Pi 4B
When the Pi 4 heats up beyond 80°C (176°F), the CPU is throttled to reduce the temperature and a half-full red thermometer appears on the display, if one is connected. If the temperature goes up beyond 85, the GPU, which now supports dual monitors and 4K resolution, will be throttled as well.
All models of Pi
Ways to reduce power consumption / heat on the Pi (any model):
- Disable HDMI
- Underlock CPU
- Disable onboard LEDs
- Minimize accessories
Disable HDMI
If you’re using the Pi without a monitor, you can simple turn off HDMI output like so:
/usr/bin/tvservice -o
(use /usr/bin/tvservice -p to turn back on). Add the line to /etc/rc.local to make it permanent, otherwise it will only work until the next reboot.
Minimize peripherals
Disconnect all peripherals you’re not using, such as keyboards, mouse, webcam, etc.
Underclock
Run raspi-config to simply underclock the CPU.
Disable LEDs permanently
The Pi has a couple of LEDs: power indicator, memory activity indicator, network status, whatnot. Two of those can be controlled: the red one (PWR) and the green one (ACT). By default, the PWR one is always lit as long as the power supply does not dip below 4.5V and the green one indicates memory activity.
All Pi except Zero
Edit /boot/config.txt by adding the following lines:
dtparam=act_led_trigger=none dtparam=act_led_activelow=off dtparam=pwr_led_trigger=none dtparam=pwr_led_activelow=off
Pi Zero
The brightness values of the Zero are reversed, we use ‘on’ instead of ‘off’:
dtparam=act_led_trigger=none
dtparam=act_led_activelow=on