Your RV, Motorhome or Camper Generator and How It Works

How the Generator in your RV works

In this Hub you will be given an overview of the different designs of RV Generators, how generators operate and some basic generator service tips. It will describe differences in Gas powered generators and Diesel powered generators and how they function.

This information will help you better understand your generator and often determine the cause of some generator problems.

Popular Onan-5500 Power Generator

The very common Onan-5500 Power generator that you will find in many of the motorhomes on the road toady.
The very common Onan-5500 Power generator that you will find in many of the motorhomes on the road toady. | Source

A History of RV Generators

First of all, there are people that are called "Rough Campers".

You know, those people that believe in real "roughing it" camping, using only; a tent, a sleeping bag, a backpack of dried foods, bottled water, a few matches, a snake bite kit, and not much else.

And you know what? I've been there, and I've Done That!

It was fun! Especially when I was young, healthy, strong, and had very little money.

And, later in life, when I was first married, and we had kids, I rough camped then too; at camping resorts at beaches and in the mountains. We used larger tents, nicer sleeping bags, inflatable mattress', a small cooking grill, several coolers for real food, and a few more accessories.

And that was fun too!

But, after a few years, we purchased our first tag-along camper. It had rudimentary plumbing, electric lights, and storage cabinets, a "porta-potty", and more comforts from the vagaries of the weather, and, of course, even more accessories to make our camping more fun.

Those first old campers of ours, way back then, had your basic accessories, such as electric lights, a water pump, a propane stove, and such. But, really, not a lot else, and especially not such things as Television, AC, Hot Water Heaters, microwave ovens, and all of the amenities that you will find as standard on the RV or camper of today.

RV and Motorhome Batteries

Our first couple of tag-along's, way back then, did not have a generator.

They had a battery.

This was usually, just a deep-discharge type of 12-volt DC Battery. The same as that used in an automobile.

It was usually tied down onto the front end of the tag-along, in a plastic case, to protect it from the weather, and you charged it up before you left home.

And, considering it only had to power a few 12-Volt interior lights, and maybe a small water pump to provide water at the miniature sink, it was more than adequate for a good week of fun.

Over time, if you were at a campground that provided 115-VAC at your site, the camper manufacturers added small, efficient AC-to-DC converters, so your camper battery was kept charged at the site.

And once you had an RV with AC as well as DC power, along came; dual-mode light systems (110-VAC and 12-VDC), as well as connections for small appliances. There were showers, electric Hot Water Heaters, larger water pumps, microwave ovens, and wall receptacles.

Appliances for Motorhomes

Yes, probably the most important electrical addition to the RV was when the manufactures put extra electric receptacles into the campers; in the kitchen area, in the bathroom, in the bedroom, etc.

People started bringing those favorite appliances from home; coffee makers, hair dryers, toasters, portable TV's and radios, and on and on, and on.

RV manufacturers had to react with electric breaker panels (versus those old fuses) to handle the overloads, heavier wiring for the current pulled by everything.

Finally, the world of camping expected to use such items everywhere, in state parks, in the woods, alongside streams and lakes, and pretty much everywhere they went.

So, the next "necessary item" for the typical camper of today is, you got it, a good Electric generator.

We all want that power, everywhere, all of the time.

At the flick of a switch!

Modern RV Generators

Today, the average camper or RVer, travels much further to reach their camping destinations.

They often have to stop for the night at an interim campground or two along the way, or they may do the Walee-World thing, or stop and sleep at a Rest Stop, or just at a public parking lot. And then move on in the morning.

When taking such trips, they usually have a fridge that is packed with fresh food, and beverages, and are able to eat very good meals and then sleep in that comfortable bed in the camper.

Myself, I have pulled into a rest area around 6-7 PM, fired up my generator, turned on the TV for local news and weather, eventually cooked a light dinner, and watched my favorite network TV shows, all with the AC running, and finally I'd go to sleep in my nice cool camper, on my own bed.

I will often leave the generator running, usually all night, along with a couple of roof fans, re-charging my house batteries, and providing just enough background noise to drown out most of the outside noise from the comings and goings of other vehicles, campers, and truckers in the rest area.

I will get up in the morning, make fresh coffee, toast a muffin, and boil or fry an egg for a hot breakfast, maybe even take a hot shower, all before I shut down my generator, and continue my trip.

Now, I have a Motorhome, with a built-in generator, that is designed especially for the appliances in my RV, and, of course, it is ridiculously easy to operate.

