Figure 1:12 V, 18 W PSU. Note that sticking tape on some glossy components helps to balance their radiation.
I let the power in these images work at 70% of the rated load - about 1.1A until thermal equilibrium is reached. The ambient temperature is 15°C (since the temperature offset can be entered, it is easy to show how much the temperature is outside the ambient temperature).
I measured three PSUs:
The output capacitance of the first PSU is poor;
The second PSU is from AliExpress and its output capacitor has a low ESR;
The third PSU was modified on the second basis using Rubycon output capacitors and Schottky output rectifiers.
According to my initial research, the components that need to be replaced most are the 12V output capacitor and output rectifier, a UF5404 3A fast recovery (50ns) part. I replaced this rectifier with the SR540 5A Schottky. From the images, it can be seen that the difference is very obvious (except for the tape on several components, there is a strip from the upper left corner to the lower right corner of the shell, but the effect is small but obvious).
Figure 2: Thermal image of the first PSU assembly and shell.
Figure 3: Thermal image of the second PSU assembly and shell.
Figure 4: Thermal image of the third PSU assembly and shell.
Unfortunately, the color of the image cannot be directly compared because the application of the camera does not allow freezing of the temperature scale (a more advanced camera can enable this function). Despite this, the results were surprising and it was curious.
Some surprising data
Now let's take a look at these components. Although the output capacitance of the second PSU is better, the temperature of its rectifier is actually higher by 5°. Schottky's temperature is 32° lower than the second PSU. Or it can be said that it is 33° higher than the ambient temperature and the second PSU is 65° higher than the ambient temperature.
Switching transistors and receivers have very low temperatures on the first PSU and 35° on the other two PSUs.
The temperature of the output capacitor is not as bad as the first test I remember. It shows an extremely nonlinear relationship with the current, well, I2R. The Rubycon temperature is at least 10° lower than the factory capacitance.
The shell temperature also brings some surprises. We believe that the worst first PSU case has the lowest temperature! It is likely to get the hottest at 1.5A, but it is still good at 70% load. Its hot spot is on the output component.
The second PSU has better factory capacitance, the highest hot spot, 45 degrees higher than the ambient temperature, and has moved to the transistor area.
The hot spot of the modified PSU is also on the transistor, but it is 39 degrees higher than the ambient temperature. Above the output assembly, the temperature is about 10° lower than the second PSU.
Even if the performance is improved, I can still use these PSUs only at their rated output of around 50%. Moreover, using the unmodified PSU under the same current seems OK. But... to be honest, these shouldn't let the big guys know.
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