Corsair RM750 Power Supply Review

The all-new RM sits third in the PSU hierarchy behind the AX(i) and HX models. But third doesn't mean bronze, literally, as the RM, available in capacities from 450W to 1,000W is rated at 80 PLUS Gold, uses fully-modular cabling and has a zero-fan mode at low loads. In effect, then, it takes some of the good bits out of other Corsair supplies and amalgamates them into one new model.Corsair says RM is optimised for silence, backing up the assertion with knowledge that the 135mm fan isn't activated until 40% load, based on an ambient 25°C room temperature. Even when it does kick in, the company informs us, the fan is markedly quieter than rival solutions.

Cables	Cables, type, length, plugs on cable
Main	20+4-pin (60cm)
ATX/EPS	P4+P4 (65cm)
PCIe 1	2x 6+2-pin (60cm-75cm)
PCIe 2	2x 6+2-pin (60cm-75cm)
Peripheral 1	4x SATA (70cm)
Peripheral 2	4x SATA (70cm)
Peripheral 3	4x Molex (75cm) + 1 floppy
Peripheral 4	3x Molex (75cm) + 1 floppy

Amps/watts and voltage	3.3V	5V	12V1	-12V	-5VSB
Rail amps	25A	25A	62.5A	0.8A	3A
Maximum rating	150W		750W	9.6W	15W
Maximum rating continuous	750W @ 40°C ambient

Corsair uses Japanese-made, 105°C-rated main hold-up and secondary capacitors, which is good news, and the 80 PLUS Gold certification means that there isn't a great deal of heat produced when converting AC to PC-friendly DC, enabling the RM750 to be equipped with a quiet fan that, at most times, doesn't even switch on until 300W or so is being pulled from the wall.

Corsair RM750 Features & Specs
Max. DC Output	750W
PFC	Active PFC
Efficiency	80 PLUS Gold
Modular	Yes
Intel Haswell Ready	Yes
Operating temperature	0°C - 40°C
Protections	Over Voltage Protection Under Voltage Protection Over Power Protection Over Temperature Protection Over Current Protection Short Circuit Protection
Cooling	135 mm Riffle-Bearing Fan (NR135L)
Semi-passive operation	Yes
Dimensions	150 mm (W) x 86 mm (H) x 180 mm (D)
Weight	2.2 kg
Compliance	ATX12V v2.4, EPS 2.92
Warranty	5 years

Voltage Regulation and Efficiency Measurements

Corsair RM750
Test	12 V	5 V	3.3 V	5VSB	Power (DC/AC)	Efficiency	Fan Speed	Fan Noise	Temp (In/Out)	PF/AC Volts
20% Load	10.641A	1.972A	1.959A	0.986A	149.74W	89.63%	0 RPM	0 dBA	40.82°C	0.923
	12.045V	5.060V	3.367V	5.065V	167.06W				38.64°C	230.2V
40% Load	21.699A	3.976A	3.950A	1.186A	299.70W	91.95%	0 RPM	0 dBA	41.25°C	0.974
	12.007V	5.028V	3.338V	5.043V	325.94W				38.76°C	230.1V
50% Load	27.129A	4.974A	4.951A	1.590A	374.64W	92.06%	0 RPM	0 dBA	44.64°C	0.982
	11.987V	5.020V	3.331V	5.020V	406.95W				40.76°C	230.2V
60% Load	32.582A	5.979A	5.950A	2.000A	449.59W	91.94%	0 RPM	0 dBA	46.71°C	0.987
	11.965V	5.012V	3.326V	4.995V	489.02W				41.13°C	230.1V
80% Load	43.702A	8.010A	7.970A	2.415A	599.51W	91.28%	1240 RPM	40.5 dBA	44.09°C	0.992
	11.925V	4.991V	3.311V	4.967V	656.75W				48.58°C	230.0V
100% Load	55.497A	9.048A	8.998A	3.040A	749.32W	90.51%	1390 RPM	43 dBA	44.42°C	0.994
	11.886V	4.974V	3.300V	4.928V	827.85W				49.89°C	230.0V
110% Load	61.910A	9.058A	9.012A	3.044A	824.24W	90.14%	1390 RPM	43 dBA	45.03°C	0.995
	11.865V	4.968V	3.295V	4.923V	914.45W				50.81°C	230.0V
Crossload 1	0.096A	18.014A	18.002A	0.004A	151.50W	84.42%	650 RPM	31.4 dBA	42.63°C	0.932
	12.035V	4.978V	3.369V	5.085V	179.47W				47.73°C	230.3V
Crossload 2	62.451A	1.001A	1.003A	1.001A	755.25W	91.04%	1390 RPM	43 dBA	45.49°C	0.994
	11.879V	5.025V	3.323V	5.026V	829.60W				51.71°C	230.0V

The RM750 didn't have any problem whatsoever operating at very high ambient temperatures, and as you can see from the table above, the fan only spun at 80% load and above. However, given the not-so-good capacitor choice in the secondary side, the fan engaged rather late, which puts a ton of stress on the Chinese caps. These are rated at up to 105°C, but we still aren't so sure about their reliability under such tough conditions, especially in the long run. But Corsair apparently trusts these caps o they wouldn't provide this unit with a five year warranty. 

Voltage regulation on all rails was good enough and can easily meet the mid-level competition, while overall efficiency was high, allowing the unit to easily clear Gold requirements at 115 VAC input. Finally, output noise is also kept at low levels, even with the fan spinning at full speed. Corsair meant business when they talked about super-quiet PSUs

• Pro's
• Delivered full power at 45°C
• Ultra-quiet operation
• Tight enough voltage regulation on all rails
• High efficiency
• Low ripple at +12V
• Semi-passive mode
• Fully modular
• 5 year warranty
• Compatible with the Corsair Link Software (but an extra cable is needed)
• Modular cables are flat and stealth
• Accurate readings of the Corsair Link software
• Nice looks and finish

• Con's
• Choice of capacitors in the secondary side
• The fan engages rather late
• Limited functionality of the Corsair Link software because the PSU isn't digitally controlled

The new Corsair RM PSUs address users that hate noisy components and want the quietest possible PSU without having to pay a fortune for it. Nor do these have the restrictions of passive PSUs, like small capacity and installation restrictions. The RM750 I tried today is without any doubt one of the quietest PSUs I have ever tested, passive ones not included, and it owes its nearly silent operation to its specially designed fan and semi-passive operation. However, I must add here that I didn't feel comfortable with the fan engaging as late as it did, and I would prefer it to spin up earlier to protect sensitive components, like electrolytic caps. I also don't agree with the caps choice Corsair made, since they went with Ltec, a brand with a bad reputation. I can understand the desire to keep cost down, but increased internal temperatures are part of the day-to-day routine in a semi-passive unit, and you absolutely have to be careful about the components going into such a unit. But Corsair seems to trust the platform and its components since they provide this unit with a five year warranty, covering those electing to go with the RM750 should anything go wrong.

The RM750 performed well overall, its price is fair for what it offers, and its fully modular design is an ace up its sleeve. You can also monitor +12V current output and fan speed if you buy Corsair's optional Digital Bridge and download the Corsair Link software. Now, some of you may complain because the Digital Bridge wasn't included in the bundle, but it would have raised the final price, which Corsair didn't want, especially because it can only obtain two RM750 readings.