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Motorhome advice: A beginner's guide to habitation electrics


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Ah, the old days, when motorhomes and campervans were habitually referred to as ‘caravanettes’ by the masses and living in the ’van was a far simpler affair. Cookers were lit with a match, and fridges and heaters needed no 12V power as push-button piezo igniters did the job of firing them up.

Mains hook-up was rare and, with probably just a few lights in the habitation area, no leisure battery was thought to be needed. Of course, you had to be careful – too much late-night reading would result in a flat battery and a dead engine the next day. These days, though, motorhomes bristle with electrical equipment and, increasingly, cutting-edge tech. 

The electrical systems found in motorhomes

Two fundamental electrical systems are fitted into the modern motorhome: mains 230V AC – the same as in a bricks-and-mortar home – and 12V DC. Both have different jobs to do, but they work together at certain points, with mains, at times, powering heavy loads such as heater, fridge, hot water boiler and battery charger and 12V providing power for the systems that control them.

Power outlets are often provided, too, with 12V and mains sockets fitted throughout the interior. Then there’s the fresh water pump, lighting, tank level indicators, cooker flame ignitors, toilet flush pump, extractor fans – the list goes on, with all these using 12V power.


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What is a motorhome's leisure battery?

The heart of the 12V system, and one of the most important items, is the leisure battery. This is a unit dedicated to powering the living area, not only providing enough energy, but also making sure you do not wake up to a flat vehicle battery and a dead engine. The name references the ‘leisure’ aspect of motorhoming and allows for easy identification, but it’s really a misnomer as there’s nothing leisurely about its life.

This is the hardest working piece of kit in any motorhome and, importantly, the power it provides allows the ’van to also function when away from the mains electricity provided on a campsite hook-up.

For a battery to do its job it must be charged and this is achieved in two main ways. The first is using the base vehicle’s battery charging system. When en route, the leisure battery is connected to the engine’s alternator, which charges and tops it up. When the vehicle is stationary a special device, called the split-charge relay, separates the leisure battery from the engine’s battery so that using living area electrics does not draw power from the latter and destroy its ability to start the engine.

Charging system number two only works when the motorhome is hooked up to a 230V mains supply. A mains-powered charger is permanently installed and specifically designed to meet the needs of the leisure batteries – charging, and keeping the batteries topped up. This can be left switched on for long periods. Some charging systems play a dual role, also charging the engine battery once the leisure battery is fully charged, while still keeping the two separated. The leisure battery feeds a distribution box with dedicated fuses rated for each circuit.

Sometimes, there’s a heavy-duty switch (often with a red plastic control knob), which isolates all the 12V electrics for when work is being done, or the motorhome is out of use. All the 12V functions are managed by a control panel (often mounted above the inside of the habitation door) with switches and indicators for all the systems – pump, lights, etc – and gauges that tell the state of charge of the batteries and the levels of fresh and waste water (grey) tanks.

What is a hook-up lead?

Once on a campsite pitch, you’ll find a bollard with a mains socket that will supply your motorhome with 230V electricity. The cable that connects bollard to motorhome is known as the hook-up lead and is usually coloured orange and is heavier-duty than a domestic extension lead. Connection is made via blue plastic plugs – the blue signifying that the plugs are designed to be used to connect 230V supplies up to a maximum load of 16A.

To protect them from the elements they’re shrouded. One end has male pins and connects to the bollard, the other, female, plugs into the motorhome's externally mounted hook-up point. It’s best to plug the female end into your ’van first then connect to the mains, while, to disconnect, it’s safest to first remove the male end from the bollard. Protection is provided by an over-current (usually rated at 16A) circuit breaker and RCD (residual current device) at the bollard.

Inside the ’van, the mains distribution is similar to that at home, with another RCD and over-current breakers protecting mains circuits – battery charger, fridge, hot water boiler, heater, etc. The RCD detects faulty appliances or wiring and disconnects the power if a fault occurs.

Powering a motorhome'e fridge

Motorhome fridges are divided into two types: three-way and compressor-types. It seems counterintuitive, but a three-way fridge actually uses heat to make it function. The heat causes the refrigerant gas to circulate and do its job and can be powered in three ways, hence the name. When driving, a 12V element powers it. When hooked up to mains, a mains equivalent is used and, when camping away from the mains, it’s a tiny gas flame that provides the heat.

There are two control systems used to switch from one energy source to another: manual or automatic. The manual system requires you to operate a selector switch according to the situation, while the auto detects the appropriate energy source and switches to it. Look for an indicator lamp/control switch on the fridge with an ‘A,’ this tells you it’s an automatic unit.

