Rear on/off button missing?



The higher end Cooler Master units seem to have the On/Off button missing, but what up what that? Did they simply forget? Off course not, let us first have a look at the following scope image:


Sweex 650W power supply boot

This is the booting process of the Sweex 650W power supply with 500W load. The thing with computer power supply is that they have a large amount of capacitors which draw a lot of current when the power comes on. In the above picture can you clearly see the peak current (inrush current) which happens at the moment the power is switched on. With this unit we have a peak value of 33 Amps. It's not that hard to imagine that a high loaded 900W unit will draw even more current... The thing is that these power-on/off buttons also have to deal with the AC current flows and in some cases the button just isn’t good enough. That's where Cooler Master came up with the innovative idea to have a high power relays instead to deal with the large current flows, they have also developed a circuitry which spreads out the power-on current drawn which makes the inrush current a lot smaller. Here is what we measured with the Cooler Master UCP 900W 100% loaded:


CoolerMaster UCP 900W 100% loaded booting process

As you can see the Cooler Master unit has no problem to score lower then the Sweex unit. Another interesting thing we saw during the day was the booting process of the Stability Power 500W unit, have a look at how it struggles to get its voltage rails flat with a 380W load applied:


Stability Power 500W booting process

Thermal Imaging Tests

An ideal conductor has zero resistance, unfortunately that is still not the case with semiconductors and so there always some heat that you will have to get rid off when using a AC-DC switching power supply like those we use in our computers. The more power you draw from your PSU, the more current will flow through the high power diodes or transistors/fet's, knowing that they are not ideal conductors but always have a small amount of resistance it not that hard to imagine that the more power is needed the more the PSU's will heat up at the inside. Thermal tests are not to be neglicted, unfortunately we did not have the time to stress test each unit over larger periods of time, non the less did we get to see some very exciting media which show some of the idea's CoolerMaster has been thinking of when developing their units.

In the two videos below you can see with thermal imaging camera where the heats is expelled from the power supply. The first one is a generic unit:



And this one is from a Cooler Master UCP 700W PSU:



With the UCP 900 you can see how the PSU is designed to have only one airflow direction, meaning that heated air can have only one way out and that's at the outside of the case. With generic units that is not always the case, more ventilation holes is not always better because the pressure of the fan will blow the air in different directions and if there are two ways to exit the PSU housing then the air will take both exits: some heated air will travel back into the pc housing. For some this may seem only details of course but you can not debate about the fact that CoolerMasters design will not be the best way to get the heated air out of your computer as fast as possible. But to be honest, it are these details which define a better product from a lower quality one, and it are these details which are quickly looked over when reviewing these power supply's.