A modern caravan has basically three electrical systems on board. The first system is to provide the lights that replicate the road lights on your car. The second system is designed to allow 12 volt lights and accessories to be run from a battery in your caravan and finally the third system is designed to allow you to plug in to a volt socket on a caravan site and allow the use of the same equipment you would normally just plug in to a socket at home. Skip forward a few years and a rear fog light became mandatory, so a further upgrade was made to the lighting electrical system to allow the rear fog light to be installed.
These were usually old car batteries.
Understanding Caravan and Tow Car Electrics | Caravan Chronicles
Originally, you would have to take this battery out of the caravan and charge it at home using a standard car battery charger. The 12 volt systems are split into two. The first, and as we have seen, the oldest is the caravan road lights, that is to say the lights that are required by law to have on all trailers.
Due to the size of a caravan front marker lights white are required and from side marker lights orange on longer caravans. The road lights are usually a complete system with all the supply and earth connections being separate from any other electrical system on the caravan.
One of the most common faults with road lights is problems associated with the earth lead, but more of that later. However, with the advent of the 12S, this was taken care of. The second 12 volt system is the supplemental system. The design of the supplemental system has to take into account a number of things: A simple connection from the car battery to the leisure battery in the caravan achieves this, but there are problems with this type of connection. So how can we do this safely? The fuse will blow before any damage can be done by the car attempting to use the leisure battery as a source of power.
This fuse is typically rated at 15 or 20 amps.
Understanding the Leisure Battery Charging Circuit. How do we do this? Actually its quite simple. A separate lead from the car battery to the 12S socket or 13 pin socket has a relay connected in line with it. The cable that connects this circuit MUST be 2. This is to ensure that the circuit is not connected to other circuits and to make sure the higher current required cannot be fed through other devices if a fault should develop.
You will find out shortly why each caravan 12 volt system has a separate earth cable only earthed when it is connected to the car. When the starting battery was charged, the voltage rose to On some of the more expensive voltage sensing relays you can adjust the voltage. This is achieved by another relay, this time installed in the caravan.
The incoming feed from the car goes to a relay. This relay is controlled by sensing the voltage on the circuit that powers the fridge. Remember we said that we. Why should we want to do this? Well, there are good reasons. It also ensures that the caravan leisure battery cannot supply any voltage to the towing vehicle for starting the engine. The lighting system on modern cars has grown more complex over time. To make sure caravan road lights can work with all cars, a simple standard is adopted so that you can plug virtually any caravan into any car and all the road lights will work.
In order to make sure this can happen, the road light system on a caravan is kept completely separate form the other 12 volt systems. So, to avoid accusations of failure to harmonise, the European Commission simply altered the legal voltage limits — nothing actually changed! For further info read: The volt system is exactly the same as your house wiring.
It allows you to use the same appliances you do in your home and works in the same way. The volt system is not connected directly to any of the 12 volt systems in the caravan. How do you get volts in your caravan? These leads are different to the ones you have in your house in so far as they use different connectors. When connected, this lead provides a volt supply of up to 16 Amps. In the UK some caravan sites are limited to 10 Amps, and on the continent, this can be limited to 6 Amps or even lower.
Note that in Europe, the connectors mat be different, not all have adopted the standard blue 16 Amp connections yet. Simply this is a special switch that looks at the current on the incoming wire live and returning down the neutral wire. You can test the ELCB by pressing the little test button on the device.www.cantinesanpancrazio.it/components/wypahuse/
Understanding Caravan and Tow Car Electrics
It should cause the switch to turn off when pressed. These are the modern equivalent of fuses. This charger is a bit more complex than the cheap car battery chargers that you can buy from your local car parts shop. It has to do several things — firstly, it has to be capable of charging the leisure battery, second, it has to be capable of supplying enough current to allow you to use all the 12 volt appliances in the caravan… your water pump, interior lights etc.
