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Nexus NX-4000 PSU

June 15, 2003 -- by Mike Chin

Product Nexus NX-4000 400W Power Supply
Manufacturer Nexus / Fortron-Source
Supplier Nexustek Netherlands
MSP US$110

The Nexus NX-3000 PSU, reviewed here last fall, may arguably have become the most popular PSU ever marketed as a quiet PC component. Nexus is undoubtedly hoping to repeat their success with the NX-4000, a higher power follow-up. Note that the retail box is cosmetically identical to that of the NX-3000 except for the labeling. Why change a good thing?

If the Nexus NX-4000 looks familiar in the photos below, that's no surprise. Like ExoticPC's SilenX 400W, the last PSU to be reviewed here, the NX-4000 is also based on the Fortron-Source FSP400-60PFN. At least visually, the primary differences are the labels and a different fan.

The fan is a model DF1208SH by Dynaeon Industrial Co. Ltd. rated at 0.2A at 12VDC. A quick search on the Dynaeon web site failed to bring up this particular model, but several conclusions can be made from the information on hand:

The designation SH -- S most likely means it is a sleeve bearing, probably chosen because it rattles and chatters less than the ball-bearing version. The H usually stands for High Power or Speed.

The 0.2A current rating of the fan is close to the 0.18A rating of the 80mm "H" fans I found on Dynaeon's site. They are rated for 2900 RPM, 41 CFM (cubic feet per meter) and 34 dBA -- all of which fall in line with the characteristics of typical PSU fans.

There are intake vents only on the side opposite the fan. Many other PSUs, including the Nexus NX-3000, have vents on the "bottom" or cover as well. Airflow behaves much like liquid in that it takes the shortest path or least resistance, which means that excessive venting may actually reduce airflow over the HS by allowing the air to take shortcuts via the shortest path. Having the intake vents only on the back panel means the air is forced to travel the entire length of the heatsinks in the PSU before it is blown out. This is probably better for cooling.

The PSU has Active PFC, which is generally a good thing for electrical efficiency. It also has universal input voltage, which allows the unit to be used on any AC line in the world without switching manually.

From the Nexustek web site...

Features:

  • Real silent power supply, only 21.7 dB(A) in idle mode
  • High efficiency
  • Output over voltage protection
  • Short circuit protection on all output
  • Reset Table power shut down
  • Approved by: TÜV, CSA, UL, NEMKO, FCC, CB & CE
  • Internal 80mm fan with wiregrill
  • Unique coupling of internal heat sink to the case of the power supply to increase overall heat dissipation area
  • 100% burn-in under high ambient temperature (50C)
  • Vacuum-impregnated transformer
  • MTBF: 100K hours at 25C
  • 100% Hi-pot tested
  • Line input fuse protection
  • Active PFC
  • Complies with EN61000-3-2
  • AC input full range

Specifications:

  • Remote ON/OFF Control: The power supply shall accept a logic open collector level which will disable / enable all out put voltage (excluding +5V standby)
  • Temperature range: operating 0C~50C; storage -20C~+80C
  • Temperature coefficient: 0.01% / C
  • Transient response: output voltage recovers in less than 1ms max. following a 25% load change
  • Hold-up time: 17 ms minimum at full load & nominal input voltage
  • Dielectric withstand: input / output 1800VAC for 1 second, input to frame ground 1800 for 1 second
  • Humidity: 5~95% RH
  • Efficiency: 65% min. 70% typical, at full load
  • Power factor correction: > 0.96 at full load
  • Power good signal: turn-on delay 100ms to 500ms
  • Overload protection: 150% max.
  • Inrush current: 80A cold, 120A warm at 132 VAC
  • Over voltage protection: +5V : 6.82V(max.)
  • +3.3V : 4.5V(max.)

