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AC Generator & Inverter Sizing Calculator

Determine surge LRA load and running wattage of Inverter vs Non-Inverter ACs for home backup systems.

Live 2026 Data
Inverter Type Pure Sine Wave
AC Capacity 0.8 - 2.0 Ton AC
Min Generator 3.0 - 5.0 kVA
Startup Current LRA Surge Handling

1. Enter Configuration Parameters

Frequently Asked Questions (FAQ)

Why do Non-Inverter ACs need much larger generators?

Non-Inverter AC compressors turn on at 100% speed instantly, drawing a massive starting current (LRA) which is 3.5x to 5x higher than their running current. Inverter ACs start slowly and ramp up speed, consuming very little surge current.

How much power does an AC consume per hour?

A typical 1.5 Ton 3-Star inverter AC draws about 1.0 to 1.2 kW per hour during active cooling. Over an 8-hour period, it consumes roughly 6 to 8 units (kWh) of electricity, depending on the temperature setting and ambient outdoor heat.

Is a 5-Star inverter AC worth the extra cost compared to a 3-Star AC?

Yes. A 5-Star inverter AC is roughly 15-20% more energy-efficient than a 3-Star AC, saving about 150-200 units annually. For a standard tariff of Rs. 8.00/unit, this translates to savings of Rs. 1,200 to Rs. 1,600 per year, offsetting the price premium in 2 to 3 years.

What temperature should I set my AC to for maximum savings?

Set your AC to 24°C or 25°C. According to the Bureau of Energy Efficiency (BEE), every degree increase in the AC temperature setting saves approximately 6% of electricity. Setting your AC to 24°C instead of 18°C can reduce your AC's power consumption by up to 36%.

How does tonnage relate to room size for air conditioning?

AC tonnage measures cooling capacity (1 Ton = 12,000 BTU/hr). Standard sizing rules: up to 100 sq ft requires a 1.0 Ton AC, 100–150 sq ft requires a 1.5 Ton AC, and rooms larger than 150 sq ft need a 2.0 Ton AC to cool effectively.

What is ISEER rating, and how do I read it?

Indian Seasonal Energy Efficiency Ratio (ISEER) measures the ratio of heat removed to the energy consumed over a typical year. A higher ISEER rating means higher efficiency. Currently, 5-Star ACs require an ISEER of 5.0 or above, while 3-Star ACs require 3.8 to 4.9.

Does running an AC in sleep mode actually save money?

Yes. Sleep mode automatically increases the set temperature by 1°C per hour for the first two hours (up to 2°C). This aligns with the natural drop in body temperature and ambient night temperatures, saving up to 10-15% of night power consumption.

About This Calculator

Target Audience: Homeowners & buyers sizing AC capacity and calculating energy consumption

What Does This Calculator Do?

This calculator determines the generator (DG Set) or home inverter capacity required to safely start and run your air conditioner during power cuts.

How to Use It

  1. AC Tonnage: Select 1.0T, 1.5T, or 2.0T capacity.
  2. AC Technology: Select Inverter AC or Non-Inverter AC.
  3. Star Rating: Choose the BEE Star rating.

The Logic Explained Simply

  • The Concept: Electric motors (like AC compressors) require a surge of current to start (LRA - Locked Rotor Amps) which is 3x to 5x higher than their running current. Inverter ACs start slowly and don't experience this massive surge, making them inverter-friendly.
  • The Formula:
  • Running Load (kW) = Nominal power based on rating
  • Surge Load (kW) = Running Load * Surge Factor (1.2 for Inverter, 3.5 for Non-Inverter)
  • Recommended Inverter (kVA) = Surge Load / Inverter Power Factor (typically 0.8)

Real-World Calculation Breakdown

For a 1.5 Ton 3-Star Non-Inverter AC (running load of 1.4 kW):

  1. Starting Surge Load: 1.4 kW * 3.5 = 4.9 kW.
  2. Minimum Generator/Inverter Sizing: 4.9 kW / 0.8 power factor = 6.1 kVA.
  3. Recommendation: You need a minimum 6 kVA generator. A standard 1.5 kVA home inverter will overload and shut down immediately.

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