Towing without a supplemental braking system is dangerous RV driving

A motorhome is an excellent choice for traveling. Everything is self-contained and you have the comfort and security of sleeping in your own bed and cooking your own food. The only caveat is that they are large, so using it as a daily driver to go shopping or sightseeing in a national park just doesn’t work out very well. Fortunately, motorhomes are equipped with trailer hitches, making it easy enough to tow a smaller vehicle for your touring while the motorhome is parked at your campsite. Towed vehicles can include a vehicle placed on or in a trailer or loaded onto a tow dolly, but the most common method is to use a tow bar to flat tow your vehicle – commonly referred to as towing four-down.

There are a number of vehicles capable of being towed four-down but there are exceptions, so you’ll need to check with your manufacturer to see if your choice is flat towable. If it is, the next step is to verify that your coach is capable of towing your vehicle of choice. Larger Class A coaches have ample capacity, and some can tow as much as 20,000 lbs. but some smaller Class C motorhomes may only have a 3,500 lb. towing capacity, which will limit you from towing any vehicle that exceeds that weight rating.

In addition to the rating stamped on the trailer hitch, you’ll also need to look at the Gross Vehicle Weight Rating (GVWR) and the Gross Combined Weight Rating (GCWR) of your motorhome. The GVWR shows you the maximum amount of weight that the motorhome can safely weigh. The GCWR indicates the maximum safe weight of both the coach and any trailer or towed vehicle and will always be higher than the GVWR. For example: if you have your coach loaded to the maximum GVWR (let’s just assume 32,000 lbs. as an example) and your GCWR is rated at 36,000 lbs. it leaves you with 4,000 lbs. as the maximum safe weight of the towed vehicle or trailer. Your trailer hitch may be rated at 10,000 lbs. but you must limit the towed weight to the lesser value of the hitch rating or GCWR. If you do not load your coach to the maximum GVWR, then the difference between the GCWR and your actual coach’s weight when fully loaded will increase and you may be able to tow a bit more than the 4,000 lbs. in the above example.

The GCWR also assumes that you have brakes on whatever is being towed. If you have an enclosed or flatbed trailer it will most likely have brakes on those axles that are designed to work in conjunction with a brake controller in the tow vehicle. As long as you have installed a trailer brake controller in your motorhome, you’ll be fine. But when you flat tow another vehicle – it’s a different story. A car, Jeep or truck has its own braking system that is controlled by the driver when driving that vehicle. When you hook up to a motorhome to flat tow the braking system on the motorhome and the braking system on the towed vehicle are two separate entities. They do not work together, so you have no towed vehicle brakes when towing.

Fortunately, there are a number of third party supplemental braking systems on the market that will allow you to safely tow your vehicle and be compliant with the GCWR requirements.

Questions sometimes arise as to the legality of towing without a supplemental braking system, which varies according to state or province. I’ve also heard a few arguments from RV owners about not spending the money on a supplemental braking system because “you can hardly feel the towed vehicle behind the coach”. While the towed vehicle is a small percentage of the total weight, especially on a large tag axle diesel pusher, tests have proven that there still will be a difference in stopping distance during a panic stop. A study taken by Roadmaster and published on their website showed a 34’ class A motorhome took 132 feet to come to a complete stop from 50 miles per hour. When a medium size car was connected to the motorhome the stopping distance increased to 209’. When a supplemental braking system was added to the towed vehicle this distance decreased to 137’. Those extra 72’ can make the difference between safely stopping in time or being involved in an accident should an emergency stop be required.

Another reason for a supplemental braking system is to protect yourself and others during a breakaway situation. Some systems include this and some offer it as an optional accessory, but in either case this is something that every supplemental braking system should have. A breakaway system consists of a switch that is mounted on the towed vehicle and is connected to the coach via a small steel cable. Should the towbar fail or for any reason the towed vehicle becomes disconnected from the coach while driving, the cable will activate the breakaway switch and the supplemental braking system will apply the towed vehicle’s brakes to safely bring the vehicle to a stop and prevent a runaway that could possibly impact another vehicle.