Output Characteristics

AC Input
100~240 VAC, 10-5A, 60-50 Hz
DC Output
+3.3V
+5V
+12V
-12V
-5V
+5VSB
Load Regulation
-/+5%
-/+5%
-/+5%
-/+5%
-/+5%
-/+5%
Line Regulation
-/+1%
-/+1%
-/+1%
-/+2%
-/+2%
-/+1%
Ripple + Noise
50mV P-P
50mV PP
120mV PP
120mV PP
100mV PP
50mV PP
Min Load
0.3A
0.1A
0
0
0
0
Normal Load
14A
14.25A
6A
0.4A
0.15A
1.0A
Max Load
28A
40A
15A
0.8A
0.3A
2.0A
Max Power
235W
180W
9.6W
1.5W
10W
Max Power
380W
9.6W
1.5W
10W

For those who like to examine labels, here's the one for the NX-4000:

The photos with the cover removed show massive aluminum heatsinks:

Note that the main printed circuit board is so densely packed that additional circuitry was moved to two smaller PCBs mounted vertically on opposite sides of the main PCB, and a third vertical PCB behind the power switch. On the photo below, a green headed thermistor can be seen glued and clamped to the edge of the heatsink. One presumes this is the thermistor in the fan speed control circuit.

Connectors

There are a total of 7 wire sets:

  • 3 cables, 16" long, each with a single 4-pin IDE drive connector
  • 1 cable, 20" long, with one 4-pin IDE drive connector and one floppy drive power connector
  • 1 cable, 20" long, with two 4-pin IDE drive connectors
  • 20" long cable for main 20-pin ATX connector
  • 20" long cable for dual 12V (P4) connector
  • 3.3V connector on another 20" wire set.

Three of the cables terminate in one 4-pin connector each. None of the cables are very long (generally a good thing for standard size PCs), and all are close to the same length.

TEST METHODOLOGY

Parameters Tools
DC load on PSU DBS-2100 PSU load tester
Ambient temperature
Any number of thermometers
Fan / DC voltage regulation
Heath / Zenith SM-2320 multimeter
AC power
Kill-A-Watt Power Meter
Noise
Heath AD-1308 Real Time Spectrum Analyzer

The core PSU test tool on SilentPCReview's test bench is the DBS-2100 load tester, made (in Taiwan by D-RAM Computer Company) specifically for testing computer power supplies. The machine consists of a large bank of high power precision resistors along with an extensive selection of switches on the front panel calibrated in Amps (current) and grouped into the 5 voltage lines: +5, +12, -12V, +3.3, -5, +5SR. Leads from the PSU connect into the front panel. It is shown above with leads from a PSU plugged in.

To ensure safe current delivery, the DC output connector closest to the PSU on each set of leads is hooked up to the load tester. This ensures that the current delivered is distributed to as many short leads as possible. When pushing a PSU to its rated output, the heat generated in the wires can be an issue.

The PSU is tested at 5 DC output power levels:

  1. 65W: A very typical DC power draw by many system at low / modest load.
  2. 90W: Established previously as a typical max power draw of a mid-range desktop PC.
  3. 150W: For higher power machines.
  4. 300W
  5. Maximum (400W)

Care is taken to ensure that the load on each of the voltage lines does not exceed the ratings for the PSU. The PSU is left running 5~10 minutes at each power level before measurements are recorded.

The DBS-2100 is equipped with 4 exhaust fans on the back panel. A bypass switch toggles the fans on / off so that noise measurements can be made. The resistors get very hot under high loads.

Kill-A-Watt AC Power Meter is plugged into an AC outlet on the side of the DBS-2100 in the above picture. The AC power draw of the PSU is measured at each of the 4 power loads. The Kill-A-Watt is used to measure:

Efficiency (in AC-to-DC conversion) at each power level. This is the efficiency figure provided by PSU makers. It is obtained by dividing the DC power output (as set on DBS-2100 load) by the AC power consumption. Efficiency varies with load, and also temperature. PSUs seem to run more efficiently when warmer, up to a point. Generally, they are least efficient at low power and most efficient at 40~80% power load. The main advantage of high efficiency is that less power is wasted as heat -- this means a cooler PSU that requires less airflow to maintain safe operating temps (read: quieter.)

