Motorhome Electrics Book

Preface

Caravan, campervan and motorhome electrical systems are put together from mostly standard vehicle components designed for a substantially different purpose - to provide electricity for moving vehicles - not for those at rest.

As a direct result, such systems lack energy production and storage for more than a night or two. Using the electrical system beyond this time overly-discharges the batteries, seriously reducing their life and capacity, especially with vehicles in irregular use.

A further and major problem is the lack of competent service. Auto-electrician training does not include solar systems. Solar-system training does not cover vehicle charging systems. But in recreational vehicles, these systems often interact and, as any number of unhappy owners will assert, it is difficult to find anyone who can rectify the (often quite simple) cause of subsequent electrical problems.

Appendix 1 lists two small (WA) companies that have expertise in this field. Future editions will list further such organisations: the author would be grateful for feedback.

Similar problems afflict cruising yachts, but the level of awareness and expertise is higher in the associated industries. Many marine electricians have bridged the knowledge gap between alternator charging systems and other sources of energy. It is worth seeking assistance from them for complex electrical problems.

Chapter 1 - Basic Electrics

Introduction - Given sufficient incentive, electrons will flow through conductive materials such as a copper wire. Incentive may be chemical (a dry battery); the effect of sunlight upon a form of silicon (solar cell); a coil of wire moving in a magnetic field (alternator); or even squeezing certain pieces of quartz (stove lighters)….
Electron flow - …electron flow starts ands stops at the speed of light [but] individual electrons move only a few centimeters each minute…
AC/DC - With direct current, electrons move in one direction only - their action is a bit like a band saw in that work is performed by movement in one direction only. Alternating current is…
Resistance - Can be useful and its effect is exploited in heaters and light globes - but resistance is mostly undesirable - especially in 12 and 24 volt systems…
Energy and power - Energy is a measure of the ability to perform work. Power (measured in watts) is the rate at which energy is generated or used.
Watts - Enable decisions to be made without continually specifying voltage and current…
Watt confusion - Whilst invaluable, the term ‘watts’ can confuse. Microwave ovens (and electric motors) are rated in terms of the work they do - not the energy they use. Each typically uses twice the rated wattage…
Power factor - Mains and inverter powered appliances may require 20%-30% more power to be available than they actually use...
Voltage, current and resistance - Their simple inter-relationship is the key to understanding electrical systems…

Chapter 2 - The Problems Outlined
Charging - … by imposing the alternator’s voltage across the battery. The greater the difference between alternator voltage and the battery voltage the greater the rate of charge. A standard voltage regulator prevents overcharging but also prevents batteries from attaining full charge…
Battery limitations - Lead-acid battery life is directly related to the state of charge (the higher the better); and the depth of discharge (the most economic being 50% of nominal capacity). The energy available for use is thus…
Solar woes - Most [solar] modules produce less than 70% of the energy that many people thought they’d bought. Here’s why…
Microwave ovens - Use more energy than generally realised but are rarely suspected because…
Cable size errors - Nominal sizes may seriously mislead. Cable marketed as ‘4.00 mm’ may be of that overall diameter, not of 4.0 mm.sq. conductor size as intended to be used. This and other concerns explained…
Fundamental causes - Systems run out of energy, and batteries prematurely fail because…
Practicable solutions - Solving the problems variously or collectively enable:

A large battery bank to be charged in a few hours
Almost doubling usable battery capacity
Dramatically extended battery life
The ability to stay indefinitely on solar power
Having fully-charged batteries at most times
Optimising solar module usage
Reducing consumption via efficient appliances
My own vehicle has been doing all of this, with little attention, since 1996.

