What Will a 400 Watt Inverter Run?

As an Amazon Associate, this site earns commissions from qualifying purchases. For more details, click here.

When in comes to powering appliances, we usually think of thousand watt inverters. But a 400W inverter can run various appliances rather well. 400 watts might be sufficient if you don’t need a lot of energy intensive appliance loads, so let’s see what it can actually do.

A 400W inverter can run a 12V fridge for four hours, and also small coffee machines, laptops, TVs, fans and food mixers. The inverter power source will determine how long these appliances can run.

What Can a 400 Watt Inverter Run?

This inverter can run any number of appliances as long as it is less than 400 watts. If the load exceeds 400 watts, you will need a larger system. Here are some common household appliances that will work with a 400 watt Ampeak Power Inverter.

  • 12V fridge: 60 watts
  • Blender: 400 watts
  • Blu-Ray player: 35 watts
  • Chest freezer: 350 watts
  • Electric blanket: 200 watts
  • Fan: 50 to 150 watts
  • Food mixer: 300 watts
  • Laptop: 100 to 200 watts
  • Lights: 60 watts
  • Mobile phones: 2 to 5 watts
  • TVs: 80 to 300 watts

A 400 watt inverter can also run an air cooler (65W), aquarium pump (25W), cordless drill charger (70W) and a dehumidifier (240W). There are many other appliances and devices that should work, so check the label to see if it will run on this inverter.

Keep in mind that the appliance watts provided here is for reference only. Some blenders may use less than 400 watts on low settings, while others may need more power when set to high. Laptops built for gaming will use more power than one designed for business.

An inverter needs a power source to work. In off grid systems that usually means a battery bank. A 35ah battery can run a full 400 watt inverter load for an hour. To run the load longer, use a large battery.

How Long Can a 400W Inverter Run Appliances?

It depends on the load and the battery size. As long as it does not exceed 400 watts and there is enough battery, the inverter will keep running.

A 200 watt laptop will run for about two hours on a 400 watt inverter and a 35ah battery. But if you double the battery capacity to 70ah, the inverter will last for four hours.

A 400 watt inverter can run several appliances aside from the ones mentioned here. You can mix and match appliances as long as the total is less than 400 watts. Be certain though you are using the right wire size for best results.

If you load a 400W blender, you won’t be able to run anything else on the inverter. For appliances with lower power consumption, add the total and multiply by running hours.

Suppose you want to run a TV, fan, Blu-ray player and a couple of lights. Add up the watts:

  • TV: 100W
  • Two lights: 120W
  • Fan: 50W
  • Blu-ray: 35W
  • Total: 305W

That is 305 watts, no problem for a 400W inverter. Next, multiply by the number of hours you need to run this load.

If you want to run it for 5 hours:

305 x 5 = 1525

That is 1525 watts. Now you need a battery that can supply this power. Which would be 135ah or 275ah if you don’t want to fully discharge it.

How Many Batteries Do I Need to Run a 400W Inverter?

The answer depends on how many devices are loaded onto the system. You also have to consider the load runtime.

The formula is inverter load x runtime = battery size

If you put a 200W load on a 400W inverter and want to run it for two hours, you need a 12V 35ah battery.

The conversion formulas are:

watts / volts = amps
volts x amps = watts

In our example we have a 200 watt load. If you decide to use a 12V battery, the calculation looks like this:

200 / 12 =16.6

A 200W inverter load draws 16.6 battery amps an hour. To run for two hours you need 33.2 amps.

16.6 x 2 = 33.2

The nearest battery size available is 35ah, so a 35ah 12V battery can run a 200W inverter load for two hours.

Batteries are also available in 24 volts. Higher voltage batteries can hold twice as many watts as a 12V, which is why they are ideal for heavy duty use.

Suppose you put a full 400 watt load on the inverter for 5 hours. How many batteries will you need?

400 watts x 5 hours = 2000 watts

2000 / 12 = 166.6

You need 166.6 amps to run a 400 watts for five hours. There is no 166.6 battery so you should get a 12V 200ah battery. The Renogy 200ah 12V is what we will go with because of its dependability.

Battery Depth Discharge and Inverter Runtime

200ah is the minimum battery capacity. If you use lead acid batteries, a 400ah battery capacity is recommended.

Lead acid batteries have a depth discharge rate of 50%. Meaning you need to charge the battery when capacity drops to 50%.

So while a 200ah lead acid battery can run a 400 watt inverter load for five hours, it will lead to a full discharge. Fully discharging batteries leads to rapid wear and tear which is why manufacturers recommend charging when capacity drops to 50%.

A 400 watt inverter will keep running as long as there are enough batteries. In the case of lead acid that means doubling the capacity so you can run the inverter load.

24V vs. 12V Batteries

Another option is to use a 24V battery. If we go back to the same scenario but use a 24V battery instead of 12V, your 400 watt inverter load can run longer.

400 watt load x 5 hours = 2000 watts

2000 / 24 = 83.3

The same inverter load only pulls 83.3 amps, compared to 166.6 on a 12V battery. A 24V 200ah battery is going to last almost twice as long as a 12V 200ah because the system draws fewer amps per hour.

You can connect two 12V batteries in a series to convert them into a 24V battery bank. Note that some inverters are designed for 12V or 24V systems, not both, so before you buy, make sure the electrical system will work with your batteries.

Efficiency Ratings of 400W Inverters

Because of inverter inefficiency, power consumption will be higher than the power load. The greater the efficiency rating, the fewer watts are wasted.

Old inverters used to have an 85% efficiency rating, so up to 15% energy is lost when DC is turned into AC. Today most inverters have a 90% to 93% efficacy.

The type of inverter you choose is important. There are two options, pure sine wave and modified sine wave. Pure sine wave inverters are more efficient and recommended for most appliances.

There are some good modified sine wave inverters though. If you are not sure, contact the inverter manufacturer and ask if you can run appliances on their system.

400W Inverter Frequently Asked Questions

How many batteries does a 400 watt inverter need?

It depends on the load, how long you want to run it and the battery depth discharge. If you want to run a full 400 watt load for 5 hours, you need at least a 200ah battery. Double the capacity to 400ah if you do not want the battery fully discharged after 5 hours.

How many amps does a 400 watt inverter draw?

The inverter draws 3.33 amps at 120V and 33.3 amps at 12V. The conversion is watts / volts = amps.

How long will a 12V battery run a 400W inverter?

100ah is 1200 watts, so at 400 watts an hour, the battery will be discharged in 3 hours.

Will a 400 watt inverter run a mini fridge?

It depends on the power drawn by the fridge. If it draws 100 watts an hour, the inverter will last for four hours. For more about running a fridge off an inverter, click here.

Should I use a pure sine or modified sine wave inverter?

Pure sine wave inverters provide better performance. But if you are on a budget, modified sine is an option. Just make sure it is compatible with your appliances.


A 400 watt inverter is only as effective as its power source. If you want to run appliances, make sure the total is less than 400 watts and the battery is enough. By calculating how long you need to use the appliances, you can do a lot with a 400 watt inverter.