Power backup system provides the electrical power to any electrical appliance/ equipment in case of Main Grid Power failure.
Power backup system consists of Inverter (DC to AC Converter), Power Storage (Battery) and Rectifier (AC to DC Converter) Charging Module.
It depends on the requirement to run the number of electrical appliance/ equipment simultaneously in case of Main Grid Power failure.
To calculate the backup power, the VA/ wattage of all electrical appliance/ equipment (like Fluorescent Light, Compact Fluorescent Light, Ceiling Fan, Microwave oven, Heater, Geyser, Air Conditioner, Electric Iron etc., which you wants to run ‘simultaneously’ in case of Main Grid Power failure) is to be added.
Normally you can run few fans and lights including Television & PC on 1 KVA power backup. But heavy wattage equipments like Microwave oven/ Heater/ Geyser/ Air Conditioner/ Iron etc. can run on higher KVA power backup, since each requires more than 1000VA (or 1KVA) power.
Following is the approximate VA (Power) for general household appliance. So you can calculate the power backup requirements based on how many appliances you want to run ‘simultaneously’ in case of Main Grid Power failure.
Formula : Power in Wattage = Power in VA x Power Factor
Power Factor of different appliances are different. On some critical appliance it is defined and mentioned in the specification. It usually varies from 0.6 to 1.0.
“Back-up time” is the period of time in minutes for that the UPS will support the load when the incoming grid power fails, typically this can be few minutes and can go upto many hours, it depends on the batteries connected, charging condition of the battery & the load connected to the UPS.
An Inverter/UPS is a device that helps in providing uninterrupted power to a electrical appliance in case of Main Grid Power failure and provide charging the battery when Main Grid Power is available. Most of Inverter/UPS have DC to AC converter and AC to DC converter. Some UPS used for PCs, Servers etc. have inbuilt small size battery for short time power backup. An Inverter/UPS can also be called a Power Backup System or UPS (Uninterruptible Power Supply) with or without Power Storage (Battery).
There are three types of Inverters/UPS.
The offline / standby UPS (SPS) offers only the most basic features, providing surge protection and battery backup. The protected equipment is normally connected directly to incoming utility power. When the incoming voltage falls below a predetermined level the SPS turns on its internal DC-AC inverter circuitry, which is powered from an external storage battery.
The SPS then mechanically switches the connected equipment on to its DC-AC inverter output. The switchover time can be as long as 25 milliseconds depending on the amount of time it takes the standby UPS to detect the lost utility voltage. The UPS will be designed to power certain electrical equipment, such as a home appliances or personal computer, without any objectionable dip or brownout to that device.
In line-interactive UPS, the separate battery charger, inverter and source selection switch have all been replaced by a combination inverter/converter, which both charges the battery and converts its energy to AC for the output as required. AC line power is still the primary power source, and the battery is the secondary. When the line power is operating, the inverter/converter charges the battery; when Main Grid Power fails, it operates in reverse.
In On-line UPS, all the power going to the loads is firstly converted from AC to DC and then back to AC, which means the power is dissipated as heat even then the mains is available. Furthermore, this is happening all the time, not just during a Main Grid Power failure, and while running equipment that draws a lot of power. The biggest disadvantage of the online UPS is its inefficiency.
Home UPS is series of UPS used for domestic purpose. This may be of Square wave, Modified Square wave or Pure Sine wave. It is generally a Standby type of UPS.
Based upon the different technology used to convert DC power into AC power, following types of output is available.