Corsair Gold: AX850 Power Supply

Corsair’s new AX850 has 80 Plus Gold certification for 90% efficiency, totally modular cables, a hybrid passive/active cooling for silent operation, and is backed by a 7-year warranty. It’s perfect for a Silent Gaming Rig in a thermally advanced case.

Product	Corsair AX850 (CMPSU-850AX ) ATX Power Supply
Sample Supplier	Corsair
Market Price	US$199

Corsair is arguably the most successful new power supply brand to emerge in
the retail computer components landscape in the past few years. Ostensibly a
memory (RAM) company for many years, Corsair’s partnerships with major PSU makers
— first Seasonic, then Channel-Well and Enhance — and aggressive markting/distribution
efforts have established the brand firmly as a major player in power supplies.
Corsair’s PSU lineup is very extensive, with 21 models ranging from an entry
level 400W to the newly introduced 1200W 80 Plus Gold certified AX1200.

The AX series includes two other models, the AX850 and AX750, so designated
for their rated output power. Corsair sent us an sample of the AX850 for review.
It’s obvious to anyone who pays close attention to retail computer power supplies
that the Corsair AX850 is based on Seasonic’s successful high-efficiency 80
Plus Gold certified X-series, two models of which we have reviewed, the X-650
and the new fanless X-400. Looking at the Corsair web pictures of the AX750,
we’d bet it is based on a Seasonic X-750, too.

PACKAGING & FEATURES

The AX850 retail box is big and impressive like all the other Corsair PSUs. Very nice packaging, including a soft pouch for the PSU and velcro-flap bag for all the output cables. The essence of the product: Power supply and all the cables. Some are sleeved, others are in the flat data-cable style introduced with Corsair’s very first power supplies. The flat profile makes those cables easier to route in some cases, important if you like the cables in your PC tidy and mostly out of sight..

 

Corsair AX-850 FEATURE HIGHLIGHTS
FEATURE & BRIEF	Our comment
Supports the latest ATX12V v2.31 and EPS 2.92 standards and is backward compatible with ATX12V 2.2 and ATX12V 2.01 systems	Good.
Low-profile, flat cable design reduces air friction and helps maximize airflow through the computer’s chassis	OK.
Completely modular cable system allows you to use only the cables you need. Power supply upgrade and replacement is easy, as the cables only need to be disconnected at the power supply	Like Seasonic X-series.
An ultra-quiet 120mm double ball-bearing San Ace fan from industry-leader, Sanyo Denki delivers excellent airflow at an exceptionally low noise level by varying fan speed in response to temperature	Like Seasonic X-series.
Ultra Low Noise – Hybrid Silent Fan Control: Fanless mode of operation (0 rpm) up to about 20% load, a quiet, low fan speed cooling mode for typical loads up to around 50% load, and a higher performance cooling mode for more demanding loads.	Like the fan-equipped Seasonic X-series.
High-quality Japanese capacitors provide uncompromised performance and reliability	Many high end PSUs flaunt this feature.
80 Plus Gold certified to deliver at least 90% efficiency at 50% load	OK.
A dedicated single +12V rail offers maximum compatibility with the latest components	The madness of multiple 12V lines are behind us finally.
Safety: UL, CUL, CE, CB, FCC Class B, TÜV, CCC, C-tick	Very good.
Over-voltage and over-current protection, under-voltage protection, and short circuit protection provide maximum safety to your critical system components	The more the merrier.
Universal AC input from 90~264V, Active PFC for PF value of 0.99	Like most high end PSUs on the retail market.
MTBF: 100,000 hours	Very good.
Seven year warranty and lifetime access to Corsair’s legendary technical support and customer service	Excellent.
Size: W150 x L160 x H86 mm	Slightly longer than normal.

 

VISUAL TOUR

The AX850 is finished in what looks and feels like tough black paint with white
and, predictably, gold accents. Like the Seasonic X-series, the casing is very
robust, made from a thicker than usual sheet metal.

The casing is robust and rigid. The only exhaust vent is on the back panel, and the DC outputs are entirely modular. The label has precise specifications.

