Sizing a Generator for Your RV: Everything You Need to Know

2 weeks ago

Sizing a Generator for Your RV: Everything You Need to Know

The open road, the freedom of choosing your destination, the ability to wake up to a different view every day – that’s the allure of RV travel. But even when you’re embracing the wilderness, you likely still want to run essentials like lights, charge your phone, keep food cold, or perhaps even run the air conditioner on a hot day. This is where a generator comes in, providing portable power when you’re off the grid.

However, simply buying a generator isn’t enough. Buying the right generator, specifically one that is properly sized for your RV’s needs, is crucial. An undersized generator won’t power your appliances, leaving you frustrated. An oversized generator wastes fuel, money, space, and creates unnecessary noise. This guide will walk you through everything you need to know to size the perfect generator for your RV adventures.

Why Does Generator Size Matter?

Think of your RV’s electrical system as a thirsty plant. The generator is the water source. If the water source is too small (undersized generator), the plant doesn’t get enough water to thrive (your appliances won’t run or will trip breakers). If the water source is a fire hydrant for a small houseplant (oversized generator), you’re wasting a lot of water, likely flooding the area, and paying for more than you need (wasting fuel, carrying excess weight, spending more money upfront).

Proper sizing ensures:

Reliable Power: All your necessary appliances run without issue.

Appliance Longevity: Appliances receive the correct power, preventing damage.

Fuel Efficiency: You’re not burning more fuel than necessary.

Cost Savings: You avoid the higher purchase price of an unnecessarily large unit.

Reduced Weight & Noise: Smaller generators are typically lighter and quieter.

Understanding the Basics: Watts, Amps, and Volts

Before you can size a generator, you need to understand the basic electrical units:

Volts (V): This is the electrical "pressure" or potential difference. Most RVs in North America use 120-volt (120V) AC power.

Amps (A): This is the flow rate of electrical current. It’s how much electricity is moving through the wires.

Watts (W): This is the rate of power consumption or production. It’s the Volts multiplied by the Amps (W = V x A). Generators are typically rated by their wattage output.

The Crucial Distinction: Running Watts vs. Starting Watts

This is perhaps the most critical concept in generator sizing:

Running Watts (or Rated Watts): This is the continuous power an appliance uses once it’s up and running.

Starting Watts (or Peak/Surge Watts): Many appliances, especially those with electric motors (like air conditioners, refrigerators, microwaves, power tools), require a much larger burst of power for a few seconds to start up than they do to run continuously. This surge can be 2-3 times their running wattage, or even more.

Your generator needs to be able to handle both the total running watts of everything you want to use simultaneously AND the highest starting watts of any single appliance you might start while other things are running.

The Step-by-Step RV Generator Sizing Process

Follow these steps to determine your power needs:

Step 1: List Every Appliance You Might Use

Think about all the electrical items in your RV (and potentially outside, like a coffee maker or portable grill) that you might want to use. Don’t forget things like lights, phone chargers, and the RV’s internal converter/charger.

Step 2: Determine the Wattage of Each Appliance

This is the information-gathering phase. You can find wattage (W) or amperage (A) information on:

Appliance labels (look for a sticker or plate).

Appliance user manuals.

Online searches using the appliance’s make and model number.

If you only find Amps, multiply Amps by Volts (usually 120V for AC appliances) to get Watts (W = A x V). For example, a 10-amp appliance needs about 1200 watts (10A x 120V).

Step 3: Identify the Running Watts and Starting Watts for Each Appliance

List out the Running Watts for everything. For appliances with motors, find both the Running Watts and the Starting Watts. The starting watts might be listed explicitly, or you might need to estimate it based on general guidelines (e.g., an RV air conditioner often has a starting wattage 2-3 times its running wattage).

