Cooler Master Real Power Pro 850 W Power Supply Review
By Gabriel Torres on March 21, 2008
Real Power Pro is the high-end power supply series from Cooler Master, featuring models from 550 W to 1,250 W. We reviewed the 850 W model (a.k.a. RS-850-EMBA), which features a big 135 mm fan, dual-transformer design and six +12V rails, being targeted to high-end systems featuring three or four video cards. According to Cooler Master this unit was labeled at 50° C and can deliver up to 1,000 W during peaks. Let’s see whether this is true or not and also let’s take a trip inside this unit.
As you can see, this power supply uses a big 135 mm brushless fan on its bottom (the power supply is upside down on Figures 1 and 2) and a big mesh on the rear side where traditionally we have an 80 mm fan. We like this design as it provides not only a better airflow but the power supply produces less noise, as the fan can rotate at a lower speed in order to produce the same airflow as an 80 mm fan.
This power supply, like all high-end power supplies, has active PFC, which provides a better usage of the power grid and allows Cooler Master to sell this product in Europe (read more about PFC on our Power Supply Tutorial). As for efficiency, Cooler Master says that this product has 81% efficiency at 170 W, 85% efficiency at 425 W and 82% efficiency at 850 W. Of course we will measure this to see if what the manufacturer claim is true. Keep in mind that more expensive power supplies have an efficiency of at least 80%. The higher the efficiency the better – an 80% efficiency means that 80% of the power pulled from the power grid will be converted in power on the power supply outputs and only 20% will be wasted. This translates into less consumption from the power grid (as less power needs to be pulled in order to generate the same amount of power on its outputs), meaning lower electricity bills.
The main motherboard cable uses a 24-pin connector (without an option to transform it into a 20-pin one) and this power supply has one ATX12V connector and one EPS12V connector.
This power supply comes with eight peripheral power cables: two auxiliary power cables for video cards using 6-pin connectors, two auxiliary power cables for video cards using 6/8-pin connectors, two cables containing three standard peripheral power connectors and one floppy disk drive connector each and two cables with four SATA power connectors each.
One thing we liked about this power supply is the fact that each cable is properly labeled, especially because the 8-pin video card auxiliary power connector and the EPS12V connector are very similar.
The number of available connectors is more than enough even for the most high-end enthusiast willing to build a rig with three or four video cards, a very high-end CPU and lots of hard disk drives. One good thing about this power supply is that each video card connector is installed on an independent +12 V rail, which provides a better power distribution and protection. We will talk about this in details later on “Power Analysis” section.
Even though this power supply carries an amazing number of SATA power plugs – eight – for a better power distribution and facilitate the installation of a system with lots of hard disk drives and optical units we think that it would be better if Cooler Master used three cables with three SATA plugs each instead of just two cables with four SATA plugs each.
On this power supply wires on the main motherboard, peripheral and SATA cables are 18 AWG, while wires on the EPS12V, ATX12V and all video card cables are 16 AWG, which is perfect.
On the aesthetic side Cooler Master used nylon sleeving only on all cables, but this protection comes from inside the power supply housing only on the main motherboard cable.
This power supply is manufactured by Enhance Electronics and on their website there is no model that is identical to Real Power Pro 850 W, so it seems that this model is manufactured exclusively for Cooler Master.
Now let’s take an in-depth look inside this power supply.
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.
In this page, we will have an overall look, while in the next page we will discuss in details the quality and rating of the components used.
This power supply uses a dual-transformer design, as you can see on the pictures below (traditionally power supplies use only one transformer). In theory this design enables the power supply to deliver more current to its secondary. This same design is used on some other power supplies we’ve seen like StarTech.com WattSmart 650 W, Tagan TurboJet TG1100-U95 1,100 W and Enermax Galaxy 1000 W.
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.
This power supply stage is flawless, as it has two Y capacitors and one X capacitor more than needed, plus a ferrite ring on the main power cable.
In the next page we will have a more detailed discussion about the components used in the Real Power Pro 850 W.
