IN ONLINE UPS THERE IS A DOUBLE CONVERSION AC TO DC THEN DC
TO AC.SO THERE IS NO INTERRUPTION IN ONLINE UPS WHEN MAIN
SUPPLY FAILS.BUT IN OFF LINE UPS THERE IS ONLY ONE
CONVERSION AT A TIME EITHER AC TO DC OR DC TO AC WHICH
SWITCH OVER WHEN CAHNGE OVER DONE.
In an online UPS there is AC to DC conversion using a rectifier, DC to DC boosting and finally DC to AC conversion simultaneously at the same time. Online UPS is in operation and supply power to the load with mains power on.
An offline UPS charges the batteries when mains power is on and supplies power to the load when mains fail.
Online UPS is- the ups is connected to power supply and the
equipment is connected to the UPS.i.e ups does 2 works
here,they are:1) give the supply to the equipment.2) charge
the batteries in the UPS from the supply. this is online ups.
offline ups: the supply is connected to the ups and the same
supply is connected to equipment,i.e the supply charges the
ups and also the equipment. then if there is a failure in
the power supply then we disconnect the equipment from
supply and connect it to ups.this is the disadvantage of
this so we shifted to online UPS long ago.
example for the online UPS is: the ups we use for the
computers in our home
On line UPS connection to the user is automqatically, so
there is an electical interlock between it and power
network . The logic of this inter lock is when power
network is on the UPS is diconnecterd from the user and
when power network is off, the UPS become connecterd to the
In addition, on line UPS are used supply some important
equipment in some applications permanently such as process
computer, PLC or realys in industrial plants.
Off line UPS connection to the user is manually. So when
the power network is off, somebody has to connect the UPS
to the user by closing a breaker or contactor.