Coolmax Taurus CF-300 Fanless ATX PSU

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May 26, 2004 by Mike Chin

Product
Coolmax Taurus CF-300 Fanless PSU
Manufacturer
Coolmax
MSP
US$120

Fanless PC components are becoming more common. As fans comprise the major sources of noise in computers, fanless operation is generally regarded as the ultimate in silent computing. This goal is not without challenges, however, as forced air cooling by fans is integral to PC design: Fans are assumed for cooling the CPU, the case and the power supply in all the prevalent standards and guides.

The PSU generates a fair amount of heat, depending on...

  • how efficiently it converts AC into DC voltage, and
  • the power requirements of the system it is running.

Making the PSU operate safely without a fan in a typical ATX tower case is a serious challenge. The PSU is located at the top where the hot air rises and pools, and one of the designed exhaust paths for heat in the tower case is through the PSU. Anyone who has experimented with electronics and fan cooling can attest to the huge cooling advantage even a small amount of airflow (say <10 CFM) has over passive air convection.

Still, fanless power supplies are appearing in greater numbers in the marketplace. Where there is a demand...

The Coolmax Taurus CF-300 is the second fanless ATX power supply to be reviewed by SPCR. It is the lowest power model in a range of fanless PSUs offered by Coolmax. The others are rated for 350W, 400W and 480W. Like virtually every computer power supply we've seen thus far, it is manufactured in China.


Unlike ordinary PSUs, the fanless Coolmax Taurus features a casing made from extruded aluminum pieces.

Coolmax appears to have started in 1992 as a "thermal solutions provider" making AC and DC fans, then gradually expanded its product range to include heat sinks, external enclosures for hard drives, optical drives, cables, case mods and power supplies. It is not clear whether they manufacture the PSUs themselves or subcontract it out to one of the big OEMs.

COOLMAX TAURUS FEATURE HIGHLIGHTS

FEATURE & BRIEF COMMENTS

Real No noise Design.

No fans, so if there's no humming or bussing...

High performance components are designed for extra long life and provide maximum system performance

Doesn't everyone say this?

Heavy duty transformers designed to support high performance system several drives

OK.

Cable-tube on main power cables for better cable routing and neatness(optional)

More useful for simplified inventory control than for users.
Aluminum Chassis(optional)
Yes.

Built in EMI filter, low ripple noise

OK.

Over voltage, Over power and Short circuit protection

Not unusual.

Designed refer to UL, CSA, TUV regulations. Meet Intel ATX12V/ATX 2.03

Safety certificates are less plentiful than others. Does not conform to ATX12V/ATX 2.0 in at least regard; see comments in SPECIFICATIONS.

Compatible with all leading processors including Pentium III, 4 and AMD Athon XP

Hard to sell one that isn't.

SPECIFICATIONS

There are some discrepancies between the label on the PSU and the data provided on the Coolmax web site. The following was compiled from on the web site, as it is more complete.

Coolmax Taurus Model FL-550ATX (CF300)
AC Input
115 VAC/ 4A or 230 VAC/ 8A, 50-60 Hz
DC Voltage lines
+3.3V
+5V
+12V
-12V
-5V
+5VSB
Max Output
25A
30A
15A
0.8A
0.3A
2A
Maximum Output
180W
180W
1.5W
9.8W
10W
279W
* Efficiency is specified as >60% at full load.
* Designed refer to UL, CSA, TUV regulations. Meets Intel ATX12V/ATX 2.03

The numbers look quite substantial and promising. They are what you would expect from a legitimately spec'ed 300W PSU. However there are oddities.

1. A temperature is specified on the web site specs: The number given for the CF300 is 75°C. The numbers provided for the higher power models are 83, 83, and 89°C, respectively. The problem is that there is no indication of what these numbers represent. Certainly they cannot be the maximum ambient operating temperatures; they are much too high. The operating ambient temperature cited by the most reputable PSU companies is 50°C. Perhaps they refer to the maximum safe temperature of core components such as the MOSFET devices? Without more clarification, these numbers are essentially meaningless.

This calls into question the temperature at which the maximum rated power can be achieved. As many readers may be aware, the ambient temperature around the PSU in a typical modern PC is likely to be 35~45°C, and PSU power output capacity drops rapidly when the thermal limit is reached. We do not know the maximum temperature at which the power output of the Coolmax can be assured. This is of particular concern in a PSU without a cooling fan.

2. Despite the last statement in the specifications table above, the efficiency of 60% minimum at full load does not meet the Intel ATX12V/ATX 2.0 requirements, which calls for 70% under “Full” load, 70% under “typical” load, and 60% in a “light” load or idle condition. For a fanless PSU, the 60% efficiency figure is not promising. It means 40% of the AC power is lost as heat inside the PSU. So in delivering 150W in DC voltage, according to this spec, the PSU would generate as much as 100W within itself, which is a lot of heat to evacuate without a built in fan. We hope this is a typo... or that Coolmax is being very conservative with their efficiency spec.



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