B) FLOAT AND BOOST CHARGER
This system consists of a Float charger and a Boost charger. In this system the battery will
normally float across the float charger so that in case of power failure the battery can
maintain the load without interruption.
However, after heavy discharge of battery, the battery is placed on boost mode of operation.
At that time load is taken care by float charger and boost charging is done by Boost charger.
Now if supply fails, the battery will be connected to the load bus through the DC contactor
and take care of the load.
During normal operation the tap cell diode will be reverse biased. In the event of power
failure during boost charging (with battery isolated), the output voltage will start dropping. As
soon as it drops slightly lower than the cell voltage the diode will conduct thereby
maintaining the voltage at the load bus (though lower in magnitude) to avoid complete
interruption of load supply. However, after this brief interval, the DC contactor will energize
thereby connecting the battery to the load bus and restricting the original load voltage. This
arrangement provides an uninterrupted DC supply to the load.