Understanding The Inverter

A Basic Guide

We frequently receive questions about inverters, leading us to create this basic guide. The goal is to help you better understand how inverters work and to dispel some common myths.

How to size an Inverter, and analogies for better understanding

Inverters convert 12-volt battery power back up to 230-volt, also known as ‘shore power’, enabling you to operate regular household appliances. The size of the inverter you’ll need is based on the highest wattage of the appliance you intend to use (or add together two or more appliances if you intend to use them at exactly the save time, e.g. a normal household fridge and a Nutribullet. We then recommend adding an extra 20% to this total.

For instance, a fridge may be 250W and a Nutribullet 800W, so we would need a 1200W inverter.

Once you install the 1200W inverter, we can’t then use a 1500W coffee machine, as this will cause the inverter to shut down.


Think of an inverter as a helper for your caravan or motorhome’s energy system. Batteries store energy in a form called DC, but many of our everyday appliances need energy in a form called AC to run properly. An inverter’s job is to convert, or change, the energy from DC to AC so you can use your appliances like you do at home. It’s crucial to choose an inverter that matches both the appliances you want to use and the battery you have, to ensure everything runs smoothly and efficiently. It’s a crucial piece of equipment that allows you to use things like your fridge or microwave when you’re traveling!

To help convey the relationship between the three, a great analogy would be to think of a car representing our battery, a trailer representing our load, and the fuel tank representing our solar.

Practical Considerations: Battery Size and Load Capacity

The larger the load, the more powerful the vehicle needed to tow that load, and the larger the fuel tank required to run the vehicle.
You wouldn’t tow a big caravan with a small hatchback, you might get a wee way down the road, but it will start overheating, the transmission will start to protest and the brakes will get hot.

Why? Because it’s not fit for purpose.

Think of a single 100Ah battery as a small car, it will handle small loads like low amp charging, but if you try to run a coffee machine or charge ebike batteries it will start to protest. It might work a few times but like the car (whose clutch is now slipping) it won’t last for as long as it should.

If we move up to a mid-sized car, we can do a lot more with it – in our analogy this would be a 200Ah battery bank with its larger ‘fuel tank’ to handle the load.

So it would be fine to run a coffee machine a few times a day, some e-bike charging, limited microwave use, etc. However, frequency does come into play – if you drink ten coffees a day you will probably need a bigger bigger ‘fuel tank,’ meaning you’d need a larger battery bank and more solar panels.

If you’d also like to use high power appliances like a hairdryer, coffee machine, e-bike, microwave, toaster, CPAP machine etc. you’ll need to get a really solid, good quality ‘tow vehicle’ with plenty of power. Consider a robust battery bank of 300Ah or greater, so you have the power, and you’d then also need a larger ‘fuel tank to feed the engine’ (so more solar panels).

Seasonal and Geographical Factors

Solar power generation varies significantly between summer and winter. In winter, you may need to double your solar capacity to meet the same energy needs you have in summer. So if you calculate 400W to meet your needs, you will actually need 800W. This is because the solar harvest in winter is only half that of summer (and sometimes less).

This is often why there can be several ‘correct’ answers to the same question.

You might read, we have xyz batteries and abc solar and we use all these appliances and never run out. But what isn’t said is that they only use the rig in summer so only need half the solar of a full-timer. 

Another consideration is your location. Solar yield can also be influenced by your geographical location. For instance, you’ll harvest less solar energy during winter in the South Island compared to Northland.

Battery Types: A Quick Note

This is meant a guide to give a basic understanding, the battery references are based on AGM batteries. If you have lithium Iron Phosphate batteries, the size of bank will be smaller, but also based on the depth of discharge of your particular battery.

At Motorhome Solar, our preference for Victron Inverters stems from their consistent reliability and advanced technology. We value providing straightforward, efficient power solutions to our motorhome and caravan owners, and Victron aligns with our commitment to quality and dependability. Their inverters are versatile, user-friendly, and durable, making them a practical choice for those looking to simplify their solar power setups on the road. In choosing Victron, we aim to offer solutions that are both technologically sound and easy to manage, aligning with the diverse needs of our community.

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Efficiency and Reliability

Victron Inverters are efficient and reliable, converting DC power into AC power to operate household appliances seamlessly. Their advanced technology ensures optimal performance, making them a top choice for dependable power solutions.

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Variety and Versatility

Victron offers a range of inverters to suit different needs, from compact models for smaller loads to robust units for high-power appliances. They integrate well with other Victron products and are compatible with various battery types and solar panels.

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User-Friendly and Durable

With a user-friendly interface, Victron Inverters allow efficient monitoring and management of power usage. They are durable, sustainable, and designed to withstand varying environments, contributing to long-lasting and eco-friendly power solutions.

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