In search for a 5s Li-ion battery balancing chip

[m.k]

Hey guys, as this is my first appearance in this forum, I think I should probably introduce myself a little. My name is Michael i am 23 years old and i guess you would call someone like me college student. I'm an Austrian and studying in Germany at the moment (more like mechanical engineering so my lacking electronic skills are not as embarrassing ). I've been watching eevblog for years, and now i have a question.

Background of this project is: I want to build a tool battery. For the DeWalt XR system. Yes I totally know one can buy one for 40 bucks, but hey I guess I'm not the only insane person here, right? With the XR system no switching is done in the battery. Overvoltage is taken care by the charger, Overtemp by the tool and the charger. Undervoltage protection is built in in low drain tools, with high drain you change out the battery before the voltage gets too low. No parasitic resistance where it's not needed.

Leaves balancing. In original DeWalt packs there is a balancing (or equalizing?) IC which is active all the time i guess. I don't know if the charger does balance the cells. It does have a connection to each cell but hey, there is balancing going on in the pack so I am not sure. I did disassemble the charger to see if a balancing chip is used but the PCB is glued in tightly and i was afraid to break it. The information to come to this conclusion is drawn from a very good and useful blog article of someone disassembling his battery pack. Mine is - you guessed it - gooped all over so you can't see a thing from the PCB.


source: https://syonyk.blogspot.de/2016/09/dewalt-20v-max-30ah-battery-pack.html

To build my own battery I'm now searching for such an chip used in the original pack, which just does balancing (or is that called equalizing?) and none of the whole protection stuff. Chips i found either do balancing and protection and are therefore huge (like huge amounts of pins) or even need external transistors which lets this little project get quite complicated. Buying a typical chinese protection board from ebay is a consideration, but in fact they are kinda big and i would have to hack it to just do balancing. And they are not thaat dirt cheap for probably not even a genuine chip and using just a fraction of the capability.

I thought maybe someone here has worked with such a device in the past and wants to share.

(As it will most certainly be a SMD device this would be my first attemt at a PCB. Oh boy )

[m.k]

Okaay, i recently picked the project up again and if someone comes across this and want to know how i did it, well i did nothing. The Charger did balance the battery in a little measurment i made today and if the selfmade battery works out i will measure the cell voltages now and then to see if the balancing from the charger is sufficient.