And, often, right beside me, might be a Class-C, a Fifth-Wheel, a Tag-Along, all with their own built in generators, providing those creature comforts we are all spoiled with. Ain't camping life a rough life?

And, even if you don't have a built in generator, many campers use portable power generators when they camp in a rough site somewhere.

There are many good Portable Generators around, and they are relatively cheap, for what you get. So, they very popular with many campers today.

Understand how your Generator works!

How a Generator works

If you have and use an Electric Generator, you must understand how it works and your responsibilities to assure that it is there when you need it. First of all, It has to start, easily and quickly. Then it has to run, smoothly, automatically, and efficiently.

Here are some basic facts about generators that everyone of you probably already knows, but I am going to list them here anyway.

There are four basic functional sections of an Electric Generator. Of course you can tear a generator down to smaller and smaller working pieces, but I am not trying to teach you to be a mechanic, rather I want you to know how one functions from a high level, and from that you will understand the importance of those pesty preventive maintenance parts, and why they need to be monitored and replaced occasionally.

The functional sections are;

  • a fueled Motor
  • a Fuel System
  • an Electric Starter Motor
  • an Electric Power Generator

The Fueled Motor

OK, Generators are run by a fueled motor of some kind. Usually gasoline or diesel. Today, there are many different designs of motors themselves from the simple to the complex.

An example I can use here is a simple, cheap gasoline powered lawnmower motor. The one I am using here has two cylinders.

The cylinder contains a piston which is connected to a crankshaft, and it has a fuel input port and an air input port, as well as an exhaust port. The other cylinder is the same, but the two are designed so that when one cylinder is firing, the other one is getting fuel and air to fire.

This whole assembly is mechanically designed so that you will get continual firing and exhaust and the crank shaft will turn from all of this combustion action in the cylinders.

In a Diesel motor, the spark plug is gone, and the combustion is achieved via high compression of the diesel fuel.

Both types of motor are designed to use their form of combustion to keep the crankshaft of the motor turning.


One of the most important things to watch is your generators motors lubrication. Your generator motor used oli to keep all of those mechanical parts running smoothly, as they rub against each other. You should always assure that you have an adequate amount of oil in the motor, and that the Oil Filter on the motor is changed as scheduled by the manufacturer.


Some Electric Generators are Air-Cooled, and do not use a water-antifreeze cooling liquid. But as your generator gets larger, it will often have a cooling system similar to an automobile engine. When this is the case, you need to check the level of the coolant reservoir regularly, and the level is kept within limits. And, as with an automobile, consideration must be paid to the antifreeze levels and strength for the season and region where you are using the generator.

The Fuel System:

RV Electric Generators are either gasoline or Diesel designs, and operato on one or the other of these fuels.

Gasoline Combustion-

A simplistic explaination- A stand alone gasoline Generator, gets it's fuel from it's own fuel tank, and it is usually fed via gravity to the carburetor on the motor. In the Carburetor, the gasoline is mixed with air (or oxygen) and injected in to the motor's cylindar where a spark is provided via a spark plug.

This spark, causes the mixture to explode, and forces the piston in the cylinder to open, this moving the shaft of the motor. All of this is done via mechanical timing which keeps the motor turning.

In a Coach, with a built in gasoline Generator, the functions are the same, but the gasoline comes from the Coach's main fuel tank.

Diesel Combustion-

A simplistic explaination- A stand alone diesel Generator, gets it's fuel from it's own fuel tank also, and it is fed via a fuel injection system directly into the cylinder of the motor, and mixed with oxygen there, and then the piston is moved to compress the diesel fuel, to the pressure necessary for it to explode.

There is no spark needed, nor a carburator on a diesel motor. When the fuel mixture explodes, it forces the piston to move open in the cylinder, thus turning the shaft of the motor. This cycle repeats itself via mechanical timing which keeps themotor turning.

Fuel System Service:

There are several things in a Generators fuel system that will at times require service; these are ; 1-a FUEL FILTER, 2a- a Carburator Fuel Jet, or a 2b-a Diesel Fuel Injector Jet, and on a gasoline motor, 3- a spark plug.

If the Fuel Filter gets dirty or bocked, even partially, the either no, or the wrong amount of fuel will be provided to your motor, and it will not run, or if it runs, it may miss or turn off sporatically.

In a Gasoline Generator, the SparkPlug is something that will, over time need replacement. They canbe come fouled with carbon or dirt, and eventually the contacts will wear out.

