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[nextpage title=”Introduction”]

Silent Pro M is the latest power supply series from Cooler Master, featuring modular cabling system and single-rail design, with 500 W, 600 W, 700 W, 850 W and 1000 W models available. Today we are going to test the 850 W version from this series (RS-850-AMBA-J3), which is scheduled to reach the market by the end of this month, and see if it will survive our tests.

Cooler Master Silent Pro M 850 W power supplyFigure 1: Cooler Master Silent Pro M 850 W power supply.

Cooler Master Silent Pro M 850 W power supplyFigure 2: Cooler Master Silent Pro M 850 W power supply.

Silent Pro M 850 W is 6 ½” (16.5 cm) deep, using a 140 mm fan on its bottom and featuring active PFC, of course. As mentioned Silent Pro M 850 W has a modular cabling system, but the motherboard main cable (22 7/8”/58 cm) and two cables with two ATX12V connectors (that together form an EPS12V connector) each (25 ½”/65 cm) come straight from the power supply housing. These three cables have a nylon sleeving that comes from inside the power supply.

The power supply comes with the following cables on its modular cabling system:

  • Six cables with one six/eight-pin auxiliary power connector for video cards each (19 ½”/49.5 cm).
  • One cable with four SATA power connectors each (19 ¾”/50 cm to first connector, 4”/10 cm between connectors).
  • One cable with three SATA power connectors each (19 ¾”/50 cm to first connector, 6”/15 cm between connectors).
  • One cable with two SATA power connectors each (19 ¾”/50 cm to first connector, 4”/10 cm between connectors).
  • One cable with three standard peripheral power connectors and one floppy disk drive power connector (15 ½”/39 cm to first connector, 7 7/8”/20 cm between connectors).
  • One cable with three standard peripheral power connectors (15 ½”/39 cm to first connector, 7 7/8”/20 cm between connectors).

All cables use 18 AWG wires with the cables from the modular cabling system being flat.

Cooler Master Silent Pro M 850 W power supplyFigure 3: Cables.

The number of cables is perfect for an 850 W product, and the highlight here is the presence of six independent cables using six/eight-pin connectors for video cards, allowing you to install up to three very high-end video cards on your system without the need of using any kind of adapter.

Now let’s take an in-depth look inside this power supply.

[nextpage title=”A Look Inside The Silent Pro M 850 W”]

We decided to disassemble this power supply to see what it looks like inside, how it is designed, and what components are used. Please read our Anatomy of Switching Power Supplies tutorial to understand how a power supply works and to compare this power supply to others.

This page will be an overview, and then in the following pages we will discuss in detail the quality and ratings of the components used. The first thing that caught our attention was that all capacitors used are Japanese from Chemi-Con.

Cooler Master Silent Pro M 850 W power supplyFigure 4: Overall look.

Cooler Master Silent Pro M 850 W power supplyFigure 5: Overall look.

Cooler Master Silent Pro M 850 W power supplyFigure 6: Overall look.

[nextpage title=”Transient Filtering Stage”]

As we have mentioned in other articles and reviews, the first place we look when opening a power supply for a hint about its quality, is its filtering stage. The recommended components for this stage are two ferrite coils, two ceramic capacitors (Y capacitors, usually blue), one metalized polyester capacitor (X capacitor), and one MOV (Metal-Oxide Varistor). Very low-end power supplies use fewer components, usually removing the MOV and the first coil.

On this power supply this stage is flawless. It has one X capacitor and two Y capacitors more than required, plus an extra ferrite coil and an extra X capacitor after the rectification bridge.

Cooler Master Silent Pro M 850 W power supplyFigure 7: Transient filtering stage (part 1).

Cooler Master Silent Pro M 850 W power supplyFigure 8: Transient filtering stage (part 2).

In the next page we will have a more detailed discussion about the components used in the Cooler Master Silent Pro M 850 W.

[nextpage title=”Primary Analysis”]

On this page we will take an in-depth look at the primary stage of Cooler Master Silent Pro M 850 W. For a better understanding, please read our Anatomy of Switching Power Supplies tutorial.

This power supply uses three GBU806 rectifying bridges in its primary. Each bridge supports up to 8 A at 100° C if a heatsink is used or only 3.5 A at 100° C is a heatsink is not available. Unfortunately a formal heatsink isn’t used but the three bridges are screwed together. At the nominal 8 A current the power supply would be able to pull up to 2,769 W from a 115 V power grid, but at 3.5 A we have a maximum theoretical AC power of 1,208 W at 115 V. Assuming 80% efficiency, the bridges would allow this unit to deliver up to 966 W without burning them. Of course, we are only talking about these components, and the real limit will depend on all the other components in this power supply.

Cooler Master Silent Pro M 850 W power supply
Figure 9:
Rectifying bridges.

The active PFC circuit uses three FCPF21N60N power MOSFET transistors. Unfortunately we couldn’t find this component being listed on the website from the manufacturer (Fairchild).

