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Liitokala Lii-600 : Some improvements on thermal dissipation problems

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Filippo52:
Here I am again talking about the Liitokala Lii-600. Unfortunately, even if someone has read these posts of mine, there have been no contributions on the main topic of heat dissipation. However, as promised, I also looked for solutions on my own for the mosfets used in tracks 2 and 3 of this device. As you remember from the figures in my first post, these mosfets are without any type of heat sink and are therefore subject to the dissipation possible with only the to-220 container with which they are equipped. and 2-3W of dissipation is enough to reach and exceed 100°C.
I found the solution you see in this photo



As you can now see, the two MOSFETs of tracks 2 and 3 are also equipped with heat sinks. They are semiconductor heatsinks with to-220 package with these dimensions
width 30mm
length 25mm
height 12mm

Unfortunately I have to tell you right away that the adaptation is quite tiring and if anyone has easier ideas to follow they are always welcome:
To install them I had to remove the two mosfets by desoldering them. It is then necessary to install three vertical feet where you can then reinstall the mosfets after having bent the terminals at 90°.
The feet must be of adequate section for good reasons:
- they must carry currents of 3 A without problems and overheating
- they must allow robust unslading
- they must carry the weight of the heatsink which will remain raised compared to the motherboard
I placed a square of silicone plastic under the heat sink as an insulator to avoid contact with the underlying components of the motherboard which would be disastrous:
Furthermore, for the left heatsink you will have to do various things. A small part of it will overlap the "flatcable" connection socket with the display and this will make it more difficult to reinsert it and above all to operate the blocks; but with a little patience it can be done. Furthermore, as you can see from the photo it will be necessary to remove an upper left corner to leave space for one of the pins on which the Liitokala container closes.
For the right heatsink, however, it is necessary to move the 16V 100uF capacitor which otherwise would end up partly under the heatsink or in any case too close to the cooling fins.
Moving this capacitor is an operation that in my case proved difficult and must be done with great care. The holes where the capacitor is soldered are "through" and when installing the insulated extensions (which are red and black in the photo) you must make sure that they are soldered well on both sides of the printed circuit board. In my case, in fact, after having reassembled this capacitor, one contact was missing (perhaps the hole in the printed circuit was not tinned well or it had been damaged during the operations) but the LiitoKala no longer turned on again.

I had to redo everything and in my case I moved the capacitor to the other side of the printed circuit, placing it in a horizontal position; I can assure you that there is space to close the box.
By doing this in the holes where the capacitor was soldered you can pass two pieces of the "lead" of a resistor easily soldering on both sides and then overlap the capacitor.
I think the solution is easier to implement, you can see it in the following photo



We can now redo the calculations.
The mosfet alone in air had a thermal resistance of 62.5 °C/W and with just 2 W it exceeded 100°C
Now we have a heat sink that alone has around 15°C/W, the contribution of the mosfet if well fixed with thermal paste is around 4-5°C/W; we are at a total of 19-20°C/W and we can dissipate 5W before approaching 100°C.
Furthermore, things are more similar to heat sinks, practically self-built, placed on tracks 1 and 4.
Now all the Liitocala tracks can be used without fear of having dangerous mosfet temperatures.
As always, if you have any doubts, I'm here as far as I can.
A greeting

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