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Corsair RM750i Power Supply Review

Corsair is revamping its RM line, adding the letter "i" to highlight a more advanced digital interface — today we check out the RM750i.

Efficiency, Temperature And Noise

Efficiency

Our efficiency testing procedure is detailed here.

Using the results from the previous page, we plotted a chart showing the RM750i's efficiency at low loads, and loads from 10 to 110 percent of the PSU's maximum-rated capacity.

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Efficiency is pretty high for the standards of this category (750 W - 80 Plus Gold) at both light and normal loads. Compared with the older RM750 model, this unit offers a significant improvement at light loads, while at higher loads (20 – 100 percent) the efficiency difference is small.

Efficiency At Low Loads

In the following tests, we measured the efficiency of the RM750i at loads significantly lower than 10 percent of the device's 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 #12V5V3.3V5VSBPower(DC/AC)EfficiencyFan SpeedFan NoisePF/AC Volts
11.201A0.498A0.479A0.200A19.64W66.49%0 RPM0 dB(A)0.844
12.119V5.000V3.332V4.991V29.54W115.1V
22.432A0.998A0.990A0.400A39.74W78.40%0 RPM0 dB(A)0.935
12.114V4.999V3.332V4.988V50.69W115.1V
33.668A1.495A1.500A0.600A59.88W82.86%0 RPM0 dB(A)0.960
12.110V4.999V3.331V4.984V72.27W115.1V
44.887A2.002A1.980A0.800A79.74W85.07%0 RPM0 dB(A)0.970
12.105V4.998V3.330V4.980V93.74W115.1V

At very low loads the PSU performed pretty well, with its efficiency surpassing the 80 percent mark during the last two tests, with 60 W and 80 W loads. In addition, the PSU operated in passive mode throughout the testing, although the ambient temperature was close to 40 °C (104 °F).

You will find several screenshots of the Corsair Link software below, which we took during our load test sessions.

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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 will take four measurements: one each at 100, 250 and 1000mA, and one with the full load the 5VSB rail can handle. 

Test #5VSBPower (DC/AC)EfficiencyPF/AC Volts
10.101A0.51W76.12%0.066
5.037V0.67W115.1V
20.251A1.26W79.75%0.142
5.033V1.58W115.1V
31.002A5.02W81.63%0.319
5.013V6.15W115.1V
43.002A14.89W79.80%0.422
4.960V18.66W115.1V

The 5VSB rail is highly efficient even at very light loads. The low consumption in idle mode surely played a key role in this.

Power Consumption In Idle And Standby

Mode12 V5 V3.3 V5VSBPower (AC)PF/AC Volts
Idle12.120V5.007V3.337V5.005V8.65W0.474
115.1V
Standby0.05W0.005
115.1V
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In the table above, 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).

"Vampire power" is very low, one of the lowest we have ever measured. The previous RM750 model also has very low power consumption at idle.  (Vampire power, also known as standby power, refers to the power devices’ waste just by being plugged in and not in use.)

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 (RPMs), and the delta between input and output temperature. The results were obtained at 40 °C (104 °F) to 47 °C (116.6 °F) ambient temperature.   

The next chart shows the cooling fan's speed (RPMs) and output noise. We measured acoustics from 1 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 anechoic chamber was below 18 dB(A) during testing, and the results were obtained with the PSU operating at 40 °C to 47 °C ambient temperature. 

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The following charts illustrate the fan's output noise and speed over the entire operating range of the PSU. The same conditions of the above chart apply to our measurements, though the ambient temperature was between 28 °C (82.4 °F) and 30 °C (86 °F). 

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We noticed something strange during our extended cross-load tests. Although with high ambient temperatures the passive mode lasted for a long time, with normal operating temperatures it lasted for only a couple of minutes. We don't have an explanation for this; however, we should mention that we encountered the exact behavior in an RM1000i unit, which we evaluated recently. In any case, even with the passive mode being inactive, the fan spins at very low speeds most of the time so it is almost inaudible. Up to around a 600 W load the PSU is dead silent, and this means that it will be the ideal choice if you want to build a super-quiet system.

Aris Mpitziopoulos is a Contributing Editor at Tom's Hardware US, covering PSUs.