CoolerMaster Silent Pro M2 720W PSU

TESTING

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

SPCR's PSU Test Platform V4.1. is the basic setup for the testing. It is a close simulation of a moderate airflow mid-tower PC optimized for low noise. There is one major change: The primary testing is done with the PSU NOT inside the hotbox but atop it, out of the heat path. This is in recognition of several realities that prevail today:

• In SPCR's earlier test platforms, the internal temperature varied proportionately with output load. The tested PSU was subject to this heat, and operating ambient temperature rose with increased load, reaching >40°C and often much higher at full power. This was a realistic simulation of a mid-tower PC case where the PSU is mounted conventionally at the top back portion of the case.
• The vast majority of "serious" PC cases for the home builder place no longer position the PSU at the top back corner. They put the PSU at the bottom/back corner, mostly out of the path of heat from the other components in the case. This design concept took root with the Antec P180 going back over 5 years, and dominates the DIY case arena. This means the PSU generally has to dissipate only its own heat.

Now, we've reversed our approach: The PSU is tested briefly in the hotbox only to check what happens to noise, fan speed and temperatures when it is used in an outmoded case design.

Acoustic measurements are performed in our own anechoic chamber with ambient level of 11 dBA or lower, with a PC-based spectrum analyzer comprised of SpectraPLUS software with ACO Pacific microphone and M-Audio digital audio interfaces.

REAL SYSTEM POWER NEEDS: While we test the PSU to full output 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 40W and 300W, because it is the power range where most systems will be working most of the time. It is true that very elaborate systems with the most power hungry dual video cards today might draw as much as another 150~300W, but the total usually remains under 600W.

TEST RESULTS

The ambient temperature was ~22°, and the ambient noise level was ~10 dBA.

1. EFFICIENCY — This is a measure of AC-to-DC conversion efficiency. The ATX12V Power Supply Design Guide recommends 80% efficiency or better at all output power loads. 80% efficiency means that to deliver 80W DC output, a PSU draws 100W AC input, and 20W is lost as heat within the PSU. Higher efficiency is preferred for reduced energy consumption and cooler operation. It allows reduced cooling airflow, which translates to lower noise. The 80 Plus Bronze standard requires 82% efficiency at 20% load, 85% efficiency at 50% of rated load, and 82% efficiency at full rated load.

At the super low 20W load, efficiency was low at 60% but rose as the load was increased. 80% efficiency was reached around 70~75W. It easily exceeded 82% efficiency at 20% of rated power, which in this case is 144W; at 150W, 86% efficiency was reached. A high of nearly 89% efficiency was reached at 200W, and this high plateau was maintained to over 400W. This is way beyond Bronze; it is higher than 80 PLUS Silver requirements and almost at the 90% required for Gold. By 500W, the natural higher load efficiency sag was in evidence, but better than required efficiency was maintained to full rated output.

There was no issue with crossloading. With over 90% of a 459W load on 12V, naturally, efficiency improved over the standard loading.

2. VOLTAGE REGULATION refers to how stable the output voltages are under various load conditions. The ATX12V Power Supply Design Guide calls for the +12, +5V and +3.3V lines to be maintained within ±5%.

The critical 12V line was very well regulated. It started a touch at very load load, +0.17V (1.4%). It dropped gradually as load was increased, reaching a low of 11.94V (-0.5%), not at full power, but at 500W. The 5V line was not quite as good, starting a touch high at 5.12V (+2.4%) and down to 4.8V (-4%) at full load. 3.3V ranged from 3.34V to 3.22V (+1.2% to -2.5%). The VR on the 12V line is excellent, and that on the lower voltage lines are well within ATX specs, even if not quite stellar.

3. AC RIPPLE refers to unwanted "noise" artifacts in the DC output of a switching power supply. It's usually very high in frequency (in the order of 100s of kHz). The peak-to-peak value is measured. The ATX12V Guide allows up to 120mV (peak-to-peak) of AC ripple on the +12V line and 50mV on the +5V and +3.3V lines. Ripple on all the lines was excellent at all power levels, staying under 10mV at all power levels up to around 200W, and only exceeding 30mV momentarily at full load only. This is excellent.

4. POWER FACTOR is ideal when it measures 1.0. In the most practical sense, PF is a measure of how "difficult" it is for the electric utility to deliver the AC power into your power supply. High PF reduces the AC current draw, which reduces stress on the electric wiring in your home (and elsewhere up the line). It also means you can do with a smaller, cheaper UPS backup; they are priced according to their VA (volt-ampere) rating. Power factor was very goodfor this model, running at or close to 1.0 (not never quite reaching it) through most of the loads.

5. LOW LOAD TESTING revealed no problems starting at very low loads. Our sample had no issue starting up with no load, either, but the power draw of 13.3W was a little higher than most recently tested PSUs. The 0.8W power draw in standby (power switch on but computer off) meets the <1W requirement.

6. LOW & 240 VAC PERFORMANCE

The power supply was set to 500W load at va rious AC input voltages. Most full-range input power supplies achieve 2~3% higher efficiency with 220~240 VAC, compared to 110~120 VAC. SPCR's lab is equipped with a 240 VAC line, which is used to check power supply efficiency for the benefit of those who live in higher mains voltage regions. We also used a hefty variac to check the stability of the PSU under brownout conditions where the AC line voltage drops from the 120V norm.

Efficiency improved to over 92% at 240VAC. The sample passed the 100VAC minimum input at 400W (398W) load without any issues, with a 1.1% drop in efficiency. Neither voltage regulation nor ripple changed appreciably during these tests.

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