Trying to understand the under voltage issue

Question

Using this script to provide a power report, I am getting the following while powering the Pi with iPhone power brick and the official Raspberry Power supply brick:

-- using official Raspberry Pi Power Supply on Raspberry Pi 4
$ bash vcgencmd_power_report.sh
vcgencmd get_throttled (0x0)
vcgencmd measure_volts:
     core volt=0.8560V
  sdram_c volt=1.1000V
  sdram_i volt=1.1000V
  sdram_p volt=1.1000V
Temperature: temp=49.0'C
-- using iPhone power brick on Raspberry Pi 2
$ bash vcgencmd_power_report.sh
vcgencmd get_throttled (0x50000)
  under-voltage has occurred since last reboot
  throttling has occurred since last reboot
vcgencmd measure_volts:
     core volt=1.2000V
  sdram_c volt=1.2000V
  sdram_i volt=1.2000V
  sdram_p volt=1.2250V
Temperature: temp=31.5'C

From here its obvious that the RPi is happy with the official power supply and not with the iPhone power brick.

The specs says that power supply should be 5V. I am not sure if I am supposed to add up all the volt numbers or what? From the report, the sum of all the volt entries is 4.156V on the official power supply and 4.825V on the iPhone power brick.

Why is the Pi happier with the official power supply if the voltage is lower? Or am I reading the report wrong?

Milliways · Accepted Answer · 2024-02-20T01:36:01.123

Those voltages have NOTHING to do with the power supply and are internal supplies which are designed to change depending on CPU load.
The only way is to measure the voltage on pin 2 or 4.
If you do this be careful that you don't short any pins (use du-pont cables to connect to the header).

The internal voltages on a Pi2 are different to Pi4.

vcgencmd get_throttled (0x50000)  
  under-voltage has occurred since last reboot
  throttling has occurred since last reboot

indicates that you had a low voltage which may have caused the Pi To throttle.

Probably not even a power supply problem but a problem with inadequate cables as you should be able to use an Apple 18W charger - I have used one with my Pi5.

See https://raspberrypi.stackexchange.com/a/51616/8697 for an explanation.

Trying to understand the under voltage issue

1 Answers1