Power Factor (PF). This measurement can be read directly off the Kill-A-Watt. In simple terms, it tell us how much AC power is lost to harmonics (unnecessary electromagnetic energy) while driving the PSU. In practical technical terms, it is the difference between the measured V(oltage) x A(mperes) and AC power in Watts. PF varies somewhat depending on load. The ideal PF is 1.0, which means no AC power is lost. A PF of 0.5 means that to deliver 100W in AC to a PSU, your electric company actually uses 200W and this is often shown in your electric bill as savings (depends on your electric utility company and your account with them). 100W is lost or wasted. Active PF Correction (PFC) power supplies usually have a PF of >0.95. Passive PFC units usually run 0.6 - 0.8. Non-PFC units usually measure 0.5-0.7.

PF is not significant in terms of noise, heat or performance for a PC, but it is relevant to electricity consumption and energy conservation. Here is a simple illustration of worst and best case scenarios based on real tests I conducted on real PSUs (not published): A non-PFC low efficiency PSU vs an Active-PFC high-efficiency PSU.

Parameters
64% efficiency/ 0.5 PF PSU
78% efficiency / 0.99 PF PSU
DC power delivered
300W
300W
AC power consumed
467W
385W
Lost as heat in AC/DC conversion
167W
85W
Total AC power used*
934W
388W
AC power lost to harmonics
467W
3W
Total power wasted
634W
88W

*Total AC power used: This is what your electric bill would be based on, assuming you drove your PSU to 300W steady DC output, which is unlikely.

As you can see, the differences are remarkable, especially the bottom figures. If you are running large numbers of PCs, there's absolutely no question of the benefits of high PFC and, to a lesser degree, high efficiency.

The Heath / Zenith SM-2320 digital display multimeter, a fairly standard unit, is used to measure the fan voltages and the line voltages of the PSU output. The latter is done via the terminal pin on the front panel, above the connections for the DC outputs from the PSU.

Fan Voltage Measurements - The following three photos were taken in response to some inquiries about how I measure fan voltage while the PSU is running. This is the most convenient way I have found to measure the voltage to the fan in the PSU while it is running. My thanks to Terry W. for the needle / pin suggestion.

The first photo below shows a modified 4-pin plug and lead recycled from an old PSU. On one end of the red wire, a steel pin (the kind used in way too many numbers to package men's dress shirts) has been cut to about 3/4" length, and soldered on, with the sharp point bare. The metal socket in the IDE connector on other side was squeezed so that it holds the end of the multimeter probe tightly.

The photo below shows the pin poked through the + fan lead inside the PSU. The pin makes contact with the wire inside the insulation. This allows the + voltage to the fan to be measured without soldering, cutting, or any modification of the PSU or its fan.

Finally, the above scene with the camera zoomed back. The needle is insulated with a bit of duct tape, and the red wire placed along the PSU output wires before the cover is put back on. The black (negative) lead from the multimeter is connected into any black lead on any PSU output connector for the fan voltage to be read. After the testing is done, the pin is removed, and generally, the pierced holes in the fan lead insulation is small enough that a little rubbing is enough to almost make them disappear.

The Test Lab is a spare kitchen measuring 12 by 10 feet, with an 8 foot ceiling and vinyl tile floors. The acoustics are very lively and allows even very soft noises to be heard easily. The PSU under test is placed on a piece of soft foam to prevent transfer of vibrations to the table top. Temperature in the lab is usually ~20C. This is something of a problem as PSUs usually operate in environments that easily reach 45C. Sited next to or above the CPU, the PSU is always subject to external heat. This brings us to the next topic...

In-case Thermal Simulation

The solution is a AC bulb in an empty case with the PSU mounted normally. The distance between the bottom of the PSU and the top of the bulb is about 7 inches. All the case back panel holes are blocked with duct tape. The only significant exit for the hot air in the closed case is the PSU, which is then subject to a fair amount of heat. Still, the bottom front panel case intake hole is very large. In testing, the front of the case is moved so it hangs over the edge of desk, over free air, to ensure good fresh convection airflow. There are no case fans. This is probably more heat than would be seen by a normal PSU, because in a real case, there are usually other air exits, and at least one case fan.

In previous reviews, a 100W bulb was used for all tests. In this test, a small refinement was introduced: A 60W bulb is used for the 65W and 90W load tests; a 60W bulb seems a more realistic heat source for those lower power loads. The 150, 300 and 400W tests use the 100W bulb.

