The online UPS is ideal for environments where electrical isolation is necessary or for equipment that is very sensitive to power fluctuations. The basic technology of the online UPS is the same as in the standby or line-interactive UPS.
However, with the advances in technology, the online UPS unit was once only used for very large installations of 10 kva or more. Now they are available as a common consumer device, supplying 1kva.
The initial cost of the online UPS may be higher, but its total cost of ownership is generally lower due to longer battery life. However, it typically costs much more, due to it having a much greater current AC to DC battery-charger/rectifier, and with the rectifier and inverter designed to run continuously with improved cooling systems. It is called a double-conversion UPS due to the rectifier directly driving the inverter, even when powered from normal AC current.
In an online UPS, the batteries are always connected to the inverter, so it isn’t necessary to have a power transfer switch. When a loss of power occurs, the rectifier just drops out of the circuit and the batteries keep the flow of power steady and unchanged.
Online ups comes with different model and company but they basically are two main types according to load.
For Indutry Load UPS comes with transformer base because of its jerk or peak load at the starting of the load.
For IT Load UPS comes without transformer base due to its static load in starting or in running time.