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Nexus RX-8500 850W Power Supply

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Nexus reaches out to serious gamers with a power supply claimed to be the quietest 850W model available. The company has a long reputation for quiet computer products, so if the idea a quiet PSU for a gaming rig appeals, read on.

August 25, 2009 by Mike
Chin

Product
Nexus RX-8500
850W ATX12V v2.2 Power Supply
Manufacturer
Nexustek
Sample Supplier
EndPCNoise
Market Price
US$160

Nexus is a long-established brand specializing in quiet PC components, mostly fans, power supplies, heatsinks and cases going back nearly a decade. Some Nexus products have long been used as reference quiet products at SPCR, the most notable being the Nexus 120mm "Real Silent Case Fan". Back in the day, some Nexus power supplies were also among the quietest available. In recent years, quiet power supplies became much more widely available as competition in this sector intensified, and the Nexus NX-8050 and 8060 were good and quiet, but no longer exceptional. The Value 430 put Nexus back on top as it turned out to be the quietest fan-cooled PSU ever reviewed.

The RX-8500 is a different animal altogether. It is the first Nexus PSU to enter the super high power realm; this 850W was joined recently by the RX-1K, a kilowatt model that appears to be part of the same series, with identical casing, fan and modular cables. With such high power ratings, there’s no doubt that the target audience is the "serious" gamer (which always sounds like an oxymoron). Nexus claims that the RX-8500 is "the quietest 850 Watt model in the market." Such a claim is quite bold, because these days, there are many 850W power supplies that can be described as very quiet.


The biggest box of all Nexus PSUs.

It’s quite well packed.


It’s modular and comes with many output cables, but several thick cables are permanently attached.

Nexus RX-8500 Feature Highlights (from the product web site)
FEATURE & BRIEFOur Comment
80% efficiency; a minimum of 80%
efficiency guaranteed at all loads!
It’s not 80 Plus certified, and 80% is no longer exceptional. 80 Plus Silver and Gold models offer up to 90% efficiency.
Inaudible performance with Real Silent 13.5cm fan
Big fan usually means lower speed and noise… but we’ll find out.
Modular, sleeved cables.Good
Overvoltage and short-circuit protectionOK.
– Excellent airflow, honey-comb grill
– Active PFC

– ATX12V V2.2
All pretty standard.

SPECIFICATIONS

Surprisingly, Nexus does not provide complete specifications for the RX-8500. Virtually no technical details are provided. There is only a table showing in/out power.

Nexus RX-8500 Specifications
AC Input
115V/230V 15A/7.5A 50/60Hz
DC Output
3.3V
5V
12V1
12V2
12V3
12V4
-12V
5Vsb
Max Output
24A
30A
20A
20A
20A
20A
0.8A
3A
Max Combined
170W
760W
6W
15W
Total Power
829W

EXTERNAL TOUR

The RX-8500 has a standard black finish with wire fan grill. The 135mm diameter fan is a bit bigger than the standard 120mm. The mesh exhaust grill is nicely open for airflow. There’s an on/off switch and AC power socket.


The case looks like it was meant for a model with 110/220 VAC input switch.


A 135mm fan, obligatory black finish. There is one vents other than the main exhaust, next to the attached cables, of which there are five. These cables are quite thick and cumbersome.


The 10 output connectors are clearly marked. The main ATX and the 12V Aux outputs must be the 12V3 line.

 

OUTPUT CABLES

The Nexus RS-8500 comes with many output cables.


All the cables are nicely sleeved. Some are ~3′ long.

Permanently wired, sleeved:

  • 1 – 18" cable w/ ATX 20+4-pin motherboard connector
  • 1 – 18" cable w/ Aux 12V 4-pin connector
  • 1 – 18" cable w/ Aux 12V 8-pin connector
  • 2 – 18" cable w/ PCIe 12V 6+2-pin connector

Modular, sleeved:

  • 2 – 18" cable w/ 6-pin PCI-Express connector
  • 2 – 36" cable w/ 3x SATA connectors
  • 2 – 36" cable w/ 3x 4-pin Molex and 1x floppy connector

INTERIOR

The components are laid out on a PCB that fills the available space.


Conventional layout, quite small heatsinks for the rated power.


