Inverters for Caravans and Motorhomes
Almost every motorhome and many caravans use an inverter. These clever electronic devices take the low voltage direct current (DC) power from our batteries and convert it to the same high voltage alternating current (AC) that our household sockets deliver.
This allows us to have 240 volt mains power with us no matter how far we are from the nearest power point.
Selecting an inverter
When selecting an inverter, you have two major decisions to make … capacity and waveform.
Capacity is easy to understand so lets deal with that first. An inverter that is rated at 1500 watts will run 240 volt appliances up to a total of 1500 watts continuously (not just for 5 minutes). The surge rating so often quoted in flashy eBay adverts for inverters can be largely ignored. This is the amount of power that the inverter will supply for a second or two only. Many appliances require larger quantities of power at start up. This ability to cope with surge current allows these appliances to run from the inverter. Almost all inverters are happy to supply twice their normal rating for a second or two.
When considering your inverter capacity, keep in mind that generally speaking, the larger the inverter capacity, the less efficient it will be when you use it for small appliances. For example: If 1500 watt inverter is quoted as having a peak efficiency of 90%. This 90% efficiency will most likely only be delivered when the inverter is delivering 1300 watts. If you only require 300 watts from the inverter its efficiency may fall to just 60%. In practical terms, this simply means that you should always select the smallest inverter that will meet your needs.
Consider as well that there are (as always) no free lunches … if you install a 6000 watt inverter and plan to use it at full capacity, you are going to need a trailer load of batteries or a portable nuclear reactor to be able to keep power up to it. A 6000 watt inverter will require at least 250 amps at 24 volts to deliver that 6kw (or 500 amps at 12 volts). This would completely deplete your 200 amp hour battery bank in less than 30 minutes.
As a general guide, an inverter for motorhome will probably fall into the 800w – 1800w range.
Wave form basically describes how closely the inverter matches the power that you get from your household power socket. Inverters fall into two distinct groups: those that produce pure sine wave power, and those that don’t. If the inverter that you are looking at does not say “Pure Sine Wave”, then there is a very good chance that it is not.
Inverters that are not pure sine wave are often described as one of the following:
- Modified sine wave
- Modified square wave
- Quasi sine wave
Pure sine wave inverters are typically more expensive to manufacture and accordingly more expensive to purchase. This gap has narrowed considerably in the last few years.
There is nothing wrong with inverters that produce something other than pure sine wave. They work just fine with the majority of 240 volt appliances. But the key word there is majority. There are a growing number of devices that will simply not function when asked to use anything but a pure sine wave. Some devices will instantly self destruct.
We have an excellent Trace brand 1500watt inverter in our motorhome. It produces modified sine wave power. A few months ago I purchased a fairly high tech soldering station. About 4 seconds after plugging this into the power produced by our inverter, it emitted that dreadful electronic death smell and promptly expired, never to solder again.
The battery charger that was supplied with my new camera lasted a little longer (15 minutes) before it went the same way. These are the exceptions – I have run many other appliances successfully for years – but that makes the loss of these two no less painful.
We don’t often buy new electrical devices, but when we do it is with huge dread that I plug them into the inverter for the first few times.
My advice is to buy a pure sine wave inverter if at all possible and completely avoid this issue.
Some inverters have battery chargers built into them. This effectively makes them work in reverse; when you attach 240volt mains power to the vehicle, the inverter switches to charger mode, stops converting low voltage DC into high voltage AC and instead charges you battery bank. This is often a very economical solution – an inverter/charger usually costs a lot less than an inverter and a separately purchased smart charger.
It is likely that you are going to want to tuck your inverter out of sight somewhere. A remote control lets you turn the device on and off and perhaps get status information from somewhere more convenient.
Auto Start / Standby
This is a very useful feature that saves battery power by putting the inverter into a kind of sleep when 240volt power is not needed. It negates the need to manually turn the inverter on and off when required.
Some inverters go one step closer to a “one-device-does-all” by adding a regulator for your solar system. I am personally not a big fan of this approach, preferring to use a dedicated solar regulator.
Don’t think for one second that the power produced by an inverter is any less lethal than the stuff that invisibly leaps out of the mains system and kills people. It is exactly the same stuff and can inflict the exact same perhaps fatal shock.
Inverters use large amounts of power, they therefore need heavy cables and very good quality connections. An inverter that is drawing 100amps from the battery will melt a small cable in a few seconds – a loose connection will become very hot very quickly. When installing and wiring an inverter take great care to get every connection tight and secure.
- Buy an inverter that is large enough to meet your needs but not over capacity.
- Select a pure sine wave inverter to avoid issues with some appliances.
- Wire the inverter with the correct sized cables and make sure every connection is 100%
- Treat the power it produces with the greatest respect.
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