Chapter 3 - Alternators
Dynamo/Alternators - A 140 amp dynamo was the size of a four-litre gas bottle. It became essential to develop a more efficient device…
Alternating current output - Batteries store direct current so the alternator output is…
Controlling output - Obtaining adequate output at low engine speed, and limiting output at high…
Charging limitations - An associated regulator causes the alternator to maintain a constant voltage output - thus a higher output alternator may charge flat batteries faster but it cannot…
Hot-rated alternators - Able to run at their rated output (instead of the 70% or so of standard alternators)…

Separate (charging) systems - There’s a lot to be said for a second alternator, regulator and batteries used solely for the vehicle’s ‘house’ system…
Future systems - …a gradual change to 42-volt alternators charging 36-volt batteries. By 2012 this will be a different book - but in the meantime…

Chapter 4 - Voltage Regulators
Overview - The regulator totally controls the alternator’s output and ensures that batteries are not charged beyond 70%…
An inherent limitation - A standard voltage regulated system cannot and does not charge batteries to an adequate level for recreational vehicle use…
Regulator modification/change - Altering or overriding the regulator’s decisions can change the charging regime into one better suited. Three step (smart) regulators do just that…
Three-step regulators - A resume of what’s available and how they work…
Connecting a three-step regulator - Installation may consist only of running a few cables - others may need a minor cable change within the alternator. It’s best to upgrade the alternator anyway…
Isolating diodes - A new approach…
Emergency repair - How to get home if the regulator fails…
Caution - Never disconnect an alternator whilst the engine is running - here’s why….

Chapter 5 - Conventional Batteries
Overview - All lead-acid batteries work in much the same way - none stores energy as electricity per se….
Construction - There are three main types of commonly-used lead-acid batteries. Each best suits its intended usage, and is constructed accordingly…

Battery charging - Lead-acid batteries prefer to stay fully charged - compromise is necessary…
Standard charging system - The ‘standard’ charging system is the simplest, but a long way from the best. With such systems, deep-cycle batteries are never adequately charged…
Desirable charging - One of the best ways to charge a battery is that used by quality solar regulators and smart regulators. Phases include ‘initial bulk charge’, ‘absorption’, ‘floating’, and occasional ‘equalisation…
Charging efficiency - The overall charging process is 85%-90% efficient so….
Starter batteries - Provide heavy current but for a very short time. Energy draw may be less than 3% of the battery’s capacity…
Deep-cycle batteries - Inherently rugged construction enables repeated discharge (to 50% or so). If the system has been correctly designed, these batteries win hands down. Otherwise…
Marine batteries - Little point in using them except in boats…
Golf cart/traction batteries - A good buy unless you can afford top quality deep-cycle batteries and maintain them properly…
Maintenance-free batteries - work best in cold climates…
Defining battery capacity - starter and deep-cycle battery performance is each described in different ways…
Cold cranking amps (CCA) - There are several ways of defining [CCA] but all measure the current sustainable….
Reserve capacity - The time that a full-charged battery can be discharged at 25 amps before…
How many CCA? - In warmish countries a petrol engine needs about 80-90 CCA/litre. Diesel engines need….
Deep-cycle battery ratings - How much energy the battery can store and release…
Battery charge & life - Battery life is closely related to the depth of regular charging and discharging. By increasing the former, and decreasing the latter battery life can be dramatically extended…
Checking battery condition - Quick and simple test gives useful approximation…
Battery capacity and age - Usable capacity falls at a rate that is mainly related to maintenance and usage - rather than actual age…
Battery capacity & temperature - the warmer it is, the shorter its life…
Battery capacity - Needs to be scaled to match available charging capacity as well as intended usage…
Self-discharge - Starter batteries can lose up to 20% of their charge each week. Deep-cycle batteries may lose… How floating a battery extends its life etc…
Undercharging - Most batteries die because the charge/discharge cycle causes active plate material to be shed. A sure sign of excess shedding is….
Overcharging - Rare - but it happens, particularly when….
Sulphation - Sulphur combines with the lead… can sometimes be restored by….
Pulsing - Recent developments claim to prevent and even reverse sulphation - these claims are….
Battery additives - Better to keep the batteries charged….
Water loss - Correctly charged batteries should lose some water. How much is….
Recombinant caps - best avoided in mobile usages…
Safety - Batteries must be treated with respect. Wear a face shield or at least goggles…a dropped spanner can cause thousands of amps to….
Battery configurations - Connecting for various voltages and currents: some ways are better than others. An absolute no no is…
Twelve or 24 volts? - The higher the voltage, the smaller the cables required…
Voltage conversion - How to run 12 volt things from a 24 volt system…