The power supply’s casing is a departure from the normal dual
C-shaped clamshell. The metal is thicker and fits together very precisely.

The very high quality120x25mm Sanyo Denki fan first encountered in a Seasonic D12-850 is used here. Unlike the X-series, this is a 2-conductor DC fan that is voltage-controlled, not a 4-conductor PWM fan. The clear plastic piece on the edge of the fan is a baffle designed to minimize airflow short-circuit (where intake air flows through to the exhaust vent without doing any cooling). With minor changes for higher power output (such as dual filter capacitors and bigger finned heatsinks), the interior of the AX850 looks very similar to the Seasonic X-650/750. As in the X-series, the output connector PCB is where the DC conversion from 12V to 5V and 3.3V takes place. Top quality components are used everywhere. The three spider-like heatsinks look the same as the ones used in the Seasonic X-400 Fanless.

OUTPUT CABLES

1 – ATX connector (58cm) 20+4 pin
2 – CPU connector (58cm) 4×2 (8-pin)
1 – CPU connector (58cm) 2×2 (4-pin)
4 – PCIe (58cm) 6/8-pin
2 – four SATA connectors (82cm)
2 – two SATA connectors (55cm)
2 – four 4-pin IDE connectors (82cm)
2 – one floppy drive connectors on adapter (11cm)

Note: These modular cables are not identical to
the ones used on the Seasonic X-series. They use different connectors which
look similar, but the keying is not the same.

TESTING

For a fuller understanding of ATX power supplies, please read
the reference article Power
Supply Fundamentals. Those who seek source materials
can find Intel’s various PSU design guides at Form
Factors.

For a complete rundown of testing equipment and procedures, please
refer to SPCR’s
PSU Test Platform V4.1. The testing system is a close simulation of
a moderate airflow mid-tower PC optimized for low noise.

Acoustic measurements are now performed in our anechoic chamber with ambient level of 11 dBA or lower, with a PC-based spectrum analyzer comprised of SpectraPLUS software with ACO Pacific microphone and M-Audio digital audio interfaces.

In the test rig, the ambient temperature of the PSU varies proportionately
with its output load, which is exactly the way it is in a real PC environment.
But there is the added benefit of a high power load tester which allows incremental
load testing all the way to full power for any non-industrial PC power supply.
Both fan noise and voltage are measured at various standard loads. It is, in
general, a very demanding test, as the operating ambient temperature of the
PSU often reaches >40°C at full power. This is impossible to achieve
with an open test bench setup.

The 120mm fan responsible for “case airflow” is deliberately
run at a steady low level (6~7V) when the system is run at “low”
loads. When the test loads become greater, the 120mm fan is turned up to a higher
speed, but one that doesn’t affect the noise level of the overall system. Anyone
who is running a system that draws 400W or more would definitely want more than
20CFM of airflow through their case, and at this point, the noise level of the
exhaust fan is typically not the greatest concern.

Great effort has been made to devise as realistic
an operating environment for the PSU as possible, but the thermal and noise
results obtained here still cannot be considered absolute. There are too many
variables in PCs and too many possible combinations of components for any single
test environment to provide infallible results. And there is always the bugaboo
of sample variance. These results are akin to a resume, a few detailed photographs,
and some short sound bites of someone you’ve never met. You’ll probably get
a pretty good overall representation, but it is not quite the same as an extended
meeting in person.

REAL SYSTEM POWER NEEDS: While we test the PSU to full
output in order to verify the manufacturer’s claims, real desktop PCs simply
do not require anywhere near this level of power. The most pertinent range of
DC output power is between about 40W and 300W, because it is the power range
where most systems will be working most of the time. To illustrate this point,
we
conducted system tests to measure the power draw of several actual systems
under idle and worst-case conditions. Our most power-hungry overclocked
130W TDP processor rig with an ATI Radeon X1950XTX-512 graphics card drew ~256W
DC peak from the power supply under full load — well within the capabilities
of any modern power supply. Please follow the link provided above to see the
details. It is true that very elaborate systems with the most power hungry dual
video cards today might draw as much as another 150~200W, but the total should
remain under 500W in extrapolations of our real world measurements.

