kevin working on rv generator
Inspired by our generator’s death in October 2020

This article is an RV generator guide to the basics such as what they do, why you need them, and how to choose the best solution for your situation. The best lessons are learned the hard way and we educated ourselves about RV generators out of necessity. We’ve consolidated all of our research in one article to help if you need to replace your RV generator or want to buy a new one.

Our hard lesson started when our 7500-watt onboard Onan generator wouldn’t start in Moab. The RV gods saw all of our well-laid autumn travel plans and laughed.

Part of traveling in an RV full-time means things are constantly breaking. In October, our solar production was low and we needed a generator to charge our batteries. We changed our travel itinerary leaving Moab two weeks earlier than planned and headed to Salt Lake City for generator service.

RV Electricity For Beginners

RVs typically have two electrical systems.  A 12-volt DC system (similar to automobiles) powers lights, fans, water pumps and other electronics. A 120-volt AC system (similar to home-based power) powers air conditioners, appliances and other common household electrical items. 

As discussed in our solar blog post, we get most of our energy from the sun and it is stored in our 12-volt batteries.  We use that stored energy to power the 12-volt system as well as an inverter. The inverter changes the stored energy into 120-volt AC to power the other side of our electrical system.  It works great for us for the majority of the year but is not always sufficient or practical. 

What does a generator do for an RV?  

Another source of energy is needed for the cloudy days when the sun does not generate enough energy or for RVs without an extensive solar and battery storage system.  The most common RV energy source is a generator.  It creates a lot of energy quickly using the energy-dense fossil fuels readily available.   

A generator converts mechanical energy into electrical energy.  In an RV generator, this is done with an internal combustion engine powered by either diesel, gasoline, or propane.  These generators output 120-volt AC power that can be directed into the RV electrical system.  It can be used to directly power the 120-volt appliances or can be routed into a charger to refill the onboard battery storage for use in the 12-volt system. 

Can you boondock without a generator? 

As noted above, we get most of our power from the sun and we are a power-hungry home.  You can survive without a generator if you have a low power usage lifestyle, other dense power sources onboard (i.e. propane), and a properly designed solar and battery storage system. 

However, if you prefer some of the creature comforts like a residential refrigerator or find yourself in places that may need air conditioning then a generator can certainly be worth the investment.  They are also handy for cloudy weeks or when the sun is lower in the sky during the winter months.  The generator becomes essential for charging batteries during those times.  Some smaller Class B motorhomes can compensate with a second alternator on their chassis engine. 

Do I need an inverter generator for my RV? 

RV generators are typically either conventional generators or inverter generators. They both provide power. However, price and clean energy functionality set the inverter generator apart. Inverter generators are better for the health of your electronics and are preferred over conventional generators.

What is an inverter generator?

In a home, the power from the grid is a “clean” pure sine wave. Your electronics will work better and have longer lives when powered with this pure sine wave. An inverter generator provides this pure sine wave AC power with less noise, better fuel efficiency, and fewer emissions. Inverter generators are generally more expensive than conventional or contractor generators.

What is a conventional generator?

Conventional generators are often referred to as contractor generators and have many disadvantages.  Contractor generators are less fuel-efficient, emit more emissions, and produce significantly more noise.  I can assure you that none of your neighbors will appreciate the contractor generator noise.  

They also produce only AC power in a dirty wave pattern known as a modified (or step) sine wave.  This is not the kind of power you would find at home from the grid and a lot of electrical equipment is not designed with this dirty power in mind.  While it can be fine for some items and unnoticeable in others it can still shorten the life of certain appliances or decrease their performance. 

The primary advantage for the contractor generator is the price.  They are typically significantly cheaper than an inverter generator. 

Should I buy an inverter generator or a conventional generator?

We recommend everyone skip the contractor generator and find an inverter generator.  If not for yourself, do it for your neighbors. They will appreciate the quiet. There are some very cost-effective options available now for gasoline/propane-powered inverter generators. 

Guide to Selecting the Best RV Generator 

There are a few factors to consider when selecting the best unit. Fuel source and power output will be the main factors to guide your RV generator decision.