Chapter 6 - Specialised Batteries
Sealed batteries - an overview….
Gelled electrolyte - …the battery maintains an internal pressure that is critical for its operation…
Charging gel cell batteries - Will accept an initial charge as high as 320 amps for an 80 Ah. battery!…
Self-discharge [of gel cells] - Well under 1% a month in temperate climates but…
Recharging a flat gel cell - Can sulk like teenagers, but there are ways and means…
Absorbed glass mat batteries (AGMs) - Extremely rugged. Charge faster and more deeply than conventional batteries from a standard vehicle system…
AGMs: their life span - Theoretically less than a properly maintained lead-acid battery. But in practice…
Pros and cons of sealed batteries generally - Faster and deeper charging from conventional sources, better withstand deep discharges. But larger, heavier, more…
Nickel-cadmium batteries - Excellent choice but their cost excludes them except for the truly rich….

Chapter 7 - Battery Monitoring
Voltage measurement rarely works - A flat battery may present as fully charged after a few seconds on a fast charger. A fully charged battery may present as virtually flat if… Batteries must be rested for a long time before a voltage measurement…
Energy monitoring - Measures what goes in, what comes out, deducts one from the other and subtracts system losses, then displays…
Rough and dirty guides to charge and discharge - Only approximate, but better than not knowing at all…
Hydrometer readings - Messy, but the only way to check individual cells…

Chapter 8 - The Ability to Restart
Unsuspected traps - Traditional manual or even solenoid switching can still leave you with flat batteries…
Voltage-sensed switching - Delays charging the house battery until the starter battery is adequately recharged…
Choosing and mounting solenoids - Capacity varies with usage. There are also big variations in quality. Mounting the right way up is not obvious…
Diode isolation - An old but reliable system now regaining favour because recent developments enable…

Chapter 9 - Solar Energy
How much energy? - Despite inefficiencies there’s enough to be useful…
Module output - Solar modules only produce their claimed output in certain applications and exceptional operating conditions. These do not usually include 12 and 24-volt systems. Here’s what they really produce in…
Temperature matters - Most modules lose about 0.5% of their output for every 1 degree C temperature rise. At 30 degrees C this may be up over 13%…
Self-regulating modules - To describe most of these as ‘self-regulating’ is like describing a starving person as being on a ‘self-regulating’ diet…
Interconnection - How to connect modules for increased voltage, increased current - or both…
Module output and location - Output varies with location and season but readily obtainable sun/hour maps enable output to be….
Housing modules (fixed or portable) - Pros and cons of each…
Module orientation - Mounting them flat is surprisingly effective. Usually cheaper and simpler to add a little more capacity than…
Isolating diodes - Their losses may exceed any gain…
How many modules? - Full worked details of assessing…
How much battery capacity? - Nominal battery capacity is best limited to …

Module life - Ironically, solar cells degrade in sunlight...
Measuring module output - Connecting an ammeter directly across the module, - but not advisable with large arrays because….
Module failure - Most apparent failures are traceable to broken external leads or faulty connections…
Solar regulators - Their types and the need to use them. Programming is not hard but…
Remote readout - Some enable the readout to be located well away from the rest of the system…
Buying a regulator - Better to spend a bit more - the more costly regulators have all-but essential facilities including extensive monitoring…
Series/shunt regulators - The correct type must be used….
Paralleling charge sources - There can be unexpected bonuses - but also unexpected traps. It’s often best to isolate….
Installing a solar regulator - Generally straightforward….

Chapter 10 - Wind Power Generators
Where effective - Output usefully begins at winds above 15 km/hr. Installing to work well and safely is no trivial matter…
Wind run - Calculating the most likely output. Also simple and cheap (<50 cents) way of checking wind speed...
Propeller braking - Mechanical braking is essential to safeguard…
Shunt regulation - Dumps excess power into a resistance bank. Provides some automatic braking…
Evaluating and buying - Lack of performance standards necessitates careful evaluation. Here’s what to check….