Step 4: Decide Which Appliances You Will Run Simultaneously

This is key. You probably won’t run the microwave, air conditioner, coffee maker, and hair dryer all at the exact same second. Plan for your most likely power-hungry scenarios. Common scenarios include:

Lights + TV + Charging devices

Lights + Refrigerator + Microwave (for a few minutes)

Lights + Refrigerator + Air Conditioner (this is often the highest demand scenario)

Step 5: Calculate Your Total Running Watts

Add up the Running Watts of all the appliances you identified in Step 4 that you plan to use at the same time.

Example Scenario:

RV Air Conditioner: 1500 Running Watts (4000 Starting Watts)

Refrigerator: 150 Running Watts

Lights (various LED): 50 Running Watts

TV: 100 Running Watts

Converter/Charger: 500 Running Watts (this is often running in the background)

Total Running Watts = 1500 + 150 + 50 + 100 + 500 = 2300 Running Watts

Step 6: Calculate Your Total Starting Watts (The Peak Requirement)

This step accounts for the power surge needed when a motor kicks on. Take your Total Running Watts from Step 5. Then, identify the single appliance on your simultaneous list with the highest Starting Watts. Subtract its Running Watts from your Total Running Watts, and add its Starting Watts.

Using the Example Scenario from Step 5:

Highest Starting Wattage appliance is the Air Conditioner (4000 Watts). Its Running Watts are 1500 Watts.

Total Starting Watts = (Total Running Watts – AC Running Watts) + AC Starting Watts
Total Starting Watts = (2300 – 1500) + 4000
Total Starting Watts = 800 + 4000 = 4800 Starting Watts

Step 7: Select a Generator that Meets Both Needs

Your chosen generator must have a Running Wattage capacity equal to or greater than your calculated Total Running Watts AND a Starting Wattage (or Peak Wattage) capacity equal to or greater than your calculated Total Starting Watts.

In our example, you would need a generator rated for at least 2300 Running Watts and at least 4800 Starting Watts. Generator manufacturers list both ratings. Look for a generator that meets or exceeds these numbers.

Step 8: Add a Buffer

It’s wise to add a 10-20% buffer to your calculated needs. This accounts for:

Appliance wattages being slightly higher than rated.

The generator performing slightly less efficiently than rated, especially in challenging conditions (like high altitude – generators lose about 3.5% of their power for every 1000 feet above sea level).

Future appliance purchases or changes in your power usage habits.

Applying a 20% buffer to our example:

Required Running Watts: 2300 * 1.20 = 2760 Watts

Required Starting Watts: 4800 * 1.20 = 5760 Watts

You would look for a generator rated around 2800+ Running Watts and 5800+ Starting Watts. A generator rated at 3000 Running Watts and 6000 Starting Watts would be a good fit for this example scenario.

Typical RV Power Needs (General Estimates)

While calculating your specific needs is best, here are some common RV scenarios and the typical generator sizes required:

Minimalist (Lights, Fan, Charging, Water Pump): 1000-2000 Running Watts / 1500-2500 Starting Watts (often achievable with smaller inverter generators).

Moderate (Above + Microwave OR Coffee Maker OR Hair Dryer): 2000-3000 Running Watts / 3000-4000 Starting Watts.

Comfort (Above + 1 RV Air Conditioner): 3000-4000 Running Watts / 4000-6000 Starting Watts. This is a very common need for many RVers.

Maximum (Above + 2 RV Air Conditioners on a 50A Rig): 5000-6500+ Running Watts / 7000-8000+ Starting Watts.

Note: Running two ACs simultaneously on a 50A RV requires significant power, usually closer to the 50A outlet limit (which is roughly 12,000 watts, though the generator doesn’t need to match the full shore power capacity, just the load you’ll apply). A 5000-6500W generator is typically needed to manage this, sometimes with soft starts installed on the ACs.

Other Factors to Consider When Choosing a Generator

Beyond size (wattage), several other factors are important for RVing:

Type:
- Conventional Generators: Louder, heavier, less "clean" power (can be an issue for sensitive electronics). Generally cheaper for their wattage.
- Inverter Generators: Quieter, lighter (for their output), produce clean "pure sine wave" power (safe for laptops, TVs, etc.), more fuel-efficient, often have parallel capability. Generally more expensive. Often the preferred choice for RVers.

