Autoelectrical Installation Services

UK Suppliers of Autoelectrical Parts to


Motor Trade




Motor Factors

Commercial Vehicle Bodybuilders

Road Haulage Fleets


Passenger Transport

Bus Workshops

Taxi Operators

Farm Workshops

Agricultural Engineers

4x4 Enthusiasts


Hire Companies


Special Vehicle Builders

Van Conversion Specialists

System Manufacturers

Specialised Vehicle Onboard Auto Electrical Power Systems for Vans and Commercials

A vehicle onboard electrical power supply enabling use of 240 volts ac (uk mains voltage), or 110v ac electrical equipment may be required for certain off grid applications.

Off grid power systems allow Service Vans, HGV trucks, Motorhomes, Caravans, Camper vans, Ambulances, Catering Trailers,4x4,Utility Vehicles, Canal boats & Marine vehicles to operate stand alone off site for varying periods of time subject to system design.

Mobile Autoelectrical Installation Service - Shropshire & Mid Wales

Leisure vehicles

Motor home, Caravan, Camper van, or Vehicle conversions with living quarters may require an electrical supply facility at 230v a.c mains voltage to power a laptop, television, fridge, or other domestic equipment. A typical off grid power system for leisure vehicles will include a number of auxilliary batteries used as the power source for an inverter. These auxilliary batteries will require periodic charging either from a vehicle split charge system run from the engine alternator, or from an external power supply. Auxilliary battery reserve capacity will introduce limitations.

Utility Service Vehicle Conversions

Panel vans, 4x4, & trucks modified for specialist utility service or local authority use may require inverter power systems to provide a power supply at 110 volts a.c or 240 volts a.c for
Portable tools for site work ,eg drills, grinders, saws, electrofusion welders, pumping equipment.

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

Mobile catering kitchens may require a 110v or 240v supply via a distribution board with Arc fault Detection Devices (AFDD's), Residual Current Devices (RCD's) and Residual Current Breakers with Overcurrent (RCBO's) for certain equipment.
Adequate lighting to allow safe working, safe food handling and hygiene, can operate from the vehicle battery (12v or 24v) system or from Mains hook up power / generator.
Aim to reduce power consumption by specifying cooking equipment which will mainly operate from bottled butane or propane LPG gas.
An inverter may be required to run appliances such as fridges, freezers, maintaining temperature control when off-grid.
An inverter may be specified to run microwave ovens for short periods of time.
Adequate ventilation may require fitment of extraction and ventilation fans.
For commercial applications a suitable generator or remote 240v mains hook up often provides best power source with an inverter system available as a power backup.
A changeover switch offers the facility to select between external or generator hook up power supplies and onboard inverter supply systems.
Inverter power equipment relies on sufficient batteries with adequate reserve capacity and battery charging facility.
Solar panels can provide an additional means of topping up batteries.
Availability of hot and cold water for handwashing is an additional consideration towards hygiene.
Sinks and exposed metalwork may require equipotential bonding to meet wiring requirements.
Key legislation : The Food Safety and Hygeine (England) Regulations 2013.

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.


Where 240 volt medical equipment, monitoring, oxygen compressor and lighting equipment. The mobile nature of operations may require onboard engine driven power generation equipment, with auxilliary batteries and inverter system as a back up.

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 Alternator & Battery 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). Many modern vehicles are fitted with 'Smart' alternators where the alternator voltage regulator is controlled from an external module such as the Powertrain control module (PCM).

UK domestic appliances operate at 230-240 volts AC mains. A variety of power supply systems exist to provide 110v or 240v AC onboard power to suit application and requirement.

External Power Supply whilst Vehicle Stationary

A suitable power source can be supplied while stationary from :

  • Mains "hookup" cable
  • An external 240v power supply via BS4343 blue plug wired through a Residual Current Device (RCD) may be used to supply power to a stationary vehicle for powering mains equipment.

  • 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.

    Inverter Input Power Supply Cabling

    A 12v battery powered or 24v d.c. input to 110 volt / 240 volts a.c output (DC - AC) inverter can draw large amounts of current from vehicle batteries dependant on load.

    Inverter power supply cabling should be adequately specified to allow for loads and cable run distance. heavy duty battery cable will almost certainly be required to carry the power supply, with circuit comprising of rated fusing and power supply isolation device.

    Auxilliary Batteries

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

    Lead Acid Batteries

    Lead acid battery has advantages of relatively low cost but generally designed for short duration high current output during vehicle starting.
    Major disadvantages of Lead acid type batteries 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 dedicated charging systems.
    Lithium power packs may add increased portability of electrical supply on site.
    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.

    Auxilliary Battery Charging from vehicle power source - Split Charge System

    The vehicle alternator may be used to recharge both primary starter battery and secondary auxilliary leisure battery banks allowing battery recharge whilst idling or when the vehicle is being driven. Installation of a split charge relay or battery management system allows auxilliary battery charging and possibility of power supply 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 be 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 secondary battery charging method uses a heavy duty blocking diode fitted in the line 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 recharge. 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 is not suitable for use on vehicles fitted with Smart charge alternator 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 auxilliary leisure battery charging - Sustainable Power

    Sustainable alternative energy sources may be used to recharge auxilliary leisure batteries
    such as
    Photovoltaic Cells : use of solar panels as a battery charger.
    Wind powered generator if sufficient capacity can be achieved.
    Water Power : The flow of water can be used to provide kinetic energy to drive hydroelectric generators.

    Solar Panel Battery Charging System

    An off grid or vehicle solar panel battery charging system will require :

  • Solar Panels
  • Battery Charge Controller
  • Auxilliary Batteries
  • Leisure battery charging from mains supply hookup

    When the vehicle is parked where a 16A mains 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.

    Electrical 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) .

    Wiring Regulations

    Electrical Installations in caravans and motor homes should comply with section 608-** of the IEE (IET) 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.

    Using Less Energy & 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.