The PSU must cope with the heat generated by the light bulb plus whatever heat it generates within itself. In real systems, there would be other air exhausts paths and mostly likely at least one case fan. So a Panaflo 80mm L fan was mounted on the back panel of the test case and connected to a voltage controller. The PSU is run through its load range with and without the fan turned on, to 7V, which is about the level at which most PC silencers would run their case fan. It is a reasonable simulation.

Noise Measurements

The old Heath AD-1308 (portable half-octave Real Time Spectrum Analyzer with sound level meter functions) used in previous PSU reviews has been retired. Its usefulness was always questionable due to its inability to measure below 40 dBA and its unknown accuracy.

For this review, I used a highly accurate calibrated B&K model 1613 sound level meter on temporary loan from the University of BC's acoustics lab.

This professional caliber SLM dates back to 1978, weighs over 10 pounds, and is completely analog in design. It has a dynamic range that spans over 140 dB. The microphone used has a 1" diaphragm that's very responsive to low sound levels and low frequencies. The unit's absolute sensitivity reaches below 0 dBA -- at one point in the midband (1kHz) I was seeing -4 dBA for background noise in the UBC anechoic chamber. The image below shows the core controls and display. FYI, the display is showing 42 dB -- A weighted as per the dual-concentric knob on the bottom of the photo.

Noise readings were taken with the microphone positioned at 1 meter distance, facing the PSU fan. The ambient noise level in the live test room was ~26 dBA, which is too high for accurate readings on the lowest fan noise from the PSU.

These measurements cannot be compared directly with any previous noise testing done in SPCR reviews. Being done at 1 meter distance, it is somewhat comparable to manufacturers' specs. Note, however, that differences in the temperature of the test conditions, and the fact that my noise measurements were made in a live room rather than an anechoic chamber, makes such comparisons not quite valid, either. Because of the higher background noise level in my live test room, and the high degree of reflections from boundaries (walls, ceiling, floor), my measurements generally run considerably higher than they would be in an anechoic chamber. I would guesstimate as much as 6~8 dBA higher.

As usual, noise measurements are accompanied by descriptions of subjective perceptions. The measurements provide only part of the picture.

TEST RESULTS

Measurements were made at 5 output power levels: 65W, 90W, 150W, 300W and 400W. The PSU was allowed to run for 10~15 minutes at each power level before measurements were recorded. The room temperature was 24C.

A. Load on the PSU

LOAD
65W
90W
150W
300W
400W
+12V
24
36
60
144
168
+5V
20
20
40
80
145
+3.3V
16.5
26.4
39
66
78
-12V
2.4
3.6
3.6
3.6
3.6
-5V
1
2
2
2
2
+5VSR
1
2
2
4
4

B. On test bench, in 24C ambient temperature

AC Power
104W
136
210
410
560
Efficiency
62.5%
66%
71%
73.2%
71.4%
Power Factor
0.96
0.97
0.97
0.98
0.98
Fan Voltage
6.6V
7.1V
8.2
11V
11.9V
Noise*
32 dBA
33dBA
34 dBA
43 dBA
46 dBA

C. In thermal simulation case, over light bulb, with Panaflo 80L case fan on at 7V

AC Power
108W
143
218
416
560
Efficiency
60%
63%
69%
72%
71.4%
Light bulb
60W
60W
100W
100W
100W
Case Temp
27C
27C
29C
30C
30C
Exhaust Temp
30C
32C
35C
43C
46C
Fan Voltage
8.1V
8.6V
9.8V
11.7V
12V
Noise*
34 dBA
34 dBA
37 dBA
46 dBA
46 dBA

D. In thermal simulation case, over light bulb, with case fan turned off

Case Temp
31C
32C
33C
34C
35C
Exhaust Temp
34C
37C
38C
43C
46C
Fan Voltage
8.8V
9.6V
11V
11.8V
12V
Noise*
34 dBA
37 dBA
43 dBA
46 dBA
46 dBA

E. In thermal simulation case, over 100W light bulb, case fan at 12V

Output Power
Case Temp
Exhaust Temp
Noise
400W output
29C
42C
46 dBA

ANALYSIS

1. VOLTAGE REGULATION was excellent, within -/+2% on all lines in any combination of loads. It was often within -/+1%. The low and high voltage seen on each of the main lines is shown:

  • +12V: 11.75 to 12.24
  • +5V: 4.85 to 5.12
  • +3.3V: 3.37 to 3.4

This is far better than the -/+5% load regulation specified by Nexus.