We were very curious to check what components were chosen for the power section of this power supply and also how they were set together, i.e., the design used. We were willing to see if the components could really deliver the power announced by Cooler Master.
From all the specs provided on the databook of each component, we are more interested on the maximum continuous current parameter, given in ampères or amps for short. To find the maximum theoretical power capacity of the component in watts we need just to use the formula P = V x I, where P is power in watts, V is the voltage in volts and I is the current in ampères.
We also need to know under which temperature the component manufacturer measured the component maximum current (this piece of information is also found on the component databook). The higher the temperature, the lower current semiconductors can deliver. Currents given at temperatures lower than 50° C are no good, as temperatures below that don’t reflect the power supply real working conditions.
Keep in mind that this doesn’t mean that the power supply will deliver the maximum current rated for each component as the maximum power the power supply can deliver depends on other components used – like the transformer, coils, the PCB layout, the wire gauge and even the width of the printed circuit board traces – not only on the specs of the main components we are going to analyze.
For a better understanding of what we are talking here, please read our Anatomy of Switching Power Supplies tutorial.
This power supply uses two GBU1006 rectifying bridges connected in parallel in its primary stage, which can deliver up to 10 A (rated at 100° C) each, so the AC rectification circuit can handle up to 20 A. This stage is clearly overspec'ed: at 115 V this unit would be able to pull up to 2,300 W from the power grid; assuming 80% efficiency, the bridge would allow this unit to deliver up to 1,840 W without burning this component. Of course we are only talking about this component and the real limit will depend on all other components from the power supply.
This power supply uses two STW25NM50N power MOSFET transistors on its active PFC circuit, which can handle up to 22 A (at 25° C) or 14 A (at 100° C) in continuous mode, or up to 88 A (at 25° C) in pulse mode each.
On the switching section this power supply uses two STW20NM50 power MOSFET transistors in two-transistor forward configuration, which can deliver up to 20 A (at 25° C) or 12.6 A (at 100° C) in continuous mode, or up to 80 A (at 25° C) in pulse mode, which is the mode used.
As we mentioned this power supply uses a dual-transformer design. The configuration used is really interesting. Instead of the primaries of the two transformers being connected in parallel, they are connected in series.
The primary section is controlled by a CM6800 integrated circuit, which is a very popular active PFC and PWM controller combo. It is located on a printed circuit board that is located at one of the edges of the power supply.
This power supply uses a slightly different configuration from what we’ve seen to date, so we drew a simplified schematics of its secondary for a better understanding, see Figure 12.
The +5 V and +3.3 V ouputs use the traditional configuration used by power supplies with a forward switching design. For the +5 V and +3.3 V outputs the two transformers are connected in parallel and each output uses two Schottky rectifiers in parallel each. Instead of sharing the same transformer output with the +5 V output, the +3.3 V line uses its own transformer output, which is great.
The +5 V output is produced by two STPS60L45CW Schottky rectifiers connected in parallel, which support up to 60 A (30 A per diode, measured at 135° C) each. The maximum theoretical current the +5 V 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 (which in this case is made by two 30 A diodes in parallel). Just as an exercise, we can assume a typical duty cycle of 30%. This would give us a maximum theoretical current of 86 A or 429 W for the +5 V output. The maximum current this line can really deliver will depend on other components, in particular the coil used.
The +3.3 V output is produced by other two STPS60L45CW Schottky rectifiers connected in parallel, which support up to 60 A (30 A per diode, measured at 135° C) each. The maximum theoretical current the +3.3 V 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 (which in this case is made by two 30 A diodes in parallel). Just as an exercise, we can assume a typical duty cycle of 30%. This would give us a maximum theoretical current of 86 A or 283 W for the +3.3 V output. The maximum current this line can really deliver will depend on other components, in particular the coil used.
The +12 V output, on the other hand, uses a very unique design, using a partial synchronous configuration. On a synchronous configuration the two diodes (rectifying diode and freewheeling diode) are replaced by two power MOSFET transistors (called control MOSFET and synchronous MOSFET, respectively). This power supply continues using rectifying diodes (four in parallel, to be exact), adding two power MOSFET transistors to do the freewheeling part. Two freewheeling diodes were kept to make sure the power supply is avoiding cross-conduction (i.e., the rectifying diodes and the syncrhonous MOSFETs are not conducting at the same time).
