BMS

Update 2011-03-12

First of all, I am not using the Elithion system as stated below.  This was part of the EV Components disaster (see Batteries page if you want to know a little more).  No matter how the EV Components litigation comes out I will not be re-ordering the Elithion system again.  I always thought this system was way to expensive and the only reason I ordered it was because EV Components was going to set it up for my battery pack and they offered a two year battery pack warranty if you included the BMS.

Since the time of the original order, about a year now, I have read a lot of information about the LiFEPo4 cells and followed the debate/flame wars about whether or not you need a BMS and top balancing vs bottom balancing, etc.  I do not want to participate in this debate.  But I do tend to sympathize with the point of view of simpler is better.  I do think that low voltage cutoff and high voltage overcharge detection is needed.  For that reason I am going to use the mini-BMS from Clean Power Auto. I like the philosophy of this design.  The designer comments frequently on the DIY Electric Car forums and he seems to have a reasonable approach.

With this system I will not have individual cell reporting.  Each cell is monitored for over-voltage, under-voltage, and over-temperature, but only the exception condition is reported, not the actual cell voltage or temperature.  I have decided that this is a reasonable tradeoff for a simpler and less expensive system.

Finally I want to comment on my own BMS efforts.  When I started this project I wanted to build my own BMS.  I started off with a Stellaris microcontroller kit from TI (I work for TI), and I connected it to a TI battery cell monitor dev board.  I used this on my 4-cell pack of TS-160.  It was fun, and I can see how to build this system, but it is simply taking me too long to do the board design, component selection, etc, and I want to get this thing on the road.  So I am now taking the buy vs build approach to pretty much everything for this project.

Update

Decided to use the Elithion system and ordered it from EV Components along with the battery order.  They will fit the system correctly for my battery pack and deliver all the pieces I need.  I really wanted to build my own BMS but just don't have the time to do that and get the conversion done.


(Original Post)

Table comparing battery management systems:

http://liionbms.com/php/bms_options.php#Fancy%20BMS

elithion - company that makes lithium battery electronics

http://liionbms.com/php/index.php

Hardy EV - BMS

http://www.convertthefuture.com/index.php

Volt Blocher charging battery balancer (shunt)

http://www.voltblocher.com/

Elite Power Solutions has BMS for thundersky battery packs (s2kev blog complains about these)

http://elitepowersolutions.com/products/index.php?cPath=6

Here is "MiniBMS" pointed out by someone on the Austin EV mailing list:

http://cleanpowerauto.com/MiniBMS.html

Application note from TI about cell balancing:

http://focus.ti.com/lit/an/slua524/slua524.pdf