How To Choose The Right Dc To Ac 230v Power Inverter

WHAT IS A POWER INVERTER?

First of all, let's start with the definition. What is a power inverter? 

A power inverter is a device which converts battery power into mains power, i.e. it transforms 12V direct current (DC) into 230V alternating current (AC).

230V AC is the power supplied to our houses by utility companies, and this is the power required by most normal household appliances such as lights, TVs, fridges etc.

There are two main types of inverters:

• Off-grid inverters, which work as a standalone system and require batteries (typically used in caravans, cars, boats or locations without access to mains power)
• On-grid or grid tie inverters, which require mains power to work (typically used in household solar systems and take input directly from solar panels)

In this article we are going focus on off-grid inverters only - i.e. inverters which can be used to build an off-grid 230V solar system.  

WHICH POWER INVERTER SHOULD I CHOOSE?

So, which off-grid inverter is best for your battery / battery bank in a caravan, motorhome, boat or for a standalone off-grid solar system?

In order to answer this question, you will need to consider three key points:

• Type of inverter: Modified sine wave / Pure sine wave
• Power rating (wattage) of the inverter
• Input voltage (specifically in the case of a standalone solar system)

TYPES OF INVERTER - MODIFIED SINE WAVE VS. PURE SINE WAVE INVERTERS

The type of power inverter you should choose depends on the type of power output you require. Pure sine wave inverters provide an output which follows a sine wave harmonically. This is similar to utility-supplied grid power. These inverters switch polarity ("+" and "-") between power cables smoothly; gradually increasing or reducing the voltage as required (in case you were wondering why inverters have to switch polarity: this is the essence of alternating current; polarity changes occur approximately 50-60 times per second).

In contrast, a modified sine wave is a simulation of the pure sine wave output, where the inverter sharply increases or decresases the voltage in order to switch polarity. As a result, the output form closely matches pure sine wave but still has much greater distortions.

As you can see from this example, though the modified and pure sine wave produce the same levels of output, the pure sine wave inverter produces a much smoother and less erratic output.

Ok, this seems very scientific, but what impact does your choice of inverter have in practice?

1. Modified sine wave output is not suitable for certain appliances; particularly those with capacitive and electromagnetic devices such as: a fridge, microwave oven and most kinds of motors. This also includes some types of printers, as well as capacitive fluorescent lights etc
2. Typically, modified sine wave inverters operate at a lower efficiency than pure sine wave inverters
3. Modified sine wave inverters are usually significantly cheaper than pure sine wave inverters

To sum up: although modified sine wave inverters can work well with many appliances including light bulbs, mobile phone chargers and office equipment, if your budget allows, we would always recommend buying a pure sine wave inverter.

DETERMINING THE POWER RATING OF YOUR INVERTER

If you need to power small appliances such as a mobile phone charger or energy efficient light bulbs, you don't really need to buy a 2000W power inverter because it will consume significantly more power (even in standby mode) and work very inefficiently with small appliances. On the other hand, if you connect a coffee machine to a 150W inverter you will quickly blow a fuse (if not the inverter itself).

Therefore the power rating of the inverter should be chosen based on the power consumption of your load. The following table contains the typical power consumption of some standard household appliances and the recommended inverter rating.

*Appliances marked with a star are likely to have a starting power consumption several times greater than their normal working power (typically this is caused by electric motors). This should be taken into account when choosing the correct size of inverter. For example, even though electric lawn mowers have a normal working power of 1000W, their starting power is over 4000W. This means that an inverter with a continuous power of 2000W is not suitable, because its peak power is limited to only 4000W. Always take into account the starting power requirements of your equipment - especially devices with electric motors - when choosing the right inverter.

**These appliances do not have an electric motor inside, but still have a variable power consumption with power spikes. Therefore they require a larger inverter than would be needed for other appliances with a similar nominal power rating.

Please also note: this table is provided for general guidance only. The actual power consumption of your appliances, as well as starting power requirements, may vary considerably. In all cases you will need to check the specifications of your equipment to find their continuous and starting power requirements.

If more than one device is connected to the inverter, the total power consumption should be the sum of all appliances used. This will determine the total inverter power required.

DETERMINING THE INPUT VOLTAGE OF YOUR INVERTER: 12V OR 24V

If you are looking for an inverter for your 12V leisure battery in a motorhome, caravan or boat, there isn't much choice in terms of the input voltage - you will need a 12V to 230V inverter, because your battery is 12V.

However, if you are building a standalone off-grid solar system (e.g. in a house, garden, shed or farm), then you can choose the voltage of your battery bank, and consequently, the input voltage of the inverter.

Instead of a 12V battery bank, you may choose to build a 24V battery bank (2 x 12V batteries wired in series will produce 24V). In this case you can use a 24V DC to 230V AC inverter, rather than 12V DC to 230V AC. This set-up will provide some important benefits:

• The input current for the inverter will be two times smaller for 24V than for 12V, making the inverter and the entire system safer and more reliable
• The cables between your battery and the inverter do not have to be as thick as those used for a 12V battery bank and inverter.

This is particularly important for large standalone solar systems with 2000W inverters. For such power levels, our recommendation is to opt for a 24V battery bank and an inverter with a 24V input voltage.