Coolmax offers up a line of power supplies with detachable cables that they say is also very quiet. We run them through the SPCR PSU test routines to check acoustics, thermal behavior, power delivery and stability. Those seeking high current on a single 12V line will be pleased.
July 10, 2005 by Devon
Cooke with Mike Chin
| Product | CoolMax Taurus CU-400T / CU-600T 400W / 600W ATX power supply w/ detachable cables |
| Manufacturer | CoolMax Technology Inc. |
| Market Price | 400W: ~US$60 / 600W: ~US$120 |
CoolMax sells a number of power supplies under its Taurus marquee. SPCR has reviewed a
Taurus before: CoolMax
had one of the first fanless power supplies on the market in
its CF-350B. Their CU-x00T series bears little resemblance to the fanless model,
but CoolMax still refers to it as a Taurus. To add to the confusion, the manual
and the label on the power supply list the model number as AP-x50X, with CoolMax’s
“official” model number listed in parentheses.
The distinguishing features of the CU series are detachable cables
“EZ Wires” and a three-way fan switch that is common to most
of CoolMax’s fanned models. It is also available in three different finishes:
Glossy black, a dark silver-gray, and a metallic white. Three different capacities
are available, of which we are testing two: The 400W model and the 600W model.
The remaining model comes in at 500W.
In the box: The power supply, two bundles of cables, an AC cable, plus
an eight page manual.
The eight page manual is really four pages long: The remaining pages are
completely blank. Aside from the colorful front cover, there is nothing to identify
CoolMax as the company responsible for the product, and it even lacks the usual warranty and copyright notices. No contact information (not even a web
site) is included with the product.
The
Coolmax company’s web site provides an address for their head office in Taiwan, but no phone number was listed. Customer service seemed to be limited
to e-mail or post. However, a related web site for Top Tech USA, which is the US arm for Coolmax, does provide a page of US contact information that includes an address, telephone number and email address. No warranty or service information of any kind is provided.
| Feature Highlights from the manual of the CoolMax Taurus | |
| FEATURE & BRIEF | COMMENT |
| Smart detachable cable design allows you to connect cables you actually need, therefore improve internal airflow and avoid system clutter. | A good reason to buy a unit with detachable cables. |
| Innovated voltage sensor circuit reduces voltage drops, make sure the PSU provides enough power to your system. | A variant of the standard voltage regulation circuit that measures the voltage at the ATX plug instead of at the source of the wire. |
| All kinds of protection circuits (OVP/OPP/SCP). | Maybe not literally all kinds, but these are probably the most important. |
| High efficiency: not less than 75% at full load. | This seems slightly dated; 75% efficiency isn’t especially high these days. |
| Externally selectable 3-band TMS (Thermal Management System: Auto/Low/High) to meet vast majority end users’ demands. | It’s nice to have options. |
| 12cm fan. | The de facto standard these days. |
| S-ATA ready. | Another standard issue feature. |
| Cable-tidy design and user friendly Ohm-Leg plugs. | Mesh sleeves for the cable sets. Ohm-Leg? Your guess is as good as mine. |
Depending on where you look, the specifications for the power supplies give
conflicting information. Amperage ratings and even the number of rails are incorrectly
listed on CoolMax’s web site: There is an erroneous rating for a -5V rail. However,
double checking the pin hole in the ATX connector revealed that no such voltage
was supplied, as per the more recent ATX12V specs. The spec label for the 400W
model is shown below:
A couple of things stand out in the specs for the 600W model:
- The +12V rail is rated for 32A well over the 20A limit that Intel
recommends on a single +12V rail. - The +5V rail is rated for a whopping 60A, double many other similarly rated
power supplies.
The fact that there is only a single +12V rail for a power supply of this capacity
means that the power supply does not comply with Intel’s latest ATX12V v.2.x PSU Design Guide. Most likely it was designed to conform to ATX12V v.1.3, which is the only
version of the specification that lacks the -5V rail but does not specify multiple
+12V lines for capacities above 20A. However, no mention of ATX12V could be
found in any of the documentation related to the power supply. The box does
say “ATX Power Supply”, but ATX is not the same thing as ATX12V, and
no version number is listed.
