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  • Malcolms

    ALL YOU NEED TO KNOW

    about Caravan Electrics

    Written by

    Malcolm Keen

    Keen Electronics Limited

    www.keenelectronics.co.uk tech@keenelectronics.co.uk

    2012 Keen Electronics Limited

  • Contents Foreword .. 1 Introduction ... 1

    Basic Electrical Theory . 2 A Simple Introduction ... 2 Commonly used Terms . 3 Battery Capacity 4 Fuses ... 4 The Difference between a.c. and d.c. 5 So why use a.c. ? .. 6 Road Lighting . 8 Fault Finding 9

    12 Volt Internal Lighting & Equipment . 10 Fault Finding 10

    240 Volt Electrical Equipment ... 11 Fault Finding ... 12 Leisure Batteries .. 13 Fault Finding ... 14 Measuring current drain 14

    240 Volt Safety notes ... 15

    Useful Information

    12N Plug Connections ... 16 12S Plug Connections .... 16 13 Pin Plug Connections ... 17 240 Volt Mains Plug Connections ... 18 How to use a Multi Meter . 19

    Glossary of Terms .... 20

    References and further reading .. 22

    Malcolms All You Need to Know about Caravan Electrics

  • Foreword Ive spent a lifetime working in the electronics industry and the last 20 years designing alarms for the caravan industry. During that time I have received countless phone calls from caravan owners and technicians asking for advice. This had led me to believe that a simple to understand guide explaining the basic theory of electricity coupled with easy to follow steps to diagnose common electrical problems would be welcome. I do hope that you the reader will agree with me, once you have read some of the following sections. Please note that electricity is a large subject so we can only scratch the surface in this book. However, I have given some references at the end of this guide for those of you interested in learning more.

    Introduction Things always go wrong at the most inconvenient time. Then you cant find the information you need to sort out the problem. Phoning your caravan dealer or the equipment supplier outside office hours only gets you talking to an answer phone. But this easy to follow guide may well be your saving grace, and earn you Brownie points with your partner or children or boss. I know that a little knowledge can be a dangerous thing, but often a good guide, coupled with a dose of common sense can sort out many basic problems. Of course having a few simple tools is necessary. But most of us who have caravanned for a few years have learnt the hard way that not having a few basic tools can lead to much frustration. Caravanning can be very relaxing, but not if you are sitting in the dark when your neighbours are watch-ing TV or if the shower packs up half way though washing your hair. This guide has been divided into the following main sections :- Basic Electrical Theory Road lighting 12 Volt Internal lighting and equipment 240 Volt Electrical Equipment This will help you to find the information you need to resolve your problem. I strongly recommend that you read the Basic Electrical Theory section. This is a simple mans (whoops should be persons) guide to electricity. There are also some diagrams showing connections to the older 12N and 12S plugs together with the now standard 13 pin plug. Finally a word about safety. The 240 Volt mains supply can kill, so please only carry out the tests in this book. If you are at all unsure leave it for a qualified electrician to sort out the problem.

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    Malcolms All You Need to Know about Caravan Electrics

  • Basic Electrical Theory A Simple Introduction To many people electricity is a great mystery, but we use it to light our caravan, power our water pump, television, radio, mobile phone and many, many more things. Most of us know that electricity either comes from a battery or from the mains supply (240 Volts). It is then connected through a switch to our appliance. Many text books compare electricity with water, as we can see water flowing from a tank though a tap into a basin. Although we cant see electricity flowing, the same general principle applies. Lets look at this with a couple of diagrams

    Water Electricity Our water tank holds a certain number of gallons (or if you prefer litres) of water. This is its capacity. Our leisure battery holds a certain number of Ampere Hours of charge. This is its capacity. In both cases the larger the tank or the battery the greater the capacity. Our tap or switch enables us to control the flow of water or electricity respectively. Our basin needs a certain number of gallons of water to fill it. This is the drain or load that it puts on the tank. For example if the tank holds 10 gallons and the basin holds one gallon, then we can only fill the basin 10 times before the tank is empty. Our light needs a certain current to operate it. This is the drain or load that it puts on the battery. For example if the light draws 1 Ampere and the battery stores 100 Ampere Hours of electricity then we can only use the light for 100 hours before the battery is flat.

