What size generator do you need for your RV or travel trailer? There’s more to this decision than just adding up appliance demands. You need to consider how and where you’ll use your generator, what type of power you need, and where you’ll use your generator power. Here’s what you need to consider when you’re buying a generator for portable RV shore power.
Measuring Output: Continuous and Surge Power
Maximum generator output is measured in two ways: continuous and surge power. Both measurements are important for determining if a generator makes enough power for your RV.
The sustained output of the generator is rated in running watts. This is the maximum current the generator can make while it’s in regular operation.
The temporary output of the generator is rated surge watts or peak watts. This is the maximum current the generator can make over brief periods. Generators are usually designed to sustain surge output for 60 seconds. Electric motors require two to three times as much power to start then they require to run. Surge output compensates for these “reactive” loads. Motors aren’t just found in tools and small kitchen appliances. They’re also used to drive compressors in air conditioners and refrigerators, as well as fans in heat and air units. Since these are the largest power draws in an RV, having enough surge power is critical.
Factors Affecting Generator Output
You probably don’t want to buy a generator that makes just enough power for your RV. Instead, you want something that comfortably makes the power you need. By using less than maximum output, you reduce noise, fuel consumption and generator wear. Take these factors into consideration when you’re shopping for a generator.
The harder you run your generator, the sooner it will wear out. Manufacturers generally recommend limiting usage to 85-90% of maximum output.
Dual fuel generators are popular, because they let you use inexpensive propane when it’s available, as well as gasoline for convenience. Burning propane doesn’t produce as much power as gas. This lowers the generator’s output by about 10%.
Just as the engine in your RV or truck loses power at high elevations, so does the engine in your generator. You can expect output to fall by about 3% for every 1,000 feet of elevation. If you’re camping in the Rockies, you may see output drop by as much as 25%. You may need to install a high elevation kit. This replaces the carburetor jets, compensating for the lack of air available to the engine.
The more power your generator puts out, the faster the engine runs. In turn, this increases the noise it generates. If you don’t want to drive yourself or your neighbors crazy, it’s better to get a generator that isn’t constantly stressed. Manufacturer specifications for noise vary widely, with measurements taken at 25 or 50 percent load from distances ranging from 10 to 30 feet away. The decibel scale is logarithmic, so every 10 dB represents a doubling of noise. Here’s how these measurements relate to real world sounds.
Fully enclosed generators typically have noise levels at or below 65 dB at 50% load, measured 30 feet away. Partially-enclosed generators range from the mid 60s to mid 80s under load. Open frame workplace generators might be cheap, but the biggest units can reach decibel levels in the high 90s under load.
Do I Need an Inverter Generator?
Standard generators send power from the alternator directly to the outlets. Due to electrical interference and engine speed fluctuations, this power is “dirty.” It doesn’t make a smooth transmission from positive to negative polarity like the power you get from the grid. This dirty power is hard on electronics, prematurely wearing out televisions, sound systems, computers and other appliances.
An inverter generator converts power from the alternator to DC power, then back to AC. By decoupling power output from generation, it eliminates these fluctuations. The resulting “clean” power is identical to grid power. Total Harmonic Distortion (THD) for an inverter generator is usually well under 3%, while THD for a standard generator ranges anywhere from 15-30%.
Which one is right for you? That depends on how you use your generator. If you regularly go boondocking and want to use all of your devices, get an inverter generator. If you mostly use your electronics when you’re connected to the grid at an RV park, and rely on your generators more for stops to cook meals and power your air conditioner, a regular generator is fine for your needs.
Do I Need 120 or 240 Volt Power?
The vast majority of RV and travel trailer owners only need 120 volt power. 240 volt power is used exclusively for air conditioners used on the largest recreational vehicles and electric clothes dryers. However, you’ll probably end up with a 240 volt capable generator, if you have high power demands.
