UPS (uninterruptible power supplies) are essential for business and computer systems in environments where data loss or component damage from power spikes and surges is an issue. They are also used in industrial settings and for medical MRI, cath lab and other sensitive equipment.
UPSs are designed to keep electrical loads operational during utility power outages and provide a clean AC output for varying durations depending on the type of unit. They are often used with devices such as PCs and servers, but they can be applied to any load that may be sensitive to the consequences of power anomalies like voltage sags, brownouts and line noise, as well as switching transients and harmonic distortion.
The most basic UPS is an offline or standby UPS that only provides basic surge protection and battery backup for short durations. It senses when incoming utility power dips or spikes, and when the incoming voltage is low it turns on an internal DC-to-AC inverter circuitry powered from an internal battery. It can be manually switched to bypass if a technician needs to work on the device.
The more advanced online UPS offers similar technology, but with an internal rectifier and inverter that can operate continuously rather than in a switch-mode when powered from normal utility current. This allows the UPS to offer much higher current output for inductive loads like motor startup and compressors, or for more critical loads that are extremely sensitive to power fluctuations, such as a medical MRI system. They are more expensive than an offline UPS but typically have a much longer runtime on their batteries, sometimes for hours at a time.