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    Malcolms All You Need to Know about Caravan Electrics

  • Basic Electrical Theory One big difference between water flowing and electricity flowing is that water flows through a single pipe, but electricity needs two wires. The electricity has to flow down one wire, though the light (the load) and back through the other wire to the battery. This then completes the circuit. So you can see that for most electrical appliances power is supplied from the battery, controlled by a switch, and fed to the appliance. This is the case whether the appliance is a light or a television. What is inside the appliance makes no difference, other than the amount of current drawn from the battery. Commonly used Terms

    Sometimes it is not clear what the commonly used electrical terms mean. We have Volts, Amperes (often called Amps) and Watts and Ohms. Lets look, briefly at what these mean and how they are related. We need a little Maths but it is quite simple.

    Volts are like a head of water, the higher the voltage the greater the current flow into a given load. The higher our water tank is mounted the greater the flow of water into our basin.

    Amperes refer to the flow of current down the wire, through the load and back to the battery. This is like the flow of water measured in gallons per hour flowing through the pipe.

    Watts refer to the power being used by the load. We are familiar with light bulbs rated at 60 watts or 100 watts. We are also familiar with electric heaters rated as 1KW (1 Kilo Watt which is 1,000 Watts). The definition of Watts is Volts multiplied by Amperes. So in the diagram on the next page the battery voltage is 12 Volts and the current flowing is 2 Amperes then:-

    Power (P) = Volts x Amperes = 12 x 2 = 24 Watts

    Ohms refer to the resistance of a wire or an appliance. The resistance of our piece of wire is similar to the restriction our water pipe puts on the flow of water. The smaller, or longer the pipe is, the greater the restriction and the lower the flow of water.

    Resistance (R) = Volts / Amperes = 12/2 = 6 Ohms Ohms Law is the simple formula used to calculate the relationship between voltage (V), Current (I) and resistance (R) and is usually expressed as I = V/R or V=IxR or R=V/R where V = Voltage, I = Current and R = Resistance

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    Malcolms All You Need to Know about Caravan Electrics

  • Basic Electrical Theory

    Diagram showing 12V battery feeding 24 Watt lamp Battery Capacity

    Now we need to consider battery capacity. As mentioned before we refer to leisure batteries by their Ampere Hour capacity. When I started caravanning a 60 Ampere Hour battery was quite normal. These days with more 12 Volt appliances in caravans larger batteries are commonplace, typically 110 Amp Hour (110 A Hr)

    The term Ampere Hour is quite simple to understand, it means exactly what it says. A 110 Amp Hour battery can supply 1 Amp for 110 hours. Or 11 Amps for 10 hours. In practice however, if high currents are drawn, such as is the case when using a Motor Mover, the capacity is reduced. Also if the battery is allowed to go flat (deep discharge) the capacity can be permanently reduced. For those of you who are interested in more details please read the section Leisure Batteries.

    Fuses

    Next we need to understand what fuses are for. These are a very important part of any electrical circuit as they prevent excessive current from being drawn in the event of a fault in the wiring or in an appliance. Im sure that you are aware that if you short (join) two wires together coming from your leisure battery, or from the mains electricity supply, you will blow a fuse (or bring out an over current trip). This is because the current drawn from the battery is only limited by the very low resistance of the wiring. So a very high current could flow, possibly causing a fire as well as damaging the leisure battery. So it is important when replacing a fuse to use the same current rated fuse. Dont replace a 1 Ampere fuse with a 10 Ampere one. You must find out why the 1 A fuse keeps blowing.

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    Malcolms All You Need to Know about Caravan Electrics

  • Basic Electrical Theory The Difference between a.c. and d.c.

