UPS - Uninterruptible Power Supply

UPS stands for Uninterruptible Power Supply and is a power supply device, which works when the usual power source is interrupted.

UPS is used to keep critical systems like monitoring, SCADA, communication and alarm systems running even when power is not available form main source.


A typical UPS circuit is shown in Figure.

In the normal condition, commercial AC (alternating current) power is sourced and converted to DC (direct current), which is then supplied to an inverter, and charges a battery.

When the commercial power source is interrupted, power charged in the battery is converted to AC and supplied to the load.

The UPS has a rectifier to convert AC supply to DC for charging the battery, a DC to AC inverter to convert the battery output to AC voltage, and a battery to act as a source of power during normal power interruption.

Other components like protection, fuses, indication, surge controlling circuit etc., are also built into the unit.

The following points should be checked as maintenance tasks:

• Check for abnormal noise, smell and heat in UPS

• Check for looseness in each connection

• Check appropriate time for battery replacement

• Check for clogged ventilation opening

• Ensure spare fuses are kept in stock and are easily accessible nearby.