Running the numbers
Our testing procedures can be found at this link.
Efficiency
| Load | 10pc | 25pc | 50pc | 75pc | 100pc |
|---|---|---|---|---|---|
| Efficiency | 84.8pc | 91.2pc | 92.7pc | 91.4pc | 90.8pc |
Efficiency, as expected, is excellent from 25 per cent to 100 per cent load.
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 | +0.6pc | +0.4pc | +0.5pc |
| 50 per cent | +0.4pc | +0.4pc | +0.5pc |
| 100 per cent | -0.5pc | -0.3pc | -0.5pc |
Most supplies overvolt with little load and undervolt when stressed. We're seeing barely more than a one per cent swing from the highest-to-lowest figures, which are the best we've witnessed so far in 2012.
Regulation - cross-load
How about providing uneven loads that stress particular voltage rails? In the first attempt, we've put 65A 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 | +0.8pc | +0.9pc | -0.5pc |
| Cross-load 3.3V/5V focus | -1.3pc | -0.9pc | +0.5pc |
Hammering one part of the PSU power delivery while using just a small portion of the other can throw cheaper supplies of out kilter. There's little variation going on here; you're looking at just over two per cent from a best-to-worst-case scenario.
Ripple
| Line/Load (mv - p-p max) | 3.3V | 5V | 12V |
|---|---|---|---|
| 10 per cent | 10mV | 15mV | 15mV |
| 50 per cent | 15mV | 15mV | 20mV |
| 100 per cent | 15mV | 20mV | 25mV |
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 - the raison d'etre of this supply.
Per-line ripple is roughly one-third of what the ATX specification permits - the figure that Corsair liberally quotes in the accompanying literature. The 12V ripple at full load is usually the worst figure, in pure mV terms, with AC suppression being hardest to control under this load, but the AX860i's 25mV is very good even for a high-quality supply.
Temps
| Temperatures | Intake | Exhaust |
|---|---|---|
| 10 per cent | 28°C | 33°C |
| 50 per cent | 32°C | 35°C |
| 100 per cent | 37°C | 39°C |
Our sample's fan doesn't activate until the load hits roughly 30 per cent, though, rated at Platinum, wasting such little energy means the supply remains cool at all times.
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 | 610rpm | 20cfm | Very quiet |
| 100 per cent | 1,450rpm | 55.0cfm | Quiet |
The supply's effectively silent at low loads; the fan switches on momentarily and then stops when the load is below 240W on our Chroma test-harness. Put it in our high-end PC and, surprisingly, it remains silent while we bust out the guns in Max Payne 3, running on a GeForce GTX 680 graphics card.
We also managed to load a real-world PC up by swapping out the GTX 680 for a couple of ultra-high-end, wattage-guzzling GeForce GTX 590s. The fan switches on, certainly, but it can't be heard over the din produced by the remaining fans in the machine.
