The Raspberry Pi will deliver an "Under-voltage" warning when operating below 4.63 volts, as measured at GPIO pin 2 or 4. In Raspian OS, a lightning bolt appears in the upper right corner of the display.??In Raspberry Pi OS, a "Low voltage warning" text appears in the display upper right corner.??"Under-voltage detected!" is also logged in dmesg for each occurance.
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Often the cause is too much voltage drop in a poor USB power cable. I have taken apart flimsy USB cables where the wires were not soldered and relied upon the rubber molding to contact the pins.
USE A BEEFY USB CHARGING CABLE designed to fast charge smart phones and laptops.
$5 USB A to C
$6 USB-C to C
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To see what the Raspberry Pi internally measures on the 5V input, enter on the terminal:
? vcgencmd pmic_read_adc | grep EXT5V_V
You will be surprised at the voltage drop in most USB supply cables!
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With all USB loads attached, enter in the terminal:
?dmesg | grep Under-voltage
To see if "Under-voltage" is occurring.
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I have used these to successfully power my RPi5 with NVMe SSD:
$13 YIPIN HEXHA 10-32V DC in to 5.2V 6A dual USB-C
$10 Klnuoxj 8-32V to 5V. 5A. USB-C PD Converter.
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The RPi5 will run fine with 3A or more at 5V, if there is no USB load, but a 5A 5.2V supply is recommended to draw the maximum 1.6A from the USB ports.
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The USB-C Power Delivery 3.0 standard specifies 5 volts at 3.0 amperes, but the PD protocol allows for requesting higher current. The Raspberry Pi 5 wall wart acknowledges a PD request for 5 amperes. Normally, the RPi5 is configured to use USB-C Power Delivery (PD) protocol,
to negotiate 5A from the PD capable Raspberry Pi 5.1 volt mains power adapter, and shuts down if it fails to get PD acknowledgement that 5 A is available.
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Add a line to the config.txt of the Raspberry Pi to ignore the USB Power Delivery communication and assume that the power supply can provide 5v and 5A.
sudo
rpi-eeprom-config –edit Then
add the line:
PSU_MAX_CURRENT=5000
Or add the
following to the end of //firmware/:
usb_max_current_enable=1
Zero if the USB port current limiter was set to the low-limit during boot, non-zero if the high limit was enabled.? Enabled if the USB Power Delivery (PD) supply claims 5A max-current OR if forced in config.txt
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Forcing the RPi5 boot to ignore Power delivery will allow many 5.2 volt non-PD USB power adapters and automotive USB outlets to power the RPi5.