    So far we have considered a battery as being the source of electricity. This type of electricity is called d.c. (or often D.C.) which is an abbreviation for direct current. What this means is that the voltage and current flow are constant with time. If 1 Ampere is flowing then it flows all of the time. (Or until the battery goes flat, or the switch is opened). So if we plot a graph of battery voltage against time it will be a straight line, as shown below:-

    Diagram showing d.c. Voltage with time But Im sure you all know that the mains electricity we use in our houses is a.c. (or A.C.) This is an abbreviation for alternating current. Now this can still light our lamps, heat our ovens, power our televisions and so on. But the difference, apart from the higher voltage which we will talk about later in this section, is that the voltage changes or alternates with time. So if we plot a graph of voltage against time it will look like this:-

    Diagram showing a.c Voltage with time

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    Malcolms All You Need to Know about Caravan Electrics

  • Basic Electrical Theory Now the first difference is that the voltage reverses its direction, smoothly going from a positive (+) flow to a negative (-) flow. One full cycle is made up of two half cycles. Now if this voltage is powering a light, that light will operate just the same as if being powered by d.c. The changes in the direction of the voltage, and current flow occur at a frequency of 50 cycles per second (now called Hertz, no not after the car rental company but in honour of Heinrich Hertz for his early discoveries about electromagnetism in 1865). In England our mains supply is at 50 Hz (or cycles per second). Whereas in America their mains supply is 60Hz. Our conventional filament lamp bulb consists of a tungsten element (a winding made of thin wire) inside a sealed glass bulb, which the air has been removed from. When switched on this element glows white hot and dims when the current is switched off. This is thermal inertia, meaning that when current is removed the light does not go out instantly, but goes to red then out. In the same way that some electric fires with wire elements on a ceramic former slowly change colour when switched off, but still give out some heat for many seconds. So it is this thermal inertia of the light bulb which prevents it from flickering when fed from an a.c. supply. Of course, if the supply frequency was very low, say 1 cycle a minute, then the change in current would be visible to the eye. So why use a.c. ? In the early days of electricity d.c. was commonly used but today only a.c. is used to provide electricity to our homes. Over a long cable run power is lost in the cable itself. So you may start out with 240 Volts at the generator, but only receive 180 Volts at the cable end. This power loss due to the resistance of the cable is similar to the loss of pressure down a very long hose pipe. You start off with a high pressure at the tap but at the end of the hose the pressure is much less. This is due to the resistance offered by the pipe. If a larger pipe is used then this pressure loss is reduced. In the same way the power loss down our electric cable can be reduced if we use thicker cable. But its not practical to run wire that is an inch or two in diameter around the country. Now the reason that a.c. is used is that we can change the voltage of an a.c supply using a transformer. We are all aware of the high voltage mains cables on pylons that bedeck the country. These operate at very high voltages, 132,000 Volts when I was a lad, but now 330,000 Volts is commonplace. The reason for this very high voltage is quite obvious to those of you who remember the magic formula Power = Volts x Amps. So to transmit say 100 Mega Watts (100,000,000 Watts) from the power station generating the electricity to a town using it can be done with small power losses by using a high voltage. So at the power station the voltage is stepped up by transformers for distribution over the grid. Then at the town it is stepped down, often in stages, by more transformers, until it supplies 240V to your house.

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    Malcolms All You Need to Know about Caravan Electrics

  • Basic Electrical Theory The theory of transformers and more detail about a.c. theory is beyond the scope of this guide. But in the same way that we consider a battery charger to be powered by 240 V a.c. and to produce 12 V d.c. we can consider a transformer to be powered by 240 V a.c. and to produce 24 V a.c. Or the transformer can increase the voltage, as is done between the generators in the power station and the overhead high voltage cables on the pylons. The section 240 Volt Electrical Equipment deals with the a.c. supply used in a caravan. It also explains the use of earth leakage and over current circuit breakers, used to prevent electrical shock and fire risk. These are often referred to as trips as they trip or switch off the current when an excessive current flow is detected.

