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Choosing the right Power Inverter for your Motorhome or Caravan

A power inverter, or mains inverter is essential if you want to run ordinary domestic mains appliances in your motorhome, RV or caravan when you are off grid away from a mains hookup. An inverter converts the 12V or 24V direct current (DC) from your motorhome, RV or caravan battery to 230V mains voltage alternating current (AC) so you can run your mains powered televisions, lights, computers, power tools etc from your battery.

We have a variety of power inverters for your motorhome or caravan that ranges from 300W to 2000W with both pure and modified sine wave outputs and available in both 12V and 24V versions.

Pure sine or modified sine?

There are two main types of inverter, modified sine wave and pure sine wave, this refers to the waveform the of the AC output and how it is generated from the DC supply from your battery. We don’t need to be concerned with how these waveforms are generated but the end result is that a modified sine wave inverter is cheaper than a pure sine wave inverter and will run most but not all appliances whereas a pure sine wave inverter produces a cleaner output that is essentially identical to your mains supply at home so will run all appliances.

For lights, non-digital microwave ovens, power tools and other motor driven loads a modified sine wave inverter is fine but the output can cause slight interference on some televisions, audio devices and computers.

What size inverter do you need?

Inverters are sized by the output in Watts, eg. 500W, 1000W, 2000W. To work out what size inverter you need we need to work out how much power (Watts) the devices you want to run from it will use. Add together the wattage of all the devices you would want to use simultaneously then add another 15% to allow for a little overhead and pick an inverter with at least that continuous wattage.

If you know how many amps your device will draw but not the wattage it is a simple calculation to get the watts:


So if you have a device that draws 1.5 Amps it is 1.5 x 230 which give us 345W so a 500W inverter would suffice.

Our power inverters all have overload protection which means if you do try to run more than it can handle it will shut down until the overload is removed.

Devices with induction motors such as power tools and particularly those that start under load, such as compressors and pumps may require 2 to 6 times their wattage rating during start up so allow some extra overhead if using these kind of devices.

Hang on, isn’t mains voltage 240V not 230V?

This is a common misconception, it used to be the case that mains voltage in the UK was nominally 240V but the official standard across Europe has been 230V since 2003 but a lot of people are not aware of this and it is still commonly referred to as being 240V.

As part of the EU harmonisation in 2003 the UK mains voltage was set at 230V with a tolerance of +10%/−6% (216.2V to 253V) and in 2008 this was widened even further to 230V ±10% (207V to 253V) so the voltage from your mains sockets at home can vary within that range and it won’t affect the operation of your equipment.

How much current will it draw?

You need to make sure your batteries have enough capacity to run the inverter with your chosen devices. To obtain a rough estimate of the current (in Amps) the batteries must be able to deliver, simply divide the total power consumption in watts by 10 (this allows for some overhead for the inherent inefficiency in the voltage conversion).

Example: if the total wattage of the devices you want to run at once is 500 Watts, the power source must be able to deliver:

500 divided by 10 = 50 Amps

How long will it run for?

Operating time is dependent on the capacity and condition of your batteries and the total wattage of the devices you are running. Battery capacity is measured in Amp/hours or Ah, eg. 100Ah.

To give a rough estimate of the running time divide the Ah rating of the battery by the current (in Amps) that the inverter will draw for the devices you want to run (see “How much current will it draw” above).

Example: if your total current draw is 50 Amps as per the example above and your battery is rated at 100Ah:

100 divided by 50 = 2 hours

Therefore a fully charged 100Ah battery in good condition should be able to run a 500W load for approximately 2 hours.

All our mains inverters protect you against running your battery completely flat, once the input voltage drops to certain level the inverter sounds an alarm to let you know the battery power is getting low and if it is left to continue, drawing more power, the inverter will eventually turn itself off to ensure your battery isn’t run completely flat.

Even with nothing connected to the output an inverter will still consume a small amount of power so it can drain your batteries if left switched on continually so it should always be turned off when not in use.

If an inverter is connected to the vehicles main starting battery it can be used whether or not the vehicles engine is running, however the inverter may not operate while the engine is starting since the battery voltage can drop substantially during cranking.

Is installing an inverter difficult?

Installing an inverter is pretty simple but there are a few precautions to take. If you are not comfortable with doing this yourself then we can arrange to have it installed for you.

Larger inverters, for example 2000W can draw up to 200A from your batteries so large diameter cables for the input are a must and you should keep the feed as short as possible. For higher output models 50mm2 cables no more than 1.5m long are advisable and all connections must be made with properly crimped lugs. A separate fuse fitted as close to the battery as possible is always a good idea and if you are installing a separate isolation switch make sure it can handle the maximum current the inverter will draw.

Can I easily switch between a 12V and mains supply?

Yes, we can supply you with the necessary equipment to install a dual supply so that you can easily switch your caravan or motorhome mains sockets from an external mains hookup to your inverter as required. There are a few things we need to know to advise you on this so please contact us to discuss your requirements.

What about solar charging?

We are big fans of solar power, it’s free and green so what’s not to like? To keep your batteries topped up while off the grid you might want to look at our portable folding solar panel battery charging kit.

OK, so how do I buy an inverter?

That’s the easy bit now you have learned the ins and outs of inverters, just browse our range of mains inverters here and if you still have any questions you can contact us here.