Chapter 11 - Generators
AC/DC generators - Available from 150-5000 watts but many unacceptably noisy, and banned in National Parks and many private sites….
Output ratings - Few can maintain peak output for more than a few minutes - but most are rated as if they could…
DC output - Some generators have an additional 12-volt output - this may be too low for battery charging. The solution is to…
Motor-generators - Big (3-7 kVA) generators mostly installed in large motorhomes. Unless backed up by batteries and inverters, must be run even for minor loads…
Frequency accuracy and stability - Most are adjustable. Here’s a simple way to tell if all’s correct...
Quietening small generators - readily done, but the traditional box lined with egg cartons is close to useless…
Building your own - a few useful pointers…

Chapter 12 - Inverters
Inverter sizing - Buying a larger inverter than you think you need is not necessarily the best approach…
Minimum power settings - The size of load that causes an inverter to automatically switch on/off is pre-settable….
Phantom loads - Many appliances continue to draw power when switched off - these ‘phantom loads’ may cause an inverter to remain operating when nothing else is running…
Assessing the needs - Total only things that really will be on simultaneously, ignoring such…
Electric motors - Inverter sizing may need rethinking if you run anything with an induction motor. These motors…
Paralleling inverters - Some inverters may be paralleled for increasing output - but…
Inverter warning - Many cheap imported inverters are incompatible with… They may be used… but must not be connected into the main wiring system…
Safety - While in standby mode the network may appear dead when checked with a meter, but becomes alive when touched…

Chapter 13 - Lighting
Efficiency - For similar output, some lights draw four times as much energy as others….
Fluorescent - Made in a wide range of wattage, size and colour temperature, these tubes and globes….
Halogen - Twice as efficient as incandescent globes … all produce a lot of ultra-violet so it’s best to….

Chapter 14 - Refrigeration
Absorption cycle refrigerators - Relying on external heat, this type may be run from a gas flame or an electric element…early examples were marginal in tropical areas but later ones are…
Compression cycle refrigerators - those made for recreational vehicles use dc-operated compressors and may be run from solar energy…
Electric only - or three-way (gas 12/240 volt) - An energy efficient 12 or 24 volt compressor driven fridge is probably the….
Top versus door opening - Top opening refrigerators are inherently more efficient but can be….
Cyclic operation - Refrigerators cycle in a typically 40:60 on/off ratio. Energy consumption may vary...
Freezers - Use several times the energy of a fridge - mostly because of insulation losses. It is essential to locate them so that…

Chapter 15 - Water Pumps
Pump ratings - The wattage rating of a pump motor is a measure of the work it does- not the energy…
Pump types - Diaphragm pumps are more costly, have more moving parts. They are generally more efficient, are self-priming and not damaged by….
Turning them on and off - Pressure fall is detected by a switch that starts the pump. The pump is turned off when pressure in the line…
Accumulator tanks - Reduce pump operations and smooth water flow…
System installation - Start-up currents are high so cable needs to be heavier than…
Pipe friction - A pipe’s resistance to liquid flow is awesome! Flowing liquids also dislike sharp…

Chapter 16 - Electric Toilets
Most problems are caused by the macerator having inadequate cabling or by…

Chapter 17 - TV Antennas & Cables
Practical TV antennas - Are an inevitable compromise between size, signal gaining ability, the need to be pointed directly at the transmitting….
VHF/UHF - Regional areas use smaller transmitters at UHF frequencies - with a good antenna, signals can be received 70 -100 km away. Small country towns have….
Antenna types - A lot is known about them but because of sometimes jumbled signal patterns, there’s also an element of chance. This can mislead people about the virtues of specific antennas. Look for an antenna that….
Connecting the antenna - Connect via the shortest possible path using low-loss cable….
Antenna (masthead) amplifiers - Do not attract a stronger signal, but increase the level of what’s already there. They are effective in…
Satellite TV - A 900 mm (or preferably 1200 mm) dish will provide good signals in clear sky conditions, but signals…
Television receivers - Need to be sprung mounted, or bolted rigidly in place (like car batteries they will not withstand…

Chapter 18 - Communications
Overview - Cellular telephone systems provide good coverage in terms of population, but not geographical area. Coverage is thus good in…
HF radio - Based on a long-outdated technology that precludes further development, but has romantic appeal. There are however better….
Installing HF radio - Antenna cables must be kept away from power cables, and particularly electric brake leads. Incoming signals are only millionths of a volt so correct antenna and…
HF antennas - Either manually tuned (which involves getting out of the vehicle to do it), or automatically tunes (which doesn’t). The tuner unit is…
Satellite telephone/fax - Vehicle-mounted installations use either a whip antenna, or an active dome-shaped antenna that searches for the satellite… require less transmitted satellite power and thus call charges may be….
Email - Email can be sent from laptops and small hand-held devices. No special requirements for installation but some laptops will not run from….
Future systems - Multiple low-orbiting satellites will interface and interact with cellular systems to provide both local and global coverage…

