Float and Boost Charging of Batteries

Float charging is used where the battery rarely gets discharged.  A typical application where float charging can be used would consist of the float charger, battery and the load in parallel.  During normal operation, the load draws the power from the charger.  When the supply to the charger is interrupted, thebattery steps in.

Float charging of a battery involves charging the battery at a reduced voltage.  This reduced voltage reduces the possibility of overcharging.The Float charger ensures that the battery is always in the charged condition and is therefore considered "floating".  The Float charger starts by applying a charging volltage to the battery.  As the battery gets charged, its charging current reduces gradually.  The float charger senses the reduction in charging current and reduces the charging voltage.

If the battery gets drained, the float charger will again increase the charging voltage and process continues.  Float chargers can be connected indefinitely to the batteries.

Boost charging involves a high current for short period of time to charge the battery.  It is generally if the battery has been discharged heavily.  Boost charge enables the quick charging of depleted batteries.

For instance, a two volt lead acid battery which has been discharged will initially be boost charged with a charging voltage of around 2.35-2.4 volts.  However, as the battery voltage rises, the charger will switch over to the float charge mode with a float voltage of 2.25 volts.

Most battery chargers come equipped with provisions for both boost and float charging.