Inverter: An inverter is an electronic power device that facilitates continuity of electricity when mains power fails. The inverter is supported by batteries as the power source. The batteries are charged by the Inverter when the electricity is available. When power fails the inverter converts the DC power from the battery to meet the AC power requirement of the User’s load.
An inverter has the following key elements
Mains Power sensing circuit: When the AC Power comes below 110VAC or above 280VAC or if there is a total mains failure, the system automatically switches to the back-up source of power.
Battery charger: A module that charges the battery when AC comes and prepares battery to give back energy in case of mains power failure.
Inverter (DC-to AC converter): A system that would convert the energy stored in the battery/batteries to give back-up power to appliances i.e. 230VAC 50Hz.
Types of Inverter:
Modified Square Wave: Modified Square Wave (or “Modified Sine Wave” and “Quasi Sine Wave”) output inverters are designed to have somewhat better characteristics than Square Wave units, while still being relatively inexpensive. Although designed emulate a Pure Sine Wave output, Modified Square Wave inverters do not offer the same perfect electrical output. As such, a negative by-product of Modified output units is electrical noise, which can prevent these inverters from properly powering certain loads. For example, many TVs and stereos use power supplies incapable of eliminating common mode noise. As a result, powering such equipment with a Modified Square Wave may cause a "grain" or small amount of "snow" on your video picture, or "hum" on your sound system.
Pure Sine Wave: Pure or True Sine Wave inverters provide electrical power similar to the utility power you receive from the outlets in your home or office, which is highly reliable and does not produce electrical noise interference associated with the other types of inverters. With its "perfect" sine wave output, the power produced by the inverter fully assures that your sensitive loads will be correctly powered, with no interference. Some appliances which are likely to require Pure Sine Wave include computers, digital clocks, battery chargers, light dimmers, variable speed motors, and audio/visual equipment.
Back up Time of Inverter: Backup Time delivered by an Inverter depends on the Battery capacity connected to the Inverter (keeping the load same).
The AH capacity of the battery and the load connected to it (watts) will determine the back up time. For example: In the above case if you connect 135 AH battery with the inverter the back up time will be 2 and ½ Hours where as if you connect 150 AH battery then the back up time will be 3 Hours. The back up time will increase if you use lesser load.
How to choose a right kind of battery?
Battery plays a major role in the working of an inverter.
Normally the following 3 types of batteries are used for inverter applications. Deep Cycle Flooded Lead Acid Battery (thick flat plate), Tubular Battery & VRLA (SMF) Battery.
Deep Cycle Flooded Lead Acid Battery - Also known as thick flat plate batteries, these are considered to be specialist batteries for the inverters. These batteries require regular top-ups (once in 2-3 months) with distilled water and a little bit of maintenance. These batteries give medium to High Life.
Tubular Batteries - These batteries consists of tubular plates and give very Long life (up to 5- 6 years) . These also require minimum maintenance and regular top up. These batteries are most suitable for longer and frequent power cuts.
VRLA Batteries - These are widely used for UPS and solar applications. Though many people use it for inverter applications but it is not the best solution for areas experiencing longer power cuts. These batteries are sealed type and totally maintenance free. They give low to medium life.
In addition to the power and quality of Charger, life of a battery is determined by the depth of discharge during each cycle. One cycle comprises of the battery getting fully charged using mains power and then discharge in the case of power cuts. If the battery is only partially discharged during each cycle then the cycle life will be much greater.
Further to that a battery’s shelf life is an important factor which indicates that if a battery is lying with a dealer for longer duration it requires to be recharged for a specific duration with ample top up before it is used. Temperature affects the performance of a battery as well. High temperatures can thus provide increased performance in terms of back up time, but at the same time the rate of the unwanted chemical reactions will increase resulting in a corresponding loss of battery life.