The other fridge version is a compressor-type. This is similar to your fridge at home but it runs on 12V, not mains. And it does this all the time, so you just switch it on and forget about it. The disadvantage with this type is the fact that it consumes more precious leisure battery power and the hum of the compressor can disturb light sleepers. However, it’ll not deplete your gas supply reserves, so it’s popular among people who camp away from mains supplies and travel to where gas is hard to get. Compressor fridges are also more tilt tolerant and can work at higher outside temperatures.

Heating and hot water in motorhomes

In terms of heating and hot water systems, there are several types to choose from. Most heating systems produce their heat as hot air, distributed throughout the interior using a fan and system of ducting to distribute the heat. The most used brand is Truma and its Combi unit, which combines a 10-litre storage hot water boiler with the blown-air heater function. Individual units are available also though, and you may come across a convector fire for space heating and a separate boiler.

All these heaters are primarily powered by the ’van’s gas supply, but most in the UK also work on mains electric (when hooked up) – with both energy sources being used together when fast warm up is needed. Older units have manual controls, but these days most are operated using a fully programmable unit with an LCD screen. This allows you to set on and off times, room and hot water temperatures and select energy sources easily.

More upmarket units, such as those made by Alde, are now fitted in even mid-range ’vans and these provide hot water in the same way (and are fully programmable), but provide heat using concealed wet radiators – the result is near silent heat with even better distribution.

Diesel (and petrol) drawn from the vehicle’s tank is the other fuel used for heaters, with Truma offering a diesel-fired version of the Combi. Webasto and Eberspächer also make compact blown-air heaters that are found in campervans. Webasto produces the Dual Top, a unit very similar to the Alde, but powered by diesel. The advantage is that they don’t use gas so, as long as you have fuel in the tank, you’ll never be short of heat. However, they can draw more power from the leisure battery that the more common gas-fired units.

Modern electrical technology in motorhomes

‘Now you can control your home from your phone’ – we’ve all seen the TV ads for home automation products such as Hive, which use a smartphone app to control of domestic equipment. Increasingly, the same is true of motorhomes. Initially, apps were introduced to control a single, or a couple of functions, with Truma’s iNet system, for example, allowing the setting of its heating and air-conditioning systems.

Now things are moving up a gear, with products that let you control and view the status of many of the life-support systems on board and functioning in conjunction with the motorhome’s built-in control panel.

Lighting in motorhomes

It’s fair to say that one relatively recent technical innovation that’s been of greatest benefit to motorhoming is LED lamps. These last far longer than ordinary filament bulbs and, importantly, use a fraction of the energy, thus helping to preserve battery power. And the good news is upgrading you ’van’s lights to LEDs is often easy as, in almost every case, there’s an LED equivalent lamp to fit. Specialist sellers are online and at motorhome shows throughout the year.

Another worthwhile upgrade is a solar panel. Fixed to the roof, these help charge batteries by converting sunlight into 12V electricity, controlled by a regulator to prevent over-charging (see Shop, p180). And, in the last few years, the price has tumbled, making them even more affordable. The latest types (the original, rigid-type, have bulky alloy frames) are very thin and semi-flexible so they can lie flat on curved roofs. Some are even self-adhesive, making installation even easier. Inverters connect to the 12V system and produce mains power – these can be a very useful thing if you’re camping off-grid.

They’re easy to fit (some are portable) and come in two flavours: the cheaper, modified sine wave type produces a rather crude version of mains electricity that sensitive electronics don’t like. Far better is the pure sine wave version, which mimics mains far more accurately and runs just about all 230V equipment safely. They’re available in a range of sizes, from 100W output to 3,000W and up.

But beware, as the amount of power drawn from your leisure battery can be huge and flatten batteries very quickly. The average low-wattage kettle is rated at 1,000W and this equates to more than 80A of current draw – enough to empty an average-sized (100Ah) leisure battery in less than one hour. You’ll need massive cables to cope with an 80A current draw, too.

Should I add a second leisure battery to my motorhome?

Given the above, adding a second leisure battery or a larger-capacity one can be both worthwhile and relatively easy if you have the space. The thing to check here is fitness for purpose and quality.

In simple terms, there are two types: the average car battery designed to give lots of power for a short length of time – when starting the engine for instance. Leisure batteries need to be able to give smaller amounts of juice over a long period. The cheapest, sold as leisure batteries, can be just a car battery with a leisure battery label applied, while the very best are made much the same as batteries designed to power electric vehicles.

The National Caravan Council has a verified battery scheme where it tests batteries for efficiency, and it’s well worth buying batteries that are tested and approved (look for an NCC Approved tick sticker).

The latest technology in batteries is lithium versions. These are lighter, charge faster, offer higher efficiency and last far longer – the drawback is cost: a 100Ah lithium will set you back close to £1,000, where the equivalent high-quality traction battery will cost around £300.

This feature was originally published in the January 2018 issue of MMM magazine. Want to read more like it? Subscribe to MMM magazine today!

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