Tracker brownout protection

Tracking System
1

Hi,
What are the dangers of mistakenly letting a Tracker One run on its internal battery until the battery dies, without any external power source?
Is the Tracker One running Tracker Edge firmware protected from a brownout or any other dangers from this (unwanted) situation?

Thanks,
Gustavo.

EDIT: @eberseth or @rickkas7 may you have any thoughts on this? Thanks

2

I would probably avoid doing that. The nRF52840 won’t be damaged, but you do risk damaging the cellular modem if the device shuts off while trying to connect to cellular because of insufficient battery power.

1 Like
3

Thank you.
What would you set as the minimum level/SoC of the battery: 10%, 20%, 15%?
Thanks again.

4

That’s a tricky question. If you stay connected to cellular, you can probably go lower because connecting it what causes problems, especially on 2G/3G, less so on LTE Cat M1.

The next problem is that the SoC is not linear. You’ll find there’s a very long tail where the SoC is less than 1% and the device continues to run, for many hours running constantly in normal operating mode, at least with LTE Cat M1.

I’m just throwing out random-ish numbers here, but I would probably go with 5% for LTE Cat M1 and 10% for LTE Cat 1/3G/2G.

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5

I found this variable in the tracker source code (tracker.cpp):

constexpr int TrackerLowBatteryCutoff = 2; // percent of battery charge

Is this variable the one I can change to, let's say, 10 and then at 10% the tracker will go to sleep?

I can see this function uses that variable and is executed in the void Tracker::loop() function:

evaluateBatteryCharge();

It would even send a low batt warning?

TrackerLowBatteryWarning

I could not find docs to configure or use this feature.
Thanks!

Maybe @eberseth you have some knowledge in the area? Thanks

6

Yes, that is the spot to change for another value. It should apply a software limit and wake up from sleep (if applicable) to check on battery state.
I think you are trying to set the limit higher, and that is fine. We picked 2% because it was the best trade-off of remaining time versus temperature changes and wake schedule to perform limit checks. I would not recommend going lower than 2%.
The issue with running the battery very low is that the battery and the TSOM PMIC can compete when getting close to the the 3V undervoltage limit. If the built-in battery over-current-under-voltage protection circuit is tripped first then it may require you to open the cover and manually disconnect the battery to get running again.

7

Thank you for the extra info, Eric.
Gustavo.