(Including Li-On, Li-Poly and LiFE)
Ive had Li-On batteries Ive salvaged from a laptop sitting around for a few months and Ive finally found a place to use them. I have a safe Charger in place Based on one of Microchips Charging IC's. I can vary the charging rate to be anywhere from 0 to 500mA. I have a larger IC (That I havent used) thats able to be used to charge up to 1 Amp (Same Family, just bigger ).
So, for the application I want to put it into (Im basically replacing NiCad batteries from a old drill to Lithium Ones, They fit quite well and have enough space for a PCB or Protection foam). The whole reasoning behind this project is to reuse and re-purpose something (ie laptop batteries)
So bottom line, I know I need protection circuitry to prevent the batteries from Over Discharging, and Ive seen such protection PCB's online. Now For all intensive purposes, I would like to make my own (however, If this is unfeasible to do, I'll just buy the PCB for the protection circuitry). Overcharging isnt much of a problem Nor is Consuming alot of current (they are rated for 4000mAH) since the battery charger takes care of the overcharging problem. So the problem to tackle is Over discharging. From My understanding, the point where they get cut off is around 2.5V.
Can this be done with a simple Comparator circuit, a mosfet and a voltage reference?. Im thinking Once Vbat Reaches 2.5V, The mosfet will turn Off and Cut Power to the main Circuit so you cant use the drill anymore.
2nd Question: Can I used 2 Chargers In series to charge 2 Batteries in Series? Ie, Wire up One Charger with one battery, and do the same with the 2nd Battery but in series. I do plan on using the batteries in Series (this drill was only 6V or So-Its really old but it worked fine until the batteries died). See attached Diagram. Im only doing this so the cells get balanced when they are charged and so I dont have to get another charging IC.