Coolmax CU-400T & 600T Detachable Cable PSUs

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TEST RESULTS

For a fuller understanding of ATX power supplies, please read our article Power Supply Fundamentals & Recommended Units. Those who seek source materials can find Intel's various PSU design guides, closely followed by PSU manufacturers, at Form Factors.

For a complete rundown of testing equipment and procedures, please refer to the article SPCR's Revised PSU Testing System. It is a close simulation of a moderate airflow mid-tower PC optimized for low noise.

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 precise 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.

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 far too many variables in PCs and far 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 reasonable overall representation of that person, but it is not quite the same as an extended meeting in person.

REAL SYSTEM POWER NEEDS: One very important point is that the while our testing loads the PSU to full output (even >600W!) 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 65W and 250W, because it is the power range where most systems will be working most of the time. To illustrate this point, we recently conducted system tests to measure the maximum power draw that an actual system can draw under worst-case conditions. Our most powerful P4-3.2 Gaming rig drew ~180W DC 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 SLI could draw as much as another 150W, but the total still remains well under 400W in extrapolations of our real world measurements.

SPCR's high fidelity sound recording system was used to create MP3 sound files of this PSU. As with the setup for recording fans, the position of the mic was 3" from the exhaust vent at a 45° angle, outside the airflow turbulence area. The photo below shows the setup (a different PSU is being recorded). All other noise sources in the room were turned off while making the sound recordings.

Ambient conditions during testing were 23°C and 20 dBA, with input of 120 VAC / 60 Hz measured at the AC outlet.

CoolMax Taurus CU-400T TEST RESULTS
DC Output (W)
65
90
150
200
250
300
400
AC Input (W)
95
123
200
263
337
404
550
Efficiency
68%
73%
75%
76%
74%
74%
73%
Intake Temp (°C)
26
28
30
32
33
34
37
PSU Exhaust (°C)
36
40
44
48
52
56
64
Fan Voltage
4.8
4.8
6.7
9.2
11.2
12.1
12.4
Noise (dBA/1m)
21
21
26
36
39
40
41
Power Factor
0.65
0.65
0.67
0.68
0.68
0.69
0.69

NOTE: The ambient room temperature during testing varies a few degrees from review to review. Please take this into account when comparing PSU test data.


CoolMax Taurus CU-600T TEST RESULTS
DC Output (W)
65
90
150
200
300
400
500
600
AC Input (W)
90
117
185
238
354
478
600
730
Efficiency
72%
77%
81%
84%
85%
84%
83%
82%
Intake Temp (°C)
28
28
29
31
32
35
38
39
PSU Exhaust (°C)
32
34
38
40
43
50
57
59
Fan Voltage
4.7
4.7
6.5
8.5
11.4
11.9
11.8
12.4
Noise (dBA/1m)
21
21
26
34
39
40
40
41
Power Factor
0.64
0.65
0.67
0.69
0.70
0.71
0.71
0.72

NOTE: The ambient room temperature during testing varies a few degrees from review to review. Please take this into account when comparing PSU test data.

ANALYSIS

1. VOLTAGE REGULATION remained within the ±5% spec for all but one measurement, and tended to stay within one or two percent. The out of spec reading occurred under the full 600W load on the +5V line, where the voltage was 6% below 5V. At lower output levels, this rail was perfectly stable. Given how well most systems tolerate fluctuations in voltage and how difficult it is to build a system that draws even 300W, this is only a theoretical failing. In real use, this power supply should be just as stable as any other model.

CU-400T (400W)

  • +12V: 12.20 to 12.42
  • +5V: 4.91 to 5.09
  • +3.3V: 3.20 to 3.33

CU-600T (600W)

  • +12V: 11.80 to 12.07
  • +5V: 4.73 to 5.00
  • +3.3V: 3.36 to 3.39

2. EFFICIENCY in the 400W model was on par with the power supplies on the market three years ago. It's been a while since we've reviewed a unit with efficiency in the low 70's. The small heatsinks also perform poorly; the difference between intake and exhaust temperature was among the highest we've measured, indicating more heat buildup inside the PSU than with most other models. .

Fortunately, the 600W model is a different beast altogether. Although efficiency is poor at the low end, it does reach 80% efficiency at a modest 150W output and stays in the low-to-mid 80's under high load. This is very good performance.

Compare the total AC power draw at 300W DC output: The 400W model produces 50W more heat to achieve the same output. Not only does this reduce the life of the power supply and increase AC electricity consumption, but it also raises the amount of heat in the computer case.

With the 600W model at full output, a lot of the current was running through the three 3.3V wires in the ATX header. These wires were hot to touch under this load, and may not have safely sustained this level of power delivery indefinitely . Like the fluctuation in the +5V line, this is mainly a theoretical criticism, but it does mean that the power supply had difficulty delivering the load it was rated for.

3. POWER FACTOR:

In spite of claims on the CoolMax web site about Power Factor Correction being optionally available, neither of our units performed as though they had PFC of any sort. The 0.65-0.71 performance is typical of power supplies without PFC.

4. FAN, FAN CONTROLLER and NOISE: The test environment is live, so readings are higher than would be obtained in an anechoic chamber readings, due to reflections and reinforcement of sound waves off the walls, ceiling and floor.