I recall one incident I experienced where a supplemental braking system with breakaway device saved me from some major damage. I had recently rebuilt my towbar and decided to replace my locking towbar and hitch pin set while I was at it. Shortly after we left for a long trip and not more than an hour down the road, I heard and felt a large jerk on the back of the coach. I looked in my rearview camera and saw that our Jeep was following us about 10’ back from the coach. I knew that something had failed in the towbar, so I pulled over to the side of the road and got out to investigate. I saw that the main 5/8” hitch pin that holds the towbar into the coach’s hitch receiver had failed, allowing the tow bar to pull out of the hitch and drag along on the ground. The safety cables held and kept the Jeep behind me and the breakaway cable applied my M&G supplemental braking system on the Jeep, keeping it at a distance from our coach. Had I not had a breakaway system, our Jeep would undoubtedly have plowed into the back of our coach once I attempted to slow down, damaging both the front of the Jeep and the rear of the coach. Our safety cables were stretched beyond being useable but I had kept the old set of locking hitch pins and a spare set of safety cables along, so I replaced them, reconnected the towbar and happily went on our way with no damage to either vehicle.

Types of Supplemental RV Braking Systems

Supplemental braking systems are available in several different versions. Some systems are portable and can be taken out of the vehicle when not needed while other systems are permanently installed into the vehicle. In either case, these systems will provide supplemental braking ability to the towed vehicle. Both methods have pros and cons so let’s look at the differences and see which method works best for you.

Portable systems are placed upon the floor of the driver’s footwell. They operate by actuating an arm that clamps onto the brake pedal. These units use 12-volt battery power to actuate the arm that connects to the brake pedal and use decelerometers to detect when the vehicle is decelerating. The main module is a box that contains the mechanism and sensors and rests on the floor, but generally must be placed against the driver’s seat so that the box stays in place when the brake pedal arm extends so that the box doesn’t move instead. Some of these systems may have additional brackets to help keep it from sliding while others simply rely on the seat cushion to prevent it from moving rearward when the brakes are applied. If you want a portable, you’ll have to consider how soft your seat cushion is and whether that will affect your choice of portable braking system. Popular systems are available from a number of manufacturers, such as Blue Ox’s Patriot 3 system, Brake Buddy’s Classic 3 and Select 3 systems, Roadmaster’s Even Brake system and Rvibrake’s Rvibrake 3.

Another caveat to a portable system is that they still do require some installation, so you can’t just drop it into any vehicle and expect it to work. You will need to mount a breakaway switch to the front of your vehicle and run its wires back to the footwell where they will plug into the brake controller. You’ll also need to provide a 12-volt power receptacle to plug the unit into. Many cars will have a 12-volt receptacle that is connected to the ignition key switch. That won’t work because the receptacle will not have any power when you are towing. You may have to install a constant-hot receptacle someplace in your dash area.

While these installation tasks are minor compared to a system that is permanently installed, you still have to deal with setup every time. This begins by placing the unit on the floor and connecting the clamp on the arm to the brake pedal. Then plug in the breakaway wires and power cord and position the unit so that it can’t move backward when the brakes are applied. You may also have a calibration routine to go through, depending on the manufacturer of your braking system. Once you are done towing you will have to disconnect the wires, remove the clamp from the brake pedal and find someplace to store the system.

The last consideration is that these systems use sensors to sense when the vehicle is decelerating because there is no communication between the towed vehicle and the coach. If you are using the coach’s Jake brake to slow down when descending a downgrade, the supplemental system will unnecessarily apply the brakes on the towed vehicle because it assumes you are braking. This can result in excessive wear and heat buildup when traveling in the mountains.

A system that is permanently installed takes a bit more labor to install but, once installed, it’s pretty much a hands-off forget-about-it system. The simplest is NSA’s ReadyBrake, which is permanently attached to the towbar. This is basically a surge brake system that senses the forward pressure of the towed vehicle under braking. As the module moves, it pulls on a steel cable that runs through the towed vehicle’s engine compartment to the area around the brake pedal. This cable attaches to the brake pedal and applies pressure to the pedal in response to the pressure applied to the towbar mounted actuator.

A number of popular systems are available for gasoline powered motorhomes. These use an actuator that attaches to the towed vehicle’s brake pedal, generally via a cable. The cable is behind the brake pedal so it doesn’t get in the way when driving the vehicle. Most use a decelerometer sensor to sense the rate of deceleration but are also connected to the motorhome’s brake light switch so that the brakes will only apply when the driver steps on the brake pedal in the motorhome, preventing any brakes from dragging when descending steep grades. Common systems include Brake Buddy’s Stealth system which is a dual-mode system that can also use the cockpit-controlled module to actuate trailer brakes as well as towed vehicle brakes.

