Undervoltage? Check your USB cable

Apropos RPi Undervoltages: By running vcgencmd get_throttled on the Pi, you get an indication of whether the Pi is throttled (temperature) or is having and undervoltage or has seen either of those conditions since it booted. When I set up my new Ender 5 with Octopi, I noticed the undervoltage symbol when I was running off of the supposedly 3.5A USB port in the Tasmota WiFi outlet strip I use to switch lights and power for the printer.
I experimented and noted that whether the Pi was in an undervoltage condition depended very much on the USB cable. I tried a couple of different ones and even the thickest (based on diameter, not necessarily wire gauge inside) allowed the Pi to experience an undervoltage when running off the USB port on the WP9 that it did not experience when connected to the Pi power supply. Curious, I made up a cable to power the Pi from the USB port on the WP9 directly to the Pi using the two +5V pins and two ground pins on the GPIO. I used two twisted pair from an Ethernet cable, probably AWG 24. This cable runs fine with no undervoltage being detected by the Pi. The supply is good, the cables not so much.
The moral to the story is that it might not be the power supply, it might be the USB cable.

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Yes, just as foosel recommends in her FAQ: Pi Undervoltage/power issues: I had a strange lightning bolt/temperature symbol with an exclamation mark popup in my navbar, what does that mean?

Sounds a lot like what I've written about the subject.


It most certainly does!