Essential knowledge: inverters

By: Alan Johnson and Denis Dwyer

Choosing an inverter takes a bit of background knowledge, but the right one can be helpful on long-distance trips.

Essential knowledge: inverters
Essential knowledge: inverters

WHAT IS A power inverter? How does it work? And why is there such a huge disparity in prices? With inverters costing anywhere between 50 and a few thousand dollars, it’s no wonder people are confused.

A power inverter changes 12V DC power (as used in automotive applications) into conventional 240V AC power, allowing access to mains power in the bush with no generator and no noise. Is it too good to be true? Well, sort of.

While inverters provide access to 240V power, it isn’t necessarily the same as our powerpoints at home. Inverted power comes in two forms: modified sine wave and pure sine wave. This is important, especially today, as more and more appliances require pure sine wave (like your power at home).

Most entry-level inverters actually output modified sine wave and are only suitable for lights, shavers or other basic electricals. Pure sine wave is appropriate for all reprogrammable devices — computer and camera batteries, medical equipment, etc.

Inverter size is measured in watts, and can vary from 100-2000W, or more. Most inverters are capable of outputting a higher wattage on start-up or peak power, but the ratings are based on the power they can continuously output.

Bigger is not necessarily better, and your best course of action when deciding which to buy is to gather the appliances you most often want to use and note the watts required to run each one, which should be marked on the appliance. If what you need turns out to be a large number, it might be better to use a generator.

For most recreational/camping uses, 300-600W will be sufficient and run satisfactorily off your 100Ah auxiliary battery at the 20-hour rate.

We also have to consider that creating 240V from a 12V source is not a totally efficient process and losses of up to 20 per cent are common. So, if you need 200W your inverter should be 240W, which usually means a 300W model. Again, consider your uses – if the appliance can be run directly on 12V it is more energy efficient.

Inverters also draw high amperage, and as a result you run the risk of flattening your battery unless you are running the car or have a dual battery management system. If you do use power from the inverter while stopped, make sure you calculate your usage and draw rates.

Pure sine wave inverters featuring toroidal transformer technology are the premium choice for a long-lasting, reliable unit that will also generally deliver the higher start-up wattage required by some power tools. For example, while the inverter is rated at 300W it may be able to deliver 500W in a short burst at start-up. It may also deliver a higher peak power load.

Not all inverters are the same. For basic appliances modified sine wave units will most likely do the job, but if you want an inverter to suit all applications, a pure sine wave inverter is the better choice. Only purchase one with the wattage you will need, because a higher capacity unit will use more power from your battery. A 300W inverter at full load on a 100Ah battery will flatten the battery in just 100 minutes.

And try to use the inverter while you are travelling, to minimise power loss on the auxiliary battery when stationary. If you are going to use the inverter while stationary, the use of a genuine deep-cycle battery is recommended. Multiple batteries connected in parallel can be used to increase usage time.

Inverter technology
Sine Wave


Modified sine wave



Limited appliances


Pure sine wave



Suits all appliances

Torodial transformer

Pure sine wave



Suits all appliances

WORDS Alan Johnson and Denis Dwyer
Source: Caravan World Dec 2011

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