I have a raspberry pi 3B+ model that I bought back in February 2019.

For sometime, I "remember" it was working fine (although I can say from experience - memories can be deceiving).

Then I sort of forgot about it and left it off for a while. Recently, about 2~3 days ago, I resurrected that Raspberry Pi again. And noticed random reboots - for no apparent reason - probably due to all the updates it got after being brought back to life again.

I googled and found the usual suspects mentioned: power supply and here again.

Thankfully, I immediately checked back to the power supply I bought from here and was grateful to find out that my power supply was rated at 2,5A and hence completely suitable to work with the Raspberry Pi. \(^o^)/

I also looked into Syslog and found no suspicious (some sort of power-related) messages. (should they be there? Dunno!)

Needless to say the random reboots, did occur, sometimes three~four times immediately one after the other, within a few minutes of each other, or the Pi could go on running for 2 days and then reboot.

I suspected at this stage that it might be a software issue. I reinstalled Raspbian from scratch (no NOOB!) and rebooted. Sadly the problem was back almost immediately.

I installed NOOB and proceeded to install RiscOS. After booting up, it seemed to run snappy (not surprising). No reboots in the 20~30 min that it took me to orient myself with RiscOS and try to find out 'how to shutdown or reboot from within the RiscOS'.

Short of someone hacking into my Pi for no good reason and rebooting it (#paranoid), I "felt" at this stage, this must be a Raspbian kernel issue or some firmware issue of some sort. Tempted to install Kali or Ubuntu (32bit/64bit) or even something more exotic like Gentoo, but being the masochist that I am, I decided to install the full Raspbian OS again - from the NOOB this time. And so I whiled away that whole sunny sunday.

After rebooting the problem seemed to have disappeared. I left the Pi running for 2 days, checking back every evening and finding out that indeed it had been running non stop, until last night, when it had rebooted. ಠ_ಠ

I restarted my "tasks" manually on the Pi (manually on purpose, Cron could've fixed the job but I wanted to find out why the Pi reboots). And just now, as the cat didn't let me sleep, I got up anyways, and checked that the Pi had once again rebooted. (╯°□°)╯︵ ┻━┻

Googled and found out about dmesg and now I see these messages about under voltage there.

[    6.328679] random: 7 urandom warning(s) missed due to ratelimiting
[    6.361729] ieee80211 phy1: rt2x00_set_rt: Info - RT chipset 5390, rev 0502 detected
[    6.415268] ieee80211 phy1: rt2x00_set_rf: Info - RF chipset 5370 detected
[    6.484518] ieee80211 phy1: Selected rate control algorithm 'minstrel_ht'
[    6.487084] usbcore: registered new interface driver rt2800usb
[    7.287338] Under-voltage detected! (0x00050005)
[    8.297779] uart-pl011 3f201000.serial: no DMA platform data
[    8.469399] 8021q: 802.1Q VLAN Support v1.8
[    8.525940] Adding 102396k swap on /var/swap.  Priority:-2 extents:1 across:102396k SSFS
[    9.045327] IPv6: ADDRCONF(NETDEV_UP): wlan0: link is not ready
[    9.045370] brcmfmac: brcmf_cfg80211_set_power_mgmt: power save enabled
[   16.820673] Bluetooth: RFCOMM ver 1.11
[ 1519.024627] brcmfmac: brcmf_run_escan: error (-52)
[ 1519.024641] brcmfmac: brcmf_cfg80211_scan: scan error (-52)
[ 6530.222765] Voltage normalised (0x00000000)
[ 6532.302543] Under-voltage detected! (0x00050005)
[ 6536.462131] Voltage normalised (0x00000000)
[ 6540.622579] Under-voltage detected! (0x00050005)
[18679.342533] brcmfmac: brcmf_run_escan: error (-52)
[18679.342547] brcmfmac: brcmf_cfg80211_scan: scan error (-52)

Like I said, the power supply is advertised as a 2,5A supply. And I have no external devices connected to the Pi that don't have their own power supply. It is basically running in a headless mode.