It should be noted that I have no way of testing line regulation, so AC conditions are steady-state, not dynamic as it would be (potentially) in a real PC. The AC input as measured by Kill-a-Watt is usually within a couple of volts of 120V. I have no way to vary input AC voltage at this time. However, with the NX-4000's full-range AC input feature, line regulation may be a moot point.

Although over-capacity output was not tested seriously, the load was increased for a minute to force the PSU to deliver 440W, 10% over its rated maximum power: The NX-4000 withstood this abuse without a hiccup.

2. EFFICIENCYwas moderate in the sub-100W range, but improved to >70% when the PSU was pushed harder, rising to maximum of 73% at 300W. This is good performance.

3. POWER FACTOR was excellent, as it should be with the active power factor correction used in the NX-4000.

4. FAN VOLTAGE: The voltage to the fan started at a low 5.3V. It does not stay that low, however. At the 65W load, without any external heat to the PSU, the fan voltage ramped up steadily over a 10 minute period to 6.6V. In the actual use simulation, the fan voltage at 65W load was 8.1V.

The fan voltage appears to have a more-or-less linear relationship to power output and temperature. In other words, in the NX-4000, any increase in internal temperature always results in an equal proportionate increase in fan voltage up to the maximum 12VDC output to the fan.

This is quite different from the NX-3000, which keeps the fan voltage under 6V up to over 150W output, and then ramps the voltage up steeply thereafter. The behavior of the fan controller in the NX-3000 makes for a fan that varies less in noise during normal PC usage, and also keeps it at a lower speed over a wider range of power loads. The NX-4000 is less advanced in this regard.

5. NOISE measurements were still far from ideal despite the highly accurate professional SLM and 1 meter measuring distance. The test environment is too live and too noisy, and it was evident from the start that higher than normal readings were obtained. (See explanation in Test Methodology section.) Note for example, how the noise measured with the fan at 6.6V was 32 dBA, and with the fan at 8.6V, it was only 2 dBA higher. There is no question that neither is quite right. The difference should be bigger; certainly the first measurement should be lower. It is the effect of the relatively high ambient noise that's causing the high readings. Having said all that, the readings at higher levels are probably not as far off the mark.

Subjectively, the NX-4000 is quiet only at lower power levels. In a direct A-B comparison, it is considerably noisier than its brethren, the NX-3000. The fan used in the NX-4000 is not in the same class as the one in the NX-3000. It has a bit more bearing noise, and because it ramps up to higher speeds much sooner, considerably more turbulence noise as well.

The linear relationship between fan voltage/speed and temperature definitely hurts the noise performance of the NX-4000. The NX-3000, in comparison, has a dramatically different "stepped" curve in the fan voltage vs temperature curve that keeps the fan spinning fairly slowly up to a much higher temperature. This is similar to the behavior of the SF2 fan control circuit in the Seasonic power supplies.

Here is the noise data for the NX-3000 from Nexus. Note that this graph is not identical to the one shown in the original SPCR NX3000 review. The measuring microphone distance here is the correct 1 meter; in the original test, it was conducted at 0.6 meters.

Now here's a noise graph for the NX-4000 of data obtained under the same conditions. Note that the power test points are not identical to those in the NX-3000 graph. The virtually straight line shows clearly the linear relationship between fan voltage/speed and temperature I refer to.

The claim of 21.7 dBA @ 1 meter is probably correct at turn-on, but it is significantly higher under a normal low load (65W). The above graphs shows ~32 dBA at a power level of 160W with an ambient temperature of 27.4C. This jibes reasonably well with the result obtained in my live room testing with the PSU in the open at 24C in Table B above. But the conditions in a normal PC case are much closer to that of Table C above, where the temperature is ~30C, where the noise level at 160W jumps 3 dBA to 37 dBA.

