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Fitting Electrics in Caravan

Postby HayleyK » Wed Jul 28, 2010 9:06 pm

I am debating on buying a small caravan to do up a inside and use for weekends away. Problem is i have a small budget and for my money i have found a lovely caravan which is very dated inside and looks like a perfect project for me to do, however the seller has told me that it will need 12 v electrics doing as there is no charging system. I am totally naive to the whole electric scene and was wondering if someone could tell me if this is a big job or not, can it be done by anyone or is a proffesional needed and a rough price that i should pay to get this done.
Thanks in advance
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Postby ericmark » Thu Jul 29, 2010 9:38 am

The battery if any in a caravan can be charged in many different ways. Some involve the removal of the battery in order for it to be charged.

What needs doing depends on what power draw there is on the battery. With gas lighting and a foot operated water pump there is no need for power. As lights and water pump are added then you need to consider how much power is required.

If we consider two 8 watt lamps then around 1.4A and if you consider 3 hours use per day then a 40Ah battery (Min recommended in wiring regulation) then the battery will last around 10 days without charging. So a 70Ah leisure battery would likely last a fortnight holiday without charging.

To charge in caravan there are two methods. A mains charging unit which means a hook-up or a supply from the car while it is being towed. The latter is not very successful and the volt drop across the connecting cables mean it gets very little charge. The idea of two interchangeable batteries and a second battery carrier in car boot works a lot better as the battery being charged in boot is closer to cars own battery. There are variations on this and using a single battery and transferring every time on goes out or having a link cable car to caravan and have battery at all times stored in car is another.

Of course the car will require a split charging set-up. There is a method where the battery can be charged in the caravan while being towed and that is a special inverter unit if you do want to tour then this could be an option. Narrow boats use them to charge bow thruster batteries not seen them used with caravans.

The more normal is to have mains in the caravan and there are kits sold to do this job. Although in UK reversed line and neutral is rare on the continent it is common so normally there is some warning about reverse polarity so not quite the same as wiring a shed.

Section 721 of BS7671:2008 lays out what types of cable and the pin outs for the plugs and sockets in the 10 pages of electrical regulations for caravans it covers both low voltage (230v) and extra low voltage (12v) systems and even gives the length and size of connecting cable. Some seem to be a little OTT for example A721.55.5.1 The circuit to charge an auxiliary battery should be separate from a circuit to operate a refrigerator. This would really depend on size of auxiliary batteries and with other similar living quarters narrow boats the fridge often is powered from the auxiliary batteries although they are 300Ah.

However sites are starting to ask for the periodic inspection report before giving a hook-up so it would seem to make sense to follow the regulations so each 3 years the number of points raised is kept to a minimum.

So all wiring uses flexible cables. All cables shall, as a minimum, meet the requirements of BS EN 60332-1-2.

Some of the statements made in BS7671:2008 are incorrect. One example is A721.55.4.1 Generators and transformer/rectifier unit
If a supply is obtained from a generator or from a low voltage supply via a transformer/rectifier unit, the extra-low.
Voltage at the output terminals of the supply unit should be maintained between 11 V minimum and 14 V maximum with applied loads varying from 0.5 A minimum up to the maximum rated load of the supply unit. Over the same
load range, alternating voltage ripple should not exceed 1.2 V peak to peak.

However a standard three stage charging unit will on second stage give an output of 14.8 volts and only drop to 13.2 volts at third stage so one has to take some of the requirements with a pinch of salt.

The low voltage (230v) requirements all make sense it is the extra low voltage bits where the regulations seem to have lost their way.

Although why one should not be allowed to use a cable shorter than 23 meters to connect up the power I do not no! I would have considered where a shorter cable would reach there is no reason why it could not be shorter. The maximum length of 27 meters does make sense.
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