Much of the additional capacity that the 600W model is capable of seems to
come from the excessive 60A rating for the +5V rail. Using Ohm’s law (P = VI),
this works out to 300W far more than anyone could realistically draw
in a powerful modern system. The strength of this line is further evidence of
the ATX12V 1.3 lineage of this model. Power supplies of this vintage were designed
to supply the processor from the +5V rail rather than the +12V rail that is
commonly used today.
PHYSICAL DETAILS
In the bling department, the Taurus is fairly sedate, settling for a dark chrome
or titanium finish without any flashy colors or LEDs. The gold-plated fan grill
contrasts fairly well with the darker finish of the casing, giving it a polished
look that isn’t over the top. Two other color options are supposed to be available,
but they seemed quite difficult to find.
Note the additional switch to the right of the voltage selection switch.
This is for controlling fan speed.
The underside of the unit. The wire fan grill should not restrict airflow
much.
Ever wanted advertising inside your case? Impress your LAN-partying
friends with the “Super Noise Killer” fan controller!
One thing that marred the appearance a little was the presence of marketing
on the external casing. A pair of stickers advertising the “quiet”
fan controller are conspicuously placed near the fan vent, while the power sockets
are surrounded by text outlining the “Special Features” of the power
supply, just in case you need reminding why you bought a power supply with detachable
cables. There’s also two cautionary notes:
- PCI-Express sockets may slightly different one another, if the PCI-Express
cable connector cannot fit well at one end, please change to the other end
[sic]. - You MUST connect the 3-Pin sensor connector cable to avoid any possible
voltage drops!
Point 1 should not pose a problem for most users: Although there is a PCI-e
socket on the unit itself, even the 600W unit did not ship with the necessary
cable to make use of it.
Depending on how the internal circuitry is designed, point 2 may be of minor
or crucial importance. Almost all power supplies use a feedback circuit to regulate
the +5V line, although most designs keep this circuit within the confines of
the unit. The advantage of locating the voltage sensor at the end of the ATX
cable is that the feedback circuit does not have to compensate for the voltage
drop across the cables. Instead, the voltage is measured as close to the motherboard
as possible, hopefully leading to more accurate voltage regulation. The disadvantage,
especially in a unit with detachable cables, is that if the feedback sensor
in not plugged in, the power supply no longer has any means of regulating the
+5V line, which may lead to voltages far enough out of spec to damage the motherboard.
If the power supply has been intelligently designed, a secondary feedback circuit
should have been built into the unit that monitors the voltage internally and
does not require the user to plug it in. This would mitigate the disadvantage
of the first design. However, it is unknown exactly how CoolMax designed this
power supply, so make sure you follow CoolMax’s instructions and install the
sensor cable!
Although there is a PCI-Express socket on the unit itself, no PCIe cable
was included with either of our test samples.
The rear grill is stamped in the unrestrictive honeycomb pattern that is typical
of 120mm fan power supplies, but the holes are slightly smaller than they could
be. A wider-spaced pattern would probably be less restrictive, but the point may be moot: The open vent area is large.
A number of switches power, voltage, and fan also occupy the
rear of the power supply. These also eat into the airflow path, introducing
further impedance.
The fan switch is a non-standard feature of this power supply, and has three
settings: H(igh), A(utomatic), and L(ow). High sets the fan to full speed, in
this case, 12.4V. This option will be immediately panned by any users interested
in managing noise levels, although it may find some use in the heavily overclocked
and poorly cooled systems of gaming newbies. According to the manual, Automatic
is the default and recommended option, and probably just hands control over
to a fan controller similar to the one found in most any power supply.
The Low option is the one that will probably interest most users, although
the manual notes that “when temperature increases fast, PSU switches automatically
to level A. It also points out that the Low setting should only be used
by professionals, by which they probably mean experienced users. (Wouldn’t it
be nice to get paid for using a power supply?)
The three-speed fan switch takes up a bit of real estate for airflow.
(Ignore the yellow wire at the left it’s a wire hooked up for fan voltage monitoring in our review.)
PHYSICAL DETAILS (Continued)
The 400W and 600W models differ slightly in their internal components, and
especially in their heatsinks. The main transformer in each model has a different
model number and some components seem to have been shuffled around a bit. This
is to be expected: Higher quality components with greater capacities and higher
efficiency are necessary to output the additional power required by the 600W
model.