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    Malcolms All You Need to Know about Caravan Electrics

  • Road Lighting In the same way that our cars have sidelights, rear lights and indicators (flashers) so our caravans must also have lights. These are supplied with electricity from the tow car and work in the same way as the cars lights. For many years caravans had two plugs to connect to the tow car. The black plug, called the 12N (N standing for normal) which supplied the road lights and the 12S (S standing for supplementary) which powered refrigerators and could charge the leisure battery while the engine was running. Today the continental 13 pin plug is commonly used, where all the connections for the 12N and 12S plugs are made through one plug. Diagrams showing the connections to all three plugs are shown in the Useful Information section at the end of this guide. Lets consider the wiring necessary to operate the rear lights of the caravan. The below diagram shows the 13 pin plug connected to these lights. If you read the section Basic Electrical Theory you will see the similarity between our early examples of a battery feed-ing a load through a switch.

    Diagram showing 13 pin plug feeding two rear lights Viewed from rear of plug

    So the wiring in the car connects the 13 pin rear light terminals to the cars battery via the light switch. When the cars lights are switched off, there is no power at the 13 pin plugs rear light pins, so the caravans rear lights are off. When the cars lights are switched on, power is fed through the 13 pin plug lighting the rear lights.

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    Malcolms All You Need to Know about Caravan Electrics

  • Road Lighting All the other road lights work in a similar way. So the wiring diagram, or circuit, is very simple. In the early days of cars, the pins were connected directly to the wires feeding the light bulbs. But as car electrics have become more sophisticated this has changed. Many cars now have bulb failure electronics built in to detect if a bulb fails. If the caravans lights were to be connected directly to the cars lights, the electronics would show a fault condition. So modern tow bar electric kits include relays which perform the power switching. The relay coil is connected across the light bulb in the car and draws very little current. The relay contacts are used to switch the higher current to the caravans lights. So for each independent light a separate relay is required. So the way the 13 pin plug has been connected to the cars wiring may not be very obvious, and I would suggest that you leave any repairs to this wiring to a competent auto electrician. Modern cars are expensive to repair and making a wrong connection could leave you, in the worst case, with a car that wont even start ! Fault Finding As you can see from the diagram, the road lighting wiring is very simple, so there isnt much to go wrong. Ive listed some possible problems below, with suggested actions. None of the road lights work Check that the cars lights are working 13 pin, or 12N plug not inserted correctly, or blown fuse in the car Check for bad earth (negative) connection One light does not work Blown bulb, (replace the bulb), or blown fuse in the car Corroded contacts in bulb holder, or on bulb (switch lights off, then carefully clean) If none of the above cures the problem then there could be a broken connection in the 13 pin or 12N plug. Or if only one light is faulty, then the problem could be in the light fitting itself. Details of the connections to the road lighting plugs are given in the Useful Diagrams section. If you have a Voltmeter or a multi meter that can measure 12 Volts d.c. then you can use this to check whether you are getting Volts to the appropriate pins on the road lighting plug and then to the light fitting. If you are not sure how to use your meter refer to the section Using a Multi Meter.

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    Malcolms All You Need to Know about Caravan Electrics

  • 12 Volt Internal Lighting & Equipment Just like we take for granted our electrical and electronics appliances in our house, we tend to do the same in our caravan. While on a mains hook up the problem of current drain is not very important, unless its a cold night and everyone switches on electric heaters. But more on that is in the section 240 Volt Electrical Equipment. As you may have read in earlier sections, any electrical circuit can be simplified to a appliance being controlled by a switch, protected by a fuse and receiving its power from a source such as a leisure battery. Different manufacturers will use different methods to connect these appliances through fuses, over current circuit breakers and their individual switches. But the basic circuit remains much the same. Two other important items are the refrigerator and charging the leisure battery while tow-ing. Which coupled up and the tow vehicle engine is running, power is fed to the fridge to keep it operating. Where a spilt charger has been fitted to the tow vehicle the leisure battery is also charged, but only while the tow vehicle engine is running. Fault Finding

    None of the Lights work

    Check the leisure battery is charged and then check that a fuse has not blown. If you are on

    a mains hook up then the charger should be providing a 12 Volt supply. So a fuse or circuit

    breaker is the most likely cause of the problem.

