Uninterruptible power supply

An uninterruptible power supply (UPS) provides electrical power when its primary source fails, usually by switching to stored energy. It can also condition power against voltage disturbances.

Standby UPS: A UPS that normally passes utility power to its load and switches to battery power when supply fails. Its relay-based transfer illustrates the simplest backup-power architecture.
Lead–acid battery: A rechargeable battery that stores energy through reversible reactions between lead, lead dioxide, and sulfuric acid. It has long been a common, economical energy store in stationary UPS systems.
Data center: A facility that houses computing, storage, and networking equipment and the infrastructure needed to operate it. Data centers use UPS systems to bridge outages and protect equipment during generator startup.
Surge protector: A device that limits transient overvoltage reaching connected equipment. Unlike a UPS, it typically provides no stored energy during an outage.
Line-interactive UPS: A UPS that regulates moderate voltage changes through transformer circuitry and switches to battery during larger disturbances or outages. Its voltage regulation reduces battery use compared with a standby design.
Lithium-ion battery: A rechargeable battery that stores energy through lithium-ion movement between electrodes during charging and discharging. Its high energy density can reduce the size and weight of UPS battery banks.
Computer: An electronic device that processes data according to instructions and can store or communicate information. Desktop UPS units commonly provide computers time to ride through interruptions or shut down safely.
Voltage regulator: A device or circuit that maintains output voltage within a target range as input or load conditions change. It can correct voltage variation but does not necessarily supply power after a failure.
Online UPS: A UPS that continuously converts incoming power to direct current and then back to alternating current for its load. Continuous conversion avoids a transfer delay when the utility supply fails.
Inverter: An electronic device that converts direct current into alternating current. A UPS inverter supplies AC power from a battery’s DC output.

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