Chapter 19 - Electrical & Radio Interference
Petrol engines - Noise mostly originates from excess sparking voltage caused by wrong or…
Coil polarity - Correctly polarised, 15,000 - 20,000 volts is needed for a spark to… But up to 10,000 volts more if incorrect. This is a major cause of RFI…
Diesel & petrol - A common problem is RFI radiated from the cable between the tachometer and the…. A whine that varies pitch with engine speed is caused by….
General - Twelve/24 volt electric motors (e.g. windscreen wiper motors) can be quietened by…

Chapter 20 - Lightning Protection
The risk - The chances of being struck by lightning are generally very small, but lightning can be intense, so some people may feel safer if…
Faraday cage - Metal-bodied vehicles provide excellent protection by acting as a ‘Faraday cage’, Electrical discharges are conducted to earth via…
Fibreglass bodies - Can be protected via a conventional lightning conductor with the spike….this provides a zone of protection which at ground level is about the height…
Lightning conduction - Tyres act as partial insulators. The vehicle must not be earthed directly if there is a mains connection…

Chapter 21 - The ‘House’ System
What’s practicable - and what’s not - Away from mains voltage, electrical usage needs to be limited to … it is not practicable to run anything from solar energy that generates or transfers heat as its main…
Extra-low voltage - or mostly mains? - Using mains voltage (via batteries and inverter) provides a wider choice of often-better and cheaper appliances, Bottled gas should be used for….
Water pumps - Mains powered pumps draw too much…

Chapter 22 - Suggested Solutions
Overview - It is totally feasible to have a reliable and effective electrical system that supplies a realistic amount of power when you need it, and for as long as you need it. It is equally feasible to do so, and have house batteries that live from four to seven years…
Various solutions - The size of the system is rarely an issue - it is primarily the pattern of usage that determines what needs to be done…
Identifying the usage - Several types of usage that may overlap. Identify the closest to the following and….
Fixing the problems - The first and essential concern is obvious - it’s ensuring that batteries are full-charged and floated across a suitable supply at all times when...charging may be done by…
Energy on site - Use solar or other supplementary energy to partially supplement…or generate all that’s required so that the system is…
Electrical self-sufficiency - Such usage also hugely extends battery life…
Charging and battery alternatives - An alternative is to stay with the original charging system and to use gel cell or AGM…
Duplicating the system - An excellent approach is to leave the existing vehicle system untouched, and to install….
Campervans & commuting - Driving does not charge deep-cycle batteries sufficiently to prevent sulphation. This is less of a…
Module capacity - Do not be concerned about large solar arrays overcharging …solar regulators will ensure…
Computer-engine management systems - May preclude using smart (three-step) regulators because….
The energy required - The consumption of a wide range of electrical appliances.
Scaling the system - Estimating solar capacity required…
Battery capacity - The golden rule…
Sun hours - Energy input depends on sun/hours per day. Here’s how to know…

Chapter 23 - Extra-Low Voltage Wiring
Concerns - The main risk is of live conductors shorting with resultant cable overheating and burning…this risk is increased with…
Circuit breakers - Circuit breakers and fuses have specific roles but to cut costs some manufacturers use….
Fuses - Protect appliances rather than cables….
The wiring layout - Individual needs vary but most recreational vehicles will be generally similar to…
Cable runs - All extra-low cable runs must be kept….
Power posts - Cable runs can often be optimised or shortened by using common terminating points called….
Connector boxes - Enable cables to be paralleled. They are made to be accommodate…
Inverter feeds - Even small microwave ovens draw in excess of 150 amps…
Solar feed - Paralleled modules are best connected by running individual cables to a common…
Winch solenoid - Needs to be able to handle 200-300 amps…
Separated wiring -= Extra-low voltage cable should be run physically separate from mains cabling. In many countries this is legally required…
PVC/polystyrene a risk - PVC cable used in early caravans and motorhomes is destroyed by interaction with polystyrene insulation. Such cable must be replaced…
Cable sizing - Inadequate cable size is a major problem with many installations. The cause is due to…
Earth return - Using the chassis as a common negative lead saves cable costs but…
Wire gauges - A very real trap…
Nominal cable sizes - Cable is often sold as ‘10 amp’, ’15 amp’ etc. This is only how much current it can carry before it overheats. These ratings do not relate to voltage drop and are thus seriously misleading…
Tinned copper cable - Well worth using if close to the sea etc….
Crimp connectors - Cheap, simple and universally used - but the source of ongoing future problems if not correctly sized…
Soldering connections - This is one of those things that seems a good idea but isn’t…
Plugs and sockets - Cigarette lighter plugs and sockets lack mechanical locking. Over time…
Extra-low voltage switches - In practice mains-switches can be used if current…
Switch and meter panels - Use a separate removable panel because…

