Testing results
Our testing procedures can be found at this link.
Efficiency
| Load | 10pc | 25pc | 50pc | 75pc | 100pc |
|---|---|---|---|---|---|
| Efficiency | 84.3pc | 91.7pc | 92.8pc | 89pc | 88.4pc |
Hitting 90 per cent-plus for mid-load scenarios is important for a high-quality PSU, as it enables the supply to keep temperatures in check with minimal fan airflow. As we alluded to earlier, this is why Corsair positions this as a passively-cooled supply at up to 40 per cent load, based on 25C ambient temperature.
Regulation
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 | +0.9pc | +1.4pc | +2.9pc |
| 50 per cent | +0.3pc | +0.6pc | +1.5pc |
| 100 per cent | -1.9pc | -0.5pc | +0.7pc |
Most supplies overvolt with little load and undervolt when stressed. The only standout figure, which is still well within the ATX spec, is the 12V line's when it's tickled by a 10 per cent load.
Regulation - cross-load
How about providing uneven loads that stress particular voltage rails? In the first attempt, we've put 60A 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 | -1.1pc | +1.2pc | +2.1pc |
| Cross-load 3.3V/5V focus | -1.5pc | +1.6pc | +1.7pc |
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, and we see lots of evidence to suggest the RM750 does a good job in those instances.
Ripple
| Line/Load (mv - p-p max) | 3.3V | 5V | 12V |
|---|---|---|---|
| 10 per cent | 10mV | 15mV | 15mV |
| 50 per cent | 25mV | 15mV | 25mV |
| 100 per cent | 25mV | 25mV | 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.
Temps
| Temperatures | Intake | Exhaust |
|---|---|---|
| 10 per cent | 31°C | 34°C |
| 50 per cent | 36°C | 40°C |
| 100 per cent | 38°C | 45°C |
The temperatures represent a direct link to the fan speed. We determined the fan's trigger-point at around 280W of DC load, or just below the 40 per cent figure quoted by Corsair. Let's put this kind of figure into context for a moment. 280W DC can comfortably power a fully-built PC equipped with an Intel Core i7-4770K processor, 16GB memory, SSDs, and a GeForce GTX Titan graphics card.
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 | None | Silent |
| 50 per cent | 600rpm | circa-20cfm | Very quiet |
| 100 per cent | 900rpm | circa-60cfm | Very quiet |
Corsair's built the RM750 for near-silent operation whilst also providing decent performance. Our numbers verify that it does achieve those aims.
