1. Introduction

Uninterruptible Power Supply (UPS) is a critical device that provides emergency power during outages, ensuring continuous operation of essential equipment. One of the most important specifications of a UPS is its backup time - the duration it can supply power to connected loads when the main power fails. Calculating this backup time accurately helps users select the right UPS for their needs and manage power outages effectively.

2. Key Parameters for Calculation

Before diving into the formula, let's define the key variables:

Battery Capacity (Ah): Rated capacity of the UPS battery in ampere-hours, indicating how much charge the battery can store.

Battery Voltage (V): Nominal voltage of a single battery (e.g., 12V for common lead-acid batteries).

Number of Batteries (N): Total batteries in the UPS system (connected in series/parallel to meet voltage/capacity requirements).

Load Power (P): Total power consumption of the devices connected to the UPS, measured in watts (W).

UPS Efficiency (η): A percentage (e.g., 90% or 0.9) representing the UPS's energy conversion efficiency (some energy is lost as heat).

3. The Backup Time Formula

Explanation:

4. Step-by-Step Example

Suppose we have:

Single battery: 12V, 100Ah

2 batteries connected in series (total voltage: 24V, capacity remains 100Ah)

Load power: 500W

UPS efficiency: 90% (0.9)