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I've only got basic skills but i am trying to hack together an ESP32 + temperature sensor to send periodic readings out via Wi-Fi. I've managed to get the board to connect to Wi-Fi, read the sensor, send the data, shut down for deep sleep until its ready to repeat the process - but I'm unsure of how to handle powering the device.

By my extremely rough calculations it appears that it takes very roughly 15 seconds for each cycle to complete, and uses about 160ma while its doing so. I thus conclude that if I get a 1 watt solar charger with built in battery (the type used for powering cellphones - like this one) it should provide enough power.

My problem is this - what typically happens to these solar chargers when the battery is full and they continue to be exposed to power ? (In summer we get 2-3 times as much sun as in winter, but very variable weather, and the most important l time to read the temperatures is early in the morning when its dark in winter, so I don't want the battery to run flat).

Are there other, simple, cheap ways of powering my board from solar, preferably which don't require to much work at the component level ? If there are, are there any simple, cheap ways of measuring the remaining battery capacity and reporting this to esp32 board ? (If I know the battery status I may be able to schedule readings more or less frequently to ensure the board does not discharge ?)

Relatedly, I've found this item on Aliexpress (ie a solar charger sans battery - where you are meant to add your own battery). I'm hoping that I can combine it with a 3000mah or so flat battery and embed my ESP32 inside it for a very easy to build setup - is this a sensible solution?

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    I'm voting to close this question as off-topic because it is not about the Internet of Things, but rather about a solar charger / and or battery pack. In the SE system, questions about random consumer gear aren't really accepted unless you can supply engineering level detail about their working. Essentially, your question asks someone to guess how your solar panel and/or battery supervisor works, and guessing isn't part of the SE mission. You need documentation from the vendor. – Chris Stratton Nov 16 '17 at 22:04
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    @chrisstratton I see your point (and I'm a newbie in this particular see) but I put to you my question boils down to a question on how to power an IOT device using solar and battery. (I did read the "what's appropriate" part of the site before posting, and of-course, I believe this post is on topic here) How would you have me reword the question to make it on-topic in your eyes) – davidgo Nov 16 '17 at 22:12
  • If you step back and generalize so that you are no longer asking about that undocumented device but about what you could get instead, you would need a suitable power supply - but choosing which one to buy is a "shopping question" that is off-topic throughout the SE system, except on Hardware Recommendations SE. The SE model was never intended to be the answer to everything someone might want to know, rather it is exclusively reserved for questions fitting within its intentionally limited mission statement. – Chris Stratton Nov 16 '17 at 23:34
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    The Adafruit Feather Huzzah and Huzzah32 claim to be respectively an ESP8266 or an ESP32 with onboard circuitry to support connecting a rechargeable battery - something like that is (if it does what it seems intended to) probably going to come much closer to your needs than a USB powerbank, and at least you can get answers from them to actual engineering questions. – Chris Stratton Nov 17 '17 at 1:35
  • You might have more success if you ask on hardwarerecs.stackexchange.com – Mawg says reinstate Monica Dec 4 '17 at 7:16
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You can easily charge a LiPo battery but you must have a BMS (Battery Management System) so it won't explode when fully charged. Quite simple and cheap. Think about optimizing consumption, for example by removing on-board unnecessary LEDs. Plan for no-Sun days to calculate battery needs.

Andreas Spiess created a video which demonstrates a Solar Charger for Microcontrollers which may be useful.

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