The diodes are provided by three 40CPQ06 Schottky rectifiers, which can deliver up to 40 A (20 A per diode measured at 120° C) each. The two synchronous MOSFETs are IFRS3207, capable of delivering up to 130 A at 100° C each.
In order to calculate the maximum theoretical current and power the +12 V can deliver, we need to consider the side (rectifying or freewheeling) that provides the lower current limit. That would be rectifying side with the four 20 A diodes connected in parallel. Using the same math shown before, this gives a maximum theoretical current of 114 A or 1,371 W. Really impressive.
The +12V filtering stage from this power supply is also different from other power supplies: it provides two separated filtering sections, one for the +12V1, +12V2 and +12V3 rails and another for the +12V4, +12V5 and +12V6 rails. This is great.
We could also clearly see that each virtual rail was really connected to the monitoring integrated circuit (a PS232S), which is in charge of the power supply protections, like OCP (over current protection). OCP was really activated, as we will talk about later.
As you can see in Figure 14 this power supply has two thermal sensors attached to its secondary heatsink. One of them is used to control the fan speed according to the power supply internal temperature and the other is used on the power supply over temperature protection (OTP) circuit. We will talk more about this circuit later.
The outputs are monitored by a PS232 integrated circuit, which supports the following protections: over current (OCP), under voltage (UVP) and over voltage (OVP). Any other protection that this unit has (like over temperature) is implemented outside this integrated circuit.
On this power supply the big electrolytic capacitors from the active PFC circuit are Japanese from Chemi-Con and rated at 85° C, while the electrolytic capacitors from the secondary are Taiwanese from Teapo and rated at 105° C.
In Figure 16, you can see the power supply label containing all the power specs.
As we mentioned before, this power supply has six virtual rails, with +12V3 and +12V4 labeled with a 28 A maximum current and all the others labeled with an 18 A maximum current.
These rails are distributed as follows:
This configuration is probably the best we’ve seen to date. As you can see on this power supply each video card power cable uses a separated rail, with a higher current limit on the rails with the 6/8-pin cable.
The usual configuration on other power supplies with four video card power cables is connecting two cables on one rail and the other two on another rail. If you install two power-hungry video cards on the same rail, the over current protection may kick in shutting down the power supply even if the video cards are just running inside their specs. To prevent this from happening some manufacturers simply disable the OCP circuit (transforming the power supply into a single-rail design) or configure OCP with a value that is too high. In both cases the power supply isn’t offering any kind of over current protection.
This Cooler Master power supply solves this issue by putting each video card power cable on an individual rail, so the power supply won’t shut down if you are running up to four video cards inside their specs but will provide you with over current protection in case something wrong happens.
We tested OCP circuit and it is really active as we will discuss later.
Now let’s see if this power supply can really deliver 850 W of power.
We conducted several tests with this power supply, as described in the article Hardware Secrets Power Supply Test Methodology. All the tests described below were taken with a room temperature between 47° C and 50° C. During our tests the power supply temperature was between 49° C and 52° C.
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.
+12V2 is the second +12V input from our load tester and during our tests we connected the power supply EPS12V connector to it (on this power supply EPS12V is half connected to the power supply +12V1 rail and half to the +12V2 rail).
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.