Fuel Type: Gasoline is common, but propane (cleaner burning, easier storage but less power output), diesel (common in large motorhomes), and dual-fuel options exist.

Noise Level: Measured in decibels (dB). Look for lower numbers (e.g., 50-60 dB) for quieter operation, especially in campgrounds.

Weight and Portability: If it’s not built-in, can you lift and move it easily?

Parallel Capability: Can you connect two smaller, lighter generators together to double the power output when needed? This offers flexibility.

Pure Sine Wave: Essential for safely running sensitive electronics like laptops and medical equipment. Most inverter generators provide this.

Run Time: How long will it run on a tank of fuel at a typical load?

Outlets: Does it have the correct outlets for your RV’s power cord (e.g., 30A RV outlet, 50A RV outlet)?

Conclusion

Sizing a generator for your RV doesn’t have to be a mystery. By understanding the difference between running and starting watts, listing your potential simultaneous appliance usage, and performing a few simple calculations, you can determine the ideal wattage range for your needs. Don’t forget to factor in a buffer, consider other important features like noise level and fuel type, and choose a generator that offers reliable, clean power, especially if you plan to run sensitive electronics.

Investing the time to size your generator correctly will ensure you have the power you need for comfortable, worry-free adventures, whether you’re boondocking in the wilderness or need backup power at a campground. Happy trails!

FAQs: Sizing an RV Generator

Q1: Can I just buy the biggest generator I can afford to be safe?
A: You could, but it’s generally not recommended. Oversized generators are more expensive, heavier, take up more space, use more fuel even on light loads, and are often louder than necessary. Proper sizing balances your needs with practicality.

Q2: What happens if my generator is too small?
A: It won’t be able to supply enough power. Appliances might not start (especially those with high starting watts), or the generator might overload and shut down, tripping a breaker on the unit itself.

Q3: Do I need a special type of generator for sensitive electronics?
A: Yes, for sensitive electronics like laptops, smart TVs, and medical devices, you need a generator that produces "pure sine wave" power. Most inverter generators produce pure sine wave power, while many traditional open-frame generators produce a "modified sine wave" which can potentially damage sensitive electronics.

Q4: How does altitude affect generator performance?
A: Generators lose power output at higher altitudes because the air is thinner, meaning less oxygen is available for combustion. A general rule is a loss of about 3.5% of power for every 1,000 feet above sea level. If you plan to camp frequently at high elevations, you may need a slightly larger generator or factor this loss into your sizing calculations.

Q5: What is a "soft start" for an RV air conditioner and how does it affect generator sizing?
A: A soft start is a device installed on an AC unit that significantly reduces the power surge (starting watts) required to start the compressor. Installing soft starts on your RV’s AC units can potentially allow you to run your AC(s) with a smaller generator than would otherwise be possible.

Q6: Can I use my RV generator while driving?
A: Many RVs (especially motorhomes) are designed to allow the built-in generator to run while driving to power the rooftop air conditioners or other appliances. However, portable generators should never be used or even stored inside the RV while driving due to carbon monoxide risks. If using a portable generator while parked, ensure it is placed a safe distance from the RV with exhaust directed away from windows and doors. Always use a carbon monoxide detector in your RV.

Q7: What’s the difference between a 30A and 50A RV outlet, and how does it relate to generator size?
A: A 30A RV service provides about 3600 watts (30A x 120V). A 50A RV service (which actually uses two 120V legs at 50A each) provides up to 12,000 watts (50A x 240V, though split into two 120V circuits).

A 30A RV generally needs a generator rated at least 3000-4000 watts to run its primary AC and other items.

A 50A RV often has two AC units and requires a much larger generator, typically 5000-6500+ watts, to power both ACs simultaneously along with other appliances. Even on a 50A rig, if you only plan to run one AC at a time, a smaller 3000-4000 watt generator might suffice, using a 50A to 30A adapter (but be mindful of which appliances you can run).

2 weeks ago