Another thing to consider is that people who buy a 400W PSU likely do so because they need the extra headroom. The performance at 60% power level and higher may be more pertinent to examine. Again, referring to Table C, the noise level measured at 300W output was 46 dBA, which is likley too high a reading because of the live room and reflections. The Nexus spec sheet chart shows 39.5 dBA in 27.4C ambient. This is certainly not very quiet; it is less than 1 dBA less than at full power.

At these 300-400W power levels, air turbulence dominates the sound, which is noisy like most PSUs tested. And perhaps it should be: With current technology, it does not seem realistic to expect low noise in fan-cooled PSUs when running loads more than ~200W. It's interesting to note is that the Nexus factory noise data shows that for 300W output, the NX-3000 and NX-4000 have virtually the same noise. But at all lower power levels, the NX-3000 is significantly quieter.

TEMPERATURES were measured for this PSU during the in-case thermal simulation tests because adequate cooling was an issue for the SilenX 400W PSU reviewed last month. That model is based on the same Fortron as the NX-4000, so it was interesting to explore whether a powerful fan makes for a thermally more stable power supply.

The short answer is yes. The NX-4000 kept itself cool enough and ran continuously without a single problem under all the tough conditions it was subjected to in my usual demanding heat simulation testing.

The in-case thermal simulation tests were done with a lit light bulb in the case. Either a 60W or a 100W bulb was used to simulate the heat generated inside a running PC. Two sets of tests were done: One with no case fan, and another with a Panaflo 80mm back panel fan (our reference fan) running at 7V. In both cases, the PSU behaved well and stayed cool enough to keep the exhaust air well under 50C. It remained, in the worst case, a good 10C cooler than in the SilenX, which shut off due to thermal protection at 57C.

Why the additional fan?

  • The Panaflo 80L case fan at 7V does not add any more noise than emitted by the PSU under normal conditions.
  • Almost every system has at least one case fan, so this is a realistic real-use application.
  • The case fan voltage was selected to provide some airflow while its noise remained masked by the PSU fan noise.

The results show that the extra fan lowered case at all loads, as would be expected. Curiously, PSU exhaust temperatures for the 65, 90 and 150 watt output levels were improved but there was virtually no difference at the higher 300W and 400W levels. It's not clear exactly what this means. Perhaps the internal heat of the PSU was the primary source of temperature gain the the PSU at the higher loads?

A final comment on load testing: Full power testing of PSUs for any length of time is a very demanding test, generally tougher than what real use conditions can demand. SPCR's bench testing is steady-state and can be extended indefinitely until the PSU burns; in real world applications, PSUs in PCs rarely get anywhere close to this kind of abuse (except maybe in a serious server room, which is a different application altogether), and the power demand on them varies up and down in a much more dynamic way, with average power loads rarely exceeding 150W for desktop PCs.

CONCLUSION

Despite being based on the same platform as the ExoticPC's SilenX 400W 14 dBA model, the Nexus NX-4000 is a different beast. It does not take high honors in the noise category, but provides excellent, stable power at quieter than normal noise levels. It is noisier than its smaller brother, the NX-3000, and considerably more powerful. It is wise to provide good quiet case cooling to keep the NX-4000 at the minimal noise level, as its thermal / fan speed curve is more geared to best cooling than lowest noise. For those needing the high 235W of the combined +3.3V and +5.5V lines and the 180W of its 12V line, plus good peak headroom above these levels, it is a good choice.

The NX-4000's strengths:

  • heavy build quality, with massive heatsinks
  • high power output with high peak capacity
  • excellent stability and voltage regulation
  • excellent self-cooling
  • good directed airflow design,
  • good quality active PFC with universal voltage input
  • reduced noise

The NX-4000's weaknesses:

  • linear fan speed control
  • noise on the high side for SPCR
  • fan quality could be improved

The NX-4000 is a solid high power PSU well suited for use in a high power desktop PC. Recommended with caution for PC silencers seeking the lowest noise. Optimized case cooling is recommended in order to keep the PSU fan from spinning up to high noise levels.

Our thanks to Nexus for the NX-4000 review sample and their kind support.

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