Switching between external power and batteries to power an Arduino?

Question

Batteries

There is an Arduino-based device - the device has a power supply that powers the Arduino and the entire harness. I would like to add 18650 batteries to the circuit in such a way that when there is voltage in the network, they are charged / recharged, when the voltage in the network is lost, the circuit is powered by batteries.
Found a similar module www.ebay.com/itm/LiPo-Charger-Basic-Micro-USB-3-7V... for li-polymer batteries, but I need for li-ion batteries.
If anyone faced with a similar problem, share your experience?

Answer 1

If you look at the mat. part, you can see that Li-Po batteries are only a subset of Li-Ion batteries. And the elements of the 18650 form factor you named are often Li-Po batteries, they just put the signature in the old style, because. in search engines they often drive in exactly this terminology. And Li-Po batteries are usually called prismatic (in the form of a parallelepiped, as in a mobile phone). So if you have a voltage of 3.7 V (charger 4.2) in the description of the batteries, then you can safely use the block for charging Li-Po batteries on Li-Ion batteries, because. their charging characteristics do not differ, and the name Li-Po on the charge control unit is given only for show off, because. Li-Po technology is somewhat younger. Probably you should not use such a block on batteries whose regulated voltages are 3.6 V,
You can also use diode decoupling as suggested by Alexeyslav, but then you will need a 4.2 V source, and with the toy from the link it’s just 5V, so for your task I would advise you to take it. By the way, I climbed the link to see the maximum current, which, however, I did not find, and in the very first line it says: “It is designed to charge single-cell Li-Ion or Li-Polymer batteries”
So no need to bother with terms Chinese sellers, I advise the site about chemical sources is very well written, and it’s nice to read, and adds understanding, I advise you to read from the very beginning after reading this page, how it all began with the vivisection of frogs, very interesting (although this is subjective, not everyone loves the history of science) .

Answer 2

Usually, in such cases, a simple diode decoupling is used, stupidly two sources are connected to the consumer through Schottky diodes. But in phones it is even simpler - the battery is always connected to the consumer, and the mains voltage charges the battery and simultaneously powers the device.
Problems with diode decoupling arise only in the case of micro-consumption (the reverse current of Schottky diodes from the battery to the charging circuit can still exceed the consumption of the device) or very huge currents (5 ... 10A and more). In my opinion, in the second option, you need to reconsider your views on backup power ... is it really necessary?
And most importantly, the diodes are rather oak devices, it is difficult to burn them.

Answer 3

Set the controller to be simple for this type of battery, although I would put a Lifepolka. They are not as explosive.
There are controllers for all types of batteries, otherwise there is a problem with overcharging or undercharging.

Answer 4

If you have a couple of free ports in arduino, you can use the charge circuit from here
There is also a description

Answer 5

Try wemos battery shield:
got.by/2x7z69
https://youtu.be/b-fWiX_TzrE