Most campers need a generator between 2,000 and 4,000 running watts, but the air conditioner usually decides the size. A small unit can handle battery charging and basic outlets; a larger inverter generator is often required to start and run a rooftop AC without shedding every other appliance.
Do not choose from RV length or shore-power plug alone. Add the loads you will use together, include the largest startup demand and check the generator’s output at your expected altitude, temperature and fuel.
Calculate the Generator Size for Your Camper
- List the appliances that must run at the same time.
- Record each item’s running watts from its nameplate or manual.
- Add the total running watts.
- Add the largest additional starting-watt requirement.
- Allow margin for altitude, heat, battery charging and future loads.
Generac’s planning worksheet lists about 1,800 running watts for a 15,000 Btu RV air conditioner and notes that motor loads require extra starting power. Dometic manuals show that generator requirements vary by exact AC model and total RV load.
A microwave’s marketed cooking watts are lower than its electrical input. Use the input label. Converter-chargers can also draw substantial power when batteries are low.
Practical Generator Ranges
About 2,000 running watts: Suitable for lights, electronics, converter charging and small appliances managed one at a time. It may run some smaller or soft-start-equipped air conditioners, but verify the AC and generator data before buying.
About 3,000 to 4,000 running watts: A common range for one rooftop air conditioner plus limited supporting loads. You may still need to switch off the microwave, water heater or converter’s high-rate charging when the compressor starts.
Above 5,000 running watts: May be appropriate for two air conditioners, large fifth wheels or fewer load restrictions. Weight, noise, fuel use and safe handling rise quickly.
A 30A, 120V RV connection can deliver up to 3,600 volt-amps from shore power. A 50A RV service uses two 120V legs and can provide far more. You do not need to reproduce the full shore-power maximum if you plan which loads the generator will support.
Air Conditioning, Soft Starts and Derating
The compressor startup is brief but can overload a generator that easily covers the running watts. A manufacturer-approved soft-start device can reduce startup demand, but it does not reduce the AC’s steady running load.
Generator output falls with altitude, high ambient temperature and some fuel types. Use the derating instructions for the exact model and size for the campsite conditions, not sea-level advertising.
Test the combination before travel. Start the generator, let it stabilize, apply the air conditioner and then add other loads one at a time while monitoring voltage and overload indicators.
Connection, Noise and Safety
- Use an RV-ready outlet or correctly rated adapter, cord and surge protection.
- Follow the RV and generator instructions for neutral bonding and grounding.
- Use a listed transfer arrangement if an onboard inverter or other AC source is present.
- Respect campground quiet hours and published sound limits.
- Secure the generator during transport and store fuel in approved containers.
- Never run a generator inside an RV, compartment, tent, truck bed with a cover or other enclosed space.
Operate a portable generator outside, at least 20 feet from occupied structures, with exhaust directed away from doors, windows and vents. Use working carbon-monoxide alarms in the camper.
Bottom line: Size from measured running and starting loads. For many campers, 3,000 to 4,000 running watts is the practical one-AC range, while lighter loads can use a smaller generator.
References: Generac wattage worksheet, Dometic RV AC generator guidance and CPSC generator safety.