Zalman ZM600 heatpipe-cooled modular power supply

TESTING

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

For a complete rundown of testing equipment and procedures, please refer to SPCR's PSU Test Platform V.4. The testing system 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 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.

The 120mm fan responsible for "case airflow" is deliberately run at a steady low level (~6-7V) when the system is run at "low" loads. When the test loads become greater, the 120mm fan is turned up to a higher speed, but one that doesn't affect the noise level of the overall system. Anyone who is running a system that draws 400W or more would definitely want more than 20CFM of airflow through their case, and at this point, the noise level of the exhaust fan is typically not audible.

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 too many variables in PCs and 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 pretty good overall representation, but it is not quite the same as an extended meeting in person.

REAL SYSTEM POWER NEEDS: 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 conducted system tests to measure the maximum power draw that an actual system can draw under worst-case conditions. Our most power-hungry Intel 670 (P4-3.8) processor rig with nVidia 6800GT video card drew ~214W 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 the most power hungry video card today could draw as much as another 60~100W, but the total still remains well under 400W in extrapolations of our real world measurements. As for high end dual video card gaming rigs... well, to be realistic, they have no place in silent computing today.

SPCR's high fidelity sound recording system was used to create MP3 sound files of this PSU. 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.

INTERPRETING TEMPERATURE DATA

It important to keep in mind that fan speed varies with temperature, not output load. A power supply generates more heat as output increases, but is not the only the only factor that affects fan speed. Ambient temperature and case airflow have almost as much effect. Our test rig represents a challenging thermal situation for a power supply: A large portion of the heat generated inside the case must be exhausted through the power supply, which causes a corresponding increase in fan speed.

When examining thermal data, the most important indicator of cooling efficiency is the difference between intake and exhaust. Because the heat generated in the PSU loader by the output of the PSU is always the same for a given power level, the intake temperature should be roughly the same between different tests. The only external variable is the ambient room temperature. The temperature of the exhaust air from the PSU is affected by several factors:

• Intake temperature (determined by ambient temperature and power output level)
• Efficiency of the PSU (how much heat it generates while producing the required output)
• The effectiveness of the PSU's cooling system, which is comprised of:
  • Overall mechanical and airflow design
  • Size, shape and overall surface area of heatsinks
  • Fan(s) and fan speed control circuit

The thermal rise in the power supply is really the only indicator we have about all of the above. This is why the intake temperature is important: It represents the ambient temperature around the power supply itself. Subtracting the intake temperature from the exhaust temperature gives a reasonable gauge of the effectiveness of the power supply's cooling system. This is the only temperature number that is comparable between different reviews, as it is unaffected by the ambient temperature.

TEST RESULTS

Ambient conditions during testing were 21°C and 17 dBA. AC input was 117V, 60Hz.

ANALYSIS

1. EFFICIENCY was very good across the board. At most loads, the power supply demonstrated an efficiency of 80% of more. At below 100W loads, the efficiency drops below 80%. Systems that actually require the high power output capacity of this PSU may not get down that low, but for a high efficiency system at idle, the ~70% achieved between 40~70W is not great.

2. VOLTAGE REGULATION was excellent; by our usual tests, none of the lines fluctuated by more than 3%. Even under crossloading (imbalanced loading), with the 12V lines on maximum load and the 5V and 3.3V lines on just 2A, the voltage regulation was excellent.

3. RIPPLE

Ripple was well within the limits specified by the ATX standards. The worst ripple occurred at maximum load, where the +12V ripple reached 18.5mV. To put that in perspective, the ATX12V spec requires +12V ripple to be below 120 mV.

+12V ripple at full power output. It was low at any load.

4. POWER FACTOR was excellent thanks to the active power factor correction circuit, staying very close to the theoretical maximum of 1.0.

5. LOW LOAD PERFORMANCE

Standby and no-load performance were both reasonably efficient, with standby coming in well under one watt, and no-load under 10W. ZM600-HP had no issues starting or staying powered on with no load applied.

6. LOW AC VOLTAGE PERFORMANCE

The power supply was set to about 75% load with 120VAC through the hefty variac in the lab. The dial on the variac was then set 10V lower every 10 minutes. Since most power supplies are only rated for operation at 100~240VAC, our test calls for a minimum input voltage of 90VAC. However, in this case, we pushed it down to 80VAC.

The Zalman ZM600-HP stood up to the drops in AC voltage admirably, even when operating well below its rated input voltage of 100V. Neither voltage regulation nor ripple changed measurably during the test, and efficiency dropped only marginally under the most severe conditions. In some other times that we played with low AC voltages,we had some fireworks: One unit shut down as soon at the voltage dropped to 100V; another sparked and failed entirely!

To be fair, these earlier tests were done at 100% load, but the ZM600-HP showed no sign of struggle even with the AC voltage was dropped to 80V!