"Under-voltage detected" and red LED blink

[edo1]

Hi

We had some power-related issue in our project. At the moment of a USB peripheral device attach, the red LED blinked, and sometimes "Under-voltage detected" message appeared in the dmesg output.
I thought that they should happen at the same time, but mostly I saw blinking only (with no errors in dmesg output).

How are they related? Does the blinking mean that we could have stability problems even without "Under-voltage detected" errors?

P.S. At the moment, the power problem seems to be resolved. It was a short (10-20 μs) voltage drop. Powering the peripheral device through a small resistance (0.2 Ω) helps to avoid voltage drop.

[pcmanbob]

Both the red LED flashing and the "Under-voltage detected" mean the same thing, it may be that the under voltage event had not actually cleared so a new Under-voltage detected was not logged.

best option is to just fix the Under-voltage so that it does not happen.

[alphanumeric]

What model Pi are you using? And what is the current rating of your power supply?
An undervolt can be the result of trying to draw more current from the power supply, than what its capable of.

[edo1]

What model Pi are you using?

Mostly I have an issue with RPi 3. I have a few RPi 2 used, and I see undervoltage message as well.
I've never seen this message at 3+ (with the same hardware setup), it looks like this model is more tolerant of voltage drop.

And what is the current rating of your power supply?

4A
https://www.meanwell.com/Upload/PDF/IRM ... 0-SPEC.PDF

[alphanumeric]

4A should be enough. Do you have nice thick wires in your power cable? The official power supply uses 18 AWG wires.

[edo1]

RPi is powered from our custom PCB through 5V pin on 40-pin connector. 5V rail on our PCB is short and wide enough.

I still have some questions

Does the blinking mean that we could have stability problems even without "Under-voltage detected" errors?

What is the minimum voltage for stable operation of the RPi? Is it the same for 3 and 3+?
Can I be sure that there is no power issue if the red LED does not blink?

 

[fruitoftheloom]

RPi is powered from our custom PCB through 5V pin on 40-pin connector. 5V rail on our PCB is short and wide enough.

I still have some questions

Does the blinking mean that we could have stability problems even without "Under-voltage detected" errors?

What is the minimum voltage for stable operation of the RPi? Is it the same for 3 and 3+?
Can I be sure that there is no power issue if the red LED does not blink?

 

https://www.raspberrypi.org/documentati ... /#pi-power

[FTrevorGowen]

RPi is powered from our custom PCB through 5V pin on 40-pin connector. 5V rail on our PCB is short and wide enough.

I still have some questions

Does the blinking mean that we could have stability problems even without "Under-voltage detected" errors?

What is the minimum voltage for stable operation of the RPi? Is it the same for 3 and 3+?
Can I be sure that there is no power issue if the red LED does not blink?

AIUI it's more an issue of the "stability" of connected USB devices (below the low-voltage threshold of 4.65V)**. However there may well also be a "knock-on" effect w.r.t. the Pi's own 3.3V/1.8V regulator which, presumably, also has a minimum input voltage which may be (IJDK) different (devices) for the P3 and P3+.
Trev.
** The original Pi supply spec. was equivalent to that for USB2 ie. 5.0V +/- 0.25V IIRC.