installationAutoelectrical Installation

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Specialised Onboard Power systems

for Service Van, HGV truck, Motorhome, Caravan, Camper van, Ambulance, Catering Trailer,4x4,Utility Vehicles, Canal boats, Marine.

Mobile Autoelectrical Installation Service - Shropshire

available in Shropshire & Mid Wales areas.

Vehicle Onboard Power Supplies enabling use of 240 volts ac (uk mains voltage), or 110v ac electrical equipment may be required on many types of vehicles including

  • Leisure vehicles
  • Vehicle conversions with living quarters such as Motor home, Caravan, Camper van.

  • Utility Service Vehicle Conversions
  • where a panel van , 4x4 or truck has been modified for specialist utility service or local authority use inverter1.jpg
    Portable tools for site work ,eg drills, grinders, saws, electrofusion welders, etc often operate at 110 volts or 240 volts.

  • Mobile Workshop Fleet Service Breakdown Vans
  • Good lighting and power supply is essential in fleet support vehicles where breakdowns may be carried out at night. Onboard mobile welding systems are available from some suppliers.

  • Catering Vehicles
  • Ice cream vans, mobile kitchens, operating fridges , freezers, ovens, and fryers from a 240v supply.

  • Mobile Exhibition display vehicles
  • Mobile shops and library vans which require 240v interior lighting and 240v electrical services. 240v power may be required to operate a computer for stock control or invoicing, and extra display lighting.

  • Ambulances
  • Where 240 volt medical equipment, monitoring, oxygen compressor and lighting equipment

  • Marine craft
  • Canal barges, Sailing yachts and motor boats with living accomodation have used auxilliary onboard power systems for many years. An excellent reference book is Payne,J.(2007) Marine Electrical and Electronics Bible.

    Vehicle Charging System Voltage

    Automotive battery systems recharged by a standard alternator operate at either 12 volts system DC (charging voltage approx 13v to 14.8v) or 24 volts system DC (charging voltage 28v). A newer design vehicle 'Smart alternator' may have the alternator voltage regulator monitored and operated by an external control unit such as the Powertrain control module (PCM).
    UK domestic appliances operate at 230-240 volts AC mains.

    Various power supply systems exist to provide 110v or 240v AC onboard power depending on application and requirement.

    External Power Supply whilst Vehicle Stationary

    A suitable power source can be supplied while stationary from :

  • Mains "hookup" cable
  • Direct from 240v power supply via BS4343 blue plug via Residual Current Device (RCD)

  • Engine driven generator
  • A seperate portable generator may be used, or a vehicle engine driven generator which may be mounted to vehicle, vehicle engine or fitted in driveline and pto shaft driven

  • DC to AC Power Inverter
  • Power Inverters convert  existing vehicle system electrical power (12v or 24v) from batteries as DC input to the required current and voltage output at 240v AC or 110v AC.

    The Inverter output may be:
    Pure Sine Wave (more expensive type used where sensitive electronic equipment is fitted)
    Modified Sine Wave(cheaper type).

    Inverter units may be parallel linked to achieve larger power output or a dynamic inverter system used.

    Inverter - DC Input Power Supply

    A "leisure" or "domestic" (deep cycle) battery bank is often used as the 12v or 24v power source to supply the inverter system.

    The main advantage of an Inverter power supply is quiet operation.
    Disadvantages include efficency losses and heat output depending on load.
    Care must be taken when mounting a power inverter to position where it is:

  • Dry
  • Adequately Ventilated
  • Secure and Vibration free
  • Extension Cabling

    Additional wiring from an inverter to 240v power sockets etc, for example extension cabling may require testing for (currently 18th edition) wiring regulation compliance.

    An inverter may draw large amounts of current (Amps) from the supply battery during use depending upon load.

    The current (A) drawn from the supply battery will lower battery voltage. When battery voltage is reduced below a set point the inverter will probably no longer function and cut out resulting in loss of output.

    Auxilliary Battery Capacity

    The ability of the inverter to operate relies upon reserve battery capacity at suitable voltage level.

    The type, size and number of vehicle batteries used to supply the inverter will determine reserve capacity.

    Cabling to Inverter

    12 volt DC to AC Inverters can draw large amounts of current from vehicle batteries and depending on type will require heavy duty battery cable to carry the power supply

    Auxilliary Batteries

    Various types of battery may be used to provide power supply to an inverter.

    Lead Acid Battery

    Has advantages of relatively low cost but generally designed for short duration high current output during vehicle starting. Major disadvantages include

  • weight
  • potential leakage of battery acid
  • emit hydrogen (potentially explosive gas) whilst charging therefore adequate ventilation is required.
  • Slow recharge period compared to other battery types.
  • May require special battery charge controller if used with vehicles fitted with an ECU controlled alternator

    Standard Leisure Battery

    Designed for slower discharge over a longer period of time. Still has weight disadvantage.

