Corsair RM750 750W Power Supply Review
The CORSAIR RM750 Power Supply
A Fully Modular PSU with Quiet Operation and Modern Standby
In Corsair’s latest power supply lineup the current RM Series includes three models: 850W, 750W, and 650W. We will be taking a detailed look at the RM750 PSU in this review. Like many previous versions, the RM Series power supplies are designed by Corsair and built by Channel Well Technologies (CWT). The RM Series is also ready for Modern Standby, which is an upcoming feature for Windows 10 that promises to improve your PC’s sleep and wake functionality.
All RM Series power supplies are equipped with fully modular cables and optimized for quiet operation. They feature Zero RPM Fan Mode and incorporate a large 135mm cooling fan is designed to deliver low noise and high static pressure. Corsair guarantees these PSUs to deliver clean, stable, continuous power, at ambient temperatures up to 50°C. And the RM series comes backed by a 10-year warranty.
Features and Specifications
Corsair RM750 PSU Features summary:
- 750W continuous DC output (up to 50°C)
- 10-Year Warranty and Comprehensive Customer Support
- Ready for Modern Standby (improved sleep-wake functionality)
- 80 PLUS Gold certified, at least 90% efficiency under 50% load
- Fully modular cables for easy installation
- Flat ribbon-style, low profile cables help optimize airflow
- Zero RPM Fan Mode for silent operation up to 40% load
- Quiet 135mm rifle bearing fan for quiet operation
- High quality components including 105° electrolytic capacitors
- Active Power Factor correction (0.99) with Universal AC input
- Safety Protections : OVP, UVP, SCP, OTP, and OPP
The Corsair RM750 power supply is rated for a combined, continuous output power of up to 750 watts at 50°C operating temperature. The PSU incorporates a single +12V rail, which can deliver up to 62.5A (750W) on the +12V outputs. The PSU includes universal AC line input (automatically adjusts the AC line voltage) and active PFC, which makes the unit more environmentally friendly to the local power grid.
Corsair RM750 PSU Specifications (from the Corsair website):
Packaging and Contents
The Corsair RM750 power supply arrived securely packed inside a standard retail box showcasing the unit’s features and specifications. The power supply is protected by foam inserts and wrapped in plastic (no fancy black velvet bag for the RM series).
In addition to the power supply, the box contains a power cord, mounting screws, an information pamphlet, cable ties, a Corsair case badge, and ten modular cables.
A Detailed Look
The Corsair RM750 power supply enclosure is painted matte black with light gray lettering and measures 160mm (6.3”) long. Note the beveled edges for a distinctive look. The back panel includes an On-Off switch and AC receptacle.
The PSU ships with a label over the back panel to make sure you understand that the fan will not start spinning until the PSU is under moderate load.
The front panel incorporates twelve modular connectors for the power cables, all nicely keyed and labeled. The power supply uses a Hong Hua 135mm fan (HA1425M12F-Z that operates in near-silent Zero RPM Fan Mode up to mid-power loads. The fan uses a rifle bearing for quiet operation and is rated for 0.36A at 12 VDC.
Fully Modular Cables
The RM750 comes with a good assortment of fully modular cables and connectors. All of the cables are the black, flat ribbon-style except for the 24-pin ATX cable which is sleeved; which makes for easy installation with a clean look and helps optimize case airflow.
Under the Hood
Here are a few pictures showing the layout and components inside the RM750 power supply. The RM Series was custom designed by Corsair and manufactured by Channel Well Technologies (CWT), one of Corsair’s long standing OEM partners.
The Corsair RM Series PSUs utilizes a modern half-bridge design with LLC resonant converter to minimize switching losses and help increase efficiency. The secondary features synchronous rectification with two DC-to-DC VRMs to produce the +3.3V and +5V minor rails from the +12V main section.
All of the electrolytic capacitors used in the RM power supply are rated for 105°C operation. For example, the two bulk capacitors are made by Su’scon and rated for 330uF, 400V and 105°C. The overall component layout is a little crowded but clean and the soldering appears good.
Testing Methodology
Establishing an accurate load is critical to testing and evaluating a PC power supply. PCPerspective’s power supply test bench can place a precise DC load on the PSU under test. Each power supply is tested under controlled, demanding conditions up to its maximum rated load (at 40ºC). Our current suite of tests includes:
- DC Load Regulation
- AC Ripple and Noise
- Efficiency
- Differential Temperature
- Noise
The Corsair RM 750W power supply was evaluated on both features and performance. A full range of equipment was used to test the power supply under controlled load conditions.
- (2) CSI3710A Programmable DC load (+3.3V and +5V outputs)
- (4) CSI3711A Programmable DC load (+12V outputs)
- (3) 220W Precision resistor load bank (+12V outputs)
- Switchable precision resistor load bank (-12V and +5VSB)
- Agilent 34401A digital multimeter (Accuracy ±0.0035% vDC)
- Extech 380803 Power Analyzer (Accuracy ±0.5% of full scale)
- DS1M12 “StingRay” digital oscilloscope (20M S/s with 12 Bit ADC)
- Extech Model 407738 digital sound level meter (Accuracy ±1.5 dB)
The following connectors were used to attach the Corsair RM 750W PSU to the PC Perspective power supply test equipment.
