My use case will put a Boron/Xenon in a cold environment (on a glacier) so I need to consider LiPo charging below 0C. I see that the bq24195 onboard has capabilities to monitor LiPo temperature. Is this broken out? If not, is there any more complete documentation for PMIC?
On a related note: what are the consequences of charging below 0C? Can these consequences be mitigate by reducing the charge rate? If so, how could this be implemented with PMIC?
I believe the Particle hardware uses a resistor instead of a thermistor, to “fake” the Li-Po Temperature.
You would need to add an external temp sensor, unless I’m remembering that incorrecly.
The BQ24195 datasheet is here.
Common Cold Weather Practice is to limit the charge current as you approach freezing (0°C), and completely disable charging @ 0°C or slightly above.
Li-Po’s can be discharged as cold as –20°C, but that’s not a “recommended” practice.
That also matches the minimum Recommended Operating temperature of -20°C for the Boron
Your Glacier Application might be a good fit for a Solar Energy Harvester Circuit that Recharges SuperCaps (ie: no batteries) ?
Or you can use Energizer L91 “Primary” Batteries that are rated down to -40°C, but you would need to replace those every 1-2 years, depending on your duty cycle and pack size. Battery swaps might not be feasible on a Glacier
Thanks Rftop, and sorry for the pause…
That’s all really helpful. I’ve not used SuperCaps - I need to look into them and their capabilities. I may well post more questions in due course.
@davidgraham, I’m working on a “Battery-Less” Boron LTE project.
I’ll be happy to share my results after preliminary trials.
I currently plan on feeding a regulated 3.3V output from a Solar/SuperCap harvester into the Li-Po connector. I believe that’s out-of-spec, but I’ve (initially) confirmed 3.3V into Li-Po connector works.
I’d rather use the 3V3 pin, but the Boron Docs say that we cant use the 3V3 pin to Power the Boron.
I had hoped that I could use 3V3 Pin if I disabled the Boron’s 3.3V regulator with the EN Pin, but I’m scared to Smoke Test it.
I don’t know what would happen between the Boron’s Regulator and Power Switch with a “back-feed” in this scenario.
@rickkas7 , can you give any recommendations for the best practice to efficiently supply a Boron LTE with external 3.3V supply, if it’s possible?
It is not possible to supply the Boron with 3.3V directly, bypassing the regulator.
The intention for special cases like this will be the B series SoM, which does not have a regulator on the module so you can use your own methods to supply the necessary voltages.
@Rftop That’s interesting. I was intending to use an external lead acid battery and solar panel to power the 5v usb input, with the lipo/supercap to provide the extra power needed for the cellular connection. If I go for supercaps I’d charge them through the lipo socket with a current limiting resistor. I guess I could put a regulator between the lead acid battery and directly supply the lipo socket.
Will the supercaps you’re using be able to supply current overnight when there’s no solar input? If so, that would be another option for me.