Will PI detect under voltage lockout during shutdown? Can PI have graceful shutdown during Under voltage lockout?

We’re working on Raspberry pi 3 B +, and we’re discharging the voltage using super capacitor for graceful shutdown.

I have a question regarding under voltage lockout detection. In one of the documentation forum it’s mentioned that Raspberry PI detects under voltage lockout if input voltage goes less than 4.63+/- 5% during the power on. We also observed the same,
We will be powering PI with POE and during ON state it is powered up with 5V and no problem in that.
But my question is that as we are discharging it through super capacitor for graceful shutdown, we want to know what will be the exact operation of PI during shutdown?
Will PI still detect under voltage lockout during shutdown? if yes,
As the super capacitor discharge voltage will decay with time, can it go below 4.63V during shutdown?
Rasp_Pi PMIC can generate output voltage i.e. 3.3V till super capacitor voltage of 3.6V. But will there be any problem of SDcard crash if PI goes to under voltage lockout during shutdown operation?
Can PI have graceful shutdown during Under voltage lockout?


Hi Raj,

I’m really not sure what exactly you’re trying to achieve or what you mean by ‘graceful shutdown’, or why you’re using a super capacitor if you have PoE? I think you’ll need to explain it a bit more clearly before you can get a good answer.

Raj, you may like to use read-only file system?
On Buster, it’s settable via raspi-config

Hi Oliver,

  1. By Graceful shutdown, i meant the data should be stored & saved successfully in the SDcard so that no data lost occur when it’s powered off.
  2. We have used Supercapacitor to make sure that the PI gets backup time to store all the data in the SDcard during powerloss. During power off POE will be off so to give some backup time we kept Supercapacitor is used.


Peter, yeah we want to backup the data in SDcard once the poweroff event occurs. so during this, the supercap will hold the PI to be on, as the super cap discharges voltage at that point can go less than UVLO limit of PI. This is the point we’re more concerned of as in PI blog they mentioned PI will have errotic behavior when it’s in UVLO.

i’m new to PI can you please explain more about settings?


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You will be better off saving data to a USB drive.
Another option is to shrink the system partition (not boot/FAT partition) leaving a little spare and fill the remaining space with another partition to save data to.

Make the system Read Only (see raspi-config -> Advanced Options -> Overlay FS).

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