Aerospace Baykee (Guangdong) Technology Co.,Ltd
Search News Category News Tags Latest News Archive Time
7 Aspects to Guide you Know What Is Offline UPS
7 Aspects to Guide you Know What Is Offline UPS


The offline UPS is a type of UPS that functions as a backup power source to provide an uninterrupted power supply to various devices and equipment when there is a power failure happened. It directly supplies the AC mains power to the load.

Working Principle

In normal conditions, it directly supplies the power from the AC mains to the AC load through a static transfer switch. Besides, the AC is converted into DC by a rectifier and then charges the battery through a charge controller. Therefore, there are two separate lines for power supplies and both lines need to pass through the transfer switch. Because the power supply is normal so the inverter doesn’t draw current from the battery flowing to the AC load.

In abnormal conditions, the basic supply power from AC mains is interrupted, so the battery now will stop charging and the inverter will draw DC power from the battery to convert to AC and provide power to the AC load through the static transfer switch.

The speed of the offline UPS switch is around 4-5ms and it’s enough to keep a computer from shutting down. But for the sensitive equipment such as in hospitals, this switching time is deadly to keep a smooth operation.

The reason why it’s called Offline UPS is that because the switch is off to draw current from the battery to the AC load which is very different to online UPS that the output power supply always stays ON and needs zero time to switching.


  • Directly supply the AC mains power to the load.
  • Only draw current from the battery to provide backup power to the load when primary power is on the outage.
  • Only need a small charger circuit.
  • No isolation between the power supply and the load.
  • Highly reduce the input voltage distortion as it directly connects to the load.
  • Use a static transfer switch.
  • Turn on only when a power failure happens.
  • No need for high-temperature tolerance for the UPS components.
  • Mainly used for electronic equipment.


  • The temperature for Offline UPS components is low because most of the time it stays off. As a result, the components can be used with a lower tolerance and requires small heat sinks which is opposite to online UPS components, so the overall cost for the Offline UPS is much lower than Online UPS.
  • In normal conditions, the battery does not need to provide power to the inverter, so the lifespan of the battery is longer than Online UPS which the battery is always on work to provide power.
  • Likewise, the overall efficiency of the Offline UPS system is much higher than Online UPS since the AC mains directly provide supply to the load and the charger is not continuously on.
  • Only a small charger circuit is required compares with Online UPS because it only needs to charge the battery instead of the whole entire load current.


  • The direct AC supply power isn’t fully isolated from the AC load which when distortion or fluctuations happens, the AC mains may damage the load due to the lack of protection between the load and the supply source.
  • Need finite transfer time from the AC mains to inverter when primary supply power fails.

When to Use Offline UPS

  • If you need to consider the cost factor, then better use Offline UPS.
  • If you don’t think the switching time is a problem for your working condition, then better use Offline UPS.
  • If you require efficiency, then better use Offline UPS such as home use.


Computers, printers, scanners, consumer electronics, POS systems, security systems.

Emergency power supplies.

Follow these steps and you will clearly know what is an Offline UPS and choose the right UPS fits into your working or living condition.

already 1 902 messages

  • Phoenix 06:15.AM  Aug.14,2022
    Hello, dear sir/madam, welcome to our website! I’m Phoenix,how should I address you?