In my previous post, I examined how to attempt to cool the hot running Raspberry Pi 4. Here I wanted to quickly touch on why the Raspberry Pi 4 runs so hot and if the upcoming new USB 3 host controller firmware is going to be the silver bullet.
CPU Power Usage
As you’d expect, higher power consumption will lead to much of the energy being converted to heat. The Pi 3 Model B+ saw it’s power consumption increase by ~50% from compared to the Pi 2 Model B. The increase from the Pi 3 to the latest Raspberry Pi 4 is around 38% without 4k video support enabled and almost 49% with 4k video-enabled.
The Alpha level firmware for the USB 3.0 Host controller sees the power consumption drop by ~300mW, which is significant, bringing the power increase from the Pi 3 B+ down to 26% without 4k and 36% with 4k enabled.
Let’s look to see how this power usage translates into CPU temperature.
CPU Temperature (above ambient)
As my measurements aren’t performed in an isolated environment with consistent temperatures. We need to consider the difference between the measured CPU temperature and the ambient room temperature subtract one from the other in order to compare results.
The Raspberry Pi 3 Model B+ idles 6.1°C warmer than the Pi Model 2, an increase of around 38%. The Raspberry Pi 4 with 4k disabled, runs 11.6°C hotter, an increase of nearly 53% over the previous generation. With 4k video support enabled, the temperature jumps up again, running 16.8°C hotter than the Pi 3 B+, a massive 76% hotter.
The alpha USB 3.0 Host firmware which we see does indeed reduce the power usage by the expected 300mW, but the temperature is not significantly impacted. Only by about 1.4°C in the 4k video-enabled scenario.
The upcoming USB 3.0 Host controller firmware update, should reduce power usage. However, there remain significant thermal issues with the Raspberry Pi 4 which remain to be addressed.