Other systems are Roadmaster’s InvisiBrake and Demco’s Stay-In-Play Duo. These systems can be used on diesel powered coaches as well, but they lack the true proportional braking available from a system that is designed for a coach with air brakes.

With a diesel-powered coach that has air brakes, you have lots of choices. If you recently upgraded from a gasoline-powered motorhome to a diesel pusher, you can continue to use your existing towed vehicle’s braking system. Or, you can upgrade to a pneumatic system that utilizes the air pressure from your coach’s air brake system to apply the brakes on the towed vehicle. The biggest benefit is that you can now get true proportional braking because the brakes on the towed vehicle will apply in the same amount and at the same time as the brakes on the motorhome. The harder you step on the coach’s brake pedal, they harder your towed vehicle’s brakes will apply. You can now coast and descend grades without any worry about prematurely applying or dragging the towed vehicle’s brakes.

These systems involve the installation of a module under the hood that generally actuates a cable that pulls on the back side of the brake pedal arm. This module connects to 12-volt battery power to operate the breakaway valve and in some cases will operate a vacuum pump to provide a source of vacuum to the brake booster behind the master cylinder so that the power brakes are in operation. A pair of wires runs to the front of the vehicle and connect to the breakaway switch while a small air hose also runs to that area to serve as a connection to the coach’s air brake system. In addition to the usual trailer light umbilical, a steel cable for the breakaway switch and an air hose are also used to connect to the rear of the coach.

Some diesel pushers come from the factory prepped for supplemental braking systems and have a quick disconnect coupler at the rear of the coach. If not, you can get a DOT approved kit to allow your diesel chassis to do that. You can’t simply tee into a brake line some place or you may risk a loss of brake pressure on the coach should the air hose to the towed vehicle fail. These systems will add a small air tank and the necessary valves to isolate the towed vehicle’s supplemental braking system from the coach’s brake system to prevent any failure from affecting the braking of the coach. The most popular pneumatic true proportional systems are the M&G Tow Brake and Demco’s Air Force One.

Note that either of these systems can be used on a gasoline-powered coach but it requires the purchase of an installation kit which includes a 12-volt air compressor that converts hydraulic brake pressure to pneumatic so that you can deliver true proportional air to the towed vehicle. These optional kits are a bit pricey but do give you true proportional braking and your towed vehicle will be ready for a diesel pusher if you decide to upgrade later on.

Selecting the correct system will depend on your needs. If you tow multiple vehicles and don’t mind living with the lack of true proportional braking and storage issues, then a portable system might be your best choice. If you want an “install once and forget about it” system, a permanently installed system should be your choice. If you are reasonably talented, you might make this a DIY installation but if not, you’ll want to have it done correctly by a certified chassis tech, such as those at National Indoor RV Centers. Electrically operated systems can be used on both gasoline- or diesel-powered coaches while pneumatic systems that tap into your coach’s air brake system can give you true proportional braking that will match the application of your coach brakes and prevent any false readings that can occur from inertia sensors used on many electrically operated systems.

Regardless of which system you prefer, it’s important to have a good supplemental braking system with a breakaway switch to be safe when towing. Towing without one is dangerous and is tantamount to driving without insurance and throwing out all your fire extinguishers. It’s just not an area to ignore.

Mark Quasius is the founder of RVtechMag.com, the past Midwest editor of RV Magazine, writes for numerous RV-related publications and a regular Contributor to FMCA’s Family RVing Magazine. Mark and his wife Leann travel in their 2016 Entegra Cornerstone.

RV Energy Management

Energy Management is simple – you just need to make sure that you don’t use any more power than is available. Battery power is finite. Eventually it’ll run out. By minimizing how many lights are on and the time they are on, battery life can be extended. Eventually you’ll need to recharge them, either by driving the coach or by running the generator. Adding extra batteries can extend that runtime as can the addition of solar panels. If you are plugged into shore power this isn’t an issue because your converter or inverter/charger will keep them charged while you use them.

AC power is a bit different. Unlike battery power, there is no reserve to draw from. You are limited to the total current capacity of your shore power pedestal or your generator’s capacity. Generators are generally sized for that particular coach so you should be able to run whatever loads you need to operate without exceeding the generator’s capacity. Of course there are exceptions where an undersized generator was specified in that particular coach rather than choosing the optional generator but those are the exception, not the rule.

