Correction -

I have taken two additional steps to try and confirm this. If I use a relay and switch the VDC to the USB port on and off it works fine. If I remove the VDC from the USB port by just taking the +wire off on the power supply it does not like that and reboots possibly because it is NOT taken away cleanly.

@crispyoz Hi

Thanks for responding and sharing your experience.
The device on the board is an Omega2S+ and it is on an OnionOmega2 pro board.
The battery is a 1100mAH LiPo 3.7V.

I have done a bit more investigation:-

Looking at this from the viewpoint of the DC voltage at the USB port on the Pro board. I can see by using a DC benchtop supply to provide the USB port with power, that if the voltage is slowly turned down from a good 5VDC, at around 3.4VDC the board resets rather than switches over to the battery for its power source. If the USB VDC is a clean solid 4-5V when the USB power is inserted into or removed from the board the power management copes and switches over nicely. However, if the VDC at the USB port drops ungracefully as it may be doing when the AC is pulled then it does not cope.

Therefore, I now believe this is not likely to be a problem with the AC but more to do with the design of the power management on this board.

I have taken two additional steps to try and confirm this. If I use a relay and switch the VDC to the USB port on and off it works fine. If I remove the VDC from the USB port by just taking the +wire off on the power supply it does not like that and reboots possibly because it is taken away cleanly.

I am now looking at a circuit that might be able to drop a relay as the power comes down but before it gets to 4VDC. Not sure if this is likely to work but I will let you know.

Thanks again!

The product being used Omega2S+ Pro carrier board
Device Firmware Version: 0.3.3 b247
Description of the issue:-

When using Omega2S+ Pro with USB power and a LiPO battery as a backup, the Omega resets when the AC power supplying the USB power adapter drops out.

For context, we live off-grid in rural NSW, Australia. We are using the Omega2S+ Pro boards for things like power monitoring and generator control etc. Our main AC power comes from a battery and inverter solar system.

Expected Behavior:- We would expect that if the AC power supplying the USB power adapter drops out that the Omega would continue to run normally.

Observed Behavior:- When the AC power drops out, the Omega resets/reboots. However, if the USB cable is unplugged from the device the Omega runs normally on the battery without resetting.

Steps to reproduce the issue:- Simulate the AC disappearing by either unplugging the USB adapter from the mains or switching it off at the wall switch, this makes the Omega reset in my scenario. This is consistent no matter what is providing the USB power. We have tried the following USB power adapters Netgear, Apple, Samsung, and laptop plug pack that has a USB power output.

Could someone who does not live off-grid and has a stable AC mains supply try and reproduce the problem for me and share their results. This would help me rule out the AC power supply to the house being a part of the problem e.g is this related to the fact we using AC power generated from an inverter?
Also, if anyone else has experienced a similar issue and/or has any advice to share.
Any help would be appreciated.
Kind regards
Phil