Fuel Source

To pick a generator, the basic first step is to determine the fuel source.  This is often determined based on the fuel sources already onboard.  A diesel pusher motorhome will likely take advantage of the large diesel storage onboard. While a gas motorhome will prefer a gasoline-powered unit or a propane unit if it already has propane onboard. 

Propane has some advantages over gasoline in regards to maintenance and repairs but you will be refilling propane more often.  A travel trailer or fifth-wheel can choose between gasoline or propane based on what fuel you are willing to transport.  I would recommend reviewing the advantages of propane in a generator.  Many gas generators can be converted to propane. 

Power Output

Next, you need to determine your desired power output capacity.  Available common RV generators range from 2,000 to 12,500 watts.  As you can imagine price, size, and noise all increase with the output. 

The largest units are more common in diesel pushers. They can power up to three air conditioners with excess for other loads.  5,000-7,500-watt units will power up to two air conditioners with excess for other loads. 

Smaller common gas/propane 2,000-2,500-watt units are on the edge of having enough power to start an air conditioner.  By adding a soft start device to your air conditioner you can solve this problem.

Or by paralleling two of the smaller generator units together, you can increase capacity.  This parallel feature is only available in inverter generators. It is very common in the RV world as the units are very portable, quiet, and efficient. 

How much fuel does an RV generator use?

Fuel consumption depends on the efficiency of the generator and the electrical load on it. Another advantage of inverter generators is they ramp up and down based on load. At a medium load, our onboard 7500-watt Onan used approximately half a gallon of diesel per hour. Contractor generators are less fuel-efficient and a 5000-watt unit will consume an average of 0.75 gallons of gasoline per hour. Your specific unit and usage profile will determine the fuel efficiency.

How long does an onboard RV generator last?   

A properly maintained and used diesel generator can last for life.  However, if things go sideways, repairs can get expensive fast.  You can also expect a long life from a gasoline/propane-powered unit. 

The key is proper maintenance and frequent usage.  The most common failure of gasoline-powered units is injector-related gas gumming issues. These can be avoided by frequent usage and maintenance.  A lot of units sit in storage off-season and that is where issues arise.  Propane can often negate some of those gumming issues but it is still recommended to regularly exercise all generator units. 

Difference between Onboard and External Generators

Security and convenience are distinct advantages of an onboard generator.  It is much harder for someone to walk away with an onboard unit. If you choose a portable unit, security should be a primary consideration.

Onboard Generators

The convenience of an onboard unit is the ability to control remotely. We turn on our generator with the push of a button inside when needed. 

External Portable Generators

A portable unit will need to be taken out of its storage spot and relocated to a convenient, comfortable, and safe running spot.  With modifications, you will also need to go outside to start and stop the unit each time you want to use it. The small built-in fuel tank will also need to manually be refilled. 

The advantages of the portable units are that they are often less expensive and you can take them anywhere. You can take them on trips without your RV or easily move into a new RV.  The portability can also make maintenance and service easier. 

Top RV Generator Options

We considered both onboard and portable generators when ours quit working. Below is a guide to the top RV generator options available.

Onboard Generators

Onan owns the onboard RV diesel generator market.  Currently, there are not many other options.  They are also a very common manufacturer for onboard gasoline and propane units.  Their units are known to be reliable, top performers.  Onan onboard generators have big price tags and service can also be expensive. 

Portable Generators

Honda makes the most popular gasoline/propane portable units. The top performers are the Honda EU series units.  They are very efficient and known to be the quietest on the market. This is the reason they are often the priciest portable option. 

Harbor Freight Predator units are growing in popularity for their low price and low noise levels.  There is a lot of evidence they are just as quiet as the Honda units and can cost significantly less.  If properly maintained, these units have advantages compared to Honda worth researching.  

The Champion dual-fuel units are also popular due to their low cost. The ability to run on gasoline or propane also attracts many RVers who appreciate the flexibility. 

To compare prices for diesel generators and other portable units, check out Electric Generators Direct. It is a guide to comparing RV generator prices but is not all-inclusive. Be sure to consider shipping costs if not included. 

Guide to Care and Maintenance of an RV generator

Regular maintenance is important to keeping your RV generator running smoothly however equally important is regular usage. Even if we don’t need to use our generator, we “exercise” it at least once a month. Exercising a generator means running it under load for 30-90 minutes. We normally use this time to run high-usage appliances such as our convection oven. It’s a great excuse for homemade baked goods.