No matter what output load was tested, the Low and Automatic fan settings always sounded the same and resulted in the same voltage at the fan. This means that even at 65W output, the internal temperature was too high to allow the Low speed controller to kick in. The manual notes that Low speed is intended for use when the system is in standby mode. Presumably, the fan would be dropped in speed still further or even turned off entirely with the <15W load at standby.

In spite of the differences in efficiency and internal heat, the two different models proved to be very similar in the noise they produced at any given power level. Both models use the same fan, and their fan controllers seem to behave similarly.

The starting fan voltage is 4.7V, low enough to put the starting noise level close to the ambient room noise. The sleeve bearing fan is quite good, although there is some very slight mechanical noise at low speeds. As the fan speed increases, a low frequency hum begins to dominate, although turbulence noise is also fairly audible. At full speed, the fan is far from quiet, but this is true of almost any power supply. In both models, the fan reaches close to maximum speed at 250-300W output (or 32-33°C intake temperature), with the peak noise measuring around 40 dBA/1m.

The fan ramped up slowly around the 150W mark, although not until it was left at this output for some time. The change in speed was gradual enough to be inaudible. When the fan speed stabilized under the 150W load, it was plainly audible but still fairly quiet.

MP3 Sound Recordings of CoolMax Taurus CU series PSUs

CoolMax Taurus CU-x00T @ <90W: 21 dBA/1m

CoolMax Taurus CU-x00T @ 150W: 26 dBA/1m

CoolMax Taurus CU-400T @ 200W: 36 dBA/1m

There was no need to make recordings at higher power levels; it's simply too loud.

Sound Recordings of PSU Comparatives

Seasonic Tornado 400 @ 65W (19 dBA/1m)

Seasonic S12-430 @ 150W (19 dBA/1m)

Enermax Noisetake 600W (2.0) @ 150W (27 dBA/1m)

Nexus 92mm case fan @ 5V (17 dBA/1m) Reference

HOW TO LISTEN & COMPARE

These recordings were made with a high resolution studio quality digital recording system. The microphone was 3" from the edge of the fan frame at a 45° angle, facing the intake side of the fan to avoid direct wind noise. The ambient noise during all recordings was 18 dBA or lower.

To set the volume to a realistic level (similar to the original), try playing the Nexus 92 fan reference recording and setting the volume so that it is barely audible. Then don't reset the volume and play the other sound files. Of course, tone controls or other effects should all be turned off or set to neutral. For full details on how to calibrate your sound system to get the most valid listening comparison, please see the yellow text box entitled Listen to the Fans on page four of the article SPCR's Test / Sound Lab: A Short Tour.

CONCLUSIONS

The CoolMax Taurus CU power supplies are capable of working in a quiet system if it is not too demanding. A high-powered, P4-Prescott system would probably be a struggle for these power supplies in terms of noise, although neither model is lacking for output capacity. The stock fan was well chosen and the fan controller changes the fan speed slowly and smoothly, although it does ramp up a little sooner than some of its competitors.

The 400W model is a bit too inefficient to deserve much consideration for quiet computing in this day and age of >80% efficient PSUs. Even though the power supply itself might remain quiet at lower loads, the extra heat added to the system may increase the speed of other thermally controlled fans or raise the CPU and system temperatures. At lower power output, the efficiency of the 600W model is not great, but it improves considerably at higher loads.

The high power available on the single 12V line of the 600W model makes it unique among today's power supplies. Most higher power PSUs are now compliant with ATX12V v2.xx, which calls for no more than 20A to be carried on a single 12V line. In most current PSUs, 32A for 12V would be split equally between the AUX12V connector and the rest of the 12V connectors. For gamers seeking to run two high end VGA cards in SLI, this means that the available 12V current is sometimes inadequate, while there is too much current for the CPU running of the AUX12V line. It's difficult to determine whether the issue is purely theoretical or has basis in actual gaming experience where the VGA cards misbehave for lack of current. With the CU-600T, since all the 12V current is on a single line, as long as the total 12V current does not exceed 32A, everything is hunky dory — at least in theory. Of course, the absence of any PCIe video power connectors is a bit of a challenge; adapters for 4-pin Molex connectors would have to be used.

There are a number of small disconcerting issues about these products.

  1. No mention of a warranty is made anywhere in the documentation, and even contact information is quite scarce.
  2. The product page on the company web site is also very inaccurate. Not only are the electrical specifications out of date, but no less than four of the listed features are wrongly listed:
    • A ball-bearing fan is listed, but our samples came with sleeve-bearing fans.
    • A minimum 450mm (~18") cable length is specified, but several cables were shorter than this.
    • PCI-Express Ready is listed as a feature, but no PCIe cable is included
    • Active or Passive PFC is listed as an optional feature, but our samples had neither, and no models with PFC could be found for sale anywhere on the web.

The information confusion does not inspire confidence. Still, the CU-600T is not a bad buy for a budget purchase, especially if you want detachable cables. The CoolMax may provide quiet performance out of the box for a lower price than many of its competitors.

Our thanks to CoolMax Technology Inc. for the opportunity to examine these power supplies.

* * *

Discuss this article in the SPCR Forums.



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