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View Full Version : Idea DIY Li-ion Battery Pack Protection/Management Circuit?


TurbineLP
Jul 23, 2004, 01:32 PM
I'm planning to build a decent-sized (4S8P) Li-ion battery pack (actually not for an RC application, but that's neither here nor there) and I've been toying with the idea of making my own protection/balancing circuit for it, like the commercial packs have.

After some searching around I found this product, the Xicor X3100:
http://www.xicor.com/folder_x3100.php

...which I think would fit the bill perfectly (assuming one can deal with the package, which is a pretty tiny surface-mount IC). The X3100 really seems to do everything - besides the basic over/undervoltage and overcurrent protection, it can also handle cell balancing and SOC indication (which would be very cool to have in a homemade pack).

The data sheet and application note even give a complete "recommended implementation" circuit, so it looks like all that would be necessary would be to build the circuit, tie in an appropriate microcontroller, and write some relatively simple code. Of course none of that is as easy as I'm making it sound, but...

Thoughts, comments?

Happy Hobit
Jul 24, 2004, 12:30 PM
Hi Thorsten,

That’s an impressive looking chip and would make one hell of a smart battery. It’s too bad that they didn’t make it stand-alone so it wouldn’t need the microcontroller.

Automatically balancing an unbalanced pack is fine but I would want to know that the pack was out of balance and by how much and adding a diagnostic display to a battery would be a bit much. (I’d be able to track the battery pack aging)

A ‘Consumer’ wouldn’t be concerned about this but I am. For a consumer product the X3100 would be great, but kind of advanced for a ‘Do It Yourselfer’.


The two most important ‘Protection’ features, in my opinion, are ‘Balancing’ and ‘Low Voltage Cutoff/Warning’ and I’d build the ‘Balancing’ into the charger and the ‘Low Voltage Cutoff/Warning’ into the airplane. (Or whatever load is using the batteries.)


Here’s a balancer idea, and it’s available commercially. ‘Suzanne’s Balancer’

LiPo Balancer - Schematics & PCB http://www.rcgroups.com/forums/showthread.php?t=157641


Zagisrule was designing a multipurpose microcontroller based charger. Maybe a balancer could be added into it.

Best homemade lipo charger design http://www.rcgroups.com/forums/showthread.php?t=242053&page=2&pp=15


There are also a number of ‘Low Voltage detector’ circuits such as,
MicroScream: $5 Audible Lipo Alarm http://www.rcgroups.com/forums/showthread.php?t=221018, that can be added to the ‘Load’.


Jay