So, the question is, time to buy a new charger a.k.a (expand the ever-growing collection of USB chargers lying around the house)?

  • You could lose the emoticons Jul 8, 2020 at 16:23
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    The 1990s called. They want them back. Jul 9, 2020 at 7:56
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    Official advice from the Raspberry Pi Foundation is to always use an official power supply, others may be tricky. In particular, "chargers" can be a problem because the demands of camera, phone & tablet charging are different, and it's not a problem if voltage sags down to 4.3v. This specially applies to the Pi 3 and 4 models. Having said that, that German site that you linked to does mention "Raspberry Pi 3b+". I have always felt that when ordering a new Pi I might as well include an official PSU at the same time. As you say, a PSU might go flaky after a time. Glad you found a solution. Jul 10, 2020 at 8:20
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    I agree. Lessen learned -> don't try to cut corners and save money by just ordering the Pi once and then realizing and ordering "some" case and PSU later. Best to order all together once. Jul 10, 2020 at 8:28
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    Someone on another forum expressed it like this: many phone chargers will give a voltage rating (such as 5v) and a current rating (like 2.5A) but the problem is some chargers cannot do both at the same time. They may give 5v at 0.5A, 1A, etc, but once the current draw rises above some level, the voltage drops (or 'sags'), so that at max rated current (like 2.5A) the voltage can be down as far as 4.3v which is still good for charging a battery in a phone or other device. A robust PSU will keep the voltage up to 5 or 5.1v (Rpi4 official PSU) at the rated current. Jul 10, 2020 at 8:55

2 Answers 2


A charger isn't a PSU. Also the cable quality can make a big difference.

In this case with a RPI3+ I would say the power supply is the most plausible cause of the reboots.

Also check after some time over ssh

 vcgencmd get_throttled;

If the ouptput is different from:


iIt means the cpu has throttled.

This can be caused by bad power supply or overheating, but the latter should only happen in case scenarios with high CPU usage.

To check temperature:

  vcgencmd measure_temp

To check voltage:

  vcgencmd measure_volts;

See vcgencmd and FAQ

  • The temperatures, I was logging regularly anyways. I forgot to mention that in the post with all the other things. The temperature never hovered around 42°C ~ 44°C. Thanks for the tip about checking voltage. I was looking for something like that. I try later in the evening and get back here. Jul 8, 2020 at 8:28
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    A charger isn't a PSU. -> point taken. I was not familiar with that issue. Thanks for informing me. :) Jul 8, 2020 at 8:32
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    Chargers can go down to around 4.3 volts. PSUs don't. Jul 8, 2020 at 16:24
  • @MichaelHarvey, thanks I didn't know that. Jul 8, 2020 at 20:15
  • To put it another way, for example many '5 volt 2 amp' rated phone chargers may be able to provide 5 volts or 2 amps but not both at the same time, which is OK for charging mobile phones or tablets because they are OK down to 4.3 volts, but a Raspberry Pi will start complaining before then. A PSU rated 5v 2A or 3A should deliver rated current at max volts. Jul 8, 2020 at 20:33

Maybe your power supply is failing. The power supply in your link appears to have an inline power switch on the 5V side. These are a bad idea and can cause voltage drop.

I suggest you buy the official power supply.


  • Thanks for the reply. I didn't know about the inline power switch. I ordered a 3-Ampere one this morning, just in case. (The only reason for ordering that particular one, was the quick delivery time, while the official one would've come later.) Jul 8, 2020 at 8:26
  • @DuckDodgers Just be careful with "USB chargers" (which all these really are, regardless of marketing) -- there are many poor ones on the market that do not meet their claimed specification. Generally I would recommend getting one from a known brand, but I am unsure what is available in Germany. Anker is usually good, and many are tested here.
    – Bob
    Jul 9, 2020 at 1:18
  • @Bob, ok thank you. :) -> this false marketing cost me a sunday of my life that will never come back. Jul 9, 2020 at 6:52

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