Chapter 24 - Measuring Voltage Drop
Overview - Avoid wasting energy and poorly working appliances because of voltage drop - here’s how to ensure all is well…
Solar - You are looking for no more than 0.36-volt difference between…
Specific cables and connections - Checking individual areas and components…

Chapter 25 - Mains Voltage Wiring
Unusual risks - Recreational vehicles are exposed to potentially dangerous conditions that are less likely in fixed premises - requirements are more stringent and have changed in recent years…
Power into the vehicle - Caravan parks are legally required to have…
Connecting cables - Regulations vary from country to country but most…
Polarity - A possible hazard is…
Residual current detection - Continuously checks the current flowing in the active and neutral lines are equal, that none is leaking to earth. If there is a leak…
Earth and neutral linking - Vital that this is done as specified - but practices vary from country to country. New Zealand and Australia for example each use a quite different method…
Inverters and RCDs - Many cheap inverters will not operate with residual current protection in place. They must not be wired into…
Change-over switches - Protect electricity workers against the output of a generator or inverter being accidentally switched across networks believed to be ‘dead’…
Cable protection - Mains cabling must be…
Certification - On completing installation, a licensed electrician issues a….
Updating installations - Electrical installation requirements are now more rigid. Very few pre mid-1995 vehicles comply. Have the wiring checked by a licensed electrician and update…
Exceeding requirements - Regulations specify only the minimum requirements - there’s a good case for exceeding…

Chapter 26 - Particularly Caravans
Delusions of adequacy - In many caravans, both cabling and connectors are almost ludicrously deficient…the problems start right here…

Checking the system - How to tell if cabling is inadequate (in caravans, it usually is!)….
Towing vehicle wiring - This too is often inadequate…
Caravan/trailer connectors - Lack of worldwide standards complicates….

Chapter 27 - Electric Brakes
Overview - How they work.
Wiring - Most brake controllers have four coloured leads - these are connected…
Braking problems - Problems are usually caused by intermittent current flow, or excess voltage drop introduced by…
Random operation - This is usually caused by…

Chapter 28 - Building Your Own
Overview - This chapter is intended as a general guide for readers with a fair background in electronics…it outlines how to build…
The working environment - A motor vehicle is a harsh electrical environment… voltage varies from…
Voltage controllers - Alternator output can be overridden by replacing … here’s how to do it for a fraction of the cost…
Variable voltage supply - General purpose circuits…

Chapter 29 - Building Your Own Refrigerator
Refrigeration basics - Heat ain’t necessarily heat!…
Heat quantity - To know the amount of heat energy we must know three things about…
Insulation is vital - Knowing what to do about it helps you build a refrigerator that is a lot more efficient than most…
Shape matters - The further away from a cube…
Construction - The compressor system can be installed remotely from the storage area…
The end result - It is feasible to build a refrigerator that uses 50%-60% of the energy of most…

Chapter 30 - Frequently asked questions
‘Can I run a three-way fridge on solar panels?’. ‘Do Uni-Solar panels really produce more than most others?’ ‘Do microwave ovens really draw twice what people think?’ ‘Why do I keep burning out halogen globes?’ Are deep-cycle batteries worth buying?’ ‘Do three-step regulators overcharge batteries?’ ‘Why will my small generator not charge my batteries?’ ‘Why do I keep blowing fuses?’ Why do I burn out solenoids?’ ‘Are AGM batteries worth buying?’ ‘Is it OK to parallel batteries?’

Appendix 1
Contact Listings

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