2 Hour Brownouts during battery test?

1

I’m testing how long a custom board can perform on battery power with hourly syncs to to notehub with an MBIS card on 8.23 firmware. When I’m around ~3.5v of battery power on a Li-Ion cell(4.7v to notecard via a buckboost) I see brownouts every 2 hours. The battery is capable of 2A pulse current. What’s strange is that the brownout messages and first message off a notecard reboot make it to the hub, but my hourly sync note never makes it. I’m assuming the issue is a combination of bad signal and low power but are there any settings in the notecard that could consolidate whatever it is trying to do to save power as I’d think this is an all or nothing type opporation->Why would a notecard restart message make it to the hub but no the sync?

 req = {
"req": "note.add",
"file": "data.qo",
"sync": True,
"body": body
}
card.Transaction(req)

Screenshot showing a mix of syncs to routes and brownouts. Syncs to routes should happen every hour

image
image1920×1193 294 KB

Notecard

“rssi”: -79, “sinr”: 8, “rsrp”: -101, “rsrq”: -7, “rat”: “lte”, “bars”: 1, “voltage”: 4.714,

Notehub

Fri 08:57:34 AM: boot (brown-out & hard reset [17326])

Fri 05:56:35 AM: boot (brown-out & hard reset [17326])

Fri 03:55:37 AM: boot (brown-out & hard reset [17326])

Fri 01:54:39 AM: boot (brown-out & hard reset [17326])

Thu 11:53:41 PM: boot (brown-out & hard reset [17326])
2

Hi @bkauf,

Based on your message (and without having access to the full trace log), it looks like you are already in a fringe connectivity situation (i.e. bars 1 and low rssi, sinr, etc values). So, you have a modem that’s already slightly more stressed in terms of the fact that it has to transmit at nearly full power.

As to why the brown-out message comes through and not your regular Notefile, that’s likely because the battery has rebounded a little so it’s temporarily in a healthier state, the modem is already “warm” due to the previous failure, and the payload is very small. So the brown-out is likely happening mid-transmission during the sync, before your Note is actually delivered. The Notecard reboots, fires its small boot note on a recovered cell, and that’s what you see. Again, hard for me to say unequivocally that’s what is happening, but feels like it.

I would STRONGLY recommend adding a LIC like the Scoop to your design if at all possible. I would also recommend using periodic syncs that are voltage-based and stay at/above 3.7V for regular syncs.

Rob

3

Hi Rob,

Thank you for the quick reply. I think you are correct the signal strength must be right on the edge of my battery power band. I have a battery with a 2A pulse current but that is likely not enough for the MBNA in the area I am testing. I will keep the voltage high for now.