The geometry of the 11-blade 135x25mm 0.25A fan looks good; the trailing edges of the blades are not parallel to the struts, which usually helps to minimize tonal noise. (See Fan Blade Geometry on page 3 of the
Anatomy of the Silent Fan for more details.) This is the same brand of fan used in the Nexus Value 430W PSU. As with the earlier PSU, the original manfacturer of this product is not known.


The primary capacitor is a 450V 560uF Teapo rated at 85°C.



There appears to be two 12VDC transformers. A guess is that the small transformer gives 5VDC, from which the 3.3VDC line is derived via DC/DC conversion.



Secondary capacitors are buried under the mess of output cable connections. These capacitors are not mentioned in the marketing blurb, so they’re probably fairly ordinary. It’s unusual to see all those trim pots on the small PCB on the left; they are probably for tweaking voltages for the various lines.

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 10~11 dBA, 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 over 1000W.
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, cooling is the main concern, not the noise level.

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:

  • Intake temperature (determined by ambient temperature and power output
    level)
  • Efficiency of the PSU (how much heat it generates while producing the
    required output)
  • The effectiveness of the PSU’s cooling system, which is comprised of:
    • Overall mechanical and airflow design
    • Size, shape and overall surface area of heatsinks
    • Fan(s) and fan speed control circuit

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

Ambient conditions during testing were 23°C and 11 dBA. AC input was 118~122V,
60Hz. .

OUTPUT & EFFICIENCY: Nexus RX-8500

DC Output Voltage (V) + Current (A)

Total DC Output

AC Input

Calculated Efficiency
+12V1
+12V2
+5V
+3.3V
-12V
+5VSB
12.10
0.96
4.98
0.95
3.40
0.96
0.1
0.1
21.3
39
54.7%
12.10
0.97
12.10
1.69
4.98
0.96
3.38
0.97
0.1
0.1
41.9
63
66.5%
12.10
1.87
12.10
1.69
4.98
1.88
3.37
2.68
0.2
0.4
63.7
89
71.6%
12.13
1.87
12.13
3.37
4.98
2.79
3.37
2.63
0.2
0.4
88.9
118
75.4%
12.14
3.76
12.13
4.91
4.98
5.41
3.37
4.62
0.3
0.5
150.4
188
80.0%
12.20
4.76
12.20
6.58
4.96
6.03
3.35
7.16
0.3
1.2
202.3
244
82.9%
12.29
7.62
12.28
6.71
4.96
7.84
3.35
8.02
0.4
1.4
251.6
303
83.6%
12.30
7.68
12.30
9.73
4.95
7.74
3.34
9.22
0.5
1.4
303.5
362
83.8%
12.35
11.47
12.34
11.43
4.95
12.35
3.31
12.24
0.5
1.5
400.2
477
83.9%
12.40
16.20
12.39
13.10
4.93
15.93
3.27
15.10
0.5
1.5
505.7
614
82.4%
12.45
16.20
12.44
25.80
4.91
18.20
3.23
19.72
0.8
1.5
701.5
885
79.3%
12.47
24.91
12.47
29.10
4.88
18.66
3.19
19.12
0.8
1.5
849.4
1092
77.8%
Crossload Test
12.38
21.70
12.38
23.4
5.21
0.97
3.32
0.96
0.1
0.1
666.3
804
82.9%
+12V Ripple: 87mV max @ 850W
+5V Ripple: 31mV max @ 850W
+3.3V Ripple: 27mV max @ 850W
NOTE: The current and voltage for -12V and
+5VSB lines is not measured but based on switch settings of the DBS-2100
PS Loader. It is a tiny portion of the total, and potential errors arising
from inaccuracies on these lines is <1W.
OTHER DATA: Nexus RX-8500
Target Output (W)
20
40
65
90
150
200
250
300
400
505
700
850
Intake (°C)
23
25
26
27
30
32
33
34
34
39
43
44
Exhaust (°C)
25
27
31
32
36
39
42
44
48
54
65
72
Temp Rise (°C)
2
2
3
6
7
7
9
10
14
15
22
32
Fan
not available*
SPL (dBA@1m)
14
14
14
14
14
18
23
28
32
32
33
33
Power Factor
0.83
0.95
0.99
0.99
0.99
0.99
0.99
0.99
0.99
0.99
0.99
0.99

AC Power in Standby: 0.9W
AC Power with no load: 10.8W
NOTE: The ambient room temperature during
testing can vary a few degrees from review to review. Please take this
into account when comparing PSU test data.

