 # How to calculate inverter and battery backup hours

A power inverter , or inverter, is an electronic device or circuitry that changes direct current (DC) to alternating current (AC).

There are different capacity of inverters like 200VA, 250VA, 350VA, 400VA, 450VA, 500VA, 625VA, 12, 850VA, 1200VA, 1450VA, 3KVA, 3.5KVA, 4KVA, 5KVA, 7.5KVA, 10KVA, 15KV, 20KVA, 20KVA etc.

The capacity of the inverter should be chosen based on how much watt of  home appliances you power at a time. Like bulbs, fan, TV, computer, refrigerator, freezer and air conditionals.

How to convert from VA to Watts?
Volts x Ampere = VA (VoltAmpere)
Volts x Ampere x Power Factor = kW (Watts)

where,
Power Factor = 0.8 (which is the max. power factor of home standard)
If you want to run 800W of appliances then,
800 / 0.8 = 1000VA
So, you should prefer inverter of 1200VA or more.

Similarly, battery for electricity storage is an integral part of the inverter. The performance of the inverter depends on the connected battery and vice-versa.

The runtime of an inverter is dependent on the battery power and the amount of power being drawn from the inverter at a given time. As the amount of equipment using the inverter increases, the runtime will decrease. In order to prolong the runtime of an inverter, additional batteries can be added to the inverter

Note: The inverter capacity is not used in backup time calculation.

The battery backup time in hours can be calculated using following formula:
Backup Time = Battery AH x 12V x N x Efficiency of Battery / Load in Watts

where,
Battery AH = Ampere Hour Capacity of Battery
N = Number of 12 V Batteries needed
Efficiency of Battery = Generally it is 0.8, which is the maximum power factor of home standard.

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