INTERPRETING TEMPERATURE DATA

It important to keep in mind that PSU fan speed varies with temperature,
not output load. A power supply generates more heat as output increases, but
is not the only the only factor that affects fan speed. Ambient temperature
and case airflow have almost as much effect. Our test rig represents a challenging
thermal situation for a power supply: A large portion of the heat generated
inside the case must be exhausted through the power supply, which causes a corresponding
increase in fan speed.

When examining thermal data, the most important indicator of cooling
efficiency is the difference between intake and exhaust. Because
the heat generated in the PSU loader by the output of the PSU is always the
same for a given power level, the intake temperature should be roughly the same
between different tests. The only external variable is the ambient room temperature.
The temperature of the exhaust air from the PSU is affected by several factors:

The thermal rise in the power supply is really the
only indicator we have about all of the above. This is why the intake temperature
is important: It represents the ambient temperature around the power supply
itself. Subtracting the intake temperature from the exhaust temperature gives
a reasonable gauge of the effectiveness of the power supply’s cooling system.
This is the only temperature number that is comparable between different reviews,
as it is unaffected by the ambient temperature.

TEST RESULTS

The ambient temperature was 21~23°, and the ambient noise
level was ~10.5 dBA.

1. EFFICIENCY — This is a measure of AC-to-DC
conversion efficiency. The ATX12V Power Supply Design Guide recommends 80% efficiency
or better at all output power loads. 80% efficiency
means that to deliver 80W DC output, a PSU draws 100W AC input, and 20W is lost
as heat within the PSU. Higher efficiency is preferred for reduced energy consumption
and cooler operation. It allows reduced cooling airflow, which translates
to lower noise. The 80 Plus Gold standard requires 90% efficiency at 50% of rated load, and 87% efficiency at both 20% load and full rated load.

At the super low 20W load, efficiency was quite good at 65%. Efficiency
rose quickly as the load was increased. 80% efficiency was reached around the
55W mark, broke 87% by 150W (easily meeting the 87% requirement at 20% load,
which is 170W), and it reached 90% at 250W. At 200~350W, ~90% efficiency was
maintained. With higher load and higher operational temperature in the SPCR
test box, efficiency dropped a bit. At 50% load (425W), with temperature at
35~38°C in our hotbox, 90% efficiency was not quite reached; it was just shy
of 89%. At full power, the efficiency dopped down to 83.4%, a full 3.6% under
the 87% required by 80 Plus Gold — but by then the internal temperature
of the hotbox was 44°C.

The failure of our sample to meet 90% efficiency at midpower is
somewhat unusual, but the drop at full power is not. The 80 Plus validation
testing is done at typical room temperature (18~28°C) while SPCR’s test
setup feeds the heat of the PSU output back into its operating ambient, which
makes for a much hotter, more demanding and realistic high power load test.
Most PSUs with 400W+ rating that we test do not match full power 80 Plus efficiency
test results due to our extremely hot conditions.

2. VOLTAGE REGULATION refers to how stable the output voltages
are under various load conditions. The ATX12V Power Supply Design Guide calls
for the +12, +5V and +3.3V lines to be maintained within ±5%.

At all load levels, the critical 12V line was within 0.23V (1.9%)
of 12V, and even at the highest loads, it never dropped below 12.08V. This is
excellent performance. The 3.3V regulation was within 0.06V (1.8%), while the
5V line was off -0.14V (2.8%) at full load. These are excellent results.

3. AC RIPPLE refers to unwanted “noise”
artifacts in the DC output of a switching power supply. It’s usually very high
in frequency (in the order of 100s of kHz). The peak-to-peak value is measured.
The ATX12V Guide allows up to 120mV (peak-to-peak) of AC ripple on the +12V
line and 50mV on the +5V and +3.3V lines. Ripple on all the lines was excellent
at all power levels, generally staying under 15mV through the lower half of
the power range. Even at maximum power, the 12V ripple stayed at just 28mV.
It’s about the best ripple we’ve measured on any PSU.

