Corsair Gold: AX850 Power Supply

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8. FAN, FAN CONTROLLER and NOISE

The fan controller's default startup voltage was just 1.5V, too low for the fan to start spinning. This is in keeping with the "hybrid" (passive/active) cooling feature of the AX850. The voltage had to reach 2.9V before the fan would spin up, and in the hotbox, this occurred at 200W load — the same level as we found with the Seasonic X-650, which differs in that a PWM fan is used. Speed at fan turn on was ~400rpm, and extremely quiet, around 12~13 dBA@1m.

The fan sped up modestly, to 15 and 18 dBA@1m at 250W and 300W, respectively. The 25 dBA@1m measured at 400W is 6 dBA better than with the Seasonic X-650, but the maximum level of 39 dBA@1m at full load is some 8 dBA louder than the Seasonic.

The overall acoustic performance is excellent up to ~400W and about average for SPCR-tested PSUs above that power level. The AX750 is certainly a very quiet PSU.

One question asute readers will ask is, "Does the fan stops spinning when the load drops?" This is an issue we've seen in other "semi-passively cooled" PSUs: Once it starts, the fan simply does not stop spinning even when load drops way below the load which triggered it to start. The answer is, YES, the fan in the AX850 did stop when the load was reduced to below 150W — but not instantly. How quickly the fan stops depends on how quickly the heat is dissipated from not only the PSU but also the case. In testing, this was checked by dropping the load after the fan started, from 200W to 90W. With the "case fan" in the test box at very low speed (~600rpm), the fan in the AX850 stopped after about 2 minutes. Exactly when it stopped was difficult to determine because the fan was running so quietly before it stopped.

Noise in a Cooler Case

One thing we've been examining is how the power supply performs outside the tough thermal conditions of our standard test. The recent popularity of cases that isolate the power supply from the rest of the system make this a relevant question, as the cooler intake air allows the fan to run slower and quieter. We examine this by running some of the high load tests with the power supply in free air, away from the tough thermal conditions of the hot-box.

Outside the hotbox, the fan's increase in speed occurred at a higher power level, and its rate of increase was dramatically lower, due to the lower temperatures in the PSU. There's little question that the AX850's noise performance is greatly improved in a case with isolated intake vent for the PSU such as Corsair's own Obsidian and Graphite models, and it would remain inaudible to over well over 500W load.

Corsair AX850 SPL: In Hot Box vs. Out
Power load
90W
150W
200W
250W
300W
400W
500W
700W
850W
in hot box
<10
<10
12
15
18
25
35
38
39
out
<10
<10
<10
11~13
12
13
17
25
35
Measurements are in dBA@1m

COMPARISONS

The comparison table below shows the SPL versus Power Load data on all the PSUs tested in the anechoic chamber thus far. It's difficult to rank them, as the measured SPL varies with power load. The units which are quietest at minimum load are not always the quietest at midload (100W~300W), which may make them louder in actual use. Then there's the noise level at 400W and up, which will determine the quietest PSUs for high power gaming rigs, during actual gaming.

The AX850's acoustics in the hotbox is near the top of the pack. At the <200W power loads, the Corsair is on par with the quietest. Even at 400W, it's a top contender and close to the best at full power. This table fails to show the dramatically improved noise/load curve when installed in a case with isolated intake vent for the PSU. In such a case, the Corsair AX850 might as well be silent; any system drawing >500W will have hot video cards that need high airflow fans for cooling, and/or multiple hard drives whose noise will drown out the Corsair.

PSU Noise (dBA@1m) vs. Power in Hotbox/Anechoic Chamber
Model
90W
150W
200W
250W
300W
400W
500W
6-700W
850W
Seasonic X-400 Fanless
<10*
<10
<10
<10
<10
<10
n/a
n/a
n/a
Enermax Modu/Pro87+ 500
11
11
11
11
14
20
23
n/a
n/a
Corsair AX850
<10
<10
12
15
18
25
35
38
39
Seasonic X-650
<10
<10
12
14
16
31
31
32
n/a
Nexus Value 430
11
11
16
18
18
19
n/a
n/a
n/a
Nexus NX-5000
11
11
12
14
22
24
25
n/a
n/a
Antec CP-850
12
12
12
14
14
26
40
44
45
Enermax Eco80+ 500W
<11
12
16
19
26
32
33
n/a
n/a
Seasonic M12D 850W
14
14
14
14
14
24
37
42
42
Antec TP-750
12
12
14
14
18
33
40
40
n/a
Chill Innovation CP-700M
15
15
15
15
17
30
34
34
n/a
Antec Signature 650
15
15
15
18
18
28
36
47
n/a
Coolermaster M700W
14
14
18
21
25
27
34
34
n/a
Cougar GX-700
15
15
18
20
25
32
35
36
n/a
SilverStone DA700
18
18
18
18
23
32
35
41
n/a
Nexus RX-8500
14
14
17
22
28
32
32
33
33
NesteQ ECS7001
22
22
22
21
23
25
36
37
n/a
PCPC Silencer 610
20
24
24
24
24
30
40
50
n/a

The green boxes are >30 dBA@1m SPL.
*<10= below the ambient of our anechoic chamber; immeasurably low @1m in any environment

Caution: Please keep in mind that the data in the above table is specific to the conditions of our test setup. Change the cooling configuration, the ambient temperature and any number of other factors, and you could change the point at which the fans start speeding up, as well as the rate of the rise in speed. The baseline SPL is accurate, however, probably to within 1 dBA.



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