Uninterrupted Power Supply (UPS)

 Uninterrupted Power Supply (UPS)

UPS provides an uninterrupted power supply when there is a discontinuity in mains power. The UPS does this by transferring the power stored in batteries when it detects an interruption in mains. Sometimes there are spikes in mains or power is low the UPS also takes care of that and provides uninterrupted power. The UPS makes use of an inverter to convert DC power stored into batteries into AC. For powering up the batteries in normal conditions, it makes use of a battery charger circuitry. Besides this, there is an additional part known as transfer switch transfer AC directly from mains to appliances under normal situation. UPS can be categorized into the following parts:

·         Batteries

·         Battery Charger

·         Inverter

·         Transfer Switch

UPS Size & Load Calculation

UPS vary in size depending on the requirement, the UPS size is represented in VA units.

VA = Volts X Amperes

The above formula is valid only if the power factor (PF) is 1. In case the power factor varies, we devise the formula as

Watts = Volts X Amperes

VA = Watts / PF

You need to make a list of all appliances that would work under the UPS and then add a few extra watts to be in a safe zone. Here let’s discuss an example of load calculation for UPS:

·         Light bulbs (x3) 100 Watts

·         Television (x1) 300 Watts

·         Laptop (x2) 350 Watts

·         Iron (x1) 1000 Watts

Now Let Us Calculate The Total Power Load For The Equipment We Have.

Power Load = {Sum Of Product Of Power Load By Each Type Of Device} X 1.5

PL = {(3 X 100) + (1 X 300) + (2 X 350) + (1 X 1000)} X 1.5 =

2300 X 1.5 = 2450 Watts

So, You Need A 3500VA UPS To Rub The Load.

Battery Size Calculations

The battery provides power through an inverter to appliances and is measured in ampere-hours Ah. For example, a battery with an 80 Ah rating will run for 20 hours if the load is 4 amperes. However, it is the load. It is doubled (8A); the runtime decreases to 10 hours. There are other factors that go along as well, like temperature, initial charge, and interrupted charring and reuse. Usually, a runtime factor of 1.5 is used if usage is under 2 hours as the time frame increases, a factor of 1.3 is used. To calculate the battery size, we use the following equation:

Load Current For 1 Hour =

(Runtime Factor x Load) / (UPS Efficiency x UPS Input)

In the above equation, if we have a load of 1500 watts, runtime factor is 1.5, UPS efficiency is 80%, and input is 24V, then the value comes out to be 117.1Ah, so we would select a battery rating of 120A