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My raspberry pi 3+ is showing undervoltage warning. I know this is a common issue and I've done a fair bit of trouble shooting, so please keep reading.

At first, I tried powering my raspberry pi with phone chargers rated for 5V at 3A. This is when I first got the low voltage warnings.

Since many forum posts suggest that phone chargers are not suitable power supplies (even if they have the appropriate power ratings, and I do not have an official Rpi charger on hand) I tried powering the the Pi from an old ATX power supply. (Soldered a microUSB connecor to the 5V lines of the power supply.. The ATX power supply is rated at 20A for the 5V line. Far in excess of what the Pi will use)

The low voltage warnings still recurred.

Then I thought it was an issue with the micro USB cable OR the Rpi's microUSB connector. So I tried bypassing the micro USB connector and powering the raspberry pi directly through it's 5V pins.

But.. I still keep getting the low voltage warnings.

To be more specific, I think I am getting what's called a "brownout". As decribed here, the red LED turns on briefly at boot and then stays off. - apparently this means that a brownout sensor has been triggered. Using the vcgencmd get_throttled command and the dmesg command, I was able to confirm that CPU is indeed being throttled due to low voltage and the low voltage warning had shown up in the kernel logs.

So.. what else can I try? Is there something wrong with the Pi? Is there something wrong with the OS? (I'm using OSMC). Am I left with no choice but to try the official power supply? They are quite expensive in the local currency :(

mahela007
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4 Answers4

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If you get a low voltage warning it is because the voltage is LOW!
This can be transient, due to poor power supply or poor cable.

The Pi3B+, Pi3A+, Pi4B use a MxL7704 PMIC chip to manage power, which has a hardware voltage detector which triggers at 4.63±0.07V so if it triggers the voltage is very low. This is triggered by hardware although the LED is controlled by firmware.

See Raspberry Pi Power Limitations

vcgencmd get_throttled will show detail:-

0: under-voltage
…
16: under-voltage has occurred

If bit 0 is 1 under-voltage is detected.

If you have an Apple (iPhone or iPad) supply they work reliably (although you still need a good cable). I have also used a Belkin 2.4A supply.

Milliways
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Stop wasting your time and buy an official power supply.

They are excellent and good value for money.

https://www.raspberrypi.com/products/micro-usb-power-supply/

enter image description here

CoderMike
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If it's about the low voltage warning popups in LXDE/openbox you find the answer at Pi my life up just above the conclusion. Just skip the usual blurb about insufficient power supply above.

In short, these popups are generated by the LXDE plugin lxpug-ptbatt without interaction from the hardware, that is, even when there is no under-voltage condition detected. You can check that by watching the logs either with dmesg or by looking at the appropriate logfiles like /var/log/syslog. Apparently it is sufficent to have a single, short voltage drop while booting for the popups to be shown again and again, all the time. That's why you get these warnings even with your 20 A power supply. I had tried something similar myself before.

The package is installed by default and maintained by Simon Long from the Raspberry Pi foundation. From these circumstances I only can conclude, this plugin and the popups serve the purpose of boosting the "Raspberry Pi original power supply" sales and the plugin can simply be removed to fix the problem.

tinkering
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For what it's worth, I have a RP 3B new out of the box, bought about a year ago and this seems to have faulty undervoltage detection. The red LED goes on and off seemingly at random, and I see 'undervoltage' warnings on the console - perhaps two or three times per hour. Sometimes the red LED is off for minutes at a time. I am using a good quality desktop 'brick' 2.5A 5V power supply with its output cable soldered to a short microUSB cable, total cable length between PSU and R-Pi about 30cm. My Fluke digital volt meter confirms the voltage (measured on the GPIO header) at 5.02V. Examination with a Rigol Digital oscilloscope does not show any anomalies. If I move the SD card, HDMI monitor and power supply to a second R-Pi (also new out of the box, same batch), the red LED stays on continually as expected and there are no undervoltage warnings. From this I would suggest there is at least one raspberry pi tellling porkies... With that said, I agree with most other posts that 99% of undervoltage reporting is almost certainly poor power supplies, over long/over skinny/poor quality cables and the like.

boatbodger
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