Difference Between Online UPS and Offline UPS – Which One is Better?
Main Difference between Online UPS and Offline UPS – Which One to Use?
UPS, Uninterruptible Power Supply is a device that supplies power in case of power failures. A UPS can be either Online UPS or Offline UPS. Both types of UPS can be used as a backup power source but there are many differences between them.
The major point that differentiates between the online UPS and offline UPS is that the online UPS supplies power from the AC mains to the Load through the rectifier and inverter combination while the Offline UPS directly supplies power from AC mains to the load.
Before going to the list of differences between Online UPS and Offline UPS, let’s discuss the basics of Online UPS and Offline UPS.
What is UPS (Uninterruptible Power Supply)?
UPS is an abbreviation for Uninterruptible Power Supply and the reason for its name is that it provides a constant supply of power without any interruption. In Normal operation, it draws current from the AC mains, and during a power outage; it draws current from its backup source.
A UPS system utilizes a DC power stored in the battery as its backup source. The UPS charges the battery from the AC mains through a Rectifier and charge controller circuit. At the same time, it supplies power to the output AC load. In case of power failure, the UPS utilizes this charged DC power in the battery and converts it into AC using an inverter and supplies it to the AC load.
Now the switch over between the sources (AC mains and the battery in case of power failure) is instantaneous. But it does take some time. This time delay during the switching may affect some sensitive electronic equipment while other devices may tolerate it in a specific range. This is where Online UPS and Offline UPS comes into play.
What is Online UPS?
Online UPS is a type of UPS that supplies power to the AC load through the Rectifier and Inverter Combo in normal operation and uses an inverter to supply AC power during a power failure. Therefore, the output power supply always stays ON and there is no need for switching. Hence, there is no time delay in switching between its sources. There is no interruption in the case of power failure even for a nanosecond.
During normal operation, it converts the AC supply from the AC mains into DC using a rectifier and charges the battery using a charge controller circuit. Now at the same time, the DC power from the charged battery is being converted into AC using an inverter to supply it to the output AC load.
In case of power failure, the UPS will stop drawing current from the AC mains and stops charging the battery. But the AC load will continuously draw current from the battery through Inverter.
Therefore, Online UPS has a zero time delay when switching its power source. It is also why it is known as Online UPS because it stays ON even during its normal operation.
Since the current drawn by the AC load is continuously flowing through its whole circuit, the temperature of the system increases. Therefore, it needs comparatively larger heat sinks and the components that can withstand high temperature and it can tolerate current flow for a very long duration. Due to such a requirement, the cost of Online UPS increases significantly.
It continuously draws current from the battery which quickly reduces the lifetime of the battery compared to offline UPS. They are more inefficient because they continuously stay ON even in normal operation.
On the other hand, it does offer high-quality output because there is no gap during the switching between the source supplies. It completely isolates the output from the AC mains. Therefore, it helps in protection against the distortions or fluctuations in the AC mains.