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Inverter Calculator | Sizing AC Load in an Electrical System | RVs & Vans

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This inverter calculator will help you correctly size your inverter for the daily load of your AC appliances in your camper.

It’s simple and straightforward to use. We’ve included a section below to answer some questions you may have.

This calculator forms part of our camper solar setup series and the wider subject of campervan electrics

And it’s just one of our electrical calculators for RVs and campervan conversions too.

Calculating the inverter size, and understanding the implications, may help you assess the appliances you actually need in your RV, look for DC alternatives or more efficient devices.

Get this right for your camper lifestyle and you can complete your DIY campervan conversion with confidence.

Check out our detailed post on campervan power inverters to see how they work and how to install them.

Need more advice and support on a specific part of your campervan electrics? Join our new Facebook Group to connect with a growing community of like minded van builders.

Build your own camper quick start guide

How do I use this inverter calculator?

  1. Enter every electrical AC device and component you’ll use in your camper
  2. Enter the watts each device uses
  3. That’s it.

Do I need an inverter?

No! If you only use DC appliances, you don’t need an inverter.

You only need an inverter if you want to use AC appliances powered by your deep cycle battery.

If you use AC appliances when hooked up and they are powered by the battery, you still need an inverter.

If you use AC appliances only when hooked up and with AC sockets on the mains circuit, you don’t need an inverter.

If you also need a converter (to convert AC power to DC), consider installing a combined RV inverter charger instead.

Can I avoid needing an inverter altogether?

Yes!

We have an article coming soon all about inverters for RVs and this explains how to avoid the need for an inverter altogether.

How do I know all the electrical devices I’ll use?

Getting a complete list of electrical appliances, devices and components you’ll use in your RV is the most critical parts of sizing the electrical system.

Underestimate it and you may run out of power.

Overestimate and you’ll probably spend more money and make your setup more complex than necessary.

Work through your typical day, considering all the appliances you’ll use along the way. 

You’ll need a complete list of all AC and DC appliances to work out the total solar battery bank.

Mark up the AC components to calculate the inverter size needed.

I won’t use all my devices everyday. What should I enter in the calculator?

The aim of the calculation to size the inverter so it can handle the AC devices you will run.

It’s important to understand the inverter is sized to cope with load at any one time. 

Even if you’ll only use your powerful hairdryer for a few minutes every couple of days, add it to the list so we can size an inverter to handle it.

How do I know if my appliance is AC or DC?

The labels or specification of most appliances state whether it is AC or DC.

Failing that, if it has plug you could use in your household sockets, it is probably an AC appliance.

How do I find the watts of each device?

The watts of most devices can be found either printed on the device, in the operating manual or the manufacturer’s website online.

Sometimes, products list the power usage in current (i.e amps). In this case, use the wattage calculator at the top of the inverter calculator above to convert the current and volts to watts.

I have more than 5 devices. What shall I do?

If you have more than 5 AC devices to list follow these steps:

  1. Enter the 1st 5 devices
  2. Press the “add more devices” button
  3. A further 5 rows are displayed for you to add more devices and another “add more devices” button

You can add upto 25 devices in total.

I have more than 25 devices. What shall I do?

Enter the 25 most powerful devices. 

Why is the minimum size inverter so small?

Inverters add load to the electrical system, even if no appliances are connected. The larger the inverter, the greater that base load.

So it’s a complete waste to install an oversized inverter for your needs.

The smallest size inverter you can get away with is one that can run the most powerful AC device on your list, with no other load.

Why is the maximum size inverter so big?

You may want to use multiple AC devices at the same time.

If so, you’ll need an inverter to cope with the total load at any one time.

The maximum size inverter assumes all your devices will be used at the same time. If this is not the case for your setup, only enter the devices you’ll use concurrently. 

Make sure to include the most powerful device if it’s bigger than the combined watts of the other appliances.

I don’t use all my appliances at the same time. What size inverter do I need?

If you only use one device at a time, you need the recommended minimum size inverter.

If you will use multiple devices at the same time, work out the highest total wattage of the combined appliances and use those to calculate the inverter size needed.

I want a much bigger inverter than the calculator has worked out. What shall I do?

We’ve included a mini calculator above to help you see the amount of battery a fully loaded inverter will use in an hour and how big the solar array would need to be to power just one hour. 

The solar array shown would need 4 good hours of sun to replace the battery energy used by the inverter.

If you expect more or less peak sun hours, adjust the solar panels accordingly.

Simply enter the size of the inverter you want.

There is a health warning on my results. What does it mean?

Inverters and AC appliances are inherently power hungry and can quickly drain batteries.

If you use a 1000w inverter fully loaded for an hour, it will drain around 84 amps from the battery. 

To replace that 84 amps, you’ll need a 1000w solar array with 4 good hours of sun.  

Remember you can only take out of the battery what you put in.

I received a message that all my devices are too powerful. What should I do?

The biggest size inverter you can realistically run in an RV or camper is about 3000 watts.

If the smallest of all your AC devices is so big it needs a bigger inverter than 3000w, consider a less powerful appliance, a DC alternative, or running it on an AC mains circuit when hooked up.

I received a message that I can’t run all my devices at the same time. What should I do?

You may not intend to run all your appliances at the same time, in which case you can ignore this message.

But if you do, consider less powerful appliances, DC alternatives, or running them on an AC mains circuit when hooked up.

The estimated battery bank size and solar array is massive. Is this correct?

Yes! It’s surprising, isn’t it?

Maybe give some thought to how you can cut back on your electrical needs.

The estimated battery bank size and solar array is much bigger than I have space for? What should I do?

Now is definitely the time to reconsider your electrical needs and how you can meet them.

Need more help calculating your campervan electrical components?

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