Stop Electron (asset tracker) from charging?

Firmware
1

I have an asset tracker electron that I’d like to install in a vehicle of mine. I’ve added a circuit to the vehicle to take care of the primary power to the electron.

The circuit is wired to shut off power when the ignition isn’t on (i.e. no power from the car 12v system when the car isn’t turned on). I don’t care about updates when the car isn’t running.

My goals are:

  1. No parasitic drain on the car battery (so deep sleep, even at a few micro amps isn’t acceptable in my scenario)
  2. I need to publish an even to the cloud when the electron loses power (i.e. when the vehicle is switched off)

The vehicle spends most of its time in Texas where ambient summer temperatures routinely exceed 100 degrees and interior vehicle temps can easily run outside of LiPo battery pack operating ranges.

Even if the asset tracker is mounted in the engine compartment where there is a bit more air-flow, radiant heat from the asphalt could still put the temps outside of safe LiPo temperature ranges.

  • If at all possible, I’d like to remove the battery from the design altogether.
  • Is it possible to detect vIn power loss with the firmware?
  • Is there a reasonable/safe way to power the electron with a capacitor to send that final “vehicle power off” message when the car is turned off? Similarly I’d like to send a message when the board starts up again. Basically, I want to be able to differentiate between “not sending updates because of a problem” and “not sending updates because it’s been turned off by the ignition”.
  • Failing the capacitor route, is there a way to enable/disable the battery charging circuitry? I’d use the temp sensor to disable charging so that I have a few more degrees to work with, in terms of operating margin since discharge temps are more forgiving than charging temps (basically I’d just shut off charging once temps exceed a certain threshold). At that point, I’d probably also switch to a tiny 100mah lipo to reduce the potential energy exposure in the event of a catastrophic failure.

Thanks in advance for any pointers!

-k

1 Like
2

Yes there is and I've come across several threads talking about this (search :mag: for disable charging will bring you several hits and I guess at least some relevant ones too)

Usually caps (even super caps) won't suffice - especially if the connection is flaky.

You can of course power your setup from the car battery direct (with some extra buffer caps and good filtering/protection against excessive voltage spikes). And with some extra circuitry you can even have the Electron detache itself from the car power and have the circuit reattache it when the car gets started again.
But I'm not sure whether that is necessary when the Electron is in deep sleep with battery charge disabled.