If the Fuel Jets are blocked then the motor will not run for lack of fuel, or if they are worn, over time, the wrong mixture will be provided,and the motor will not run properly.

You can replace a fuel filter, and maybe even a sparkplug if it isplaced conveniently for you on the engine, but you really want a trained mechanic to deal with the replacement of fuel jets.

The Electric Starter Motor-

Your Generator is started by turning the motor, until it goes through several firing cycles of several cylinders. Once they fire, the starter is no longer needed, as the motor will run on it's own.

The Starter Motor requires Voltage to turn and in your coach, this voltage comes from your House Batteries. IT takes a significant amount of current to turn your generator motor, and even more the larger the size of your motor/generator combinatoin.

You should also know that because a diesel motor uses a higher level of compression to force combustion, it will be harder to turn, and it will thus require significantly more current to turn it at a highenough speed.

The reason you need to know this is simple. There are some hefty wires coming from your house batteries to the generator of your coach.

And, you should check occasionally that the following things are done; 1- your House batteries arein good shape, and hold a strong charge, 2-Your connections to your batteries, as well as to your generator are clean, without corrosion, and they are attached tightly at each end, and 3- when your starter turns, it doesn't make weird sounds, and is turning the generator motor's shaft.

The Electric Power Generator- Again, a simple description of an electric generator. Picture a coil of wire wrapped around a shaft. This coil of wire spins inside the opening of a larget outer coil of wire.

If you can then visualize that the shaft of your generator is attached to the shaft of the fueled motor and turns when the motor turns.

Leaving all of the electro-mechanics out, if you connect a voltage to the ends of the inner coil of wire, and spin it inside the outer coil of wire, and then attach something like a charger/inverter to theends of the wires on the fixed outer coil of wire, you will get AC Voltage from these output wires.

Again, I have left out all of that complex design stuff like the magnetic metals used, the complex ways that the wires are wound, the contacts used, and on , and on. I just want you to now that there are parts in here that must be designed properly, and sometimes require maintenance.

Luckily, the generator itself is designed for minimal maintenance, and if there is a problem with yours, you need to see a trained generator mechanic.

Parts replacement suggestions

Replace When
per Mfg. manual
With a Gas Generator, I suggest keeping your old replaced sparkplug in case you need one in an emergency.
Fuel Filter
per Mfg manual
Keep a Spare, just in case, if you use your Gen a lot.
Air Filter
per Mfg manual
If the Gen is running rough, sometimes you can remove and clean the filter for better performance, temporarily.
Gas Jet
per Mfg manual
By a trained mechanic only.
Diesel Injector
per Mfg manual
By a trained mechanic only.
Fuel Lines
per Mfg manual
Check for wear or leaks, especially of you smell fuel.
DC and AC Wiring
per Mfg manual
Inpect wiring periodically for wear, torn insulation, and lose connections. Get replaced as necessary, by a trained mechanic.
Motor Oil
per Mfg manual
Check Oil Level, and change as needed, or when suggested by thr Mfg.
Oil Filter
per Mfg manual
These are easy to change, and follow the Mfg. instructions.
per Mfg manual
Use the Mfg suggested mixture of Coolant/Anti-freeze. Monitor regularly when using the Gen, and keep thelevel within the limits marked on the Reservoir.

In Summary

So, hopefully, I didn't lose you with my attempt at simplifying how an Electric Generator functions.

If I confused you, don't worry, I will now list the things that can, and should be serviced periodically. Also, if any of the terms or abbreviations is use here are new to you check out my hub on Electrical Terms. It might help.

Embarrassing! There is one little item that every Motorhome owner needs to know, if he already doesn't.

Every Motorhome manufacturer, today, that has included an Electric Generator in their design, has also added one little safety trick.

As an added function of the generator, they always run the fuel line for the generator in the main RV fuel tank, only down to the approximate level where the RV fuel tank is only 1/4 full.

This was done to avoid the situation where a camper might be out in the middle of no-where, and end up running all of the RV's fuel from the tank, using the generator, and not have enough fuel to drive to a gas station to replenish.

Yep! It used to happen, so they designed this little safety feature into their RV, to avoid it happening with their rigs. What you, as the owner need to do is remember this little fact, if you are out somewhere rough camping and go to turn your generator on, and it will not fire up.

The first thing you should do, to avoid embarrassment,is check that you have not used up too much fuel, and are now, suddenly, below that magic 1/4 tank level.

