SLUUAQ3A April 2016 – October 2022 BQ4050
If EDV compensation is enabled, the calculates battery voltage to determine EDV0, EDV1, and EDV2 thresholds as a function of battery capacity, temperature, and discharge load. The general equation for EDV0, EDV1, and EDV2 calculation is as follows:
EDV0,1,2 = n (EMF • FBL – | ILOAD | • R0 • FTZ)
EMF is a no-load cell voltage higher than the highest cell EDV threshold computed. EMF is programmed in mV in EMF/EDV1.
ILOAD is the current discharge load magnitude.
n = the number of series cells
FBL is the factor that adjusts the EDV voltage for battery capacity and temperature to match the no-load characteristics of the battery.
FBL = f (C0, C + C1, T)
C (either 0%, 3%, or Battery Low % for EDV0, EDV1, and EDV2, respectively) and C0 are the capacity related EDV adjustment factors. C0 is programmed in EDV C0 Factor/EDV1. C1 is the desired residual battery capacity remaining at EDV0 (RM = 0). The C1 factor is stored in EDV C1 Factor.
T is the current temperature in °K.
R0 • FTZ represents the resistance of a cell as a function of temperature and capacity.
FTZ = f (R1, T0, T, C + C1, TC)
R0 is the first order rate dependency factor stored in EDV R0 Factor/EDV2.
T is the current temperature; C is the battery capacity relating to EDV0, EDV1, and EDV2.
R1 adjusts the variation of impedance with battery capacity. R1 is programmed in EDV R1 Rate Factor.
T0 adjusts the variation of impedance with battery temperature. T0 is programmed in EDV T0 Rate Factor.
TC adjusts the variation of impedance for cold temperatures (T < 23°C) TC is programmed in EDV TC.
Typical values for the EDV compensation factors, based on overall pack voltages for a Li-lon 3s2p 18650 pack, are as follows:
EMF = 11550/3(1)
T0 = 4475
C0 = 235
C1 = 0
R0 = 5350/3(1)
R1 = 250
TC = 3
(1) = Divided by 3 (number of cells) if cell based compensated EDVs are used.
The graphs in Figure 7-3 show the calculated EDV0, EDV1, and EDV2 thresholds versus capacity using the typical compensation values for different temperatures and loads for a Li-Ion 3s2p 18650 pack. The compensation values vary widely for different cell types and manufacturers and must be matched exactly to the unique characteristics for optimal performance.