0 dB(A)||0.975|
We would like to see close to 70% or better under 20W of load, while it'd be nice to see greater than 80% efficiency with 40W.
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 at 5VSB under full load, or with 3A if its max current output on this rail 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|
The previous RM850x demonstrated notably higher 5VSB efficiency.
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).
Vampire power is very low 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 47°C (116.6°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 6 dB(A) during testing (it's actually much lower, but our sound meter’s microphone hits its floor), and the results were obtained with the PSU operating at 37°C (98.6°F) to 47°C (116.6°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 30°C (86°F) to 32°C (89.6°F).
Semi-passive operation doesn't last long in our cross-load tests because we start with a high load on the minor rails. Still, the fan spins slowly through most of the PSU's operating range. There's only a small window where noise lands within the 25-30 dB(A) range. In general, the fan profile is conservative, keeping the RM850x V2's noise levels low.
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Aris Mpitziopoulos is a Contributing Editor at Tom's Hardware US, covering PSUs.
Sweet, first review of this I've seen. Thanks.Reply
I didn't go into detail, but I wonder what's the use of that Gold PSU when there's a Seasonic Focus Plus Platinum 750 for a similar price ?Reply
Gold, Platinum, it doesn't really matter at this efficiency point. What matters the most, in my opinion at least, is noise output now besides the basic (reliability and overall performance).Reply
At last some scoring at the review conclusion!! I always considered the lack of score as Tom's greater weakness about their reviews !!Reply