A UPS (Uninterruptible Power Supply) is an electrical device that provides temporary backup power when the normal mains electricity supply fails or becomes unstable.

A UPS is commonly used with computers, servers, BMS controllers, network equipment, security systems and other electronic controls.

Basic UPS operation

Under normal conditions, the UPS takes power from the mains supply and provides power to the connected equipment while keeping its internal battery charged.

If the mains supply fails, the UPS automatically switches to battery power, allowing the equipment to continue operating for a limited period. Depending on the UPS size and the connected load, this can range from a few minutes to several hours.

Main parts of a UPS

• Battery – stores energy for use during a power failure.
• Charger/rectifier – converts AC power to DC to charge the batteries.
• Inverter – converts battery DC power back into AC for the equipment.
• Bypass – on many larger UPS systems, allows the load to be supplied directly from the mains if the UPS needs maintenance or develops a fault.
• Monitoring/control system – monitors mains voltage, battery condition, load and UPS alarms.

Three common UPS types

Standby (Offline UPS): Normally supplies equipment directly from the mains and switches to battery/inverter operation when the mains fails. Often used for PCs and small equipment.

Line-Interactive UPS: Similar to a standby UPS but can compensate for some variations in mains voltage without using the battery. Common for IT and network equipment.

Online / Double-Conversion UPS: Continuously converts incoming AC to DC and then back to AC. This provides a highly controlled supply and effectively isolates sensitive equipment from many mains disturbances. Often used for servers, critical controls and larger commercial systems.

Why use a UPS?

A UPS can protect equipment against power cuts, voltage dips, surges and other supply disturbances. It can also provide enough time for equipment to shut down safely or keep essential systems operating until a standby generator starts.

For BMS applications, a UPS is particularly useful for keeping BMS controllers, supervisory PCs, network switches and communications equipment operational during short-term power failures.