Running an air conditioner during load-shedding is the hardest job you can give a backup system. An AC is a heavy load, it surges hard when it starts, and it drains batteries fast. It can be done, but only with the right size inverter and a serious battery bank. This guide shows you what you actually need, and where an inverter AC changes everything.
Quick answer. A 1 ton AC needs roughly a 2.5 to 3 kVA pure sine wave inverter on a 24V or 48V battery bank. An inverter-type AC needs less and is far easier to back up. Whatever you use, the battery, not the inverter, is the expensive part.
Why an AC is such a hard load
An air conditioner has two things that make it demanding. It draws a lot of power the whole time it runs, and its compressor pulls a big surge when it starts. A basic non-inverter AC can spike to several times its running watts for a moment. Your inverter has to survive that spike, or it trips.
On top of that, an AC runs for hours, not minutes, and it uses a lot of energy every hour. That is why the battery matters even more than the inverter here. The compressor's heavy start-up draw, its locked-rotor current, is a defined motor rating; the National Electrical Code (NFPA 70) Article 440 covers how air-conditioning equipment is wired and protected.
How much power an AC uses
| AC size | Running watts (approx) | Inverter to look for |
|---|---|---|
| 1 ton, non-inverter | about 1,000 to 1,200 W | 2.5 to 3 kVA pure sine |
| 1.5 ton, non-inverter | about 1,700 to 1,900 W | 3 to 4 kVA pure sine |
| 2 ton, non-inverter | about 2,400 W | 4 to 5 kVA pure sine |
| 1 to 1.5 ton, inverter type | about 900 to 1,400 W | 2 to 3 kVA pure sine |
These are rough figures. Your AC's label shows its real rating, so check it. The inverter size allows headroom for the startup surge, which is why it is well above the running watts.
Inverter AC changes the game
There are two kinds of AC, and the difference is huge for backup.
A normal, non-inverter AC switches its compressor fully on and off. Every time it switches on, it pulls a hard surge, which stresses your inverter and battery.
An inverter AC, sometimes called a DC inverter AC, runs its compressor at a variable speed. It starts gently, so the surge is much softer, and it uses less energy overall. If you are buying an AC and you know you will run it on backup, an inverter AC is far easier and cheaper to support.
The battery is the real cost
Sizing the inverter is the easy part. The hard part is the battery, because an AC eats energy.
A 1 ton AC can use over 1 kWh of energy every hour. To run it for even a few hours on batteries, you need a large bank, which gets expensive quickly. This is why most homes do not run an AC on batteries for long. They either pair the AC with solar so the sun carries the daytime load, or they use a generator for long AC use.
Put your AC's watts into our battery backup-time calculator and you will see just how fast a battery drains under this load. It is an eye-opener.
Tip. If you are buying a new AC and plan to run it on backup, choose an inverter type and the smallest size that cools your room. It cuts both the inverter size and the battery cost you will need.
Watch out. Do not size the inverter to the AC's running watts alone. The startup surge of a non-inverter AC can trip an inverter that looks big enough on paper. Always leave surge headroom, which the sizes in the table above already include.
The realistic way to run an AC in outages
For most homes, the sensible setup is one of these. Pair the AC with solar, so the panels run it during the day when the sun is strong and the heat is worst. Use an inverter AC to keep the load and surge low. And keep a generator for long outages if you must run the AC for many hours after dark.
Trying to run an AC all night on batteries alone is possible, but the battery bank needed is large and costly. Go in knowing that, and you will not be disappointed.
For a 1 ton AC, look at a 2.5 to 3 kVA pure sine inverter on 24V or 48V, and choose an inverter-type AC if you can.
Then be realistic about the battery. The inverter handles the AC easily. Giving it hours of runtime is the part that costs money.
Frequently asked questions
Can a 1 kVA inverter run an AC?
No. Even the smallest AC needs more, because of its running load and its startup surge. A 1 ton AC needs roughly a 2.5 to 3 kVA inverter.
How long can I run an AC on batteries?
Not long without a big bank. An AC can use over 1 kWh per hour, so a normal home battery drains fast. Solar during the day is the practical answer.
Is an inverter AC better for backup?
Yes. It starts gently, so the surge is smaller, and it uses less energy. It is much easier on your inverter and battery than a non-inverter AC.
What size inverter for a 1.5 ton AC?
Around a 3 to 4 kVA pure sine wave inverter, on a 24V or 48V battery bank, with headroom for the surge.
An AC is the toughest test of a backup system. Size the inverter with surge headroom, pick an inverter-type AC, and respect how much battery the runtime needs. Do that and you can stay cool through a cut, without a nasty surprise.
