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Mod #9: Generator Install

Posted By Mark Corgan On June 13, 2008 @ 6:16 am In electrical | 18 Comments

There are many options for powering your RV when you don’t have hookups, from the basic battery to the full-blown hi-tech solar/inverter/giant battery bank setup. One of the most convenient options is a generator. While generators can be an expensive investment, always having power, whether day or night, is worth the cost to most.

Mod Difficulty:

Most class A and class C motorhomes either come standard with a built-in generator or are pre-configured to accept one. 5th wheels and toy haulers also can come from the factory with a generator, although it is generally an option rather than a standard. Travel trailers have fewer options and don’t typically, save for a few manufacturers like Arctic Fox, have provisions for a generator. But since we are talking about modding your RV, no RV has to go without a generator.

Installing a generator in an RV that is not equipped for one is a daunting project. Even if you have provisions for one, things like mounting, cooling, wiring, fuel supply, exhaust routing, noise and vibration, and accessibility all need to be seriously considered and planned for. But not to worry. Many RVers have already done this mod with great success. Some have even gone as far as retrofitting portable generators that were never designed to be mounted to or in an RV.

If you are fortunate to have an RV that is “generator-ready”, your options are straightforward. There are basically 4 manufacturers that make RV-style generators: Honda, Generac, Onan, and Kohler. There are others but these are the most popular. Of these, Onan is by far the most prevalent in factory installations. Onan not only makes the generator but also the kits, including mounting brackets, wiring, and exhaust. This makes for very clean and easy installation. The other manufacturers also provide installation kits as well. If you are doing a custom install, some of the parts included in the installation kits can still be useful. For example, if you build out a custom enclosure from one of your storage compartments, the mounting bracket can simplify any custom welding for the frame mounts.

Supplying fuel to the generator can be problematic depending on the type of RV. Class A and class C motorhomes share the fuel supply already on-board, whether diesel or gas. Toy haulers will have a fuel tank installed as part of the generator option, which doubles as a fuel station supply for filling up the toys you haul. It’s when you are doing a custom install that you must decide on the fuel to use. Some opt to use the on-board propane which is a very clean burning source. Choosing propane however has two drawbacks: 1) There is a limited supply which isn’t easily replaced if you’re boondocking, and 2) Using propane derates the power output of the generator around 10% or so. Something to keep in mind if you size the generator just at the edge of your power requirements.

If you choose not to use propane as a fuel source, you must retrofit a gasoline fuel tank. There are gas tanks purpose-built for custom mounting, which include a fuel supply outlet, vent, fuel level sending unit, and fuel filler provisions. Select the largest fuel tank that you can reasonably fit to your RV. This way you won’t be worrying about running out during an extended boondock. You should also consider how you move the fuel from the gas tank to the generator. Some generators have a low-pressure fuel pump built in but others may not. If you have to install a fuel pump, be sure to consider how you will power it and use high-quality fuel hose. Don’t compromise here.

Sound deadening is another area many have spent considerable amounts of time on. Most factory generator installations have very little to no sound deadening material at all. Basically, you get a sealed (to the inside of the RV) enclosure made of galvanized steel and, well, that’s it. A lot of sound is transferred in to the RV through the thin metal. Lining the top, sides, and back of the compartment with layers of differing sound deadening material seems to have the greatest effect. With a custom installation, you may have to experiment on what works best for your particular compartment fabrication situation.

Another consideration with a custom install is routing the exhaust. If it’s possible, try mounting the generator on the left or street-side of the RV. This way, the exhaust smell and generator noise will be reduced and will make sitting outside on the entry-side of the RV more comfortable. However, your camping neighbor may not appreciate this as they will get the brunt of the noise and smell. Routing the exhaust out the back side of the RV may be a better choice if you camp in close side-by-side quarters. Ensure you use the appropriate size exhaust tubing too so as to avoid excessive back pressure and possible overheating of the generator under heavy load.

Cooling and ventilation is also very important to account for to ensure proper operating temperatures. In a custom install, there needs to be a way to get cool air in and hot air out. RV-specific generators will have this solution already built in to the generator housing. However, putting this type of generator in an improperly ventilated compartment will overheat the generator in short order. Ensure the access door to the generator has an adequate fresh air opening sized to the generator requirements, and ensure the hot air can be exhausted out the bottom of the enclosure. This can be accomplished using an electric fan with enough flow to suck out the hot air produced by the engine-driven cooling fan.

Wiring for the generator will depend on how “automated” you want the system to be. Plugging the shore power cord directly in to the generator receptacle is the easiest way to ensure you cannot have both shore and generator power simultaneously being supplied to the RV. However, doing it this way can limit you to running the generator only when the RV is stationary as you wouldn’t want your shore power cord dangling in the wind while plugged in to the generator going down the road!

Another wiring option is to use a transfer switch. This device allows two sources of AC power to be connected at the same time to the RV, but only one source is used at a time. The generator AC output is wired in to “one side” of the transfer switch and shore power is wired in to the “other side”. A single AC output from the transfer switch provides the AC input to the RV load center. A relay inside the transfer switch then switches between the two sources as appropriate, ensuring fireworks only happen on the 4th of July.

You will have to have some way to start the generator. Installing a remote switch that can be used from inside the RV is optimal but most electric-start generators can be started from the generator itself. Do not use your RV battery as a starting battery for the generator. RV batteries are not particularly good starting batteries and can be damaged if used repeatedly in this manner. Use a dedicated starting battery. Usually, a lawnmower-size battery is good for most generator starting requirements. Anything over a 5kW or diesel generator should use something larger. Refer to the generator user manual to determine proper size.

Finally, there is still yet another installation option some have used to varying degrees of success. This is the venerable bumper mount of portable generators on travel trailers and 5th wheels. There is passionate debate on whether this is a safe idea with the argument being anything from “the generator will fly off and kill someone” to “tongue weight will be drastically reduced causing a deadly sway condition”. Properly done however, the bumper mount can be as safe as you want to make it. If you choose this route, make sure you use a qualified welder for building the generator platform, attachment points, and frame/bumper reinforcement. It is best to mount the platform to the frame rather than the bumper as the bumper is fairly thin gauge metal. Be sure you check with your RV manufacturer on whether or not the rear frame of the RV can structurally handle the additional stress as some rear walls have been known to buckle and crack depending on much weight is placed on the bumper/frame.

ModMyRV recommends these parts for this mod:

RV Generators
All Brands of RV Generators
RV Generators by Onan
RV Generators by Honda
RV Generators by Guardian (formerly Generac)

Transfer Switches
Go Power! 50 Amp Transfer Switch
Go Power! TS-30 30 Amp Automatic Transfer Switch

Exhaust Components
Onan Exhaust Accessories
Jacks Small Engines Quiet Mufflers

Fuel Tanks
Summit Racing Fuel Cells and Accessories

General Reference
How to Choose a Portable Generator for Your RV

Example Installations
Example of an Onan Installed in a 5th Wheel
RV.net Forum Thread on Custom Portable Generator Installation


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