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<ul><li><p>Malcolms </p><p>ALL YOU NEED TO KNOW </p><p>about Caravan Electrics </p><p> Written by </p><p>Malcolm Keen </p><p>Keen Electronics Limited </p><p> </p><p> 2012 Keen Electronics Limited </p></li><li><p>Contents Foreword .. 1 Introduction ... 1 </p><p> 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 </p><p> 12 Volt Internal Lighting &amp; Equipment . 10 Fault Finding 10 </p><p> 240 Volt Electrical Equipment ... 11 Fault Finding ... 12 Leisure Batteries .. 13 Fault Finding ... 14 Measuring current drain 14 </p><p> 240 Volt Safety notes ... 15 </p><p> Useful Information </p><p> 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 </p><p> Glossary of Terms .... 20 </p><p> References and further reading .. 22 </p><p>Malcolms All You Need to Know about Caravan Electrics </p></li><li><p>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. </p><p>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. </p><p>1 </p><p>Malcolms All You Need to Know about Caravan Electrics </p></li><li><p> 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 </p><p> 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. </p><p>2 </p><p>Malcolms All You Need to Know about Caravan Electrics </p></li><li><p> 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 </p><p>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. </p><p>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. </p><p>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. </p><p>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:- </p><p> Power (P) = Volts x Amperes = 12 x 2 = 24 Watts </p><p>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. </p><p> 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 </p><p>3 </p><p>Malcolms All You Need to Know about Caravan Electrics </p></li><li><p> Basic Electrical Theory </p><p>Diagram showing 12V battery feeding 24 Watt lamp Battery Capacity </p><p>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) </p><p>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. </p><p>Fuses </p><p>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. </p><p>4 </p><p>Malcolms All You Need to Know about Caravan Electrics </p></li><li><p> Basic Electrical Theory The Difference between a.c. and d.c. </p><p>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:- </p><p>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:- </p><p> Diagram showing a.c Voltage with time </p><p>5 </p><p>Malcolms All You Need to Know about Caravan Electrics </p></li><li><p> 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. </p><p>6 </p><p>Malcolms All You Need to Know about Caravan Electrics </p></li><li><p> 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. </p><p>7 </p><p>Malcolms All You Need to Know about Caravan Electrics </p></li><li><p>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 an...</p></li></ul>