I’m looking to use the Electron or E-series for a product suitable for the cold Canadian winters, which requires a minimum temperature rating down to -40 Celsius.
The Electron datasheet states that it can operate down to -20 and the E-series datasheet states it can operate down to -40. However, in sifting through the Electron BOM, the two main temperature limiting components are the MAX17043 fuel gauge and the NR3015T2R2M inductor used with the 3.3V regulator. These same parts are also used on the E-series (from the datasheet).
So should the E-series only be rated to -20 Celsius?
The other component is the SIM card connector. I believe that’s the limiting factor in very cold conditions. Since the E series uses a SMD e-sim, it’s not subject to the same issues as the physical SIM card connector.
I think the reason for the discrepancy between the E series -20°C operating temperature in store and -40°C in the data sheet has to do with note 4. The -40°C is only achievable when you don’t have a battery, but the store lists the lowest operating temperature with a battery. That should be made clearer.
Using the built in charger is exactly what I mean. And you’re right, judging by the photo is doesn’t look like it has the protection it claims. The manufacturer does custom orders so better make sure to specify it has the necessary protections.
@peekay123 I haven’t found any high density (Lipo or similar) battery that has a low charging temperature, such as -20 or ideally down to -40, so I will never have a power supply connected to the VIN pins while having the battery connected. Or do you know of such a battery?
The PMIC chip has the ability to not charge the battery until it’s above a certain programmed temp but that requires a thermistor to be attached to the battery or on the Electron board.
Particle chose to use dual resistors on the temp pin of the PMIC so it’s always reading the same temp which allows the PMIC to charge the connected battery at any temperature.
If you could figure out a way to replace the temp pin resistors for the PMIC on the Electron then you could run a thermistor to the battery and let the PMIC automatically stop charging when the temp is below 0C. Not sure how feasible that is considering the parts are probably 0402 surface mount resistors