Some of the appliances that can be set to run on gas dual fuel …. This is the same for your fridge and space heater when operating on gas. Remember, most caravan electrical systems are designed so the fridge will not run off the leisure battery… but requires that the leisure battery or small 12 volt supply is present to be able to operate of gas. This means when you are plugged in to the EHU on your pitch, the caravan is safely connected to Earth, so should any fault develop it will trip the ELCB and you will be safe… even if standing on wet grass touching the metal frame of the caravan.
Lets look at the 12 Volt systems first. Anyone with basic DIY skills can alter or adapt the 12 volt wiring on a caravan. Before you start any work, draw out on paper the existing cabling you want to alter and identify on the drawing the basic parts, including cable colours, positive wires and neutral wires. Take pictures as well so you can. Next, draw what you want to do and where you are going to connect the wires. Study the route of any new cables — is it possible to get the cables where you want them?
Are the cables going to get trapped or damaged when the caravan is moving?
If you are adding additional 12 Volt outlets Cigar lighter or accessory type sockets is the cable you are joining into of sufficient size to carry the additional load? Once you have decided what you want to do, write down a shopping list of things you will need. Wire — what length, rating and colour? Do you need any special connectors? These connectors are unreliable as they rely on a metal blade cutting through the insulation and nipping the conductor inside the cable. They cannot be reliably installed and cannot handle more than one or two amps. Soldering takes a bit of practice and the transition point between soldered and un-soldered cable is a weak point.
Soldered connections also suffer from oxidation. The best way of splicing or lengthening cables is to use crimped connections. The other thing you will need is a good pair of cable insulation strippers. All these tools and crimps can be found at places like Maplins. If you are installing a new outlet, remember to include a fuse into the circuit. Generally, you always install the fuse as close to the battery or connection where you are picking up the positive supply from. The fuse is there to protect the cable from overload in the event of damage so its no use having it near the outlet if it gets damaged near the connection to the positive supply.
Leisure batteries store energy… that is what they are designed to do. Releasing this energy in a short burst if you get the wiring wrong will be spectacular, quick and dangerous! Batteries can and do explode, wiring can and will become red hot and you could lose your caravan. Well, you may have basic DIY skills and have already altered your caravans 12 Volt wiring, but unless you are familiar with electrical wiring and by that I mean more than just putting a 13 Amp plug on to the toaster, I would suggest you get a qualified electrician in.
As most caravans are fairly simple, it will not cost too much to get the expert in. Remember, If it took you 30 minutes to empty a locker so a cable could be run, you would have been paying the electrician to do that! If you need to route a cable through the gas locker, make sure that it is well secured and cannot be damaged by the gas bottles and the terminations are well away from the locker.
Most, but not all caravan sites have a rating of 16 Amps for their hook up point. We want to find out the maximum load in watts that we can have plugged in to the caravan. We know the voltage — and we know the maximum current — 16 A, so if we use the following formula: To work out what you can plug in, look at the data plate on the equipment and it should tell you the power rating….
So add up all the electrical devices that you want to have switched on and as long as the total comes to less than Watts, you are OK. Now before you go switching on everything you own in the van, it is worth checking that the site supply is indeed 16 Amps.
Some sites in the UK are only 10 Amps, in which case your total load can only be Watts. Continental sites can have a supply rating down as low as 6 Amps in which case your total load can only be Watts remember, European supply voltage is usually Volts… so you will need to take this into account when working out the maximum load. In order to calculate the voltage drop in a given length of cable, we need to know the resistance, current in the cable and volt drop for a known length of cable for each different the different sizes cross sectional area given in mm2 for each cable used.
Here is a simple table for the most common type of single PVC cable used and its size. Voltage drop is expressed as milli volts per amp per metre. So lets look at that. Think of the brake lights on your caravan. We have a 1. Now we can use the following formula… Volt Drop x Current x length of cable and divide by to convert mV millivolts into Volts. So in our example: Now to complete our simple circuit, we also have a neutral cable earth or ground and have to calculate the voltage drop for this as well.
