"Smart" Charger


I have a lot of 18650 batteries, salvaged from laptops or power banks.
Charging them is always a chore, so let's make something smart and arduino based.

The requirements are as follow :

  • Safe
  • Cheap
  • Can manage 3 or 4 batteries
  • Display charge level and current consumption
  • Be usable with a regular 2.1A usb charger 



For the last point, we can either dumb down the max current per unit i.e. for example max 0.5 A / battery x4 ~= 2 A, or delay charging until a slot becomes available.

We'll go for the latter.

The system will be made of 2 boards, stacked on top of one another :
  • A display board : With a nice  and big color screen and the arduino (3.75$ screen ST7735 based) + outputting Axxx and Dxxx lines from the arduino over dupon connectors + 5v/GND
  • A control board, managing 3x batteries 

The idea is that the display board can be easily reused for other projects, such as 2S battery charging.

Initially;  i intended to use Nx INA219 current/voltage sensors, but it takes too much space on the small proto board i'm using, so instead we'll use INA3221, it's basically a triple INA219 inside the same packaging.

The charging board itself will be using TP4056 + protection, these are really cheap and work well.

First prototype with only one charging circuit was made, with some surprises :
  • It's really easy to power the arduino from one of the input D pins, so we'll reduce that to a minimum. Else the boards won't power of when a battery is plugged.
  • You can't measure the voltage of the battery while charging, so we'll have to stop charging for a bit, measure voltage, and then resume charging



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