Shore power pedestals vary in size. If you are running a small 20 amp cord to your RV from someone’s home you’ll be very limited as to what you can run. Battery chargers vary in current draw as to how many battery amps they are outputting. A battery charger that is outputting a full 100 amp bulk charge at 12 volts will be drawing 10 amps of 120 volt AC power. That can take up one half of your 20 amp circuit, which doesn’t leave a whole lot left. Many inverter/chargers have a setting on the remote control panel to define the shore power service. If you define the shore power at a lower level, say 20 amps, then it will limit the 120 volt power that the battery charger uses so that you can have more left to run other 120 volt items. You will need to manually set this once you are plugged into a smaller shore power pedestal.

In the above image we can see three receptacles. This is a typical 50 amp pedestal which features a 50 amp, 30 amp, and 20 amp outlets. This pedestal allows virtually any type of RV to be serviced with power. The 50 amp outlet is a 120/240 volt split-phase outlet, capable of 12,000 watts of total power. If you have an RV with 50 amp service you should have no problems powering your RV’s electrical appliances when plugged into a 50 amp outlet. Older pedestals may only be configured with a 30 amp outlet however. This is a single pole 120 volt feed, capable of 3,600 watts of total power. You can adapt your 50 amp coach to this 30 amp outlet via a dogbone adaptor but you will be severely limited in just how much you can run in your RV. If the battery charger is pulling 5 amps and your two air conditioners are pulling 12 amps each you’ll be drawing a total of 29 amps. All it takes is for the electric water heater element to kick in or someone turning on the microwave and you’ll trip the pedestal breaker and you’ll be making a trip out to the pedestal to reset it, which of course always happens when it’s raining.

Manual Energy Management

Manual energy management entails turning off some loads so that you can turn on others. If you really need to get hot water it would be best to use the propane burner instead of electric if it’s hot out. If you need to use the microwave for a bit then you’ll have to shut down one of the air conditioners so that amperage can be used by the microwave temporarily. Eventually this gets to be tiring and you’ll either find places to stay at that only have a 50 amp service or you’ll wish you had an automatic energy system.

RV Automatic Energy Management Systems

An Energy Management System (EMS) automatically performs the circuit switching procedures for you. Do not confuse a true EMS system with surge protection. Some name brand surge protectors use the term EMS in their models and descriptions. In a way, this is true because they do more than stop surges. They also protect from low or high voltage but they are still part of the surge protectors category. True EMS systems do not consider voltage levels. They only monitor the amperage draw and perform shedding of various circuits to keep the total power consumption beneath the pedestal breaker rating.

Let’s assume that you want to run two air conditioners (at 12 amps each), the electric water heater (at 10 amps), and your battery charger (4 amps in float mode). That’s a total of 38 amps, which won’t work on a 30 amp service. We’ve already switched the refrigerator over to propane so that’s out of the equation. The EMS will shed the first available load, which is the water heater so that everything else can run. You’ll then be drawing 28 amps. When the thermostat kicks out one air conditioner the load will be reduced to 16 amps so power to the hot water heater will now be restored and the new load will be 26 amps. If someone turns on the microwave and needs another 11 amps, the total draw would be 37 amps so the EMS will shed the next item on the list so now the water heater and one air conditioner will be shed. When the microwave is finished the next priority level circuit will be restored, which in this case is the air conditioner. By doing this the EMS prevents the pedestal breaker from tripping by limiting the total current.

A more recent entry into the energy management field is an EMS by Precision Circuits, Inc. This unit operates in similar fashion to the Intellitec system except it takes it one step farther. It actually interfaces with the inverter and will trigger the inverter so that it powers its output circuits rather than passing through shore power. This way when someone operates the microwave the inverter will power it rather than shedding a circuit. Should this continue for a long time the EMS will stop the inverter to prevent running the batteries too low and will shed circuits like a traditional EMS. This offers the benefit of not having to shut down your air conditioner on a hot day if other loads are going in and out. In order for this feature to function the PCI EMS must be connected to a Magnum inverter. A number of manufacturers are now using this more sophisticated system. An additional remote display panel is required – one for the inverter and one for the EMS.

