Undervoltage every 120 secs

  • I see an undervoltage warning pretty exactly every 120 sec
  • RasPi 3B+ including a Raspberry power supply (from Conrad electronic) rated 5V and 2.0A
  • I upgraded to latest OctoPi 0.17.0 - same behaviour as before
  • no USB devices connected, no Ethernet, no extensions
  • only Wifi is on, and Monitor via HDMI

Is there any service that runs every 2 minutes and might cause this ?

Hi @marvin42blue!

Referring to Raspberry.org (https://www.raspberrypi.org/products/raspberry-pi-3-model-b-plus/) you need a 2.5 A PS.
Also have a bad feeling they bundled a charger and not a power supply.

Hi Ewald_Ikemann : thanks, but I think this is wrong. In the meanwhile I connected the Raspi to a laboratory power supply, setting: 5.1V - 5A - double checked with oscilloscope and digital instrument. I never seen the Raspi pulling more than 800 mA - typical is 200mA - so this "2.5A" rating is stupid because it doesn't give any information about the ability to drive power peaks (well, I know, all these small power supplies will not provide this information) - but: I still see these undervoltage warnings, not every 120 seconds, but the time gap is a multiple of 120 secs. So I still wonder which software tool creates that sort of load, every 2 minutes ?

Try disconnecting the HDMI and compare your results.

If it were me, I would review my /etc/crontab or /etc/cron.d/* scripts to see if any of those are set for the 120 second timing.

Next, I would try this in Safe Mode to see if the condition goes away. If so, then one of your plugins has a 120-second timer event.

If it's still there in Safe Mode then temporarily disable the Pi Support plugin's check via the Settings screen and test again. Here, you'd want to watch this with something like watch cat /var/log/syslog | grep -i undervoltage perhaps, noting that the bundled Pi Support plugin is the one responsible for observing undervoltage conditions within OctoPrint.

Pi Support check for undervoltage itself is here at either 30 or 300 seconds.

There's also a network connectivity check which occurs at some frequency. You might try toggling that off to see if this has a positive effect.

You might also try toggling off SD card support in the Files side panel widget via the gear icon. (There's another timer which presumably checks for changes in its directory.)

I think there's a heartbeat timer at 900 seconds so this probably isn't your culprit.

My gut tells me that there's something writing to your microSD card at this interval. It could be within OctoPrint's space or not. For example, something could be writing to a global log in /var/log.

And finally, disconnect your serial cable to your printer and re-test. If your Pi is sinking power over to your printer then this could be the cause.


Just got curious: You say you get the message every 120 s. Usually the undervoltage (not undercurrent) flag is set, when the voltage is below 4.63V and this flag usually is reset when rebooting the Pi (https://www.raspberrypi.org/forums/viewtopic.php?t=211635).
How do you know that the flag is set every 120 s?

The Pi may draw 800mA in average, but one short current peak can set the flag. When the manufacturer says: Provide a power supply with 2.5A, I think they know what they say.

Does this issue only occur when the printer is connected to the Pi or also when it's disconnected?

...this is strange - exactly the same setup today, but no more undervoltage issues !?

I checked the syslog from yesterday with Excel: under-voltage happened quite accurately every either 118.56 or 120.64 seconds - the voltage normalised came after either 4.16 or 6.24 seconds. The files show over 300 events.

I monitored the voltage yesterday with two different digital scopes and was not able to clearly trigger a single under-voltage event, although the RasPi reported them. Even used different USB cables, short and long, 0.34 and 0.5 mm² with no effect. Also used two different microSD cards.

In all cases I had nothing connected to Ethernet and USB, not my printer and nothing else

Since the system is now running all day without any issue I'll blame it on Kharma or Santa or whatever. If it doesn't occur again, I'll close this case tomorrow.

Anyway, thanks a lot for your support !

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Check the voltage at your wall socket. Maybe that's where all this originated from. Maybe you were baking a potato in the microwave oven or your refrigerator's compressor was toggling on/off.

Hi, thanks, I had the same idea meanwhile, but no way to proof it. The system runs now for 36 hours without any trouble. I'll close this issue.

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