February 6, 2021

TT #120 12 Volt RV Battery and Control Systems, Care and More! (Part 1)

By: Rob Lowe

Featured Picture

The Covid-19 pandemic has resulted in an unprecedented increase in the number of first time RV owners. Many existing owners have taken advantage of this opportunity to change their RV, increasing the supply of used RVs for sale. This brings with it an increasing number of people seeking information about basic RV systems. Add in the sophistication of newer RV electronic systems and you have a complex set of circumstances to immerse any RV owner in. The age of the RV has a lot to do with how sophisticated the control system is. Some long-held assumptions about these systems are no longer valid, making it difficult to troubleshoot the system when there is an issue.  

All RVs depend upon a reliable twelve-volt (12V) power source, however that venerable 12-volt system has been changing under the ever-increasing demands placed on it. The next few TechTips will focus on some of these advances in RV Technology. These TechTips will focus on the systems found in a motorhome, which consists of two independent 12V systems, one for the engine and the ‘on-the-road’ systems and the second for the ‘Coach’ or ‘house control’ system. Trailers have a single ‘Coach’ power system, lacking the complexity of having two independent, co-existing systems, as in a motorhome.
The Topics covered in this group of TechTips are:
The impact of the use of Computerized Control (Multiplex) Systems (TechTip #120) (This one)
Battery Types and the Significance of Battery Type on usability (TechTip #121) 
Inverter/Charger Systems and Settings (TechTip #122)
New Products that Improve Battery Longevity and Maintenance (TechTip #123) 
The Interaction between the Chassis and Coach Battery Systems (TechTip #124)
An Alternative Battery Maintenance Approach for a Coach in Storage (TechTip #125)

Questions arise from a lack of understanding about how these systems operate, often expressed by new owners, as well as recent significant changes in the systems themselves, often overlooked by experienced RVers as they exchange their RV. This TechTip series will assist both in understanding the battery, the control and inverter systems. 

Multiplex (Computerized) Control Systems:
Multiplex Control PanelsThese are often referred to as ‘multiplex’ control systems, since they may use a centrally located computer that is signaled into action from one or more touch sensitive (multiplex) switches usually located in a ‘keypad’. The central computer may be located under the bed on some coaches, in a cargo bin near the coach battery, or behind a Rear TV on others. Recent incarnations of this type of control system, use a RV industry Standard known as RV-CAN, or RV-C for short, that allows distributed logic. This Standard allows information to be shared along a ‘coach long common wire’ or ‘Bus’ (a collection of wires). Each component (or drop) has its own computer logic and if a component is added, the others become self aware and can interact with the new component. On some of the latest RVs, this computer control is combined with the 12V fuse panel and a display panel on the unit provides the status of each fuse on an accessible menu. 

IllumaPLEX Control System One feature of the newer systems is the addition of a centrally located ‘iPad’-like display that provides touchpad control of all systems in the RV including control of all individual lighting circuits, slideouts and awnings. There are controls to set the temperature and fan control of the rooftop air conditioning, as well as the heating and ventilation systems, a vent fan or even the water pump and the water heater mode. In addition, all tank levels and battery voltage can be monitored. Using a downloadable App on a tablet or Smartphone, remote control from that device is possible once it is paired using Bluetooth. Touching the appropriate button on a Control Panel (either coach mounted or in the App), turns on or off a light and/or dims or brightens it (when the ‘button’ is depressed and held longer). These touchpads allow control of all systems from a Switch pad, the Central Control Touchpad or a Smartphone. Imagine standing out beside the slideout, near an obstruction and controlling the slideout while observing whether there is any possibility of hitting the obstruction, as the slideout deploys. That is the reality of the newer Multiplex control systems.

The ‘Bus’ interconnection between the switch panels and the computer is often a flat network (telephone style) cable. What is important is that there is no direct 12V power at the ‘switch’. The power switching takes place between the computer or multiplex controls and the light, fan, pump or slideout motor, at the command of the virtual switch. The touchpad or switch display panel often changes color or light intensity when activated and usually dims after a period of inactivity. This is a significant change from the conventional light or power switch. Another benefit is that multiple (even all) lights can be controlled from different locations by more than one touch pad. Roof vent fans, the water pump and some slide outs may be controlled near these units, since they are only needed in certain areas, or the system may require visual observation (such as when the slideout is operated) to ensure safe movement. For someone unfamiliar with this type of system, many are unaware that there may be a light dimming capability built into the control. None of these features would be available without the multiplex control system, a feature until recently, only available on the most expensive luxury coaches. Some coach features such as cargo bin lighting, are on a master control, with each light within a cargo bin still having its own on-off switch. This gives the ability to turn all power on or off from the control panel, while allowing individual lights to be manually controlled. For those upgrading, there is a learning curve that includes understanding the operation of this control system. For those new to RVing, the newest RVs have features that are far beyond most buyer expectations of a Recreational Vehicle. 

System Problems:
Failures of the control system often can be related to corrosion between the network cable plug and the receptacle at the switch pad, control panel or the computer, or at interconnections of cable extensions between the operating components. Applying Corrosion Block® to the connections often corrects the issue. Review your owner’s manuals, since some contain troubleshooting tips and advice. Occasionally turning off all 12Volt and 120VAC power, then waiting a few minutes and turning everything back on, will reboot the computers and provide proper operation.

On lighting circuits in coaches built prior to about 2014, that have multiple halogen ceiling light bulbs or multiple incandescent bulbs (cargo bin) on one circuit, it is common to have wire connections at the computer board showing brown (burned) insulation where these wires connect to the circuit board. The electrical current that the multiple bulbs on those circuits consume, can run close to the maximum that the circuit can handle. Insulation damage from the high current causes overheating of the wire, thereby scorching the insulation, when these lights are ‘on’ for long periods of time. Changing the light bulbs over to LEDs, substantially reduces the current draw. As an example: Often a ceiling lighting circuit will have six (6) to eight (8) halogen lights on it. When those halogen bulbs are exchanged for LED bulbs, the current consumed by all six or eight of the replacement LEDs is equivalent to the current consumed by just one halogen bulb! Converting the ceiling and cargo bin lights to LED, results in a significant power reduction. After exchanging the bulbs for the LEDs and properly correcting the wiring connection that has the damaged insulation, will restore safe, trouble free operation.  

On slide control systems, frequent problems can be traced back to the specific slideout control board mounted near the slideout motor. Once again, corrosion can build up on the circuit board connectors and prevent dependable operation. Applying Corrosion Block® to the connections, usually brings back proper operation. One other area that is critical for proper operation of electronic systems is a solid, clean, ground connection between the negative coach battery cable and the RV’s frame. Generally, the focus is on the ground connection to the battery, however experience has demonstrated that the ground cable to RV frame connection is as critical to proper operation of the electronic systems.

While there are other issues that come up with these systems, refer to our website and Rob’s Blog for other articles that provide insight into problems with the electric control systems. If you are unsure which articles to review send me an email and I will refer you to some appropriate articles.

Manufacturer’s Websites:
For many years, American Coach used American Technology Components Inc. in Elkhart, IN to supply their multiplex computer-controlled systems.  www.atcomp.com  574-262-1258. Newer American Coaches use the FireFly Vegatouch and Spectrum multiplex computer-controlled systems supplied by FireFly Integrations www.fireflyintegrations.com  574-825-4600

Recent Fleetwood RV models made by the REV Group (such as Bounder) use a system known as IllumaPLEX (a customized version of the PrecisionPlex) made by Precision Circuits Inc. www.precisioncircuitsinc.com  630-515-9100 


Thanks for your comment.It will be published after reviewing it.