    Lithium Iron Phosphate Battery

    Lithium Iron Phosphate (LiFePO4) batteries have become increasingly popular as power sources for inverter but may require specialised charging system.
    Lithium Iron Phosphate batteries have the main advantages of

  • Weight reduction compared to Lead acid type
  • Short Recharge time compared to Lead Acid Battery
  • Can be used as a Starter Battery
  • .

    Major disadvantage is higher initial cost of battery pack.

    Leisure Battery Charging from vehicle power source

    The vehicle's alternator may be used to recharge both starter battery and leisure battery by use of a split charge relay or battery management system which allows switching between battery banks.

    The vehicle can be fitted with more than one alternator, for example no.1 alternator to charge the starter battery and no.2 alternator to charge the leisure battery or both linked to provide greater output capacity.

    Split Charge Systems for Seperate Battery Banks

    A split charge system separates vehicle starter and leisure battery until  the vehicle engine has started then connects to link both battery banks.
    This prevents the inverter system discharging starter and leisure batteries to a level at which starter motor operation fails rendering the vehicle immobile.

    Split charging system using a Heavy Duty Voltage Sensitive Relay (VSR)

    Additional batteries may be linked via cable to the starter battery by use of heavy duty voltage sensitive solenoid relay (VSR).
    Use of a VSR allows priority charging of starter battery which must reach a preset voltage level before the leisure battery is connected to the charging system only when the engine is running and alternator charging.
    A VSR reduces the risk of discharging the starter battery to a level at which the vehicle is immobilised.
    VSR type split charge systems may unsuitable for fitment to modern vehicles fitted with Silver-Calcium type starter batteries and 'Smart Alternator' systems (since about 2007) due to powertrain control module communications with alternator voltage regulator which may allow the alternator on a 12v system to apply up to 18v output. A dedicated battery to battery charger is a recommended alternative.

    Secondary battery charging using splitter diodes

    This method uses a heavy duty diode fitted in the link wire between starter battery and leisure battery pack. The diode acts as a one way valve to allow current to pass from the starter battery to the leisure battery whilst the starter battery is at a higher voltage potential than the leisure battery allowing rechargeing. The diode blocks current from being drawn from the leisure battery when the starter motor is operated to protect cabling. This system has a disadvantage of power losses due to diode characteristics and not suitable for use with Smart charge systems.

    Secondary battery charging using DC to DC battery charger

    This preferred method uses a special battery charger to regulate charging voltage and current between battery banks. Use of a DC to Dc battery charger can provide a method of charging auxiliary 12 volt batteries from a vehicle with 24 volt charging system.

    Secondary battery used to provide cold start assistance

    Provided the connecting cables and relays are specified to carry high starter motor current draw the secondary battery may be linked via switchgear to the starter battery to improve cold starting. Care should be taken if the base vehicle is fitted with an OE battery management system. Consult manufacturer.

    Alternative energy sources for leisure battery charging

    Alternative energy sources may be used to recharge leisure batteries such as use of solar panel battery charger (photovoltaic cells) or wind powered generator (sometimes used on marine installation)  if sufficient capacity can be achieved.

    Leisure battery charging from mains hookup

    When the vehicle is parked where a site hookup (via BS4343 connector) is available a battery charger may be used to recharge the leisure battery bank whilst the vehicle is stationary.


    110 volt or 240v power can also be supplied by a dedicated vehicle  powered generator system, or by a stand alone portable generator.  Vehicle powered generators may be run from the vehicle engine or under van floor via a power take off  facility on the transmission driveline.

    415v Three phase power for heavy duty specialist & industrial applications may be provided by a larger diesel powered generator.

    Auxilliary power systems may be integrated so that the inverter system and generator systems work together during periods of peak demand.

    Safety & Circuit Protection

    240 volts ac power circuits must incorporate the following:

  • Residual Current Device ( RCD ) with adequate earth bonding to provide protection from electric shock
  • Overload protection
  • Short circuit protection
  • Please note ! Automotive electrical cable intended for use on low voltage systems is not suitable for use on systems operating at mains voltages (Why? Higher voltage potential requires better cable insulation) .

    auto electrical wiring products online shop - SMAK

    Electrical Installations in caravans and motor homes should comply with section 608-** of the IEE 16th edition Wiring Regulations. "  superceded by the 17th edition IEE Wiring regulations which apply after July 2008 superceded by the BS7671:18 18th Edition IET wiring regulations in force from .

    Periodic Inspection preferably not less than once every three years or more frequently if the vehicle is used for more than normal mileage.

    For such vehicles , the caravan electrical installation and supply cable should be tested and a report on their condition obtained as prescribed in BS7671 (formely the Regulations for Electrical Installations) published by the (IET) Institution of Electrical Engineers.

    Reducing Power Consumption

    Consider using energy saving low power consumption devices when specifying the design of your vehicle installation. This will mean the power requirement from the auxilliary vehicle batteries is reduced therefore taking longer to discharge, and allowing specification of smaller batteries thus saving weight and fuel.

    LED lights are available for both interior lighting and exterior lighting forming an effective low power consumption alternative.

    Voltage Converter page link

    We will be pleased to help with your vehicle onboard power enquiries by email subject to time constraints.