UPS Battery Backup

Overview

An uninterruptible power supply keeps connected equipment running through outages and shields it from mains disturbances. This line-interactive tower holds the load on utility power while charging an internal battery, corrects mild voltage sags and swells without drawing on that battery, and switches to a clean sine-wave inverter within milliseconds when power fails.

The chassis is a steel Enclosure housing a sealed Battery Module. The Inverter Board makes AC from the battery, the AVR Module trims line voltage, the Charger Board maintains the cells, and the Transfer Relay switches sources. A Surge Protection Module clamps transients and the Control Board runs the display and alarm.

How it works

In normal operation utility power passes through to the outlets while the AVR Module watches the line. Its tapped autotransformer and relays boost a low line or buck a high one in discrete steps, holding output within tolerance without ever discharging the battery, which extends battery life by reserving it for true outages.

When the mains fails or sags too far for AVR to correct, the Transfer Relay disconnects the line and the inverter takes over in under eight milliseconds, faster than a power supply's hold-up time so the load never sees an interruption. The Inverter Board switches the battery's DC through an H-bridge of MOSFETs, and a transformer and filter shape it into a pure sine wave at line voltage. Surge energy on the input is absorbed by the Metal-Oxide Varistor varistors and gas tube before it can reach the electronics, and the control board sounds the alarm and reports runtime over USB.