6 A (72 W)
13 A (156 W)
20 A (240 W)
25 A (300 W)
31 A (372 W)
6 A (72 W)
12 A (144 W)
17 A (204 W)
25 A (300 W)
31 A (372 W)
2 A (10 W)
4 A (20 W)
6 A (30 W)
8 A (40 W)
10 A (50 W)
2 A (6.6 W)
4 A (13.2 W)
6 A (19.8 W)
8 A (26.4 W)
10 A (33 W)
1 A (5 W)
1.5 A (7.5 W)
2 A (10 W)
3 A (15 W)
3.5 A (17.5 W)
0.5 A (6 W)
0.5 A (6 W)
0.5 A (6 W)
0.5 A (6 W)
0.8 A (9.6 W)
% Max Load
Ripple and Noise
This power supply could really deliver its labeled 850 W at a room temperature of 50° C with efficiency above 80% all the time, above 85% on tests one, two and three. If you only pull 350 W from this power supply it will work with an impressive 88% efficiency. Cooler Master says this product has 81% efficiency at 170 W, 85% efficiency at 425 W and 82% efficiency at 850 W. During our tests this power supply surpassed what the manufacturer says but at 850 W, which we saw efficiency at 1% below what the manufacturer says. This doesn’t mean that the manufacturer is lying, because usually the manufacturer measures efficiency at 220 V, which provides a higher efficiency compared to 115 V.
Voltage regulation during all our tests (including the overload tests we will present in the next page) was outstanding, with all outputs within 3% of their nominal voltages – ATX specification defines that all outputs must be within 5% of their nominal voltages (except on -12 V where the limit is 10%). In other words, on this power supply voltages were closer to their nominal numbers than what stated on the ATX specification.
Ripple and noise is another highlight from this product, as they were far below the maximum set by ATX spec (120 mV for +12 V and 50 mV for +5 V and +3.3 V). During our test number five – i.e., with the power supply delivering 860 W – noise level at +12V1 input from our load tester was 49 mV, noise level at +12V2 input from our load tester was 44.8 mV, noise level at +5 V was 33.2 mV and noise level at +3.3 V was 28.6 mV. Impressive results.
The only “problem” we faced during our tests was with its over temperature protection (OTP). On this power supply this circuit only reads the status of the temperature sensor when you turn the power supply on. While the power supply is running it seems that this circuit is deactivated.
If you run the power supply with a high load for just a few minutes and then turn it off, it won’t turn back on until its secondary heatsink cools down. During our tests we thought that we had burned the power supply, but we waited a few minutes and the power supply went back to life.
We installed our thermometer probe on the secondary heatsink to see how OTP was configured. If the secondary heatsink is over 60° C, the power supply won’t turn on. The problem, like we said, is that apparently OTP doesn’t read the sensor while the power supply is running, because during normal operation under full load the temperature on the secondary heatsink reached as high as 80° C and the unit didn’t shut down – or OTP circuit is configured to shut down the power supply when the heatsink reaches a temperature so high that we couldn’t reach during normal operation at full load.
So if you buy this power supply and you see that it is not turning on, wait until it cools down.
Now let’s see if we can pull even more power from this product.
We were really curious to see how much power this unit could really deliver, especially because the manufacturer says this unit can peak 1,000 W. Below you can see the maximum amount of power we could extract from this unit keeping it working with its voltages and electrical noise level within the proper working range.
32 A (384 W)
32 A (384 W)
24 A (120 W)
24 A (79.2 W)
3.5 A (17.5 W)
0.8 A (9.6 W)
% Max Load
Here noise level increased to around 58 mV on +12V1, 42.8 mV on +5 V and 40 mV on +3.3 V, as you can see below.
The problem here was that the temperature inside our “hot box” increased too fast, hitting 60° C, and we weren’t finding a way to decrease temperature. We should have shut down the power supply and wait for it to cool down, but no, we were brave enough to keep this 850 W power supply delivering 1,000 W at 60° C for some minutes until… boom! We exploded the power supply. We burned the active PFC transistors and the active PFC diode, see Figures 23 and 24.
Basically the manufacturer relaxed the over power protection (OPP) configuration for you to be able to reach 1,000 W – especially because all rectifiers are way overspec’ed, as we saw when we analyzed the secondary from this power supply – but the down side is that you may explode your unit if you keep pulling 1,000 W continuously.
Because of that we couldn’t see at what level OPP was configured.
