offline ups: - it is used in small office, centre. it's backup time is 15-20 minute and its mode time 10-15.it's cost may be 1500-1700 online ups: - it is used in large companies like bank, school. it's cost is very high, backup time is 4-5 hrs.
The offline UPS is in standby mode. The charger is maintaining the battery, but the inverter stage is not running. Power goes from input to output, bypassing the inverter.
In this configuration, the charger and inverter design is less, as the charger is usually in trickle mode and the inverter does not need to run continuously. On power fail, the inverter starts up and takes the load. There is a glitch in output, a few line cycles, but most loads can handle this.
The online UPS runs all the time. The charger now runs the inverter, as well as maintaining charge on the battery. The inverter supplies the load. Power goes from input to charger to inverter to output.
In this configuration, the charger and inverter design is more, as they need to run continuously. On power fail, there is no glitch, because the inverter is already running and supplying the load. Usually, there is synchronization between the inverter and the line, so that failure of the inverter can initiate fall-back to the line without glitch.