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Review: Corsair RM850i

by Tarinder Sandhu on 9 July 2015, 17:02

Tags: Corsair

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Testing results

Our Chroma load-testing procedures can be found at this link.


Load 10% 25% 50% 75% 100%
Efficiency 86.8% 91.6% 92.9% 92.1% 90.6%

The numbers are very close to those exhibited by 80 PLUS Platinum models from other companies. We reckon Corsair could have tweaked this design a touch more to achieve the Platinum qualification... but doing so, as previously stated, would mean there's little obvious differentiation between this and the HXi line. What we see is very strong 80 PLUS Gold performance.


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 +0.6% +0.5% +0.9%
50 per cent 0% +0.3% +0.6%
100 per cent -0.3% +0.3% -0.9%

Less than one per cent deviation from the 12V line is the important number. This means that however you load it, the actual voltage will not drop massively. Excellent results, with the 3.3V and 5V being even better.

Regulation - cross-load

How about providing uneven loads that stress particular voltage rails? In the first attempt, we've put 70A 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 +0.7% +0.8% -0.7%
Cross-load 3.3V/5V focus -1.1% -0.6% +1.0%

Hammering one part of the PSU power delivery while using just a small portion of the other can throw cheaper supplies of out kilter. Numbers stack up nicely against the non-cross-load tests, which is a hallmark of a premium, top-quality supply. Again, top-quality performance.


Line/Load (mv - p-p max) 3.3V 5V 12V
10 per cent 8mV 10mV 5mV
50 per cent 10mV 10mV 10mV
100 per cent 20mV 15mV 20mV

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.

Excellent performance here too. We're used to seeing premium supplies keep below 50mV at 12V and 100 per cent load; the RM850i manages to halve that for near-perfect suppression.


Temperatures Intake Exhaust
10 per cent 29°C 35°C
50 per cent 36°C 42°C
100 per cent 38°C 45°C

It doesn't get very hot at all, and the fan is switched off at low loads.

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 0rpm 0cfm Silent
50 per cent 450rpm circa-20fm Very quiet
100 per cent 1,400rpm circa-60cfm Quiet

The NR135P fan is said to be designed for low-noise operation. That's certainly the case during our tests, because even running at a full 850W the fan, spinning quickly, doesn't make a racket unlike some.