Basic RV 24-Volt Electrical System Design
An RV electrical system may not need a generator. With available battery capacity, an inverter-based system will provide silent power at all times to a host of 240-volt appliances including cooking, refrigeration, washing and air conditioning.
This basic design illustrates the requirements of an electrical system that takes advantage of the high output alternator that is common on coach-based chassis vehicles. In combination with a more extensive solar panel setup and a high capacity house battery, the requirement for an onboard generator is minimal.
Use the vehicle chassis for the main system negative (earth) connection and connect it to the negative busbar side of the battery monitor shunt. An appropriately sized positive cable completes the engine charging circuit via a charge relay and circuit breaker.
A vast solar array on the rooftop can efficiently deliver the total vehicle power requirement even on overcast days with a degree of intelligent power management. There can never be too much solar.
Try to use 24-volt DC appliances where possible. When the vehicle may still require a few 12-volt powered devices, a DC-DC converter can take power from the 24-volt house battery and convert the voltage to 12-volts just for those items.
The solar array, inverter and house battery are dependent on each other for appropriate sizing. Determine the overall battery capacity by the amount of reserve power required for miserable solar days. The capacity also needs to be large enough to handle peak loads from the inverter. Set the inverter size according to the peak load requirement. The solar array should target at least twice the daily power consumption for a good solar day.
Your vehicle electrical system can only be as good as the electrical system design and the quality of the components employed. In particular, the proper design and implementation of the heavy DC power equipment are essential.
Heavy DC wiring should be of significant size, well organised, and all circuits must be protected from an overload situation to avoid fire risk. The battery switch is an essential component that can isolate the electrical system from the battery if there is a fire or other hazard. Fuses protect each of the circuits that provide power to the system components. A battery monitor allows proper charge management of the battery.
DC Distribution Board
The DCD board works as the wiring hub of all the heavy DC circuits. It provides mounting points for all cables, a battery switch, a fused busbar system, a ground busbar and a mounting location for the Victron BMV battery monitor shunt. Other brand shunts can also be accommodated offboard.
The circuit above illustrates a design that incorporates the DCD board into a full on-chassis electrical system. For 24-volt systems, the 300-amp continuous current handling capacity is sufficient for inverter chargers up to 5,000VA.
DCDM2 DC Distribution Board
House Battery System
Construct the house battery bank from multiple pairs of 12-volt AGM Deep Cycle Batteries. For self-contained Lithium batteries with inbuilt BMS, be careful that the battery charge and discharge characteristics are compatible with the charge sources and loads - especially the inverter charger.
When using larger lithium batteries such as the Victron Smart Lithium Batteries, additional components for the external BMS are required.
Connect the positive terminal of the upper battery to the battery switch mounted on the DCD board. The negative terminal of the lower battery connects to the battery monitor shunt (which measures net current in and out of the house battery). A negative power distribution busbar on the load side provides a connection point for the negative wire of all load circuits and the vehicle chassis.
To maintain a balance between the two batteries in a 24-volt system, we recommend the use of a Victron Battery Balancer.
Understanding the battery state of charge (SOC) is essential for proper battery management. For this, we use a BMV-712 Battery Monitor which includes a Bluetooth interface to use with the free Victron Connect smartphone App. The DCD board has a location for mounting the battery monitor shunt. Note that only one side of the shunt connects to the battery negative terminal.
The inverter charger will provide AC power when the vehicle is away from the grid power. When plugged into the grid, it will be the battery charger. The size of the inverter charger depends primarily on the simultaneous power draw of any AC appliances. For example, a system capable of powering an electric kettle (2,200-watts) would use a Victron Multiplus 12/3000 product. The size of the inverter charger will also dictate the house battery capacity.
The Inverter charger DC power is sourced from a Terminal Fuse mounted on the positive busbar of the DCD board, and the ground return connects to the negative busbar. The inverter charger will determine the size of the required fuse. When larger inverter chargers with an overall fuse requirement that is greater than 300-amps are used, a pair of positive cables of equal length each connect to their own fuse whereby the pair of fuses can share the load.
Best practice will provide an Isolation Switch in the positive lead near the inverter charger if it is not located near the main battery switch on the DCD board.
House Circuit Breaker Panel
Circuit breakers on this panel feed power to the 24-volt DC consumer devices. For 12-volt circuits, a circuit breaker can feed energy to a 24-12 volt DC-DC Converter. The output of the converter will return power to an array of 12-volt circuit breakers as required for the 12-volt devices.
Essential circuits require power on a 24-hour a day basis irrespective of the main battery switch being turned on or off. A section of the house panel can be powered directly from the battery via a fuse mounted on the battery side of the battery switch.
Solar power can also be considered an essential circuit so that solar battery charging can continue when the main battery switch is turned off. A master essential circuit breaker must be used to provide full battery isolation in case of an emergency.
Connect the Solar Panel Controller to the essential circuit system via a circuit breaker on the house panel. Electrical standards require a two-pole isolator between the solar panels and the controller. The controller should be mounted close to the DCD board.
An alternative arrangement is to connect the solar controller to the main power bus that is controlled by the battery switch. However, in this case, the battery switch would need to be left on for solar charging.
Vehicle Engine Charging
Use the vehicle alternator for charging the house battery when the engine is running. Employ a 285 Series Circuit Breaker near the vehicle starter battery for circuit isolation and protection. A relay that is energised by the ignition circuit will allow power to pass when the engine is running.
An Andersen Connector at the tow bar provides power to a trailer if used. Be sure to use a proper cable size for the positive lead between the tow bar area and the engine start battery.
Hot Water System
The Hot Water System has a heating coil that takes heat from the engine cooling system to heat the water when driving. Alternatively, heating from a 240-volt element when plugged into mains power when available. Use the inverter power as another alternative provided that there is sufficient battery capacity available.
A parts list for an example system listed below. Contact Outback Marine for further guidance. We also offer a full schematic and consulting service at a time and materials rate if you require detailed guidance.