Surge Suppression: Protect against low or high voltage

Technically, a surge protector protects against surges in electrical power. But surge protectors as used in RVs do far more. In addition to surge suppression, the most popular surge protectors also protect against low or high voltage levels. Low voltage can be a common occurrence in campgrounds that have added sites over the years but failed to upgrade their electrical grid to keep pace with the increased demand. Low voltage can cause quite a bit of damage so it’s important that you purchase a quality surge protector that includes over and under voltage protection as well. First let’s define just what an electrical surge is.

An electrical surge is where the incoming voltage rises to a point significantly higher than what it’s supposed to be. A voltage spike is similar but a spike is defined as lasting for one or two nanoseconds whereas a surge lasts three nanoseconds or longer. If the voltage is high enough it can damage your electrical devices. Earlier we talked about electrical voltage and how it is a measurement of pressure. If you get a sudden surge in water pressure you are apt to blow a hole in your fresh water supply hose but if you get a sudden surge in electrical pressure you are going to blow some electrical devices or sensitive electronics equipment. Surge protectors use metal oxide varistors, commonly called MOVs. An MOV does nothing at normal voltage levels but when the voltage rises to an unsafe level the MOV will short that power to ground to protect any downstream electrical equipment.

Importance of a Quality Surge Protector 

A quality surge protector designed for RV use will also have both over and under voltage protection. Overvoltage isn’t a real common problem in an RV park but it is a distinct possibility. Excess voltage will do the same damage as a surge except it’s generally not as high a peak voltage but it lasts for much longer. The most frequent condition is low voltage at the campground pedestal. You may arrive at your campsite early and check your pedestal voltage with a voltmeter and find it within tolerance. However, once other campers arrive and start to fire up their air conditioners the voltage is likely to drop. Without an automatic surge protector you would have no protection against low voltage damage to your coach unless you constantly monitor the incoming voltage. A good surge protector will disconnect power to the coach should either low voltage or high voltage conditions appear. At that time you would have the option of waiting it out, running your generator, or using an Autoformer to boost the incoming voltage – more on that later. Quality surge protectors for RVs are available from Surge Guard and Progressive Industries and are two well respected companies that offer their product through most major RV accessory sales outlets.

Benefits and Disadvantages of Portable Surge Protectors

In the images above, we can see two portable surge protectors. Portable units have the advantage of being able to be readily moved from one RV to another. This makes for a zero installation setup with no rewiring. Just plug it into the campground pedestal and plug the RV’s power cord into the surge protector. 

The disadvantages are that it is out in the weather and could get stolen or vandalized. There are locking kits available to lock them to the pedestal but then you are trading the convenience of not having the initial install versus connecting it and securing it to the pedestal every time you go camping. If the pedestal’s receptacle is very low to the ground it’s possible that the portable unit may not fit because of the right angle plug and the bulk of the unit that needs to hang down from the outlet.

One last caveat is that the hard wired units sometimes offer a remote display option so that you can monitor the incoming power from inside the coach. With a portable unit you won’t be able to utilize that option. The actual protection levels of the portable units are generally the same as their counterparts in the hard-wired segment so there’s no advantage or disadvantage there.

A 50-amp Surge Protector from Progressive Industries

Surge Protector Installation

Hard-wired devices do take a bit of installation labor but it’s not that difficult. You simply mount the unit in the same electrical compartment that your RV’s cord is located in. Remove the power cord from the transfer switch and connect the cord to the surge protector’s input terminals. Then run a short whip cord from the surge protector’s output to the transfer switch and you’re all set. Some RV owners choose to just cut 2-3′ off the end of the power cord while some choose to buy another short chunk of cord from a home improvement store. If you have a power cord reel you’ll undoubtedly be buying a new whip. If your surge protector includes a remote display you will have to find a location for that display, mount it, and then connect it with a standard RJ11 modular phone cable. A cable is generally supplied but if you want to run a longer distance you may have to make a new, longer cable to reach the remote display panel.

