Hi to the experts,
I have observed an unusual behavior when charging my operational Airnote through its USB port, as shown in the attached image taken form the dashboard. I need again some help, please…
The charger is a switching regulator with an LC low-pass filtered output that gives 4.9 V with a current up to 1 A. It is the same one that I used for powering Safecast’s air quality monitoring device built four years ago.
The displayed battery voltage was 3.5 V when the USB charger was first connected to the Airnote. I left it there for about 35 hours, a time that I suppose should be enough to fill up completely the 3.7 V Li-Po cell while also powering the Airnote’s circuitry.
Referring to the dashboard panels, this is what happened instead:
At the beginning the battery voltage went up to about 4.32 V, but then it continued rising and after about 4 hours it reached a stable value of ≈4.89 V, very dangerous for a Li-Po cell!
At the end of the 35 hours period the charger was disconnected: in this moment the battery voltage dropped down to a safe level of about 4.22 V.
But less than 12 h after the charger was disconnected, the battery voltage went down again to the discharged value of 3.5 V: a very fast depletion process. Maybe the Li-Po cell is damaged?
During the second half of the 35 hour charging period, the battery voltage showed a few sudden drops (highlighted by a black rectangle in the attached image), going from 4.9 to 4.67 V and then up again. During this period the displayed temperatures were too high by about 5 to 10 °C (verified with an external thermometer).In the same time also the PM readings dropped. Some abnormal overheating in the circuitry?
Thank you very much for your patience, and best regards,