First understand your Power Requirement
One of the most important factors that you need to know before buying an inverter is how much power you need to run your electrical appliances such as your tv, lights, satellite or fridge. This will help you determine what size inverter to buy and how many batteries to bank.
Suppose you want 3 Fans, 3 Tube lights, 1 CFL & 1 television to operate at the time of power failure. Below is the power consumed by these items:
1 Fan – 70 Watts
1 tube light – 60 watts
1 CFL – 25 watts
1 Television – 120 watts
Therefore your total power requirement is ( 3*70 +3*60 + 25 + 120) = 535 watts
Find the VA rating of the inverter you need
It stands for the Volt ampere rating. It is the voltage and current supplied by the inverter to the equipments. If an inverter operates with 100% efficiency, then the power requirement of the electrical items and power supplied by inverter is same. But we all know that 100% or ideal conditions don’t exist in real. Most inverters have the efficiency range from 60 % to 80%. This efficiency is also called power factor of an inverter and is simply the ratio of power required by the appliances to power supplied by an inverter. Power factor of most inverters ranges from 0.6 to 0.8.
Hence Power supplied (or VA rating of inverter) = Power requirement ( power consumed by equipments in watts) / Power factor( efficiency).
Here average value of power factor or efficiency is considered i.e. 0.7
Power of inverter (VA) = 535/0.7 = 765 VA
In the market 800 VA inverters are available. So an inverter with 800 VA will be the right choice for your home.
Know the battery your inverter needs
Battery is the backbone of an inverter system. The performance and life of an inverter largely depend upon the battery quality. The next big question is how long will your batteries last? This is what we call the battery capacity. It is the battery capacity that decides how long your inverter will provide power to your appliances. Battery capacity is measured in AH which stands for Ampere Hours. Basically how many amperes will the battery discharge every hour of use. a 100AH battery with a discharge of 5 amps will last 20 hours.
This is how we determine how many batteries are needed:
Battery capacity = Power requirement (your load in watts) x Duration or runtime ( hours) / Battery Voltage (12v)
Battery Capacity = (535 watts x 3hrs) / 12v = 133 Ah
** Value of Battery voltage is taken 12V
Therefore a battery with a capacity of 130 Ah will work for you.
So if you want to run 3 fans, 3 tube lights , 1 CFL and 1 TV for 3 hours during power failure you would need 800VA inverter and 130 Ah battery.
By understanding this simple calculation you not only save yourself from the misleading information shared by inverter dealers but also help yourself in taking correct decision.