Service Section Technical Pages

Specialised Onboard Power systems for Service Van, HGV truck, Motorhome, Caravan, Camper van, Ambulance, Catering Trailer,4x4,Utility Vehicles, Canal boats, Marine .
Mobile installation service available in Telford & Shrewsbury, Shropshire areas.

Mobile onboard power at UK mains voltage 240 volts AC is required on many types of vehicles including

  • Leisure vehicles with living quarters such as Motor home, Caravan, Camper van.
  • Vehicle Conversions where a panel van , 4x4 orinverter1.jpg truck has been modified for specialist utility service use and may operate 240 volt or 110 volts powered equipment.
  • Exhibition display vehicles , library vans, etc which have 240v interior lighting and services,
  • Ambulances with 240 volt medical equipment and lighting.
  • Mobile Shops and libraries where 240v power is required to operate a computer for stock control or invoicing, and extra display lighting is required.
    Interior lighting may be 12v or 240v
  • Marine craft eg, Sailing yacht , motor boat, canal barge, with living accomodation.
  • Vehicle Charging System Voltage
    Automotive battery systems recharged by an alternator operate at either 12 volts DC (charging voltage approx 13v to 14.8v) or 24 volts DC (charging voltage 28v)
    UK domestic appliances operate at 240 volts AC mains .
    Portable tools for site work ,eg drills, grinders, etc often operate at 110 volts or 240 volts.

    Mains Voltage

    Various systems exist for supplying 110v or 240 volt AC onboard power depending on application and requirement.
    A suitable power source can be supplied while stationary from :

    * Mains "hookup" cable

    * Generator

    * Inverter to convert  existing vehicle electrical power to the required current and voltage

    An Inverter converts the the vehicle's conventional 12 or 24 volt DC battery supply input to 110 or 240 volts AC output .
    The Inverter output may be Pure Sine Wave (more expensive type) or Modified Sine Wave (cheaper type).
    Inverter units may be linked to achieve larger power output or a dynamic inverter system used.

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

    Inverters are often used in vans to convert 12 volts dc to 240 volts ac

    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

    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
    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. This reduces the risk of discharging the starter battery to a level at which the vehicle is immobilised.

    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.

    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.
    An effect of reduced starter battery voltage results in an increased current draw as the starter motor operates (see Ohms law ref : Power(Watts)=Current(I) x Voltage(v) ) causing premature failure of starter motor or cabling.

    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 achieved by a vehicle  powered generator system, or by a stand alone portable generator.  Vehicle powered generators may be run from the vehicle engine or via a power take off  facility on the transmission driveline.

    415 volt 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.

    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 Institution of Electrical Engineers.


    Reducing Power Consumption

    Consider using energy saving low power consumption devices such as LED Lighting when specifying your vehicle installation.

    This will mean the power requirement from the 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.

    Voltage Converter page link

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