Raspberry Pi 3 temperature and cooling testing :
Part 2 with a HAT tests.
Part 3 with Fan Speed Control. (Still to come)
The BeagleBoard has capes, the Arduino has Shields but the Raspberry Pi has HATS (Hardware Attached on Top) - an add-on board to provide additional functionality but which can closely cover the SOC chip and restrict the cooling airflow. There are many of these available some of which you can find here Raspberry Pi Accessories
Following on from my initial temperature tests I then decided to see what effect adding a HAT would have on the running temperature of the RPi 3. However as I did not have any of these I decided to 3D print a dummy one to RPF specifications here a OpenSCAD source for this is attached to Part 1.
One thing I should mention here though is that real HATs also contain electronic circuits that may generate some additional heat.
I started out with one that sits 10mm above theRPi 3 PCB and repeated the tests as described in part 1.
10mm dummy HAT
Not surprising there was very little difference in the results to the initial tests with enclosure cover installed, so close it was impossible to distinguish when plotted.
I therefore decided to try one that sits just 5mm above the RPi 3 pcb which is about as close as I would expect to get, for this I needed to make a cutout to clear the HDMI connector. and a slot for the GPIO pins. (after printing and fitting I realized I should have added a cutout for the Audio connector too but as this is further away from the fan I didn't feel that the slight offset would make much difference.)
5mm dummy hat
The results for these tests were again very similar to the original "with cover" tests but this time there was a noticeable increase in the maximum temperature reached on those tests that maintained a temperature below the 80'C threshold where the processor reduces its operating frequency to help keep the temperature down. This was approximately 10'C as you can see on the graph of the results below. I tried to make things easier to see with this chart (hopefully). The tests are T1 to T8 no HAT and T1H to T8H with a HAT installed.
The original test plan is:
Test# Fan Cover Heatsink Graph Colour
1 0 0 0 Brown
2 x 0 0 Red
3 0 x 0 Orange
4 x x 0 Yellow
5 0 0 x Green
6 x 0 x Blue
7 0 x x Violet
8 x x x Grey
And the results, if you click on the chart you should get a larger image.
Without a fan the 80'C threshold is reached much sooner but as you can see the heatsink still has an effect in delaying this.
Still to come: Part 3 Adding temperature control to the cooling fan to reduce noise.