    One Light doesnt work

    The most likely cause is a blown bulb in that light

    Water Pump or Toilet Flush Pump doesnt work

    Check fuse or circuit breaker for that circuit. For external (submersible) water pumps check

    that the plug is correctly inserted. These pumps can fail for a variety of reasons, so carrying

    a spare pump can be a wise investment. Always avoid the risk of a water tank running dry

    as pumps are designed to operate under water, not in air when they may overheat.

    Water/Central Heating Electrics doesnt work

    Check fuse or circuit breaker for that circuit

    Something makes a beep every minute or two

    The battery in your smoke detector, or carbon monoxide detector, needs changing.

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  • 240 Volt Electrical Equipment

    The mains electric circuit consists of a consumer unit having over current circuit breakers

    and a residual current device. This is similar to a domestic electrical supply consumer unit.

    The MCB (Miniature Circuit Breaker) protects against an overload (where too much current

    is drawn) on that particular circuit. The RCD (Residual Current Device) protects against an

    earth fault (where current flows to earth because of an earth leakage or connection to

    earth fault). The earth conductor is connected to the chassis and all metal panels of the

    caravan. The circuits supplied include the leisure battery charger, the refrigerator, a small

    number of 13A sockets and the 240 Volt lights.

    The below diagram shows, in simplified form, how these devices are connected. The mains

    electricity coming into the caravan (or house) has three wires (or conductors) these being

    the EARTH (E) which is connected to any exposed metal on appliances, the NEUTRAL (N)

    which is connected to the earth wire at the power station and the LIVE (L) which is the 240

    Volt wire. Now the appliance (or load) is connected between the L and N.

    So the load current flows through the live wire into the appliance and back through the

    neutral wire. In the event of a faulty appliance one of two things can occur.

    1) Current may flow from the live conductor to earth. In the worst case a connection could

    occur between the live and the metalwork of the appliance. This would make the appliance

    live, so someone touching the appliance could be electrocuted. The RCD prevents this from

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  • 240 Volt Electrical Equipment

    happening, as it measures the difference in current flowing between the L and N wires. If

    this difference current exceeds 30mA (0.030 Amp) then the RCD operates isolating the

    supply to the appliance. As the current flowing down the L wire should be exactly the same

    as the current returning down the N wire. If this is not the case then current is flowing to

    earth and a fault condition exists.

    2) The appliance may develop a fault where excessive current is drawn. This could cause overheating in the appliance, or if a high enough current, overheating of the wiring to the appliance. Either condition runs the risk of starting a fire. The over current trip prevents this from happening by operating and isolating the supply to the appliance.

    It is worth noting that although many appliances have three wires connecting them to the supply, some appliances only have two wires. Such appliances are referred to as being DOUBLE INSULATED. These appliances do not have a connection to the earth wire, but are designed in such a way that the user cannot touch any of the live parts. If such an appliance develops a fault it draws excessive current, bringing out the over current circuit breaker. Fault Finding No mains electricity in the caravan When on site check that the connecting lead between the caravan on mains supply pole have both connectors fully insertedswitch off supply at pole first. Then check that the supply is switched on at the mains supply pole. If the mains supply pole circuit breaker keeps coming out you may be drawing too much current. Turn off any high current appliances such as electric fires/fan heaters. Check the circuit breakers and fuses in the caravans own consumer unit Appliance not working Check the current breaker or fuse for that appliance 13 Amp Sockets These can be quickly and easily checked using a test plug. As shown in the 240 Volt Mains Plug connections in the Useful Information section. This is a SAFE way to check if a socket is both live and correctly wired. When the test plug is inserted and the socket switched on, all three lights should illuminate. For more details refer to the instructions printed on the test plug.