The Best Energy Management System for Your RV

Surges are rated in Joules. The bigger the surge, the higher the number, so you want to get a surge protector with the highest possible rating. The popular Surge Guard 34560 is rated to handle up to 1,750 Joules of power surge. It will shut down power to the coach if the voltage falls below 102 Volts or is higher than 132 Volts. Various LEDs will inform you whether the receptacle is properly wired or has a bad ground, reversed polarity, or open neutral. If it shuts down the power due to low or high voltage or an open neutral wire it will reset itself once the power returns to within tolerances. There will be a two minute, 15 second delay before power is re-energized though to allow any air conditioner time to bleed off their head pressure. If you decide that you want to bypass the voltage cutouts feature and allow power through you can defeat the unit by turning a key switch. In this mode you will still have surge suppression, however. Surge Guard also makes automatic transfer switches with built in surge protection and low voltage protection. These transfer switches are becoming very popular in recent diesel pushers due to their ability to also communicate with a multiplexed network control panel.

The Progressive EMS-HW50C is the gold standard of surge protectors. It’s rated to handle up to 3,560 Joules of surge. Low voltage cutoff occurs at 104 Volts and high voltage cutoff occurs at 132 Volts. It comes with a remote LED display that is very easy to read. In addition to displaying the incoming voltage of both poles it will also display the amperage draw on each pole as well as the frequency in Hertz. If any pedestal mis-wiring is present or any shutdown has occurred the LED display will display a 2 digit trouble code that defines the problem according to the chart that is printed on the unit as well as in the owner’s manual. The remote display can be mounted inside the coach or in the basement compartment. In this way it’s handy to locate the EMS-HW50C near the back of the compartment where it’s easy to wire and still have the remote display located near the front of the compartment where it is easy to view. The bright LED is easy to read in bright sunlight and a bypass switch is located on the remote display to bypass the power shutdown function, just like in the Surge Guard above. You have the choice of selecting either a 15 second power-on delay or a 136 second delay. Most modern air conditioners have a built in two minute restart delay so 15 seconds is the normal selection. You can also buy a second remote display that allows you to mount one in the basement and one inside the coach if you desire.

While the EMS-HW50C is the old standard, Progressive Industries also make the EMS-LCHW50 surge protector. The “LC” stands for Liquid Crystal display. Instead of a remote LED display, the LC series uses an integral liquid crystal display that is located right in the cover of the unit. The protection level is the same as its big brother but, depending on where the unit is mounted, you may have more problems in viewing the display. LCD screens just aren’t as bright as LEDs and dark places and bright places are not their friends. Coupled with the fact that the remote LED display can be located anywhere and the LED holds a huge advantage. Still, the LC series does hold a $50 price advantage over its more costly brother.

RV Batteries and Chargers

Batteries are critical to an RV. They start the engine and provide power to run accessories when driving. When parked they provide power to run lighting, water pumps, and various other 12 volt accessories. They can even be used to power an inverter to provide 120 volt AC power. Because of their heavy use they can sometimes be a source of aggravation and maintenance. Let’s take a closer look at batteries, how they work, and how to properly care for them. We’ll also delve into battery chargers and charging methods.

RV Battery vs Car Battery

A single battery may be fine to operate your passenger car but it’s just not enough power to handle the more advanced requirement of an RV. To do this, multiple batteries are arranged together into a battery bank. There are two types of batteries and each type has a different intended use. Automotive batteries are what you have in your car. They are designed to output a large burst of amperage to start the vehicle, then slowly recharge from the vehicle’s alternator. The key here is that they dump a lot of amperage in a short time, then rest for a while slowly getting recharged. Most diesel motorhomes will have two engine-starting or chassis batteries in order to crank these larger engines.

When camping, your coach electrical systems operate quite differently. They will draw fewer amps than a starter motor but they will do that over a longer period of time. For this application deep cycle batteries are used. Deep cycle batteries are designed for maximum performance by slowly draining amps from them and sustaining this draw over a longer period of time. Most coaches will have four deep cycle batteries in a battery bank to ensure that there is enough capacity to supply adequate power over a longer length of time. This can vary and some smaller coaches may only have two, while larger coaches may have as many as eight batteries in a bank.

How RV Batteries Work

RV electrical systems are 12 volt systems. Whenever you connect multiple batteries together you have to make the proper connections in order to maintain 12 volts. If batteries are connected in parallel they will retain their voltage, but if they are connected in series the voltages will add up. So, if you have a bunch of 12 volt batteries that you want to connect into a battery bank, you simply connect all of the positive and negative posts together to give you increased load capacity or amp-hours. 

