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The Vectux M-BMS
Submitted by Mik on Mon, 08/10/2009 - 14:28
The Vectux Manual Battery Management System (M-BMS) is a handy device.
I do not recommend to build one, though!
Much more details about the entire M-BMS, for the Rotary switch Array and about how it was developed can be found on Endless Sphere: http://endless-sphere.com/forums/viewtopic.php?f=14&t=6853
The M-BMS works because I have capacity tested all cells individually and arranged the worst ones in order of capacity at the positive end of the string. Therefore I can quite reliably predict where I need to focus my manual monitoring efforts.
The M-BMS allows individual voltage monitoring of the 13 worst cells and of a few good cells (for comparison). It also taps into the 12 stock battery temp sensors of the Vectrix and allows monitoring of temperature at 6 additional locations in and around the battery.
It allows individual recharging of all 13 weak cells, either with auxiliary battery packs during riding or parking, or with an external charger. It allows charging from a single cell up to 18s cells.
(After removal of the battery housing cover) the M-BMS also allows for charging of all individual 8s and 9s modules of cells with an external charger. That could be useful after periods of non-use, or repairs, to balance the battery prior to charging with the on board stock charger.
Each added tab consists of a 20A fuse directly at the cell, then 30A rated cable to the top of the battery pack. Connectors on top of the pack allow for the 8s and 9s module charging or discharging, and divide the tabs into monitoring cables (for each tab, with 15kOhm resistors in line) and recharging/discharging tabs (for the 14 cells at the positive end of the string and tab 102-028, without resistors but with an additional 10A fuse within easy reach).
That allows safe monitoring of the full pack voltage of up to 153V (due to the resistors limiting current) and limits the maximum voltage at the low resistance connections (which are easily accessible) to a relatively safe 40V.
How it works in practice:
On the right side of the switch box one can select either the entire string voltage (102s), or first 27s, or last 27s, or any of the 12 modules of 9 or 8 cells, or groups of 5s cells, 3s cells and individual cells.
And on the left are three switches that allow to select one of 18 temperature sensors in and around the battery.
It only makes sense because I have analyzed each cell, and the low capacity ones are all located at one end of the series. It's more of a learning device than a useful BMS for any other rider...
I can very efficiently identify the cell which starts to reverse charge first, by monitoring voltage drop under load, first in larger groups, then by quickly "zooming in" on the offending cell.
Here you can find the schematics: