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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 :(

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    Given that most of us don't seem to have problems even with phone chargers what might you be doing differently? Perhaps you have something attached to your Pi drawing too much power?
    – joan
    May 15 at 8:39
  • Absolutely nothing is attached. Just the network cable and HDMI cable
    – mahela007
    May 15 at 15:56
  • That suggests you have a problem with the HDMI device.
    – joan
    May 15 at 15:58
  • Ok. It's a TV. I will unplug the HDMI and see.
    – mahela007
    May 15 at 17:19
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    Sounds like a faulty Pi. I run my Pi's headless and rarely have problems with power supplies.
    – joan
    May 16 at 7:12

3 Answers 3

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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.

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  • Tried it with an apple power supply. No luck unfortunately.
    – mahela007
    May 15 at 15:59
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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

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  • If I could buy an official power supply I would. If you read the question properly, you'd know that
    – mahela007
    May 15 at 15:58
  • I did read the question - you don't say which country you are in, nor what your currency is!
    – CoderMike
    May 15 at 19:12
  • Sri lankan and Sri lankan rupees. Due to the foreign exchange crisis that occured a few months ago, imports of non essential electronics have been curtailed. It's getting better but RPi Products are still difficult to find.
    – mahela007
    May 16 at 2:17
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    Older style psu but appears in stock microchip.lk/product/…
    – CoderMike
    May 16 at 7:11
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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.

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  • "it is sufficent to have a single, short voltage drop" i.e. the voltage is low. Conspiracy theories have no place on this site. This post is factually incorrect.
    – Milliways
    Jun 6 at 9:52
  • Where is the conspiracy? It is common knowledge and stated elsewhere even in context with the Raspberry Pi original PSU that the high initial power demand of a system starting up may create voltage drops large enough to trigger a low voltage condition on the Raspberry Pi. Also you dropped the initial word "apparently" marking your comment biased. Shame on you.
    – tinkering
    Jun 7 at 10:10
  • and BTW it's your comment which is factually incorrect: '--"it is sufficent to have a single, short voltage drop" i.e. the voltage is low.__' No! The voltage was low, once upon a time when the system was booting and long before the popups appear. Everyone can check this fact using the information I provided in my answer.
    – tinkering
    Jun 7 at 10:53
  • If you can't see that your defamatory comments about Simon Long are unfounded I can't help. I have extensively studied the power circuitry and if you did the same you would realise the low voltage is detected in hardware - if you choose to hide the warning it won't change the fact that the voltage is low. If you choose to ignore the warning this is OK - the Pi will actually work down to ~4V. It is well documented that the kernel stretches the low voltage to 3sec to make it visible.
    – Milliways
    Jun 7 at 11:00
  • You still don't acknowlege that I don't deny that the hardware correctly detects low voltage conditions. The point is, the LXDE Plugin shows its warning popups even when no low voltage conditon is currently detected and that is a fact which can easily be checked. And I wouldn't even complain about the nasty popups if they were justified.
    – tinkering
    Jun 7 at 11:11

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