How Many Amps Does a 1000 Watt Inverter Draw?

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Inverters come in all sizes but all have the same function in a solar power system, convert direct current into alternating current for use by AC appliances and devices. But how many amps does a 1000 watt inverter use? Is your inverter large enough for your system amp requirements? Or do you have to buy a larger system?

A 1000 watt load on a 1000 watt 12V inverter draws 100 to 110 amps, depending on the inverter efficiency. On a 24V setup, the same 1000 watt load will draw 40 to 60 amps.

How to Calculate 1000W Inverter Amp Draw

An inverter does not draw amps until a load is connected to it. To find the amps, use the following formula:

Watt load / input voltage / inverter efficiency rating = amps drawn

If you have a 400W blender at 12V and a 1000W inverter with an 85% efficiency rating, it would look like this:

400W / 12V / .85 = 39.2 amps

The blender will draw 39. 2 amps or rounded off, 40 amps an hour. Of course it is unlikely you will run the blender for an hour, so the actual amp draw will be lower.

But using 40 amps an hour as a starting point makes it easy to estimate the amp requirements (20 amps for 30 minutes, 10 amps for 15 minutes etc.).

When calculating appliance solar panel requirements most use the following conversion:

Watts / volts = amps

And that works fine. However that does not account for inverter inefficiency, which leads to energy loss and higher amp draws. Let us use the same example earlier.

400W / 12V / .85 = 39.2 amps

If we do not factor in the 85% efficiency rating, the result will be:

400W / 12V = 33. amps

That is a difference of almost 7 amps. Does that matter? If you max out the load of your 1000W inverter, every amp counts. But if you don’t, it is not a big deal.

Is a 1000W Inverter Enough?

If you regularly load 1000 watts on the system, consider upgrading to a 1500W inverter like the Energizer 1500W. It is better to have some reserve power in case you need to run appliances instead of maxing out the load. Just like batteries, it is never a good idea to strain the inverter. Even if it is technically not overloaded, the overload indictor may flash when the load is near 1000 watts.

Theoretically a 1000 watt inverter can run a 1000 watt load. But doing so on a regular basis can damage the system. Batteries, solar panels and charge controllers should never be pushed to the limit except occasionally.

If you never load more than 50% or 70% on your inverter, an 80% efficiency is all right. You can load a 400W blender, a 100W laptop and some light bulbs and the inverter can handle it easily. While you can use a laptop for hours, most kitchen appliances are only used a few minutes at a time.

When calculating how many amps will be drawn, remember that appliance power guide charts are for watts per hour. A coffee machine consumes 900 watts per hour, but run it for a few minutes and the wattage will be nowhere near.

But if the total load is 900W that is pushing it to the limit. And do not be surprised if your 1000 watt load will not run on a 1000W inverter. Why? Because of energy loss and inefficiency, which we will explain next.

Inverter Efficiency Rating

If you want to run a refrigerator off an inverter or any other appliance knowing its efficiency rating is a must. The minimum acceptable inverter efficiency rating is 80%, though 85% is of course better.

Some inverters have 90% to 95% efficiency though they cost more. Does the 5% to 10% efficiency difference matter? In the long run it does. On paper, a 1000W inverter can load 1000 watts, but in reality the load limit could 900W or so.

Inverter inefficiency not only affects amp draws, but wattage load too. The higher the efficiency rating, the smaller the difference. However you need to consider the entire system when accounting for system losses.

Even if you have a 95% efficient inverter, that does not mean only 5% of solar energy is lost. Solar cables and wires lose energy during transmission. Solar panels have varying efficiency ratings too, and production depends on the weather.

This should not discourage you from using inverters. It only means you have to give some leeway when calculating how many amps a device can draw. If you calculate the total watt load along with the efficiency rating, you can figure out how what inverter size you need.

How Many Batteries Do I Need For a 1000W Inverter?

Inverters pull power from batteries to run appliances, so it will only run for as long as there is power in the batteries.

A 1000W inverter can run a 700W load for 45 to 55 minutes on a 100ah battery with a 50% depth discharge. If your battery allows a higher discharge rate of 30%, the running time will be longer. Again the run time will be influenced by the efficiency of the inverter and the solar power system in general.

The required batteries depend on the number of hours you need to run the load continuously. Runtime x watts = watts / volts = battery amps needed

You have a 1000W 12V inverter and you load 700 watts. 700 watts / 12 volts = 58.3 amps per hour.

Divide the amps per hour by the battery to get the run time. If you have a 100ah battery, 100 / 58.3 amps = 1.71 hours or 1 and 45 minutes more or less.

The battery will last 1.7 hours if it s completely drained, which you should not do. With AGM and other FLA batteries, depth of discharge is at 50%. So divide 1.7 hours by .50.

1.7 / .50 =3.4

That is about 45 to 55 minutes give or take.

1000W Pure Sine vs. Modified Wave Inverter

This is one of the first things you will have to decide if you want to use an inverter. Do you go with the cheaper, but less effective modified sine wave or the costlier, but superior pure sine wave inverter?

The bottom line is a pure sine wave such as the Renogy 1000W 12V Inverter is the better choice. It costs more, but you are assured it is compatible with modern appliances. Modified sine wave inverters can also generate losses up to 30%, which for many is unacceptable.

A modified sine wave inverter is acceptable for basic electronics and old devices and appliances. If there are no sensitive components on the system you can use a modified sine inverter. However, appliances today are more efficient running pure sine wave. If you are on solar power, it is all about being energy efficient, so pure sine makes sense.

The following equipment / appliances cannot run on modified sine wave inverters. You need pure sine for these.

  • Medical equipment
  • X 10 home auto systems
  • Any appliance with microprocessors
  • Any appliance with speed settings
  • Digital clocks
  • Computerized furnaces
  • Cordless tool battery chargers
  • Certain types of fluorescent lights
  • Some laptop and desktop computers
  • Anything with SCR (silicone controlled rectifier)
  • Any device that uses thyristor, a component for electronics

These are just some of the devices and appliances that will not run on a modified sine wave inverter. You should check your appliance first if they are compatible. What you can be certain is new electronics and appliances are compatible with pure sine inverters.

The one thing holding most people back is the cost. However you should consider this an investment for your solar panel system. And paying for a pure sine inverter is cheaper than damaging your appliances because they were incompatible with modified sine wave.

Tips For Buying a 1000W Inverter

Buy the right inverter type. Not all 1000 watt inverters are made equal. A 95% efficient inverter will run better than an 80% efficient unit of the same watt size. And of course a pure sine wave performs better than a modified sine wave.

Warranty. Inverters are the most sensitive part of a solar system alongside the charge controller. That is why you should buy one from a reputable manufacturer, plus a comprehensive warranty coverage.

Usage. Calculate how much you are going to load on the inverter, both in amps and watts. Use the guide given above so you will know if 1000 watts will be sufficient. Think also of your future plans and if you will need a bigger inverter.

Battery Capacity. As was indicated earlier, an inverter can only run as long as there is power in the battery bank. Decide if you need lead acid or lithium ion and take note of the depth discharge. The better the DOD, the longer your inverter can run.


Because of the energy losses inherent in the system, getting an exact figure is difficult. But with the formula provided here you can have a fairly accurate estimate of how many amps a 1000 watt inverter will draw.