Our Generator Story

We happened to have one of those “gone sideways” diesel units.  Our Onan QD7.5 came installed in our 2000 motor home, Pippi, and already had 13 years under its belt when we took ownership.  It didn’t however have many hours of usage at that point (less than 200).  We used it for the first five years and another 600+ hours with no real issues.  But then things started to go “sideways”. 

What went wrong with our onboard RV generator? 

We have had a couple of issues with our unit during our seven years of use. 

repair shop pics of when our rv generator failed

One of our first issues was a weak fuel priming pump. It was a simple issue but was still pricey to finally diagnose and rectify ($1K). 

In 2018, we had a failed inverter component.  This is almost like the blue screen of death in old computers.  As owners, we all know it could happen and know it is not cheap if it does.  A new comparable generator is $8-10K plus labor. So it still made sense to pay <$3K for the new inverter unit to keep her going. 

Finally, in the winter of 2020, we had another failure that made us reevaluate the repair vs replace choice.  The service center did a poor job diagnosing the real issue which made the problem worse.  We spent weeks at the service center while they misdiagnosed the issue multiple times.

After weeks of work including various part replacements, it was determined the necessary repair would cost almost $6k. We decided it was not economical to continue repairing our 20-year-old generator.  After $4K spent in the past couple of years plus regular maintenance, it wasn’t prudent to invest another $6K in the old girl.  We left her behind. 

Should I replace my onboard generator? 

It is a personal choice on how much should be invested in failing equipment. Repair versus replace depends upon your budget and confidence in the unit’s remaining life.   In our case, we knew our generator was not used much in her early years. The costs were stacking up to keep her running. However, we also knew the major components we had already replaced were not likely to fail again. 

We had to decide if we stick with the devil we know or move on to other options.  Luckily with the time our service center took due to their poor diagnostic methods, we had plenty of time to research alternatives.  We are very analytical so we calculated a threshold when it no longer made sense to retain the old unit.  In the end, we chose to replace our generator instead of continuing to spend money repairing her.

pippi at the mechanic

How to save on an RV generator?

We are accountants by trade and are always budget-conscious. A brand-new replacement for our onboard Onan would be close to $10k before labor. We explored several options to save money on a replacement RV generator including changing fuel sources, converting to a portable external unit, or purchasing pre-owned.

Cheaper Alternatives

We looked at various alternatives including changing fuel sources for our generator needs.  Gasoline/propane units are significantly less expensive albeit less powerful.  We eventually abandoned those options as it would not make sense for the modifications necessary and quality of life changes required. 

Essentially, we’d have to replace the fuel lines to accommodate a different fuel source for an onboard propane generator. Or we’d sacrifice the convenience of our onboard unit if we moved to a portable external unit. We didn’t want to add another step to our setup when we arrived at new locations, manage external fuel storage, or go outside to turn on and off the generator. We’re spoiled by our onboard unit and weren’t willing to compromise the quality of life we’d become accustomed to. These are the key factors that led to our decision to replace our onboard RV generator.

Pre-owned RV Generators Save Big Money

In conclusion, we knew we needed another onboard diesel Genset and Onan is really the only option in the market.  We also knew a new comparable unit would be near $10K before install labor.  That seemed excessive so we considered the pre-owned market. 

We had already called multiple RV salvage yards to get an idea of pricing for used units taken from crashed or burned RVs.  A used Onan QD7.5 unit was $5K-5.5K from these salvage yards.  We chose the used route and lucked into a relatively young unit installed for $4.5K from Arizona RV Salvage (rebranded RV Yard). 

The unit was a 2015 model with 75 hours on it.  Not as many hours as we would like to see for that age but considering her relatively young age it seemed an appropriate risk.  It has worked great for us ever since installation. 

We did find a small coolant leak and while the shop promised to stand behind the unit, they had trouble fitting us into their schedule to find the leak and repair it.  Eventually tired of waiting, we were able to identify the leak and correct it ourselves.  We are satisfied with our replacement unit and our choice to move forward without our old unit. 

RV Generator Conclusion

We hope our experiences with replacing our Onan onboard RV generator have been helpful. And most of all, we hope our overview of RV electrical basics helps guide your RV generator purchase decision.