Basic RV Generator Maintenance

RV Generator Tips

© 2010 Don Bobbitt

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Comments 12 comments

Don Bobbitt profile image

Don Bobbitt 6 years ago from Ruskin Florida Author

Thanks Jesse, I hope you enjoyed the article. MAny people don't understand that these RVs are complex equipment, and include a lot of accessories that require the concerned owner to learn many different skills, even if only to understand when something in the RV requires maintenance, or not.

Don Bobbitt profile image

Don Bobbitt 4 years ago from Ruskin Florida Author

Sorry keelym. But a Motorhome usually, either has a separate generator that, for convenience runs on the same fuel type as the RV itself. And,with either,you generator is your alternate power source for your camper accessories when you are parked and do nothave anyother power source available.

Thanks for the comment though!.

dave 4 years ago

My 1970 Travelmaster camper Lights go on for a well then go off for a well but the outlets still work its plug into the mane. it also has a battery hookup with a fuse

Don Bobbitt profile image

Don Bobbitt 4 years ago from Ruskin Florida Author

Dave, Almost all of the generators on older motorhomes require that there be at least a little load on them or they will cycle and give you poorly regulated output voltage, but yours sounds like something else.

First,you say that the lights go on and off but the outlets still work? Do you mean that if you plug a lamp into a receptacle the camper lights cycle on and off but the lamp in the outlet doesn't? IF the lamp cycles also, then I recommend that you get your generator checked, things like; 1-a clogged fuel filter, clogged jets in the carburator, rotten fuel lines to the generator allowing air into the fuel line, are some the most probable causes.

PS. Turn on a TV and see if the lights cycle then.

Good Luck.

mona 3 years ago

we have aclass c motorhome with a onan gas generator, we arent getting any fuel. does this generator have a fuel filter and if it does where is it located?

Don Bobbitt profile image

Don Bobbitt 3 years ago from Ruskin Florida Author

mona- Without any other information, on your RV or generator, I can say that almost all Onan generators are "self-contained" and that yourt fuel filter will be found under the covers.

Just find the fule line going into the generator, and it should go into the covered unit and connect to the fuel filter itself.

One other thing. Some Class-C motorhomes are built on truck frames and will have an original truck/van fuel tank. And, many of these tanks have the fuel PUMP built inside the tank itself. You should checkthat this is working properly also.

Good Luck!


Teri 2 years ago

I'm plugged into the house. I have a class c two days ago I had power today I have power only to the microwave. Nothing else. I've checked breakers and fuses and all appears well The steps work too but absolutely nothing else. Where else do I look

Don Bobbitt profile image

Don Bobbitt 2 years ago from Ruskin Florida Author

Teri- OK the steps and your internal lights are 12VDC. If they all work then your DC COACH system is OK.

If your Microwave actually works, by that I mean heats, then you have 110VAC coming into your Class-C OK.

If all of your breakers are actually functioning then your AC distribution system is OK. If your Roof AC works and you just do not have power to your appliances plugged into receptacles then you probably have ground fault receptacles that have kicked out. Find the master ground fault receptacle and reset it.


Randy 2 months ago

My gen wouldnt start or run. suspected bad carb. Onan 5500 Gold. spent the $$$ on the carb, installed it and viola, it ran, for about 5 min anyway, and not will not run again. HELP!!!

Don Bobbitt profile image

Don Bobbitt 2 months ago from Ruskin Florida Author

The two most common problems with RV generators are; the FUEL FILTER and the FUEL Pump. Over the years, I have had to replace both on several generators.

These two parts on these Onan 5500 generators are usually mounted under the generator. If you crawl under there you will see the pair mounted with a couple of screws.

If you are interested, I have written an article on how to replace these two items. It is called RV Generator maintenance, How to replace your Fuel Filer and fuel Pump.

Good Luck,


vince 6 days ago

i have a diesel gen i change the oil and filter drain water very little water came out i fill oil and water but only took 1/2 qt water it sart run then stop after 3 to 4 minn

help please thank vince

Don Bobbitt profile image

Don Bobbitt 5 days ago from Ruskin Florida Author

Vince - RV generators are air-cooled, so I'm not sure what yours is. But You didn't mention the fuel filter for the generator. Diesel fuel is a dirty fuel, so I would immediately change the fuel filter. On some Rv's the fuel filter is attached to the generator while on others, it may be mounted on the RV chassis near the Generator. This filter must be changed regularly, and I suspect it's your problem. If not, it's time to take your Rv to a service center so a PRO can check the Gen out.

Good Luck,


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