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Introduction to Motorhome Electrical Systems (Author = GeraldandAnnie.)

There are up to 3 electrical systems in your motorhome. These are:
1) Cab (engine) 12 Volts dc
2) Habitation area 12 Volts dc
3) Habitation area 230 / 240 Volts ac

1) Cab
When the vans or motorhome chassis are built, they have a single 12V battery installed which has a function similar to a car battery. It will start the engine, and is charged by the engine-powered alternator. Most motorhomes have a cigarette lighter-style socket for accessories in the cab area.

2) Habitation 12V dc
Most motorhomes have a 12V dc supply into the habitation (living) area of the motorhome, powered by one or more habitation batteries. This powers devices like a fresh water pump, reading lights, and any accessory sockets in the habitation area for a TV or radio.

3) Habitation 230 / 240V ac
All recent motorhomes are fitted with at least one mains ac outlet socket. This is powered from a hookup connection, usually in the side of the van, which can be plugged in when on a campsite. It will allow the use of standard domestic electrical appliances, such as an electric kettle, microwave, TV / DVD player, etc. It can also power a built-in fridge.

NB Mains electricity in the UK always used to be a nominal 240 volts ac. However, the EU is standardising electricity supplies across Europe at 230 volts ac. Mains voltage also fluctuates within certain tolerances, and can be anywhere within the range 216 volts - 253 volts ac.

Habitation batteries are normally lead-acid, and as such have a finite amount of power stored within them. The battery can be recharged by running the engine (and alternator), or using the on-board charger with a mains hookup from either a campsite mains outlet or a generator. The battery can also be recharged by solar panel (usually mounted on the roof of the motorhome) or by wind generator (low efficiency).

Although the habitation and engine battery will both be recharged by running the engine, the system does not normally work the other way around (i.e. the engine battery will not be charged from a hookup). For this, you would need a Battery Master or similar device, although some newer motorhomes have this facility built-in.
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