OK, it shouldn't be a surprise to anyone that this board gets H-O-T. It's not something to be held in the palm of your hand, so it's not that critical. Until it is. Because, as all/most CPUs, it halts when reaching a certain temperature in order to prevent a complete meltdown. In its case, its probably around 85-100 degrees Celsius.(I'll update the exact figure if I find it in the documentation)
So one of the key things for maximizing the use of this SBC is cooling it properly. There is currently a fan cooler solution (this one was kindly provided to me by element14 for the dedicated RoadTest), a dedicated cooling cape (a plug-in board just like HATs for Raspberry PI) and I think that we will see even more solutions in the future, possibly a dual-fan solution to heat both sides of the board, as in my testing a very primitive simulation of this reached the lowest cpu temp.
I say 'primitive' because the only thing I did was placing the board on a laptop cooler with large cooling fans, as shown in the picture.
And here is the result!
As a recap, my test results for idle cpu temps were:
1. 61,8 - 64,2 degrees Celsius with just the supplied heatsink, passive cooling
2. 50,6 - 53,4 degrees Celsius with the 5V F251R-05LLC brushless fan cooler attached
3. 48,6 - 50,6 degrees Celsius with both the 5V F251R-05LLC brushless fan cooler attached and the board placed on the laptop cooler.
So cooling from both sides improves the cpu temperature with 2-5 degrees Celsius, by just using this simulation, I bet that by using a second heatsink + dedicated fan can make a lot more difference.
LATER EDIT: It even got as low as 47,8 with my dual-active cooling setup!!!
IMPORTANT UPDATES: going under 40 degrees!!!
Enclosure update: Thanks to shabaz who had a few spares (see his article here: BeagleBone AI (BB-AI) - Getting Started )and was very kind to send them over, my BBAI now is housed in a white-plastic enclosure, which I'll try to use as a base for a dual-active cooling solution. Yes, I still haven't found shorter screws yet!:)
I've finally achieved maximum cooling with this board, let me tell you how I did it. Now I really feel I can try the machine-learning features without any worry of overheating and/or unexpected halts because of that.
Based on shabaz's enclosure, I added another tall floor under the board, where I fitted a 12V cooler powered independently from the board. I also added passive cooling to all the black chips on the top side (RAM memory, eMMC memory and the TPS659037 power management chip) and to the one on the underside (second RAM memory chip) with the help of some microporous heatsinks and now the board stays below 40 degrees in regular usage.
Here are the pix!
And the test results:
WITH underside cooling:
WITHOUT underside cooling (I took the cooler off the 'contraption'):