6 Volt Batteries vs 12 Volt Batteries 

But many RVs are using 6 volt batteries for their deep cycler applications, which are commonly used in golf cart applications. They have a heavier plate design and are more durable, plus they output more power than a 12 volt battery of similar dimensions. The only downside is that you need to connect them properly to get a 12 volt output. Basically, you connect a pair of 6 volt batteries together in series to give you a single 12 volt battery. Then you connect the positive posts of this pair together with all of the other pairs and then do the same with the negatives. The following diagrams show a four battery bank of both 12 volt and 6 volt batteries and will help explain this better.

Types of Batteries used for RVs

Batteries come in different types. For RV applications the most common are flooded batteries or AGM batteries. 

Flooded Batteries 

Flooded batteries are filled with electrolyte. This electrolyte is a diluted form of sulfuric acid. When a load is placed on the battery, the acid puts a charge on the lead plates and creates electricity. At this time some of the sulfur and oxygen leaves the acid and forms a sulfate on the lead battery plates, leaving water as the remainder. If a battery is totally discharged, the battery plates will be coated with sulfate and the electrolyte will be mostly water, which is why dead batteries can freeze in cold temperatures but fully charged batteries will not freeze. When the battery is recharged, the sulfate falls of the battery plates and recombines with the water to change it back to acid again. If the battery is overcharged (in other words excess voltage is applied to it when it already is charged up), the water can boil out of the battery and acidic vapors can leave via the vented battery caps. This reduces the water level and if it gets below the battery plates it can harm the battery. It also tends to corrode the battery connections because of the acidic vapors. Maintaining the proper water level is critical to good battery performance.

AGM Batteries 

AGM batteries use electrolyte but not in a liquid form like flooded batteries. The acidic electrolyte is absorbed into glass fiber mats that are wrapped around the lead battery plates. With AGM batteries there is no need to ever worry about adding water because there is no water in them so maintenance is greatly reduced. The battery terminals also are not as susceptible to corrosion as flooded batteries because there is only microscopic outgassing, or venting, of electrolyte vapors. The outgassing of flooded batteries means they need to be in a vented compartment and clear of anything that could create a spark. AGM batteries can be located anywhere because they truly are sealed. AGM batteries are typically used in aircraft and they can be used in any orientation, even upside down, with no negative consequences. AGM batteries also offer greater performance over a comparable flooded battery because the voltage drop curve is flatter.

Battery Chargers

We all know how easy it is to take power out of a battery. What about recharging them when they are low? Batteries in a motorhome can be charged in a number of ways depending on the current mode of operation and whether they are chassis batteries or coach batteries. 

Chassis Batteries and Coach Batteries 

First off, we need to understand that there are two separate battery banks on a motorhome – the chassis batteries and the coach batteries. 

The chassis batteries are for starting the motorhome’s engine and powering the headlights, wipers, and other chassis related accessories. When driving down the road the vehicles alternator will charge the chassis batteries. 

The “house” portion of the motorhome has a separate bank of batteries called the coach batteries. These are deep cycle batteries that will power the lights, domestic water pump, fans, and any other accessories that are related to living in the coach while parked. These batteries are kept separate from the chassis batteries so, in the event that you run them down too low, you will still be able to start the motorhome’s engine. 

A Charge Solenoid is installed to connect both the chassis and battery banks together. This solenoid is engaged whenever the ignition key switch is in the “on” position. The engine can then recharge both battery banks when driving down the road. As soon as you are parked the solenoid opens and the two battery banks are divorced once again.

Charging Batteries at a Campsite

 We don’t want to have to run the engine all the time to recharge these batteries, so we need other options. The first option is a battery charger that is dedicated to the coach’s electrical system. This charger is a 120 volt device that will be powered whenever we plug into shore power or run our generator set. In addition to charging the batteries we also need to provide clean power with consistent voltage to power the 12 volt electrical components while we are parked rather than use the batteries to power them. This device is called a converter. 

The converter is hard-wired into the 120 volt electrical system as well as the 12 volt system. It “converts” 120 VAC power to 12 VDC power to run the 12 volt accessories as well as charge the coach battery bank. So, now we have the ability to recharge the coach batteries via the engine alternator when driving or via the converter when parked with shore power or when running the generator. When boondocking we can use the batteries to provide power. When the voltage gets to that magic 50% mark, we can fire up the generator set for an hour or two to power the converter and recharge the batteries. The actual charge time will vary according to the size of the converter as well as the size of the battery bank. If the battery bank is 440 amp-hrs and it is at 50% you’ll need 220 amp-hrs to bring it to its fully charged state. If you have a 60 amp converter you’ll be looking at close to 4 hours to output that much power. Larger converters take less time but cost more.