240 volt generators have the option of running in 120 volt mode. If you use a 240 volt socket, this power is split between two hot connections. While modern RV electrical systems have no problem with this type of connection, some older systems only detect and use only one of these hot wires. This halves the amount of power you have access to. You may also run into this problem if you use an adapter to connect a 240v-ready outlet to a 120 volt outlet on your RV.
Some sellers claim that switching to 120 volt mode doubles available power. That’s because amps are calculated by dividing volts by watts. Halve the voltage, and you get twice the amps, even though actual output remains the same.
240 volt generator power doesn’t work with 240 volt home and commercial devices. Generator electricity is always single phase: all of the power switches polarity at the same time. Grid 240 volt power is three phase: it combines three 60 Hz power sources, so voltage never drops to zero. This maintains current flow through electric motors and welding electrodes.
Do I Need a Generator with DC Power?
Direct current can be handy, but it’s not a requirement for good shore power. DC ports are mostly used to charge batteries, whether they’re part of your RV or in your electronics.
12 volt connections come in two forms. Post connectors are designed to use with wires that attach to a battery. This lets you recharge flat house batteries and starter batteries. However, you’re better off using shore power to for this purpose. This lets your RV’s built-in charging system manage current flow, decreasing charge times and increasing battery life. Cigarette lighter connectors work with direct current car appliances and adapters. This makes it easy to charge a variety of portable devices. You can get adapters to use these outlets for battery charging.
Manufacturers are increasingly including USB outlets for powering and charging electronics. These are usually USB Type A ports. If you want fast charging, look for sockets rated for 2.1 amps.
USB Type C ports are capable of higher voltages and power output, letting them power and charge large electronic devices, including laptops and tablets.
A rectifier turns AC power from the generator’s alternator into direct current. Like a sine wave inverter, this filters out distortion, making this power safe for electronics.
Should I Run One Generator, or Two Generators in Parallel?
A parallel connection links two generators electrically, so they act as one unit. These connections are nearly 100% efficient: if you link two 2,000 watt generators, you’ll have access to 4,000 watts of power. These small generators don’t have RV shore power outlets, but their parallel cables usually do. This setup has both advantages and disadvantages over a single generator.
What Type of Connection Do I Need to Get Power to My RV?
Most RVs use one or more TT-30R or 14-50R outlets to connect to shore power. Many generators also come with an L5-30R socket. This outlet is mostly used for home backup power, but you can connect your RV to this socket using an adapter.
On NEMA outlets, the number after the dash is the amount of amps the connection can carry. Multiply amps by volts, and you get the number of watts the connection can handle. That means you can send up to 3,600 watts of power over a TT-30R or L5-30R connection, and up to 6,000 watts over a 14-50R connection. Large RVs use two connections to get full shore power.
How Do I Figure Out My RV’s Power Demands?
Your power demands will vary widely, depending on the size of your RV and how you use it. There are two general rules of thumb for estimating your power demands:
The largest power consumer is your air conditioning system. Each unit needs 1,100 to 3,500 watts to start, and 300-1,700 watts to run. Depending on the size of your RV, you may have anywhere from one to three units. These general estimates for total power use are mostly based on air conditioner demands.
Aside from the air conditioner, the kitchen requires the most electricity. A coffee maker uses between 650 and 1,750 watts, but not all coffee makers are the same. A drip coffee maker uses electricity for the heating element, so its power draw is tied directly to its size. However, pod coffee makers also use an electric motor to clamp down on the pod and force water into it. This uses an electric motor, making it a reactive load. Even a one cup Keurig or Nespresso coffee maker can use two or three times its rated wattage to start. What about other appliances? Here are some typical examples.
Most of the power you use outside of the kitchen comes from entertainment electronics. Here’s how much electricity the most common devices use.
This just leaves lighting and ventilation. A standard vent fan needs 100 watts to start, and just 40 watts to run. LED lighting needs between 3 and 30 watts for each bulb.
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