Cooling your Raspberry Pi - reasonable or a waste?
There are plenty of radiators and fans for the small single-board computer - but how big is the impact of using cooling? Don't get me wrong - having a cooling system is always better than having no cooling at all. But I was curious about the exact difference with the current top model (RPi 4B, 4 GB).
First of all it is good to know in which temperature ranges the computer can be used at all. The Raspberry Pi Foundation names the following values in their FAQs:
- LAN-Chip: 0 to 70 C°
- SoC: -40 C° to +85 C°
So, using the device in Oimjakon and Werchojansk is not an option at all. 🙂
But even at home using a cooling system is - depending on the load profile - a good idea or necessary as the test showed up.
The tests were executed on a Raspberry Pi 2 and Pi 4 running Raspbian Buster (unfortunately, I had no Pi 3 around for testing). For the kernel I was using the version 4.19.97-v7+ released by the foundation and the last beta release 5.4.40-v7+. The results were the same when using the same firmware; some things have changed here in the last months as the Raspberry Pi Foundation blog reports.
Beside the Idle value I also measured temperature after a 15 minute burn-in-test and 1 minute and 10 minutes after finishing the test. For generating load, I was using stress-ng:
1# stress-ng --matrix 0 -t 15m
Using --matrix 0 all available CPU cores are used, -t 15m sets the time limit to 15 minutes.
Afterwards I assembled the Pis in a simple acrylic case with 40mm fans - the fans don't have any kind of control mechanism, they always run on maximal power.
Here are the test results:
| Setup | Test | Pi 2 | Pi 4 |
|---|---|---|---|
| without radiators | Idle | 45 C° | 59 C° |
| 15 minutes burn-in | 70 C° | 83 C° | |
| After 1 minute | 55 C° | 72 C° | |
| After 10 minutes | 48 C° | 63 C° | |
| Radiators and 40mm fan | Idle | 30 C° | 37 C° |
| 15 minutes burn-in | 32 C° | 56 C° | |
| After 1 minute | 31 C° | 43 C° | |
| After 10 minutes | 30 C° | 37 C° |
I was highly suprised to see that the Pi 4 always generates a lot of heat during idle and quickly (after approximately 6 minutes) nearly hits the SoC limits. During long-term usage the hardware might get corrupted pretty soon. I was using previous Pi generations mostly without radiators - definitely a bad idea for the Pi 4.
So better invest additional 5 bucks for radiators and fans. 🙂