I have a battery powered Photon project that monitors water levels inside a water well. In order to preserve the batteries, the Photon turns on once a day to measure the water level and then goes into Deep Sleep for 24 hours before it wakes up again to take another water level measurement. I use 4 AA batteries, which supplies Vin with about 6.5V when the batteries are new. The Photon specs say that Vin can handle a maximum of 6.5V, so I use this maximum voltage to make the batteries last as long as possible. I’ve operated several Photons like this in water wells for more than 3 years with the same batteries.
I have noticed 2 types of strange behaviour which might be related. I’m wondering if anyone can explain these.
Usually when I attach the battery pack to Vin, the Photon starts up immediately. But I’ve noticed that some brand new Photons won’t start unless I lower the voltage (by using old batteries) to less than 6V. Not all Photons do this, but I’ve seen this behaviour on about 15 new Photons lately. Is this because some Photons have overload protection that prevents the Photon from turning on if Vin exceeds 6V?
I have a Photon that’s been running for 2.5 years from the same batteries and was behaving perfectly. But recently it no longer wakes up from Deep Sleep at the 24 hour interval that it’s programmed for. Its wake up time now ranges from about 24 to 37 hours, although sometimes it reverts back to its regular 24 hour interval for a few days before becoming erratic again. I checked the voltage on the battery pack when this started happening and it was about 6.1V. Can any one explain why this might happen?