ANALYSIS

1. EFFICIENCY This is a measure of AC-to-DC
conversion efficiency. The ATX12V v2.2 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 RX-8500 does not reach 80% efficiency until 150W load, which is about 17% of rated power. This is good enough for 80 Plus performance, but it’s still a high level of power for 80% efficiency, especially when efficiency is so much worse at lower levels. The fact is that most systems will idle at lower than 150W unless it’s really a beast of a gaming system. The mediocre lower power efficiency is left behind as output rises above 150W, and the unit achieves a relatively high plateau of >82% efficiency from 200~500W. Above that power output, efficiency falls again as expected in the face of rising temperature. The drop to below 78% efficiency is not unusual; it’s surprising to see it hold up as high.

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%.

The lower 5V and 3.3V lines were very stable under all but the most severe loads. The 12V line actually climbed as load increased, to a high of 12.45V at very high loads. This oddity should not be too much of a concern; it’s still within the 5% recommended variance for the 12V line. Voltage regulation in the crossload test was fine.

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 was good, but not exceptional as the load increased. The 87mV peak on the 12V line was within the 120mV maximum allowable, and the 5V and 3.3V lines were under the 50mV maximum at worst loads.

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. PF on our sample was poor at the lowest (and somewhat unrealistic) loads but improved to nearlt 0.9 by about 65W load. Near 1.0 performance was reached above 400W load.

5. LOW LOAD PERFORMANCE is significant mainly to minimize energy waste and with system that demand very low power; the latter can cause some PSUs not to start. Standby performance was fine with 0.9W draw. The unit powered up with no load, drawing about 11W, suggesting it has a built in loader to prevent low loads from causing trouble.

6. CROSSLOAD TEST – Basically the load on the 12V line was maximized while the load on all the other lines was minimized. Voltage regulation on all the lines was good, and ripple stayed well limits. There were no other changes.

7. 240 VAC INPUT – The power supply was set to 600W load with 120VAC through the
hefty variac in the lab. The variac was then dialed 10V lower every 5 minutes.
This is to check the stability of the PSU under brownout conditions where the
AC line voltage drops from the 110~120V norm. Most 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.

Various VAC Inputs: M700W @400W Output
VAC
AC Power
Efficiency
245V
716W
83.8%
120V
742W
81.0%
110V
752W
79.8%
100V
766W
78.4%

There were no surprises here. Our sample’s efficiency improved by nearly 3% at the higher VAC, and dropped a little over 1% for each 10V drop in VAC. Voltage regulation and ripple were unchanged.

8. NOISE and FAN CONTROL

The noise level at startup was a very low 14 dBA@1m and the quality of the sound was benign. However, this noise level was maintained only up to 150W load, by which point, the fan began speeding up in response to increasing heat.


The audio spectrum looks benign and very low in amplitude at up to 150W load
.


By 200~250W, the fan noise rose to 20 dBA.

By 200W load, SPL rose to 18 dBA@1m (and it was probably still climbing when the power level was shifted up — hence the screen capture above). The overall noise character was still smooth, mostly broadband. The fan speed continued to rise almost linearly in response to load (and temperature): 24 dBA at 250W, 28 dBA at 300W, and to the maximum of 32~33 dBA@1m reached at 400W. The PSU did not get significantly louder even with much higher load; the fan already seemed to be at full speed.

The voltage across the fan leads could not be monitored; it showed up as 12V at all times. This suggests some type of PWM circuit is used to control the fan speed. The main advantage of such a fan controller is that it draw slightly less power and allows most fans to run at lower speed than with a voltage controller. The fan speed could not be monitored for lack of a speed monitoring device or signal cable. However, the SPL is the essence of the fan data, and that is clearly shown in the second table above (OTHER DATA).

9. COOLING

The RX-8500 kept itself cool enough up to around 500W load, but internal temperature seemed to rise faster than normal above that point. At maximum load, the exhaust air temperature exceed 70°C, which suggests the unit should not be pushed so hard for long. Aside from the usual smell of electronic burning as full load was approached, there was no evidence of misbehavior associated with overheating. That power efficiency dropped a few point at full load is no surprise.

