As we have already explained, temperature is a very important aspect on true power supply reviews, since semiconductors lose their ability to deliver current (and thus power) as the temperature increases.
Several power supply manufacturers label their products at 25º C, which is an unrealistic temperature. Inside the computer case the temperature is far higher than that. Because of this we will conduct our tests with a room temperature between 45º and 50º C.
We will measure temperature with a digital thermometer with two probes (CompuNurse model), shown on Figure 8.
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Figure 8: Digital thermometer with two probes.
Unfortunately we don’t have a thermal chamber (a.k.a. “incubator”), which would allow us to set the exact temperature we want the power supply to run under. Because of that we had to create our own “hot box” using a cardboard box (we used the box from our Sony home theater receiver), as you can see on Figure 9. The idea is to use the hot air coming from the load tester exhaust system to heat up the power supply.
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Figure 9: Our “hot box”.
We know that this isn’t the best solution and we may be criticized for doing this, but we think this is far better than testing the power supply under a room temperature of only 25º C, for example. Frankly we think telling the truth is the best policy: we could post that we tested the power supply inside a “hot box” without showing you pictures or telling you details about it, making you to think that we have a thermal chamber, while we were just using a cardboard box.
The guys at SPCR did something similar to us, but instead of using a cardboard box they put together a wooden box with a shape similar to a computer case. Not a bad idea.
During our tests we attach one of the thermometer probes on top of our “hot box” and the other on the power supply housing, as shown on Figure 10.
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Figure 10: Location of the thermometer probes.
Next to our box we have a five pound ABC fire extinguisher (not shown on the picture) for any emergency. We know the risk of fire we have by using a cardboard box (if a power supply catches fire the fire can propagate to the box) and this is certainly the next thing we will change in our methodology. At the moment we are studying other alternatives (suggestions are welcome).
Before starting our load tests we will keep the power supply running until we get the temperature inside the box with at least 45º C. As you can see on Figure 9 we were pulling 550 W from the power supply and the power supply temperature was of 46.9º C, while the temperature inside the box was of 41.9º C (here we were waiting for the temperature inside the box to reach 45º C). We can increase or decrease the temperature inside the box by opening or closing it.
Some may argue that we could install the power supply inside a case. Actually this isn’t a good choice for several reasons. First, the length of the power supply cables wouldn’t allow us to do this. Second, we would need to keep the case open to install the cables from the power supply on the load tester. Third, we would need to have a running system inside the case in order to generate an amount of heat compatible with the one produced by a real PC, and that would be impossible to accomplish as we would need another power supply feeding this system – and where should we install it? So we would need to keep the case open for using this second power supply and since the case is open, the whole idea of using a PC case goes down the drain (we would need the case closed to really simulate a typical PC).
In fact even using a thermal chamber we would be faced with some of the challenges exposed above: the length of the power supply cables and the need to open a hole on the chamber to pass these cables from the power supply to the load tester.
