Need to design a voltage controlled switch

Thread Starter


Joined Feb 4, 2016
Hi, i am new to this forum and only recently decided to start learning/ working with electricity. I am starting a project and i was looking for your help. In this project i will be using 6-9 18650 batteries to create a 12V DC power supply. I want to be able to charge these batteries and have some sort of a circuit board or switch or anything that will be able to switch off the charging voltage supply once the voltage of the battery reaches for example 4V, and then switch back once it falls below like 3.5V. I am also going to install a solar panel as well as a mains charger, hence why i need something that will prevent from overcharging the batteries.
I have taken these batteries from an old laptop battery and i have a circuit board that has been attached inside of the battery. Can anyone explain what that circuit board is for and if i am able to use it to charge a set of these batteries without them overcharging. Maybe this circuit board could act as the voltage switch i was talking about above, or if not is there any useful functionality for this circuit board?
Any help is greatly appreciated and I am new to this forum so if i missed any important information please bare with me. Once again thanks for any help.