April 22, 2023

TT# 134 Electrical Systems in Future RVs (Part 1)

By: Rob Lowe

How about a 48-Volt (Chassis) Battery System? …. Finally!


In 1999, I read an article that automotive power systems would likely move to a 42-Volt standard. I’d read about a possible 36-volt standard and in Technical Tip #19 & 20 (See TT# 19 & 20) which were written in 1999-2000, I detailed some of the reasons and potential applications that might arise. I concluded TT# 20 with the following: "Just imagine how much better our coaches will be when this new power system hits the market in just 2 years. I, for one, can hardly wait.”


Well almost a quarter of a century later, if some recent developments are any indication, the wait is almost over. The progress has been slow with innovations making the transition more likely. Modern vehicles contain well over 100 microchips controlling features that make these vehicles run more efficiently, safer and meet the needs of the driver and passengers, while maintaining a comfortable environment within the vehicle. Some allow a form of cruise control that is automated, varying the vehicle’s speed in response to that of other vehicles, within the maximum speed set on the cruise control. Emission control systems are far more complex and sophisticated with constant feedback to the engine management computer which keeps the engine running efficiently while reducing emissions. All of these ‘computers’ require a reliable source of power.


Entertainment systems have gone from a simple AM radio to one with many frequency bands, music sources, satellite reception, GPS, and phenomenal sound amplifier capabilities. All of these, and many other demands, require a reliable source of power. Alternator capacities have grown to keep the onboard battery charged under all circumstances. The demands on vehicle’s battery have grown as it powers various computers that are constantly monitoring for a command from a remote control to open door locks, start the engine and keep settings in memory so that the interior environment can be pre-conditioned before entry of the driver, among other demands. Those systems take a lot of power, the supply of which was never envisaged when the decision was made to move the standard battery voltage from 6 Volt to 12 Volts about seventy (70) years ago. Ironically some of the electrical reasons pressuring the change then including longevity of the battery with the loads to be supplied, the size and length of the wiring required to start the vehicle’s engine and power the accessories, are the same now, as the industry has focused on the need to increase the battery voltage in modern vehicles.


The RV industry dealt with the excess demands on electrical systems that arose from the power needs for all coach systems independent of the chassis needs. Since most motorized RVs are built on a chassis supplied by another maker, early in the history of RVs, the decision was made to have two (2) power sources and systems to keep the chassis power isolated from the coach power system. This approach provided lighting and amenities using a 12-Volt source that operates when the vehicle is not plugged into a campground or other land-based power source. Early in the production of RVs, all onboard lighting was supplied by the campground power pedestal and light fixtures were similar to ones used in homes. Motorhome builders quickly realized that there was a need for power on the road and a separate ‘coach’ power source was required. With safety in mind, trailers with electric brakes had to have a battery source to provide power, if for no other reason than in the event of a ‘breakaway’ from the towing vehicle. Initially this power was a small auxiliary battery. As the need for power in trailers developed, an onboard battery system that could power lighting and some accessories such as a radio were introduced, supplementing the need for braking safety.


Modern innovations moved the decision to build a more robust power system to power the multiple 12-Volt lighting system forms in modern RVs.  One of those was the adoption of LED interior lighting as standard equipment in RVs of all types during the 2012-15 timeframe. While the RVer benefits from this transition with better lighting, far less heat being generated, and eliminating the need for bulb changes, the manufacturers benefited from the ability to substitute much thinner (20-22 gauge) wire in RVs with this new lighting provided that the fixture had an integral LED light assembly. The industry also had the ability to place the same style of fixture containing LED’s, with the adoption of a standardized light color of all lamps, in virtually any RV they produce (Motorhomes of all classes, Travel Trailer or Fifth wheels), allowing bulk buying opportunities. These manufacturers save on the cost of the wiring, the ability to source lighting components from various suppliers and the ability to integrate electronic control systems. They could also pass along a price increase for these new features in their RVs to buyers, which enjoy the benefits of this new lighting type, including much less power needed ‘to keep the lights on’.


The big advance this year was a recent development in early 2023, when Tesla announced that their new Cybertruck, which will begin deliveries in 2024, will be using a 48-Volt electrical system for all automotive functions. The electric drivetrain will utilize 800 volts. Adoption of such high voltages greatly reduces the size and volume of wire used to carry the power from the power source to the powered items. In 2023, the automotive and control systems on most ‘on-road’ vehicles are powered by a 12-Volt battery. On EVs, the powertrain has a high voltage battery pack which typically provides 400-800 volts for the drivetrain components, while a separate 12-Volt battery powers all control and automotive systems and is charged from the main battery. The exception is some Tesla models now use a 16-Volt Lithium Battery to power these systems. It is expected that with Tesla’s Cybertruck decision, all vehicle manufacturers will adopt a 48-Volt power source. This will reduce the wire size needed for the ever-expanding automotive systems and increase overall battery capacity. Alternators and the associated wiring may be smaller. I’d predict as an interim solution, that in a motorhome RV application, it will be common to see two alternators, one for automotive systems and another for the RV (coach) electrical system. Recently an alternator supplier, American Power Systems (APS), introduced a lower turn-on RPM alternator that can charge at idle or very low speeds. APS has produced a 48-Volt version that fully charges at these low speeds. That is consistent with many chassis makers supplying cutaway chassis to the RV industry, that have forbidden those RV makers from directly connecting to the chassis electrical system. Charging the Coach battery systems requires a separate alternator or a battery to battery (B to B) charging system. This B to B system works in reverse when the chassis battery needs to be charged from the coach’s AC power source. The natural progression over time of two separate systems, is a chassis power system that allows all electrical needs to be sourced from a single power source while combining the charging function into one system This new APC alternator would be a perfect solution to charge both the coach and chassis battery systems while driving or when idling in the campground.


As RV solar systems expand in size and efficiency, combined with improved inverter-chargers to power many more RV circuits, it is possible to have smaller RVs that have electric appliances. Many new components, such as RV refrigerators, have already been updated to use 12-Volt compressors. Other systems with the higher battery voltage have the potential for low voltage air conditioners, even induction cooking units that were unheard of just a decade or two ago. If RV Coach power systems move to 48-Volts, then many equipment makers will evaluate the opportunity to design their supplied equipment to operate on the 48-Volt infrastructure.


Government regulation and environmental concerns have brought the reality that portable and built-in generators will be banned within a decade. Combine that with the adoption of RVing as a lifestyle by many younger, more adventurous, connected RVers which see ‘camping’ as being ‘off the grid’ in a State or Provincial Park setting. We’ve already begun to see Class B and small Class C RVs planned and some introduced that have no propane fuel on board and some have no need for external power to operate most of their onboard systems. With the higher voltage chassis power system, it is a logical extension that coach power systems will move in that direction.


At the present time, some smaller RVs which have eliminated an onboard generator, having added a second engine driven ‘house’ alternator in its place. This system is fully integrated, starting the emission-controlled engine as required, to charge the battery, just as an Automatic Generator Start (AGS) system does on newer generator-equipped RVs. With ample modern solar systems, the need to start the vehicle engine is greatly reduced. As appliances, such as cooktops and air conditioners are designed for RV applications, they will most likely be designed to use the RV (coach) systems, while providing power to maintain the 48-volt ‘chassis’ battery. They will not require 120VAC directly from an inverter or campground pedestal to operate the coach systems. The campsite will provide power to charge the batteries that will power all onboard RV systems.       


In the next TechTip, we’ll look at EV-RVs and what the future may look like moving forward.


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