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  • Leisure Batteries

    We all use Leisure Batteries in our caravans and take them for granted, until a problem occurs. So these notes are intended to help you avoid problems and to tell you a little about these batteries. Unlike vehicle batteries, which are designed to cope with the high current drawn when the car's starter motor is used, leisure batteries are intended to supply a lower current over a longer period of time, without being charged every time the car's engine is running. However, re-charging a leisure battery should not be left for too long, as allowing the battery to go into deep discharge can reduce its capacity. There are two types of leisure battery: the conventional lead acid battery using acid based electrolyte and the more modern (and expensive) Gel cell battery, using a gellified electrolyte. The Gell cell type is considered by some to be better suited for use in caravans. If accidentally tipped over the electrolyte cannot run out with the associated risk of damage to your hands (acid burns) or corrosion to your caravan. In addition to the safety aspect, the following points are claimed :-

    Maintenance free No gas seepage Long life Better performance after deep discharge Improved recharge time Low self discharge

    So the increased cost of the gel cell battery is usually justified in a better performance and longer life. To get the best out of your leisure battery of either type I would recommend that you

    Charge your battery at least once every 2 months, when the van is not being used Charge your well battery before it goes flat, when in use For lead acid batteries check the level of electrolyte every 6 months If using a motor mover, recharge the battery after using the mover (where practical)

    If you are buying a new leisure battery and wonder what capacity battery you should purchase you can calculate it as follows. Consider whether you are going to always use sites with a mains hook up. If you are, then a 60 Ampere Hour battery may well be adequate. If you are going to use a motor mover, then I would suggest using a 110 Ampere Hour battery. If you are using sites without a mains hook up you need to consider how much the current drain will be and for how long. Appliances such as water pumps are only used for a short time, so can be discounted in a rough calculation. But lights, televisions, control gear for water heating and central heating together with alarms and tracking systems can all put a

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  • Leisure Batteries

    constant drain on the battery. If you know how many Watts an appliance uses then you can add all of these together to get the total power drain in Watts. Divide this by 12 to get the current drain in Amperes (Amps). So if this is, for example 4 Amperes, then dividing that into the Ampere Hour capacity of the battery will give you the time that the battery will supply that current. So if we take a 60 Ampere Hour battery and our example of 4 Amperes then the time is 60/4 = 15 hours. Obviously you are not going to watch television for 24 hours of each day, so you should get a longer time than we have calculated. Again if you are planning on using a motor mover, a 110 Ampere House battery should be chosen. Lastly a few points to note when changing your leisure battery :-

    Switch off the master 12 Volt switch Disconnect the mains electricity supply from the caravan Disconnect the battery terminals carefully, removing the negative one first Check for signs of corrosion, if any are present clean, then apply a little grease to the terminal Take care lifting larger leisure batteries as they can be heavy

    Fault Finding Leisure battery goes flat after a couple of weeks Charger faulty, excess current drain, faulty battery Leisure battery goes flat after a couple of days Light left switched on, faulty battery Measuring the current drain from your leisure battery To do this you need an Ammeter or a Multi Meter having a d.c. current range. Most Multi Meters need the lead marked V to be removed from the socket marked V and plugged into the socket marked I. (Dont forget to put the lead back into the socket marked V when you have finished making the measurement of current.) Set the meter to measure d.c. Amps and the highest range, at least 1 Amp. Carefully disconnect the clamp from the positive terminal on the leisure battery. Connect one lead from your meter to the clamp and then connect the other lead to the battery positive terminal. So current now has to flow through the meter to the caravans 12 Volt appliances. The meter should now display the current being drawn. If this is zero then change the current range on the meter to a more sensitive range. With everything switched off the current should be under 0.1 Amp (100mA). This current drain means a 60 Amp Hour battery should last 110/0.1 = 1,100 hours which is 46 days or just over 6 weeks.