COMPARISONS

The comparison table below shows the SPL versus Power Load data on all the PSUs tested in the anechoic chamber thus far.

Comparison: Various PSUs Noise Vs. Power Output in Anechoic Chamber
Model
90W
150W
200W
250W
300W
400W
500W
6~700W


Nexus Value 430

11
11
16
18
18
19
n/a
n/a


Seasonic M12D 850W

14
14
14
14
14
24
37
42


Enermax Modu82+ 625*

13
13
14
15
16
26
36
37

Coolermaster M700W

14

14

18

21

25

27

34

34

Chill Innovation CP-700M

15

15

15

15

17

30

34

34

Antec Signature 650

15

15

15

18

18

28

36

47

SilverStone DA700
18
18
18
18
23
32
35
41

Nexus RX-8500

14

14

17

22

28

32

32

33

NesteQ ECS7001

22

22

22

21

23

25

36

37

PCPC Silencer 610
20
24
24
24
24
30
40
50
The green boxes represent >30 dBA@1m SPL.
*Guesstimates based on the Modu82+ 425’s idle in the chamber and the Modu82+ 625’s load test.

The green colored blocks are 30 dBA@1m or greater SPL readings. The PSU that stayed quiet (under 30 dBA) to the highest load is not in this table because it has not been tested in the anechoic chamber: The Zalman ZM1000, which stayed below 30 dBA to almost 600W load. It’s idle noise is probably not low enough to match the M12D-850W, the Enermax, or the Signature 650; its measured SPL in the live test room was 20 dBA@1m, a dB or two higher than the others.

The Nexus RX-8500 has low SPL at low loads, but it ramps up in noise much more quickly in the middle-low load range than many of the others. Yet, the maximum loudness is lower than many of the others.

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

The Nexus RX-8500 is a quiet power supply at low power loads, modestly quiet at middle loads, and quieter than most competitors at very high loads. Unlike some of its precessors, this Nexus has a fan speed controller that is more linear in its response to temperature rise, at least to about 400W. The rate at which the noise rises is a bit quicker than most every other PSU tested in the anechoic chamber.

The efficiency results suggest that this PSU is not quite up-to-date with the latest technology. It does not approach 85% efficiency, which is the starting point for the 80 Plus Bronze models. The <150W power efficiency is surprisingly low as well. Mind you, Nexus makes no claim about the unit being 80 Plus approved in any way.

For extreme gamers looking to save their hearing, the noise difference between the Nexus and other quiet PSUs we’ve reviewed may be signficant. While the noise at mid-low power isn’t the lowest, and 32 dBA@1m isn’t exactly whisper quiet for 400W, it’s pretty darn quiet for 600W or even higher, because the RX-8500 fan simply doesn’t spin any faster. Many of the top rated PSUs actually get louder than 40 dBA@1m at >500W level. This is probably good for their longevity and for system cooling under high load, but they are generally noisier than the Nexus RX-8500 at >500W load. The Nexus delivers clean power, and fairly quietly even at high load.

For the quiet PC enthusiast, the noise at <200W is usually most important, and the noise level of this model is low enough to compete with some of the best rated silent PSUs as long as 200W load is not reached. On the flip side, the 850W rating is overkill. Most silencers will opt for lower power models that better reflect their power requirements.

The thick attached cables are a bit of an annoyance for a model that’s supposed to have modular cables… but this complaint applies to many other so-called modular PSUs.

The Nexus RX-8500 reflects an interesting balance: Very quiet at low load, modest in the middle, and still quite quiet at very high load. It’s hard to confirm or dispute the Nexus claim of the RX-8500 being "the quietest 850W PSU" because it depends on just how the noise is assessed. Nevertheless, the Nexus may be the perfect choice for a obsessed computer gamer who worries about his hearing.

Our thanks to Nexus and EndPCNoise for the RX-8500 sample.

* * *

SPCR Articles of Related Interest:
Power Supply Fundamentals
SPCR PSU Test Rig V.4
Coolermaster Silent Pro M700W
Chill Innovation CP-700M
Seasonic M12D-850

Zalman ZM1000-HP

* * *

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