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Efficiency, Temperature, And Noise
Efficiency
Our efficiency testing procedure is detailed here.
Using results from the previous page, we plotted a chart showing the CX750M's efficiency at low loads, and loads from 10 to 110 percent of its maximum-rated capacity.
The CX750M's efficiency is low compared to Corsair's CX650M, and under light loads this model takes last place. We wanted to see higher efficiency levels, but this platform isn't up to the challenge.
Efficiency At Low Loads
In the following tests, we measure the CX750M's efficiency at loads significantly lower than 10 percent of its maximum capacity (the lowest load the 80 PLUS standard measures). The loads we dialed were 20, 40, 60, and 80W. This is important for representing when a PC is idle, with power-saving features turned on.
| Test # | 12V | 5V | 3.3V | 5VSB | DC/AC (Watts) | Efficiency | Fan Speed | Fan Noise | PF/AC Volts |
|---|---|---|---|---|---|---|---|---|---|
| 1 | 1.208A | 0.490A | 0.481A | 0.195A | 19.67 | 60.17% | 760 RPM | 25.2 dB(A) | 0.922 |
| 12.096V | 5.057V | 3.314V | 5.062V | 32.69 | 115.0V | ||||
| 2 | 2.443A | 0.985A | 0.995A | 0.396A | 39.80 | 70.44% | 760 RPM | 25.2 dB(A) | 0.960 |
| 12.089V | 5.050V | 3.309V | 5.054V | 56.50 | 115.1V | ||||
| 3 | 3.676A | 1.475A | 1.510A | 5.044A | 59.83 | 77.15% | 760 RPM | 25.2 dB(A) | 0.980 |
| 12.083V | 5.045V | 3.307V | 5.044V | 77.55 | 115.1V | ||||
| 4 | 4.905A | 1.983A | 1.995A | 0.791A | 79.80 | 80.07% | 760 RPM | 25.2 dB(A) | 0.980 |
| 12.077V | 5.039V | 3.303V | 5.036V | 99.66 | 115.1V |
The unit barely scrapes past the 80% mark during the last light-load test. In addition, the fan could be quieter with a lower minimum speed.
5VSB Efficiency
The ATX specification states that 5VSB standby supply efficiency should be as high as possible, recommending 50 percent or higher efficiency with 100mA of load, 60 percent or higher with 250mA of load, and 70 percent or higher with 1A or more of load.
We take four measurements: one each at 100, 250, and 1000mA, and one with the full load the 5VSB rail can handle.
| Test # | 5VSB | DC/AC (Watts) | Efficiency | PF/AC Volts |
|---|---|---|---|---|
| 1 | 0.102A | 0.52 | 76.47% | 0.066 |
| 5.069V | 0.68 | 115.1V | ||
| 2 | 0.251A | 1.27 | 79.87% | 0.143 |
| 5.065V | 1.59 | 115.1V | ||
| 3 | 1.002A | 5.06 | 81.48% | 0.317 |
| 5.046V | 6.21 | 115.1V | ||
| 4 | 3.002A | 14.99 | 79.23% | 0.417 |
| 4.995V | 18.92 | 115.1V |
Strangely enough, the 5VSB rail is very efficient, taking the lead from many Gold-rated PSUs. Apparently CWT used the same 5VSB circuit found in the CX650M, which offers similar performance levels.
Power Consumption In Idle And Standby
In the table below, you'll find the power consumption and voltage values of all rails (except -12V) when the PSU is idle (powered on, but without any load on its rails), and the power consumption when the PSU is in standby mode (without any load, at 5VSB).
| Mode | 12V | 5V | 3.3V | 5VSB | Watts | PF/AC Volts |
|---|---|---|---|---|---|---|
| Idle | 12.088V | 5.061V | 3.317V | 5.071V | 12.40 | 0.756 |
| 115.1V | ||||||
| Standby | 0.06 | 0.006 | ||||
| 115.1V |
Vampire power is low with both voltage inputs.
Fan RPM, Delta Temperature, And Output Noise
Our mixed noise testing is described in detail here.
The first chart below illustrates the cooling fan's speed (in RPM), and the delta between input and output temperature. The results were obtained at 33°C (91.4°F) to 46°C (114.8°F) ambient temperature.
The next chart shows the cooling fan's speed (again, in RPM) and output noise. We measured acoustics from one meter away, inside a small, custom-made anechoic chamber with internals completely covered in sound-proofing material (be quiet! Noise Absorber kit). Background noise inside the chamber was below 18 dB(A) during testing, and the results were obtained with the PSU operating at 33°C (91.4°F) to 46°C (114.8°F) ambient temperature.
The following graph illustrates the fan's output noise over the PSU's operating range. The same conditions of the above graph apply to our measurements, though the ambient temperature was between at 28°C (82.4°F) to 30°C (86°F).
Up to around 330W load the fan's noise stays low, but it quickly increases beyond that, and above 480W the noise exceeds 40 dB(A).
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