|Battery Application & Technology
Constant-voltage (often called
constant-potential) chargers maintain nearly the same
voltage input to the battery throughout the charging
process, regardless of the battery's state of charge.
Constant-voltage chargers provide a high initial current to
the battery because of the greater potential difference
between the battery and charger. A constant-voltage charger
may return as much as 70% of the previous discharge in the
first 30 minutes. This proves useful in many battery
applications involving multiple discharge scenarios. As the
battery charges its voltage increases quickly. This reduces
the potential that has been driving the current, with a
corresponding rapid decrease in charge current as depicted
in the illustration below. As a result, even though the
battery reaches partial charge quickly, obtaining a full
charge requires prolonged charging.
Given this behavior, constant-voltage
chargers are frequently found in applications that normally
allow extended charging periods to attain full charge.
Constant-voltage chargers should not be used where there is
frequent cycling of the battery. Repeated discharges without
returning the cell to its full charge will eventually
decrease the battery capacity and may damage individual
Constant-voltage chargers are most often
used in two very different modes: as a fast charger to
restore a high percentage of charge in a short time or as a
float charger to minimize the effects of overcharge on
batteries having infrequent discharges.