ICS1722
Cells that are not thoroughly conditioned or possess an unusual cell
construction may not have a normal voltage profile. The ICS1722
uses an alternate method of charge termination based on a slight
decrease in the voltage slope to stop charge to cells whose voltage
profile is very shallow. This method looks for a flattening of the
voltage slope which may indicate a shallow peak in the voltage
profile. The zero slope point occurs slightly beyond the peak
voltage and is shown on the voltage curve graph.
Charge Termination Methods
Charge termination schemes include voltage slope, fast charge
timer and, if desired, a ten hour timer to limit total charge time.
Voltage Slope Termination
The most distinctive point on the voltage curve of a charging
battery in response to a constant current is the voltage peak that
occurs as the cell approaches full charge. By mathematically
calculating the first derivative of the voltage, a second curve can be
generated showing the change in voltage with respect to time as
shown in Figure 6. The slope will reach a maximum just before the
actual peak in the cell voltage. Using the voltage slope data, the
ICS1722 calculates the point of full charge and accurately
terminates the applied current as the battery reaches that point. The
actual termination point depends on the charging characteristics of
Charge Timer Termination
The controller uses a timer to limit the fast charge duration.
These times are pre-programmed, and are automatically adjusted in
time duration according to the charge rate selected. Fast charge
timer termination is a safety backup feature to limit the duration of
the fast charge stage. The fast charge timer is always enabled and
cannot be disabled. See Table 3 in the section Charge Rate
Selection for more information. To limit the total charge time to ten
hours, refer to the section Ten Hour Timer Mode for more
the particular battery.
information.
Figure 6: Voltage and slope curves showing inflection and zero slope points
6
GALAXY [ GALAXY POWER, INC. ]