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  • 240 Volt Safety Notes MAINS ELECTRICITY CAN KILL ! So always treat it with respect and think before working with it. Most accidents happen when we try and do things in a hurry. When dealing with mains electricity dont rush. Please follow these simple guidelines to minimise any risk. If you are not sure what you are about to dodont do it. Its better to have something not working than to electrocute yourself, or possibly others. When arriving on site and connecting a mains hook up. Switch the electricity off at the mains supply pole and then fully uncoil the cable between the caravan and the mains supply pole. ALWAYS insert the flying connector into the caravan first, then insert the plug into the mains socket on the mains supply pole. Lastly switch the supply on at the pole, check in the caravan to ensure that you a getting the mains supply in the caravan. If you need to remove a cover to inspect wiring for a fault always switch the electricity off first. Never try to poke pieces of wire or multi meter test prods into socket holes Never work on electrical appliances with wet hands, or in wet or damp conditions 13 Amp mains sockets can be easily checked with plug top tester

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  • Useful Diagrams Both diagrams are looking into the socket from the rear of the tow vehicle

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  • Useful Diagrams

    Diagram is looking into the socket from the rear of the tow vehicle

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  • Useful Diagrams

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    Malcolms All You Need to Know about Caravan Electrics

  • How to use a Multi Meter

    A multi meter is a very useful tool for fault finding and checking electrical systems. The most common uses are listed below

    Measuring VOLTAGE a.c. or d.c.

    Measuring CURRENT a.c or d.c.

    Measuring RESISTANCE

    If you are not sure what these terms mean I suggest you read the section Basic Electrical Theory, especially page 3.

    Measuring Voltage

    For measurements on your 12 Volt system you need to measure d.c. Volts. Many meters show the d.c. ranges with a = symbol. Always set the range to a higher one than you are going to measure. Check that if your meter has sockets which the test leads plug into, these are in the COMMON (black lead) and the V (red lead). On many meters the V will be marked V and R or V Ohms.

    For a.c measurements the procedure is the same, but set to a ~ range, usually 250 V. Please read the section 240 Volt Safety Notes before carrying out measurements on the mains wiring or appliances

    Measuring Current

    To measure the current drain from your leisure battery to need to measure d.c. Amperes. Many meters show the d.c. ranges with a = symbol. Always set the range to a higher one than you are going to measure. Check that if your meter has sockets which the test leads plug into, these are in the COMMON (black lead) and the I (red lead). Ensure that you connect the meter leads in series with the battery - see Page 14. Reconnect the test leads to measure Voltage and change the selector to d.c. volts after making your measurement. This avoids damaging the meter if you subsequently use it to measure volts.

    Unless you are a qualified electrician I would suggest that you do not attempt to measure a.c. current drawn by 240 Volt appliances. For a.c measurements the procedure is the same as above, but set to a ~ range.

    Measuring Resistance

    This is useful for checking fuses and filament lamps. With the test leads in the common and V and R sockets select a low resistance range, then touch the test leads together. The meter should read 0 Ohms. Now put the test leads across the fuse, again the meter should read 0 Ohms. Select a d.c. volts range when you have finished.

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  • Glossary of Terms Amp abbreviation for Ampere (A) which is a measure of the current flowing Page 2,3,14 down a wire Battery often refers to the Leisure Battery which is a specialised 12 Volt battery Page 2,4,5,13,14 designed for use in caravans Breaker a device which breaks (switches off) the supply to an appliance. See ELCB Page 4,10,11,12 and MCB Charger battery charger which charges the leisure battery, can also power the 12 Page 10,11 Volt appliances in the caravan Consumer Unit called different names by some caravan manufacturers. The unit contains Page 11 the 240 Volt mains earth leakage and over current circuit breakers, together with fuses. The fuses are often for the 12 Volt appliances Double an appliance not having a connection to the earth wire. Such appliances Insulated only have two wires and are specially designed so that live parts can Page 12 never be touched by he user ELCB Earth Leakage Current Breaker often referred to a RCD (residual current Page 11 device). This is a safety device which detects if current is flowing to earth. Once this exceeds 30mA (0.03 A) the supply is switched off. Fridge abbreviation for refrigerator. Many models can be powered by bottled Page 12 gas, 240 V electricity or 12 V supply from the tow car (only when the engine is running) Fuse a safety device that consists of a fine piece of wire inside a plastic or glass Page 4 holder. If the rated current is exceeded for a short time the wire melts, breaks the circuit and prevents excessive current from being drawn. Heater built in heaters which are powered by bottled gas. Some caravans have central heating, using radiators or under floor pipes. Hook up refers to the connection that can be made between the caravan and a Page 10,12,15 240 V socket mounted on a pole. The pole usually has a earth leakage and over current circuit breakers. Although the round sockets used are rated at 16A, frequently you can only draw 10 A or in some cases only 5 A before the over current trip operates

