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.

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.

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Figure 21: Noise level at +12V1 input of the load tester.

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Figure 22: Noise level at +5 V input of the load tester.

The problem here was that the temperature inside our “hot box” increased too fast, hitting 60º 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 60º 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.

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Figure 23: We burned the active PFC transistors.

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Figure 24: Smoked printed circuit board.

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 30º 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).