As it is exactly the same cable and length, we also have a 1. So when our brake lights work, they are working not at 12 volts, but at 8. This is a little better than before. OK, so its still not too good and your brake lights will be a little dimmer than intended. We can still improve things. If you remember, the earth cable for the road lights was on pin 3 of the 12N and the 13 Pin connection, and as it has to provide a return path for other road lights as well, it is usually a larger size — 2.
OK, thats getting better…. OK, this is easy. We have seen how we calculate the voltage drop in a given length of cable for a given load. Well, when the indicator lights are on, the calculation for the neutral cable changes.
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So, if the indicator bulb is 15 watts, and we do the calculation for the volt drop: So each time the indicator lights up, the voltage drop on the return cable increases by 0. It is important therefore when altering any wiring on your caravan or car, you should always choose the correct size. If in doubt, always go a size larger. At this point, I have to throw a few other things into the pot. How can we improve this situation? Well installing a 2. This is especially important if the charging circuit and fridge circuit also share the same earthing point.
It may be worth going up to a 4 mm2 cable if you can. Making sure the earthing point is clean and not corroded will make a difference as well. One other thing to consider is changing the rear light bulbs to the LED type. LED bulbs manufactured for use in automobiles have a wider operating voltage from around 8 volts to 18 volts and will always be a full brightness between these voltages.
A word of caution though. Some LED bulbs are only designed for show purposes and are not road legal. The reason behind this is some reflector designs rely on enough light being emitted in all directions in order to reflect off the interior of the light fitting. One of the requirements for vehicle lighting is not only the brightness of the displayed light but the surface area that is illuminated. Some LED Bulbs only emit light in one direction and nothing is reflected off the interior of the fitting. On the upside, to offset some of the voltage drop loss, when the engine is running, a cars electrical system usually operates around To enable you to do this, you will need a digital multimeter.
Set the multimeter scale to read 30 volts DC. Read the voltage displayed on the multimeter. Leisure batteries with a voltage of below For the best charging performance when the leisure battery is not in use over winter look for a charger that offers a 4 stage charging process Bulk — Absorption — Equalisation — Float. For the most accurate results using this method of measuring the state of charge SOC the battery should have been rested for at least 6 hours — i.
The use of petrol generators on most caravan sites is frowned on, mainly because of the noise. There are petrol generators that are coming on to the market that are extremely quiet, but a generator, no matter how quiet will quickly annoy you neighbours on a summers evening when all the windows are open and people are sat outside or in their awnings. However, at some events, the use of generators is increasing and at others, motor sport events for example, you will find nearly every team caravan has a generator running away in the background. A couple of important things to keep in mind when choosing and using a generator.
If you are looking to buy one for the first time, always go for a 4 stroke engine, they are always much quieter. Cheaper conventional generators have very poor voltage regulation and could damage your caravans charging system or other components. When operating your caravan on a generator, you may get the reverse polarity light illuminating. Always check your caravans handbook for advice about using a generator. A typical generator can only provide a fraction of the electrical power that you would have if you were on a EHU supply.
Most Generators are around 2Kva or about Watts, which is equivalent to just over 8 Amps, so you will be limited to what you can plug in. If you are taking a generator with you, take it in the car boot. These are heavy bits of equipment and not really suitable for carrying in your caravan.
Some additional generic wiring diagrams for you to download and print off. List detailing the 12N, 12S and 13 Pin connections on a car or caravan plug and socket. To help fault finding I have drawn out the pin connections for the 13 Pins towing socket as seen from the socket side, it will help identify which pins to check. The connections for a 13 pin towing socket seen from the socket plug side. You can download the drawing as a PDF file for printing out here: Connect two batteries in parallel.
May 30, at 3: Simon — good article. However, once the ignition switch is on the babitation relay connects caravan battery to car battery. At that point, if the van battery is very low, it could pull down the car battery and reduce its ability to start the car. Converesly if the car battery is low you will have the van battery trying to start the car nad hence blowing the fuse. How do you see those two scenarios? The habitation relay in the caravan is controlled by the power feed to the fridge circuit via pin 10 in the 13 pin connector.
Pin 10 should only become live once there is an output from the alternator…i. Even if the ignition switch is turned on in the vehicle without the engine running there should be no output on pin 10 fridge circuit that could operate the caravan habitation relay. Therefore attempting to start the vehicle with a flat battery and it drawing current from the caravan leisure battery could never happen. As a safeguard, the caravan leisure battery usually has a suitably sized fuse 20 to 30 Amps connecting it. March 30, at 8: Having just got a new BMW company car with factory fitted tow bar and electrics, I was mortified to find out that BMW do not connect pin 10!!
So would it be possible to make an adaptor that connects pin 9 to pin 10 even if I have to manually for a switch? Any advice would be welcome as I have this car for 4 years.. July 3, at Most people would think this is an upward move but I have to say that the Kuga is a far superior tow car than the X3. I too had a similar experience with the tow bar electrics and was quoted a similar price.
Having looked at the X3 and clearly stated that I was looking at a car to tow my caravan, I was concerned to find that having paid for the car, it had only the basic electrics fitted. This is normal with BMW apparently.
I broached the subject with the dealer who initially said they would address the matter. They were clearly not aware of this at the time of the sale. Furthermore, as I had clearly stated that I wanted the vehicle to tow a caravan, they as a main dealer should have been aware that the electrics were not up to the job. On a modern caravan with the anti snake ATC system, the full electrics are essential.
Quiet reasonable argument won the day and they fitted the upgrade kit at no cost. We pays our money and takes our choice. July 16, at 7: This bypasses the habitation switch. Voltage sense is on pin 10 UK, but pin 12 AU Anderson plugs only mate with the same colour and amperage plugs. Use a red Anderson plug for always connected and grey Anderson for only when engine is running. Other advantages of the Anderson plugs include — easy connection of a solar panel or an external battery charger to either battery red into tow vehicle, grey into van.
Easy connection of a 12V compressor or modified battery drill to either battery. Simon, maybe you could add some diagrams that show auto sensing fridge power connections 1 through the 13 pin plugs and 2 via Anderson plugs??? July 16, at 8: Hi In theory using Anderson plugs to connect various circuits is fine, however in Europe the regulations state that there must be a system where everything 12 volt in the caravan is disabled when the tow vehicle engine is running — hence the habitation relay — except for the fridge circuit which is separate.
Each Club hook-up bollard is individually protected against overload by a miniature circuit breaker MCB and a residual current device RCD. The MCB is a device to protect the site cabling from overloading and limits the amount of current you can draw from the supply. Hook-ups on Club sites have maximum ratings of 10A or 16A and this will limit the number of appliances you can use at one time see the How much power section. The RCD is designed to cut off the supply if a fault occurs in your connecting lead, caravan or other camping unit.
However, to maximise safety your unit should have its own RCD. Do not allow children to play around the hook-up installation or supply cable or allow them to connect or disconnect supplies. At Club Sites the supply cable plug is simply a push fit into the bollard socket, but you will find some sites with hook-ups that require the plug to be pushed in and then twisted.
With this type of hook-up a button has to be pressed to release the supply cable plug. Your connecting lead will need a plug to match this socket outlet and a connector to match the inlet to your unit, both complying with BS EN It is common however to find lesser cables where each core is only 1. This can be confirmed on the outer PVC covering of the cable where it should be marked. The maximum cable length of 25 metres should ensure it can reach the supply bollard at most sites in the UK. Always uncoil the supply cable fully to avoid it overheating on a cable reel.
The use of a second cable is not recommended, but if it is used it must be fitted with the same BS EN standard plug and connector. The connection between the two cables should be raised off the ground by the use of a propriety joining cover. Taped cable joints and ordinary 13A household plugs and sockets must not be used under any circumstances. The cable is normally coloured orange so that it is visible and avoids being damaged by grass cutting and other activities on site.