BM3 Monitor for Li-Ion / Li-Poly Battery Packs
with cell balance connector
BM3 for 3SxP battery pack
BM3 V2.0 12F675 ( 2005/12/12 )
The resistors R3,4,5, used to divide the input voltage to 1/3, and R6,7,8 divide the input to 1/2 to fix the operation range of PIC12F675 ADC,
Use 1% resistors for R4,5,7,8 and LM 7805L as regulator, the average deviation error well be better than 0.05V
So....
Voltage AN0 = cell 0
Voltage AN1 = cell (0+1)/2
Voltage AN2 = cell (0+1+2)/3
and transfer to :Voltage cell 0 = AN0
Voltage cell 1 = (AN1*2)-AN0
Voltage cell 2 = (AN2*3)-(AN1*2)
If you want to change the cut-off voltage, just change the ASM code LOW_VOLTAGE EQU D'xxx'
and UNBAL_VOLTAGE EQU D'xx' to change the unbalance detector
;---- VARIABLES DEFINE ----
;
LOW_VOLTAGE EQU D'153' ; (3.0V/5.0V)*255= 153
;LOW_VOLTAGE EQU D'158' ; (3.1V/5.0V)*255= 158
;LOW_VOLTAGE EQU D'163' ; (3.2V/5.0V)*255= 163
;
UNBAL_VOLTAGE EQU D'10' ; (0.2V/5.0V)*255= 10
; ;nominal 0.2V, actually 0.1~0.15V
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I use the ADC at 8 bits resolution, For more precise detection, you may try to rewrite the program to 10 bits resolution.
Keep the wiring short, to prevent interference from speed controller and motor, otherwise add 0.1uF capacitor between PIC pin 5,6,7 and Vss, respectively.
¡@
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Philip Sun / TAIWAN
copyright 2004