Cooler Master Silent Pro M 850 W power supplyFigure 10: Active PFC transistors and diode.

This power supply uses one big Japanese 680 µF x 420 V capacitor to filter the output from the active PFC circuit, labeled at 105° C. This is good for two reasons, first, Japanese capacitors do not leak; and second, usually manufacturers use 85° C capacitors here, so it is good to see a manufacturer using a capacitor with a higher temperature rating.

In the switching section, two IPI60R125CP power MOSFET transistors are used on the traditional two-transistor forward configuration. Each transistor supports up to 25 A at 25° C or 16 A at 100° C (note the difference temperature makes) or 82 A in pulse mode at 25° C, presenting an RDS(on) of 125 mΩ.

Cooler Master Silent Pro M 850 W power supplyFigure 11: Switching transistors.

This power supply uses a CM6802 active PFC/PWM combo controller.

Cooler Master Silent Pro M 850 W power supplyFigure 12: Active PFC/PWM combo controller.

Now let’s take a look at the secondary of this power supply.[nextpage title=”Secondary Analysis”]

This power supply uses ten Schottky rectifiers on its secondary. The maximum theoretical current each line can deliver is given by the formula I / (1 – D), where D is the duty cycle used and I is the maximum current supported by the rectifying diode. Just as an exercise, we can assume a typical duty cycle of 30%.

For the +12 V output six SBR40U60CT Schottky rectifiers are used, each one supporting up to 40 A (20 A per diode at 100° C, 0.60 V maximum voltage drop). Two of them are used for the direct rectification and four are used for the “freewheeling” portion (i.e., discharge the coil). For our math we should consider the portion with the lower current limit, which is the direct rectification one. This gives us a maximum theoretical current of 114 A or 1,371 W for the +12 V output.

The +5 V output uses two SBR30U30CT Schottky rectifiers connected in parallel, each one supporting up to 30 A (15 A per diode at 140° C, maximum voltage drop of 0.54 V). This gives a maximum theoretical current of 43 A or 214 W for the +5 V output.

The +3.3 V output uses another two SBR30U30CT Schottky rectifiers connected in parallel, giving a maximum theoretical current of 43 A or 141 W for the +3.3 V output.

Cooler Master Silent Pro M 850 W power supplyFigure 13: Rectifiers.

This power supply uses a PS224 monitoring integrated circuit, which supports over voltage (OVP), under voltage (UVP) and over current (OCP) protections. Any other protection this unit may have is implemented outside this integrated circuit. On Silent Pro M 850 W we could see two thermal sensors, meaning that this power supply really implements over temperature protection (OTP).

Cooler Master Silent Pro M 850 W power supplyFigure 14: Monitoring circuit.

Electrolytic capacitors from the secondary are also Japanese, from Chemi-Con and labeled at 105° C. [nextpage title=”Power Distribution”]

In Figure 15, you can see the power supply label containing all the power specs.

Cooler Master Silent Pro M 850 W power supplyFigure 15: Power supply label.

This power supply has a single-rail design, so there is not much to talk here.

Now let’s see if this power supply can really deliver 850 W.[nextpage title=”Load Tests”]

We conducted several tests with this power supply, as described in the article Hardware Secrets Power Supply Test Methodology.

First we tested this power supply with five different load patterns, trying to pull around 20%, 40%, 60%, 80%, and 100% of its labeled maximum capacity (actual percentage used listed under “% Max Load”), watching how the reviewed unit behaved under each load. In the table below we list the load patterns we used and the results for each load.

If you add all the power listed for each test, you may find a different value than what is posted under “Total” below. Since each output can vary slightly (e.g., the +5 V output working at +5.10 V), the actual total amount of power being delivered is slightly different than the calculated value. On the “Total” row we are using the real amount of power being delivered, as measured by our load tester.

The +12V1 and +12V2 inputs listed below are the two +12 V independent inputs from our load tester and during this test they were connected to the single +12V rail provided by the power supply.

Input Test 1 Test 2 Test 3 Test 4 Test 5
+12V1 6 A (72 W) 13 A (156 W) 20 A (240 W) 25 A (300 W) 29 A (348 W)
+12V2 6 A (72 W) 12 A (144 W) 17 A (204 W) 25 A (300 W) 29 A (348 W)
+5V 2 A (10 W) 4 A (20 W) 6 A (30 W) 8 A (40 W) 16 A (80 W)
+3.3 V 2 A (6.6 W) 4 A (13.2 W) 6 A (19.8 W) 8 A (26.4 W) 16 A (52.8 W)
+5VSB 1 A (5 W) 1.5 A (7.5 W) 2 A (10 W) 2.5 A (12.5 W) 3 A (15 W)
-12 V 0.3 A (3.6 W) 0.3 A (3.6 W) 0.3 A (3.6 W) 0.3 A (3.6 W) 0.3 A (3.6 W)
Total 166.4 W 337.0 W 493.9 W 668.8 W 818.8 W
% Max Load 19.6% 39.6% 58.1% 78.7% 96.3%
Room Temp. 47.7° C 47.3° C 46.9° C 49.5° C 47.1° C
PSU Temp. 48.2° C 49.3° C 46.0° C 52.2° C 56.0° C
Voltage Stability Pass Pass Pass Pass Pass
Ripple and Noise Pass Pass Pass Pass Pass
AC Power 194.7 W 388.3 W 573.6 W 781.0 W 994.0 W
Efficiency 85.5% 86.8% 86.1% 85.6% 82.4%
AC Voltage 115.2 V 113.2 V 111.1 V 109.6 V 106.4 V
Power Factor 0.978 0.984 0.991 0.993 0.995
Final Result Pass Pass Pass Pass Pass

Cooler Master Silent Pro M 850 W achieved very high efficiency when we pulled between 20% and 80% from its labeled capacity (i.e., between 170 W and 680 W), between 85.5% and 86.8%. If you pay close attention you will see that for test five the unit was delivering a little bit below its maximum capacity (820 W), situation where efficiency was not very high but still above the 80%, perfectly matching the 80 Plus Bronze certification achieved by this unit (82% minimum at full load and 85% minimum at typical, i.e., 50%, load).

Voltages were within the allowed range, the same happening with noise and ripple. Below you can see the results for test number five. As we always point out, the limits are 120 mV for +12 V and 50 mV for +5 V and +3.3 V and all numbers are peak-to-peak figures.

Cooler Master Silent Pro M 850 W power supplyFigure 16: +12V1 input from load tester at 818.8 W (39.2 mV).

Cooler Master Silent Pro M 850 W power supplyFigure 17: +12V2 input from load tester at 818.8 W (48.8 mV).

Cooler Master Silent Pro M 850 W power supplyFigure 18: +5V rail with power supply delivering 818.8 W (21.4 mV).

Cooler Master Silent Pro M 850 W power supplyFigure 19: +3.3 V rail with power supply delivering 818.8 W (14.4  mV).

Now let’s see if we could pull more than 850 W from this unit.

[nextpage title=”Overload Tests”]

Below you can see the maximum we could pull from this power supply with it still working within specs. The idea behind of overload tests is to see if the power supply will burn/explode and see if the protections from the power supply are working correctly. This power supply didn’t burn or explode. Even under this overloading efficiency was above 80%.

Input Maximum
+12V1 32 A (384 W)
+12V2 32 A (384 W)
+5V 17 A (85 W)
+3.3 V 17 A (56.1 W)
+5VSB 3 A (15 W)
-12 V 0.3 A (3.6 W)
Total 894.9 W
% Max Load 105.3%
Room Temp. 48.9° C
PSU Temp. 56.6° C
AC Power 1,103 W
Efficiency 81.1%
AC Voltage 105.8 V
Power Factor 0.995

[nextpage title=”Main Specifications”]

Cooler Master Silent Pro M 850 W power supply specs include:

  • ATX12V 2.3
  • EPS12V 2.92
  • Nominal labeled power: 850 W.
  • Measured maximum power: 894.9 W at 48.9° C.
  • Labeled efficiency: 85% typical, 80 Plus Bronze certified (82% minimum at 20% and 100% loads; 85% minimum at 50% load).
  • Measured efficiency: Between 82.4% and 86.8% at 115 V (nominal, see results for actual voltage).
  • Active PFC: Yes.
  • Modular Cabling System: Yes.
  • Motherboard Power Connectors: One 24-pin connector and four ATX12V connectors that form two EPS12V connectors.
  • Video Card Power Connectors: Six six/eight-pin connectors in six cables.
  • SATA Power Connectors: Nine in three cables.
  • Peripheral Power Connectors: Six in two cables.
  • Floppy Disk Drive Power Connectors: One.
  • Protections: Over voltage (OVP, not tested), under voltage (UVP, not tested), over power (OPP, not tested), over current (OCP, couldn’t test), over temperature (OTP, not tested) and short-circuit (SCP, tested and working) protections.
  • Warranty: Five years.
  • More Information: https://www.coolermaster-usa.com
  • MRSP in the US: USD 179.99.

[nextpage title=”Conclusions”]

The new Cooler Master Silent Pro M 850 W is a good power supply, presenting a high efficiency up to 86.8% if you pull up to 80% from the labeled capacity (i.e., up to 680 W), voltages within specs and noise and ripple below the maximum allowed.

The highlight of this product is the presence of six independent cables using six/eight-pin connectors for video cards, allowing you to install up to three very high-end video cards on your system without the need of using any kind of adapter.

If you are looking for an 850 W power supply for a high-end PC, Silent Pro M 850 W is a very good option, providing an excellent cost/benefit ratio for this segment.