4. POWER FACTOR is ideal when it measures 1.0. In the most
practical sense, PF is a measure of how “difficult” it is for the
electric utility to deliver the AC power into your power supply. High PF reduces
the AC current draw, which reduces stress on the electric wiring in your home
(and elsewhere up the line). It also means you can do with a smaller, cheaper
UPS backup; they are priced according to their VA (volt-ampere) rating. Power
factor was very good for this model, running at or close to 1.0 through most
of the loads and no lower than 0.89 even at just 20W load.

5. LOW LOAD TESTING revealed no problems starting at very
low loads. Our sample had no issue starting up with no load, either, and the
power draw was much lower than normal. The 0.3W power draw in standby (power
switch on but computer off) is excellent.

6. LOW & 240 VAC PERFORMANCE

The power supply was set to 300W and 730W load at various AC input
voltages. Most full-range input power supplies achieve higher efficiency with
higher AC input voltage. SPCR’s lab is equipped with a 240VAC line, which was
used to check power supply efficiency for the benefit of those who live in 240VAC
mains regions. We also used a hefty variac to check the stability of the PSU
under brownout conditions where the AC line voltage drops from the 120V norm.

Efficiency improved around 3.8% with 244VAC input at 730W load.
The sample passed the 100VAC minimum input at 300W load without any issues.
Neither voltage regulation nor ripple changed appreciably during these tests.

7. TEMPERATURE & COOLING

High efficiency kept the PSU very cool even when the fan did not
spin, at loads below ~200W. Interestingly, as the fan sped up and cooled the
PSU, there were points where the temperature rise was lower despite higher output
load. Temperature rise was kept to single digit numbers till past 500W, which
is quite good. Once the hotbox temperature rose past ~40°C, the rise went into
double digits, but still topped out at only 18°C at full power with the intake
temperature at 44°C.

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

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.

CONCLUSIONS

Corsair power supplies have been winning praise from web tech
reviewers since day one. The AX850 is certainly no exception. It is a winning
power supply in every way — electrical performance is tops, efficiency
is high enough for 80 Plus Gold, the build quality is fantastic, the completely
detachable cables are a breeze to work with, the 7-year warranty is the industry’s
longest, and the noise level is vanishingly low at almost every power level.
That it gets even quieter in an advanced case with independent cooling intake
for the PSU is an added bonus silent PC enthusiasts will love.

A little caution should be included in Corsair’s package: “The
PSU fan will probably not turn on when the computer is booted, and you won’t
notice when the fan does start spinning. That’s the way it should be.”

Almost all of the positive things we wrote about the Seasonic
X-650 can be repeated here, because the Corsair AX850 is largely a higher power
version — with a voltage control fan rather than a PWM fan. It also has
the benefit of a year’s refinement of the X-series production line. 80 Plus
Gold certified models are premier PSUs, so the near-$200 price tag is no surprise.

Naturally, with its high power rating, the Corsair AX850 is ideal
for a new cateory of PC enthusiast that has emerged in the last couple of years:
Silent Gamers. Yes, strange as it sounds, gamers who like to play those typically
violent games with all kinds of percussive noise effects from the speakers —
but without any interfering noise from the PC. With CPU and GPU power in such
profusion, and overclocking now a routine feature in almost every performance
motherboard, simply building a hot rod gaming PC is not the challenge it once
used to be. Building a hot rod that’s also silent — a sleeper, if you will
— now, that’s still a challenge, and the Corsair AX850 is a great component
for such a build.

Corsair AX850 Balance Sheet
Likes * Silent at lower power * Very quiet in typical use * Even quieter in advanced case * Very high efficiency * High quality parts & build * Totally modular cables * Excellent electrical performance * 7-year warranty	Quibbles * Sample did not quite reach 90% efficiency at mid-power load

Much thanks to Corsair
for the review sample.

Corsair AX850 receives the SPCR Editor’s Choice Award

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SPCR Articles of Related Interest:
Power Supply Fundamentals

Recommended Power Supplies
SPCR PSU Test Rig V.4
Seasonic X-400 Fanless
Seasonic X-650: Seasonic Hits
Gold
Enermax Modu/Pro87+ 500W
Antec TruePower TP-750

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