Another popular device is the inverter. An inverter does just the opposite of a converter. It creates 120 VAC power from 12 VDC. It is used to power 120 volt devices via battery power so that you don’t have to run the generator all the time. Small inverters run from 250 watts up to 1,000 watts and are installed into an electrical circuit. No battery charging capabilities exist on a basic inverter so most diesel pushers use an inverter/charger unit. These units combine the features from both an inverter and a converter. They are generally found in larger sizes, such as 2,000 watt and 3,000 watt. These inverters are connected to a dedicated 120 volt circuit breaker in the main breaker panel and also connect to the coach batteries via large diameter battery cables. They feature an automatic transfer switch that will pass shore power through when present, or switch over to battery fed inverter power whenever shore power is not present. Note that the running of the generator is the same thing as shore power in this instance. Whenever 120 VAC power is present the inverter not only passes that power through to the electrical devices fed by it, but it also acts as a converter and provides 12 volt current to power the house accessories and recharge the coach battery bank. Typical inverter/chargers have battery charging capacity in the 100 to 140 amp-hr range so they are larger and faster than a converter. When an inverter/charger is present there is no need for a converter.

Both converters and inverter/chargers feature three battery charging modes. When a battery is low on charge the first mode is the bulk mode. This mode provides full charging output to the batteries. As the battery approaches the full mark the charger will kick into absorption mode. In this mode the voltage is regulated to not be excessive so that the batteries can absorb this charge without boiling. Finally, in order to maintain a charge in a battery that is very close to full the float mode will be engaged. In this mode charger output voltage will be limited to no more than 13.2 volts so that excess outgassing does not occur. You can safely leave your batteries connected to the charger indefinitely if it’s in float mode without fear of boiling out water. Of course, this assumes that your charger’s float mode is functioning properly. If you are adding water frequently it’s time to have your charger’s float voltage checked.

Low Voltage Circuits

Motorhomes are meant to be used when 120 volt shore power is not always available. It would be a real pain if every time you walked into your motorhome you had to fumble around in the dark to start the generator so that you could turn some lights on, which is why RVs have 12 volt battery powered electrical systems as well as 120 volt AC electrical systems. 

The 12 volt system provides power to operate the interior lights and the many other 12 volt electric systems within the coach, such as fans, water pumps and furnaces. These systems will be connected to the coach battery bank via a 12 volt fuse panel that is located somewhere inside the coach. A converter or inverter/charger will also be connected so that these batteries can be recharged from shore power or when running the generator.

Powered Roof Vent Fans

Powered roof vent fans, such as the one pictured above, are found in most every RV. In addition, you’ll undoubtedly find that you have a tank monitoring system to check the levels of your fresh water, propane tank, and holding tanks. This information may be displayed on a small remote panel or incorporated into a networked touch screen control panel. Your refrigerator and hot water heater are designed to run on either 120 volt AC current or propane. But, you will need 12 volt power to operate the igniter and the control circuitry for any propane fired refrigerator. Even the light bulb inside that fridge is powered by 12 volt power. Basement compartment lighting and power awnings are other examples as are the power steps that allow you to enter your motorhome.

Battery Disconnect Switch

If you were to leave your motorhome parked for a while and shore power was not available, the various parasitic loads on the 12 volt circuits would eventually drain the batteries. RVs have a battery disconnect switch, which is generally located close to the entrance door. This switch controls a battery disconnect solenoid. This solenoid is a latching solenoid which means you send it power to move it but you do not have to continue feeding it power in order to hold it in that position. This makes it perfect for an RV application because the solenoid won’t consume any battery power when parked. Pressing the rocker switch in one direction will shuttle the solenoid to the open position while pressing the rocker switch in the opposite direction will send the shuttle in the other direction and close the circuit. This allows for an easy way to shut down the 12 volt power to the coach while you are away. If you are plugged into shore power, this is not necessary. Keep in mind that not everything will be disconnected when the solenoid is in the off position. Some loads, such as inverters, keyless entry systems and propane leak detectors bypass the solenoid and will remain active.