A123 free BMS

[Jeff]

As part of a larger project, I used a modified version of a voltage
clamp article posted in electronic design:
http://electronicdesign.com/Files/29/1155/Figure_01.gif

and homogenized it with a vclamp circuit drawing from Victor at MME:
http://www.metricmind.com/ac_honda/bms.htm

to come up with this as a finished version to accommodate A123 cells,
along with a LV detect:
http://www.evbones.com/vclamp.pdf

An image of a complete clamp:
http://www.evbones.com/cellclamp.jpg

The Vclamp is designed to attach to a parallel cell cluster, and flag
when the clamp is active, and flag for LV detect.
Each parallel cluster includes this assembly, and reports to the host
MCU that functions as a parasitic BMS on top of a GM designed battery
management system for 12V PbA batteries. In the application shown in
the images below, I welded up some clusters to test in a 72V ebike
application for validation testing.

Ebike battery pack image:
http://www.evbones.com/a123clamp.jpg

The final application uses 30 cell parallel clusters, and the clamp
transistor dissipates the heat into a copper plate that forms the
cathode and anode connections to the cluster.
Four series clusters approximates a single 12V battery, tapped
appropriately for satisfying the GM master BMS requirements, with the
parasitic cell BMS running on top of the GM system. When a cell clamp
activates, it reduces the charge current until all other cluster
clamps activate to indicate full. The LV detect section overrides the
dead reckoning BMS, and places the vehicle in a reduced performance
mode, followed by shutdown shortly thereafter.

Image of 30 cell cluster assembly before resistance welding:
http://www.evbones.com/cluster.jpg

So, basically what I donated here was a method to clamp the cell
charge voltage to a preset level, regardless of charge current, and a
simple method to flag for LV detect.

Your contribution will be to engineer a host MCU to monitor the inputs
from each of the opto isolators, and use it to control charging
current, and depth of discharge.

Have Fun! Jeff

[mikep_95133]

Jeff,

Your clamper looks a lot like Scott Davis or Bill Dube's designs. All
three designs are very similar.

Mike