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General discussion • Re: Raspberry Pi 5 discussion thread

Today i found a cheap PD compliant power supply which claims to deliver 20 watts max and i bought it. I then found out it is only 15 watts max when the current is 5 volts. Anyway, up to this point, i was using a standard 15 watt (5 volt - 3 amp) power supply with which i wasn't getting any "undervoltage" messages and it was working fine for me. I said what the heck, let's try this one, and after i connected the new supply to my Pi, it actually recognised it (i saw 15 watt PD in the bios messages). However, i am getting a lot of "undervoltage" messages in dmesg.
So, it is NOT maintaining 5V at the Pi when delivering the current the Pi needs
  • Are there any power-hungry USB peripherals?
  • Is the USB cable permanently attached or separate?
So is it a fauly unit (the power supply i mean)?
Probably not USB-PD spec compliant, but still some checks to make.
The usb-c cable is also new and rated for 65 watts.
LV power cables should be rated in amps, not watts. The voltage is only significant at high voltages, when the insulation could break down. At low voltages, only the current (which will heat the cable) is important. I doubt the cable would carry 13A at 5V, so the 65W applies at a higher voltage.
Since USB C power delivery supports 5V, 9V, 15V, 20V, 28V, 36V, and 48V, it's possible 65W means 1.35A at 48V. Unfortunately, the Raspberry Pi only works with the 5V modes.

I remember when Fido tried to explain 5V at 13A and 48V at 1.35A provide the same power to the three black kittens. The meowing after that led me to believe kittens are not unique in the way they understand electricity.

Statistics: Posted by ejolson — Tue Aug 20, 2024 12:22 am



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