Choosing the RIght RV Generator: A Quick Guide to Popular Models

If you're searching for the manual or details on the Onan 4.0KYFA-6747 RV generator, you're not alone. This is one of the most widely used generators in travel trailers, motorhomes, and truck campers.

But depending on how you use your RV, there may be other models that fit your needs better. Some generators are designed for lightweight travel trailers, while others are better suited for large motorhomes that run multiple appliances.

Below is a quick overview of several common RV generator options and the situations where they tend to be the best choice.

The Onan 4.0KYFA-6747 – A Reliable All-Around RV Generator    

The Cummins Onan 4.0KYFA-6747 is one of the most common built-in generators used in RVs. It’s part of the Quiet Gasoline (QG) series and produces about 4,000 watts of power at 120 volts, which is enough for most typical RV needs.

This generator is known for:

• Quiet operation with a sound-attenuating enclosure
• Microprocessor controls with onboard diagnostics
• Compact design for RV compartments
• Enough power to run a 13,500–15,000 BTU air conditioner with additional loads.

Because of this balance of power and size, the 4.0KYFA-6747 is often found in:

• Class C motorhomes
• Fifth wheels
• Travel trailers
• Truck campers

For many RV owners, it’s the “just right” generator—large enough to power essentials but still compact enough for built-in installation.

When a Smaller RV Generator Makes Sense   

If you have a smaller camper, teardrop trailer, or minimal power needs, a large built-in generator may be more than you actually need.

A smaller RV generator can be ideal when:

• You mostly run lights, charging devices, and small appliances
• You rely on solar for much of your power
• Your RV has limited space or weight capacity
• You prefer a portable generator for flexibility

Many lightweight RV owners choose smaller generators because they’re easier to transport and use less fuel.

When You Might Need a Larger RV Generator    

On the other end of the spectrum, some RV setups require more power.

Larger RV generators are often the best fit when:

• Your motorhome has multiple air conditioners
• You run microwaves, electric water heaters, or induction cooktops
• You frequently camp in hot climates where the AC runs constantly
• You want extra power margin for simultaneous appliances

Large Class A motorhomes and luxury fifth wheels often benefit from generators in the 5,500-watt range or higher.

Gasoline vs. Propane RV Generators    

Another factor to consider when choosing a generator is the fuel type.

Gasoline generators

• Typically provide strong power output
• Often use the same fuel supply as the motorhome
• Common in motorized RVs

Propane (LP) generators

• Burn cleaner
• Can sit longer without fuel degradation
• Often used in towable RVs

Your RV’s existing fuel system often determines which option makes the most sense.

Finding the Right Generator for Your RV   

Choosing the right generator usually comes down to a few key questions:

• How many appliances will run at the same time?
• Do you need to power air conditioning?
• Is your generator built-in or portable?
• What fuel source is available in your RV?

For many travelers, the Onan 4.0KYFA-6747 remains one of the most practical choices because it strikes a balance between size, quiet operation, and power output.

Need the Manual for the 4.0KYFA-6747?  

If you’re troubleshooting or performing maintenance, having the correct manual is essential.

You can find the operator’s manual, installation guide, and service documentation for the 4.0KYFA-6747 directly on the product page below.

https://rockymountaingeneratorsupply.com/userfiles/2002/KY%20Operators%20Manual.pdf