- (1) 20+4 pin ATX
- (2) 8-pin EPS/ATX12V
- (6) 6-pin PCI-E
- (3) SATA
- (3) Molex
Test Results
DC Output Load Regulation
To simulate demanding and maximum loading conditions, the power supply was connected to the load testers and supplied with 120 VAC. In this test we are interested in seeing how well a PSU can maintain the various output voltages while operating under different loads.
The ATX12V V2.2 tolerance for voltages states how much each output (rail) is allowed to fluctuate and has tighter tolerances now for the +12V outputs. I have also included a second table of expanded tolerances (±1% to ±6%) for reference.
The following tables list the DC voltage results for the Corsair PSU while operating on 120 VAC, 60 Hz.
The RM 750W PSU produced very good voltage regulation, which stayed within ±2% of the recommended guidelines on all of the DC outputs.
AC Ripple and Noise on the DC Outputs
The amount of AC ripple and noise present on the DC outputs was checked using a digital oscilloscope. This AC component may be present in the KHz range where most switching power supplies operate or it may be more prevalent at the 60 Hz line frequency. We adjust the O-scope time base to look for AC ripple at both low and high frequencies. The ATX12V V2.2 specification for DC output noise/ripple is defined in the ATX12V Power Supply Design Guide.
Ideally we would like to see no AC ripple (repetitive) or noise (random) on the DC outputs – the cleaner the better! But in reality there will always be some present. I measured the amplitude of the AC signal (in millivolts, peak-to-peak) to see how well the power supply complied with the ATX standard. The following table lists the ripple/noise results during all of the load tests for the main output voltages of interest.
The Corsair RM 750W power supply produced excellent AC ripple and noise suppression all the way up to the max 750W output.
Efficiency
Efficiency is defined by the power output divided by the power input and is usually expressed as a percentage. If a PSU were a 100% efficient (which none are) 750 watts of AC power going in would result in 750 watts of DC power coming out (with no waste heat to dissipate). In the real world there are always inefficiencies and power is lost in the form of heat during the conversion process. Newer revisions to the ATX12V Power Supply Design Guide V 2.2 have continued to increase the efficiency recommendations for PC switching mode power supplies and now lists both required and recommended minimum efficiencies.
We measured the AC power input to the RM 750W PSU with an Extech power analyzer while the total DC load was found by adding all the individual +3.3V, +5V, +12V, -12V and +5VSB loads together.
The overall efficiency of the Corsair RM 750W power supply is very good and easily meets the criteria for 80 Plus Gold certification, even while operating on 120VAC and at elevated temperatures.
80 Plus Program:
Note: Tests conducted at room temperature (25°C)
Differential Temperature and Noise Levels
To simulate a demanding environment, some of the warm exhaust air from the PSU under test is recirculated back to the intake through a passive air duct, which allows the PSU air inlet temperature to increase with load, up to 40°C.
The differential temperature across the power supply was calculated by subtracting the internal case air temperature (T in) from the temperature of the warm exhaust air flowing out the back of the power supply (T out).
Thermocouples were placed at the air inlet and exhaust outlet. The ambient room air temperature was 23ºC (74ºF) +/- 0.5ºC during testing.
- T out = temperature of air exhausting from power supply
- T in = temperature of air entering power supply
- Delta T = T out – T in
Sound pressure level readings were taken 3’ away from the rear of the case in an otherwise quiet room. The ambient noise level was ~27 dBA.
Surprisingly, the cooling fan started up and ran slowly through the initial low and mid power tests. Only after the power supply had been at high load and then decreased, did the fan actually stop spinning. The cooling fan resumed spinning once we loaded the power supply for testing but it remained relatively quiet. The fan speed continued to increase and the noise became noticeable at 100% load.
Final Thoughts and Conclusions
The Corsair RM750 power supply exhibited very good voltage regulation with excellent AC ripple suppression, even at full load. The power supply features a very good assortment of all modular cables and delivers good efficiency, easily meeting the 80 Plus Gold criteria. The RM750 PSU incorporates a Zero RPM fan mode and operates quietly through mid-power loads, thanks to the large cooling fan that uses a rifle bearing. The PSU incorporates a full suite of safety circuits and is backed by Corsair’s 10-year warranty.
Overall, the RM750 proved to be a very good performer (great electrical specs, high efficiency, and quiet operation). It’s really hard to find anything to complain about; but when pushed I would prefer to see some dedicated PCI-E cables supplying a single connector instead of having two connectors on the end of each PCI-E cable.
Current pricing for the RM750 PSU: $119.99 USD, Amazon.com
Strengths:
- Very quiet operation: zero RPM mode up to ~40% load
- 10-Year Warranty and Comprehensive Customer Support
- Very good voltage regulation (±2%)
- Stable power (up to 50°C) with low AC ripple and noise
- Easily meets 80 PLUS Gold certification
- Fully modular cables for easy installation and to improve airflow
- High quality components including 105° electrolytic capacitors
- Active Power Factor correction (0.99) with Universal AC input
- Ready for Modern Standby (improved sleep-wake functionality)
- Safety Protections : OVP, UVP, SCP, OTP, and OPP
Minor Weaknesses:
- Two PCI-E connectors on a single cable
Our thanks to Corsair for sending us the RM750 PSU to review!