The most noticeable difference between the two models is the size and design
of their heatsinks. The heatsinks in the 400W model are small and thin, and
do not provide much surface area. In contrast, while the heatsinks in the 600W
model are still quite small, their finned design provides them with far more
surface area, which should translate into an equivalent gain in cooling effectiveness.
The 400W model has tiny heatsinks. Are they really enough to cool it effectively?
The heatsinks in the 600W model are more substantial, although still pretty small.
An additional PCB, whose purpose is unknown, has also appeared over the AC socket.
The fan bears the name “T & T”, which stands for Tranyoung
Technology, a fan OEM in Taiwan. Deciphering the model number on their
web site reveals two important attributes: The fan is a sleeve bearing model,
and it is low speed. Although sleeve bearings don’t last as long as ball bearings in high temperature conditions, they tend to be quieter. While a sleeve bearing fan is not the best choice for a system that will see heavy
use, and thus many hours of operation under high heat, it is a good sign for
those seeking a quiet power supply.
“L” stands for “Low Speed”, “S” stands for
“Sleeve Bearing” both excellent signs.
The 0.4A power rating suggests a higher speed than most low speed
fans, however.
CABLES AND CONNECTORS
All the cable sets are removable, even the main ATX cable. The cables are sleeved
in black plastic mesh to keep things nice and tidy. The advertised “Ohm-Leg”
plugs are probably the improved Molex connectors that can be be removed by squeezing
the grips on either side of the plug.
A word of warning about the socket for the SATA connectors: The five voltage
pins for this connector protrude beyond the top edge of the plastic frame. This
means there are live, bare contacts on the outside of the power supply when
the unit is powered up. Not only does this increase the odds of an accidental
short circuit, but it could be a hazard for those who like to poke around inside
their computers while they are running (you know you’re out there).
Each model comes with seven cable sets:
CU-400T (400W)
- 16″ sleeved cable for main 20+4 ATX connector
- 17″ auxiliary 12V connector
- 16″ 8-pin auxiliary power connector for dual CPU
- 19″ cable with two 4-pin IDE drive connectors
- 2 x 24″ cable with two 4-pin IDE drive connectors
and one floppy drive power connector - 21″ cable with two SATA drive connectors
CU-600T (600W)
- 16″ sleeved cable for main 20+4-pin ATX connector
- 18″ auxiliary 12V connector
- 18″ 8-pin auxiliary power connector for dual CPU
- 27″ cable with three 4-pin IDE drive connectors
- 2 x 27″ cable with two 4-pin IDE drive connectors
and one floppy drive power connector - 25″ cable with two SATA drive connectors
The cable lengths are a little on the short side, especially the IDE drive
connectors that usually need the extra length to route the cables properly.
There are more headers on the power supply than there are supplied cables.
There is one Molex header and one SATA header that do not have corresponding
cables. As mentioned, the PCIe header also lacks a cable. At the time of writing,
CoolMax did not list additional cables as purchasable items on their web site,
and I was unable to find detachable cables for sale.
The black sleeving keeps the individual wires together. They look quite
snake-like.
As mentioned above, it is very important to remember to plug in the extra three-pin
plug that is bundled with the main ATX header.
Don’t forget to plug in the remote sensor plug!
The implementation of the 4 + 20-pin ATX header is a little unusual. Instead
of making the two parts of the plug completely separable, the extra four pins
are designed to hinge to the side when they are not needed. This reduces the
possibility that the header will be installed improperly (with the standard
design, it’s possible to fully insert the 4-pin portion without properly seating
the 20-pin header), but may pose a compatibility problem depending on the position
of the ATX socket on the motherboard.
The 20+4 style ATX connector is an unusual design.
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 | |||||||
| 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 | ||||||||
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 CoolMax CoolMax There was no need to make recordings at higher power levels; it’s simply too loud. |
| Sound Recordings of PSU Comparatives Seasonic Seasonic |
| HOW TO LISTEN & COMPARE These recordings were made with a high 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 |
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.
- No mention of a warranty is made anywhere
in the documentation, and even contact information is quite scarce. - 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.
* * *
