I'm unsure whether you PC is able to negotiate the power correctly.I found a case where a certain program can send some data via USB-C port but not via USB-A.
Anyway, comments on whether I could plug the Pi 4 into a USB-C port on my laptop? The Pi 4 is an early version that didn't work with all power supplies, only with their official power supply. I hear they fixed that in later revisions, but I do not have one of those.
I would solve this problem in a completly different manner: separate data and power.
1. Power the Pi via the 40 pin header and a good external 5V 5A power supply. If you can adjust the voltage to 5.1V. Use good cables with sufficient diameter (≥0.5mm²) and use both 5V pins and at least two GND pins in order to distribute the load. Many header sockets are only rated for 2A, and this is not enough for a Pi.
2. Build an adapter board or adapter cable from USB-C to USB-A.
2.1 Disconnect the VBUS line. VBUS will provide power from the header, and this is absolutely forbidden if this port acts as an USB device (which it will in this mode of operation). Failure to obey this rule will cause hardware damage. Normal USB A-C cables do have this connections and MUST NEVER be used in this setup unless being modified accordingly.
2.2 Keep GND connected.
2.3 Keep D+ and D- connected and make sure not to disturb the high frequency signal integrity and the differential impedance. These signals are very sensitive and require careful handling.
3. On a Pi5/CM5 add the line "PSU_MAX_CURRENT=5000" to the EEPROM settings via "rpi-eeprom-config --edit" . The Pi4/CM4 doesn't have this and doesn't need this.
This way you can keep your Pi powered permanently and connect or disconnect your PC as needed.
It's a pity that the Pis don't have an alternate way of being powered and there are no circuits that prevent backfeeding. They would have increased the production costs. So the onus is on you.
Statistics: Posted by fchk — Fri Dec 26, 2025 7:33 pm