During our tests we could clearly see the OCP (over current protection) circuit in action. When we set the +12V1 or +12V2 input from our load tester at 33 A the power supply would automatically shut down the +12 V line. So we left only the main motherboard cable connected to our load tester and increased current until the OCP kicked in and shut down the +12 V output to see at what level it was configured. This happened whenever we tried to pull more than 27 A. The power supply label, however, says that +12V1 – which is the rail where the main motherboard cable is connected to – can deliver only up to 18 A. It is normal manufacturers to configure OCP a little bit above from what is written on the label – for example, setting OCP at 20 A when the label says 18 A – but not 9 A above. Since this power supply has six rails and power is perfectly distributed, we think Cooler Master could use tighter values on the OCP circuit.
Short circuit protection (SCP) worked fine for both +5 V and +12 V lines.
During our tests we could see the speed of the power supply fan changing as the power supply temperature increased. Below 30° C it spun slowly, making almost no noise, and after this temperature it started increasing its speed, which also increased noise level a little bit, but even with it running at full speed it was very quiet.
Another good thing about this power supply is that it runs really cool, only 2 to 3 degrees Celsius above the temperature inside our “hot box.” This temperature refers to the power supply housing temperature, measured with our thermometer probe installed on the external top side of the power supply (the same side where inside the power supply the printed circuit board is located).
Cooler Master Real Power Pro 850 W (RS-850-EMBA) power supply specs include:
* Researched at Shopping.com on the day we published this review.
We were really impressed by this power supply. It could not only deliver 850 W at 50° C like the manufacturer says, but we could easily pull 1,000 W from it. Cooler Master could easily label this power supply as being a 1,000 W unit, but they decided to play it safe and label it as an 850 W unit, probably because efficiency drops below 80% when you pull 1,000 W.
Inside the unit all rectifiers are way overspec’ed and this explains why this power supply can easily deliver more power than labeled.
This unit is clearly targeted to someone building the ultimate gaming machine with three or four video cards, a very high end CPU and several hard disk drives.
What is good about this power supply is that it offers six virtual rails and each video card power cable is connected to a different rail. The usual configuration on other power supplies with four video card power cables is connecting two cables on one rail and the other two on another rail. If you install two power-hungry video cards on the same rail, the over current protection may kick in shutting down the power supply even if the video cards are just running inside their specs. To prevent this from happening some manufacturers simply disable the OCP circuit (transforming the power supply into a single-rail design) or configure OCP with a value that is too high. In both cases the power supply isn’t offering any kind of over current protection.
This Cooler Master unit solves this issue by putting each video card power cable on an individual rail, so the power supply won’t shut down if you are running up to four video cards inside their specs but will provide you with over current protection in case something wrong happens.
During our tests this power supply kept a very low ripple and noise levels, far below the maximum allowed levels. Voltage regulation was also perfect. Efficiency was always above 81%, being on the 87%-88% range if you pull less than 520 W from this unit.
Its fan is very quiet and this power runs very cool – its housing was only 2-3° C above room temperature.
The only “problem” you may have with this power supply is regarding its over temperature protection (OTP). Apparently the thermal sensor is only read when you turn the power supply on. If the secondary heatsink is above 60° C the power supply won’t turn on. So if you turn your PC off and then try to turn it back on and it doesn’t come back to life, wait a few minutes until the power supply cools down. We think that a LED indicating that OTP is active would be a great idea, because users may become desperate thinking that they have burned their power supply. At least we did.
The price is right for a product on the 850 W range. Just be careful because at Newegg.com this unit is quoted at USD 200 but you can find it costing less.
You also get a 5-year warranty (on the product manual it is written that this product has a three-year warranty, but the manual is wrong).
Even though this power supply delivers what the manufacturer promises, it may explode if you keep pulling 1,000 W from it continuously. Because of that we think the manufacturer should have configured over power protection (OPP) at a lower level, in order to prevent this from happening. The side effect is that you couldn’t peak 1,000 W with it, but at least you would have a safer product. That is the only reason we are not giving it our Golden Award seal, but our Silver Award. But don’t get us wrong: this is a very good product that provides a terrific cost/benefit ratio for users looking for a very high-end power supply.