Coolmax Taurus CF-300 Fanless ATX PSU

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IN-SYSTEM TRIAL

In-system testing has not been a part of SPCR's PSU reviews for some time, due to time constraints. The lab testing takes enough time and effort as it is. But an exception was made for the unusual CF-300.

The test system was the one assembled for the ARM System Stealth PC Foundation Kit. This system is in use still as a "temporary" backup for the main machine. The details are essentially unchanged except for the increase of RAM to 1GB.

  • Evercase 4252 case modified with top PSU intake duct and channel
  • Zalman 400B PSU (ATX12V v1.3) modified with Panaflo 80L fan
  • AOpen AK89 Max (nVidia3 Athlon 64 board)
  • AMD Athlon 64 3200+ (spec'd at 89W)
  • Zalman ZM7000A-AlCu heatsink w/ fanmate1 set to 5V
  • ATI 9800 Pro VGA with Arctic Cooling VGA Silencer (fan set to low)
  • Crucial PC3200 memory, 1MB
  • Samsung SP0802N hard drive, mounted with the supplied EAR soft grommets
  • Samsung SM-252B CD-RW Drive
  • 120mm exhaust & intake fans (as supplied in the kit) set to 5V

With identical 120mm fans running at the same speed on intake and exhaust, the slow out-blowing 80mm Panaflo fan in the Zalman PSU is matched by the air flowing in through the side duct over the slow-spinning CPU cooling fan. Overall, there is neutral air pressure in the case: About the same amount of air is actively blown in as out.

Some basic temperature measurements were taken on the above machine. Then it was shut down and the modified Zalman PSU swapped for the Coolmax Taurus CF-300. The duct was removed, and the top case vent blocked. No other changes were made to this machine.

With the fanless Coolmax in place, we have a slightly positive air pressure case: It's the CPU fan that makes the difference, which is very small, as it does not pull much air. A thermistor was placed on the back exhaust grills of the Coomax (in the same spot as during the lab testing). The following temp measurements were taken after 30 minutes in each state. Note that the ambient temperature for the in-system testing in this room (my office) was 24°C, 3°C higher than in the lab.

PSU
State
Temperature (°C)
CPU
Board
PSU
AC Power
Coolmax CF-300
Idle
50
41
43
136W
CPUBurn
61
45
49
158W
Zalman 400B modified
Idle
50
40
42
140W
CPUBurn
61
42
47
168W
Ambient room temperature: 24°C

Some observations about this PSU swap:

1) There is less forced air with the fanless Coolmax. Even though the airflow of the Panaflo 80L in the modified Zalman PSU is very low, it is enough to affect the board temperature by 3°C at maximum load.

2) The reduction in airflow is not enough to affect CPU temperature at all.

3) The Coolmax is more efficient than the Zalman, especially at higher power output. Here is a simple table showing in-system power and efficiency, based on data from SPCR tests:

PSU
Idle
CPUBurn
AC
Efficiency
DC
AC
Efficiency
DC
Coolmax CF-300
136
75%
102
158
77%
122
Zalman 400B
140
73%
102
168
73%
122

Two facts jump out:

  • The maximum power that this fairly high end system draws is just 122W, which is only about 40% of the maximum rated output of the Coolmax.
  • The temperature reached by the Coolmax in this system is far higher than on the test rig, which suggests that the positive pressure of the test rig is very advantageous for this PSU. The 49°C reached in the system with CPUBurn (at 122W DC output) was not reached in the test rig till 200W output.

BOTH 120mm FANS BLOWING IN

There was one obvious thing to try: Reverse the direction of the 120mm exhaust fan so that both front and rear 120mm fans are blowing in, causing positive pressure in the case, which should force more air out through the PSU, cooling it better in the process. The side duct for the CPU may become an exhaust port, but we will see.

Uh-oh! A Glitch!

The test system had been running CPUBurn with the Coolmax PSU for about 45 minutes when it was turned off. The PSU was not hot enough enough to burn, but definitely quite hot to the touch. The back case fan was flipped over, the PSU plugged back into AC, and the power switch hit.

No response.

The fans spun up for a few seconds and then died. The motherboard LED indicating idle current was on. With the next power button press, the fans remained motionless. I repeated this about 10 times before realizing it was not going to boot. I checked all the cables; none had been dislodged. I unplugged the PSU from AC, reset the CMOS, plugged the AC cord back in. No luck.

The only thing that could explain this was some kind of thermal circuit breaker in the PSU. Had it tripped just as power was turned off? Did the PSU get hotter after the power was turned off ? Only way to find out was to leave the PSU to cool off for a while.

Two hours later, the system powered up and ran without a hitch. I don't know what caused the shutdown; I do believe a thermal fuse may have been tripped.

Later, I discovered that every time I powered the system down, this Coolmax Taurus CF-300 sample refused to power back up until it was completely cooled off for at least an hour. It's not the kind of behavior anyone wants to see in a power supply.

Finally, I tried turning the system off within a minute after turn on, just after Windows stabilized. It still refused to start again. I had to unplug the PSU from the AC and leave it for 10 minutes before trying again -- at which point it started OK.

Temperatures were measured again.

Coolmax CF-300
State
Temperature (°C)
CPU
Board
PSU
Both fans blow in
Idle
50
43
48
CPUBurn
64
49
52
Original test results*
Idle
50
41
43
CPUBurn
61
45
49
*Front fan blowing in, rear fan blowing out.
Ambient room temperature: 24°C

The results were worse in almost every regard. Perhaps the back fan blowing in does not really create positive pressure because of the fresh air side duct for the CPU cooler. There are too many factors to sort out exactly what is happening.

For the Record: All Fans at Full Power

Just to see what this PSU will do in a high airflow system. We know the 120mm fans are capable of ~60 CFM each. They are in push/pull mode, so let's just call it 60 CFM. The 92mm CPU cooling fan is probably capable of min 35 CFM, maybe 40, and it is drawing in cool air through the side duct. There could be as much as 100 CFM of air flowing in and out of the case. Suffice it to say there was a lot of air flowing around and through in the case with all the fans at 12V. (An Aside: My bare sandaled feet were a lot cooler due to the extra air circulating under the desk.) Results?

Coolmax CF-300
State
Temperature (°C)
CPU
Board
PSU
All fans at 12V
Idle
40
33
34
CPUBurn
49
37
49
Original test results
Idle
50
41
43
CPUBurn
61
45
49
Ambient room temperature 24°C

The CPU and board temperatures are no surprise. The PSU temp at idle is very nice, but the huge jump of 15°C for just 122W DC output even with all that airflow is rather disappointing. (Admittedly, it was difficult to feel much in the way of airflow at the back of the PSU.)



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