I tested for months my low temperature custom sensor and this is the result.
If I put them without changes (original CR2450 button battery) in fridge, freezer and outside (Quebec here), the battery last few months, or less.
What you need:
- a regular smartthings multi-sensor
- a 18650 Li battery holder
- a 18650 Li battery
- a 3V stepdown converter
- a 15EDGRK-3.81mm 3p plug (screwable)
- 1 twisted dual wires from an ethernet cable
- an iron solder
you can screw directly the stepdown converter into the 3P plug,
you screw the wires from the battery holder to the 3P plug
you screw the ethernet cable to the 3P plug
you drill a small hole into the smartthing sensor and solder the ethernet cable
that's it
The converter convert the variable voltage from the 18650 battery. When full, this battery is about 4.2V, probably too high for the sensor (but I didn't test this sensor under 4.2V but I thing it's not a good idea).
I put this sensor into a freezer (-18C / OF) and the voltage of the 18650 dropped 0.15 V in 3 months. That's because the battery itself is not in the freezer, thanks to the ethernet cable.
I tested this with a 2m ethernet cable and you can probably take a longer one (no real voltage drop with those lengths).
The cost in very low:
- 18650 battery and smartthings sensor...
The result:
