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Review: be quiet! Power Zone 650W

by Tarinder Sandhu on 3 October 2013, 16:00

Tags: be-quiet

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Running the numbers

Our testing procedures can be found at this link.


Load 10pc 25pc 50pc 75pc 100pc
Efficiency 80.9pc 86.4pc 88.3pc 87pc 84.2pc

We'd want to see a supply, irrespective of 80 PLUS certification, managing at least 80 per cent efficiency across wide loads. The Power Zone isn't the best at very low loads but jumps up close to 90 per cent through the crucial 25-75 per cent range.


In terms of regulation, we're looking at just how well the supply is able to hold to the various lines. The ATX spec. has a +/- 5 per cent leeway on all but the -12V line.

Line/Load 3.3V 5V 12V
10 per cent +1.4pc +1.8pc +2.5pc
50 per cent +0.7pc +1.1pc +1.4pc
100 per cent -1.8pc -0.9pc +0.3pc

Most supplies overvolt with little load and undervolt when stressed - be quiet!'s standard regulation is good.

Regulation - cross-load

How about providing uneven loads that stress particular voltage rails? In the first attempt, we've put 50A on the 12V rails, and 1A on the 3.3V and 5V rails. This can actually be somewhat typical for a system heavy on graphics and CPU power. In the second, we've turned the tables and gone for 12A on both the 3.3V and 5V rails - highly unlikely in a real-world environment - and just 2A on the 12V - even more unlikely!

Line/Load 3.3V 5V 12V
Cross-load 12V focus -2.2pc +1.9pc +3.1pc
Cross-load 3.3V/5V focus -1.8pc +1.2pc +1pc

Hammering one part of the PSU power delivery while using just a small portion of the other can throw cheaper supplies of out kilter. The hallmark of a solid supply is little variation at the extremes of load. Just like the regular numbers, cross-load is reasonable for a mainstream supply.


Line/Load (mv - p-p max) 3.3V 5V 12V
10 per cent 10mV 15mV 15mV
50 per cent 25mV 15mV 20mV
100 per cent 30mV 30mV 35mV

The ATX v2.2 spec states that the maximum permissible ripple is 120mV for the 12V line and 50mV for others.

PSUs convert AC power into DC, but doing so requires the AC waveform to be suppressed. What we're really testing here is the quality of the supply's rectifier and any smoothing capacitors in getting rid of this unwanted up-and-down ripple. Per-line ripple is more than acceptable in all cases.


Temperatures Intake Exhaust
10 per cent 30°C 33°C
50 per cent 34°C 42°C
100 per cent 40°C 48°C

Tested at ambient conditions of 25°C and in an open environment next to the Chroma test harness, the supply becomes warm at full chat, though not overly so.

Fan performance

Temps are good but they mean little in isolation. Obtaining accurate noise readings is near-on impossible when the supply is connected to the Chroma test harness and dual-unit load-tester. We can test the manufacturer's quietness claims in a different way, by using an AMPROBE TMA10A anemometer placed directly over the centre of the PSU. The anemometer records the airflow being pushed/pulled from the PSU's fan. We can use a Voltcraft DT-10L RPM meter to measure the rotational speed of the fan, too.

Load Fan RPM Airflow Noise
10 per cent 500rpm circa-20cfm Very quiet
50 per cent 750rpm circa-40cfm Quiet
100 per cent 1,500rpm circa-60cfm Quiet

Supplies with lower efficiency ratings produce more heat than, say, Platinum-rated models. Consequently, the Power Zone 650W is very quiet with low loads. The high-quality design of the Silent Wings fan is such that it's not noticeable even when the supply is running at full capacity.