The Ins and Outs of an Inverter!

Understanding inverters

Being able to power your electronic devices on the road is increasingly important. Modern 4WD, camping, and caravanning setups feature a myriad of electronic devices, ranging from the simple laptop charger through to a microwave, kettle, or even high-end communication equipment.

It’s important therefore that the right power supply is used. Inverters come in different sizes (capacities) and use different circuitry to provide you with the power you need. But not all are created equal.

In this article we’ll look at the differences between inverter types to give you a better understanding of what type of power inverter best suits your needs.

What is an inverter?

A power inverter is an electronic device which converts DC (Direct Current) to AC (Alternating Current). As such, it does not produce its own power. It simply takes 12 or 24-volt DC power from your vehicle’s auxiliary battery and converts it to the same type found in your home’s wall outlet (240-volt AC).

This allows devices such as laptops, kettles, microwaves, and so on to be used on the road – provided of course you have an inverter with the appropriate capacity.

Commonly, there are two basic designs of DC to AC inverters. The first uses a switching boost converter to produce higher voltage DC power which it then converts to AC. The second converts DC to AC at the input (battery) level and uses a line-frequency transformer to create the output voltage.

Inverters have many uses, though we’re focussing on smaller consumer inverters used for 4WD, camping, and caravanning use. Depending on the design and quality of these units, they can produce a different shaped wave at the point of connection. The resulting frequency supplied by the inverter depends on the type of inverter and circuitry used.

Many older (and cheaper) units produce a square wave suitable for low-sensitivity, simple applications such as lighting or heating. Newer units produce a ‘cleaner’ sine wave output suitable for high-sensitivity, complex applications including laptops, communications equipment, and other electronic-circuit controlled devices.

How much power do devices use?

Knowing how much power your devices use is key to knowing what size inverter you’ll need. Essentially, the more devices you want to power while off the grid, the higher inverter capacity you will need.

Start by understanding how much power your devices consume. This information is typically detailed on a placard on the device itself, and will usually be displayed in Watts (e.g., 1000W). It also pays to understand that some devices, such as those fitted with an electric motor, may exceed this figure at start up. This is known as higher peak power draw and should be factored into your calculations when deciding which inverter is right for you.

We recommend adding 20 per cent to your base power requirements and purchasing an inverter that meets this capacity. This will allow you a reserve for the situation mentioned above, but also means you don’t need to upgrade your inverter should you add or upgrade appliances down the track.

1000W (+20%) = 1200W

So, how do I know what inverter capacity I need?

Theoretically, and using our example above, a 1000W inverter should do the job nicely. But this theory allows only for a standardised output number. It doesn’t factor in any peak or overload situations that might occur.

It’s another reason we recommend using an inverter with greater capacity than you need. Factoring in peaks and overload situations will protect your appliances and your inverter. It will also allow you to run more than one appliance at the same time.

Importantly, when running more than one appliance at the same time, you must calculate the usage of your appliances together, while also factoring in our safety margin of 20 per cent. This means your inverter is protected from overload and will serve you reliably for many years to come.

1000W + 1200W = 2200W (+20%) = 2640W

Can my vehicle battery power an inverter?

The easy answer to this question is to understand the capacity your battery offers. Every 100 Amp hours (Ah) of battery power is sufficient to supply a 1000W inverter. A typical 4WD battery provides up to 140Ah, which is sufficient for a 1400W inverter.

Importantly, this is only part of the calculation required. You also need to consider how long the battery will need to supply power. Perhaps obviously, an appliance running for two hours continuously will draw twice the Amp hours of the same appliance running for one. You don’t want to deplete your battery beyond its capabilities.

In instances where more capacity is required, its suggested you use multiple batteries in series parallel, or opt for a bigger battery. A larger 320Ah battery, for example, will happily run a 3000W inverter, or supply power to a 1000W for a longer period.

320Ah ÷ 1000W/hour = 3.2 hours

Is bigger always better?

The answer here is ‘yes’ with a ‘but’ or ‘no’ with an ‘if’. A large capacity inverter will run more appliances and run them for longer – if you have the battery capacity to back it up. But a larger inverter is also heavier, more expensive, and will draw down power from your battery more quickly.

Larger inverters also have a larger standby current draw. Simply, this means that if your inverter is left on, even when not powering a device, it will consume power from your battery. This issue can be remedied easily by switching your inverter off when not in use.

The answer is to use the calculations above and purchase the correct inverter for your application. Try to limit usage to only those times you need it and use power efficient appliances wherever possible. Remember, your setup is as useful as you make it, and it may be added to almost indefinitely. Start with an adequate setup and add to it later if you find it doesn’t match your needs.

What about sine waves?

The Australian power grid produces 240V at 50Hz for domestic consumption. This is what most appliances we use in our daily lives are designed to operate on. If you try to operate your domestic appliances on a frequency other than 50Hz, it may overheat and become damaged.

It’s why most inverters nowadays are of the pure sine wave type. This shape of wave most closely matches that of the Australian power grid and therefore will not cause damage to your appliances.

Some cheaper inverters use a modified sine wave arrangement to emulate this wave structure. However, the underlying squarer shape of this wave provides a faster switching time between each polarity change which can stress components designed for the smoother transitions of pure sine wave current.

Unless you’re only running a simple appliance such as a lamp or motor, a pure sine wave inverter is strongly recommended.

Check out our range of Inverters on our website!