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  • Glossary of Terms Igniters a spark generator inside a gas burner used to ignite the gas flame MCB Miniature Circuit Breaker. See also Circuit Breaker Page 4,10,11,12

    Ohms Law the law which relates voltage, current and resistance to each other Page 3

    Circuit Breaker a safely device that isolates a circuit from its supply if an excessive Page 4,10,11,12 amount of current is drawn. Often referred to as an MCB (miniature circuit breaker) Power the amount of energy a appliance uses, normally measured in Watts Page 3,6

    RCD Residual Current Device. See ELCB Page 11

    Resistance the resistance of an appliance determines how much current flows into Page 3,4,6 that appliance when a given voltage is applied. See Ohms Law Switch a device that isolates electricity from an appliance. For example a light Page 2,3,4 switch. Tow Bar refers to the 13 pin socket mounted close to the tow bar ball. Earlier Electrics models use 12N and 12S sockets Page 8,9

    Trip refers to a earth leakage or over current trip. See also ELCB and Over Page 4,10,11,12 Current Trip. When a RCD or MCB operates isolating that circuit, it is referred to as tripping. Hence the name trip. Volt a measure of the voltage or potential that a electrical supply has. For Page 2,3,4,5,9 example 12 V Watt a measure of the amount of power a appliance is drawing from its supply. Page 3,6 Can be calculated by multiplying the voltage (in Volts) by the current (in Amps) to give the power in Watts.

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    Malcolms All You Need to Know about Caravan Electrics

  • References and further reading

    22

    Malcolms All You Need to Know about Caravan Electrics

  • Index

    23

    Malcolms All You Need to Know about Caravan Electrics

    P

    Power 3, 6

    R RCD 11 Resistance 3, 4, 6,

    S Switch 2, 3, 4,

    T Trip 4, 10, 11, 12

    V Volt 2, 3, 4, 5, 9

    W Watt 3, 6

    A a.c. 5, 6, 7, 11, 12, 15, 18 Amp 2, 3, 14 Ampere Hour 2, 4, 13, 14

    B Battery 2, 4, 5, 8, 13, 14

    C Charger 10, 11 Consumer Unit 11

    E ELCB 11

    F Fault Finding road lights 9 Fault Finding 12 V Internal 10 Fault Finding 240V 12 Fuse 4

    H

    Hook up 10, 12, 15

    M MCB 4, 10, 11, 12

    O

    Ohms Law 3 Over Current Trip 4, 10, 11, 12

  • Notes on sources of current drain from Leisure Batteries From phone call from Robert Wilson of Kenmore caravans Kenmore have stopped selling gell cell batteriestoo expensive and customers expect them to last forever Kenmore attached date label to batteries at point of sale to avoid augments about the age of the battery. Owners usually loose the receipt and say that the battery is only a couple of years old, when it is often 4 years old, or more Robert has found that the current drain, in magnitude is Fridge Radio with security cover, draws 30mA, drops to 8mM with cover removed Status TV pre amp, if not switched through master switch Master switch controls relays which draw current all the time the switch is on Obviously alarm and tracker as well, where fitted Odds & Bods notes Lampthermal inertial of filament prevents flickering, fluorescent tubes can be seen to flicker. Reference is Wikipedia.org/wiki/hertz

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