By Dave Solberg
Dear Dave,
What size of a generator do we need for our RV? It’s a Montana High Country. Should it be an inverter generator or just a portable non-inverter? And can we get one that is wired in to switch auto? —Debra, 2021 Montana High Country
Dear Debra,
The size of generator depends on how many 120-volt components you wish to run at any given time. You will need to calculate the power requirements for items like the refrigerator, roof air conditioners, microwave, and any appliance or components plugged into outlets. You will also need to factor in the converter/charger or inverter/charger if you have one of these.
Watts used by appliances
Typically a 13,500 btu roof air conditioner will pull 2800 watts during startup and 1800 watts in run mode. You can get by with a 2500- to 2800-watt generator. However, I would recommend using a SoftStartRV™ installed on the air conditioner to reduce the startup draw. This size generator is the minimum and might be too small if you are planning to run other 120-volt components—especially if your roof air conditioner is a larger 15,000 btu one.
A residential refrigerator can run 1,500 watts, a microwave anywhere from 1,000-1,500 depending on the size, a TV 300-400, and a single-serve coffee maker draws 1,200 watts! Keep in mind, all of these will not be running at the same time. However, it is difficult to determine when they will cycle on and off during the day. Typically, if you will run only one roof air conditioner and a few appliances, you would be OK with a 3,500-watt generator.
Generator/inverter
If you are considering a portable, you definitely want a generator/inverter that will produce a pure sine wave rather than the industrial generators you find at home improvement locations or discount box stores. These produce raw power designed for power tools and lights and will ruin microprocessors in some of your electronic components. If you are looking at a permanently mounted generator such as Onan, it is already set for proper power.
Automatic transfer switch (ATS)
I do not know of any generators that have an automatic transfer switch built in, but rather an ATS box in the service compartment. If you are going with the permanently mounted version, you can get a Progressive Dynamics or Southwire ATS and run the power from the generator to the ATS as well as the shoreline cord, and then the power from the ATS to the distribution center.
Currently your rig has a shoreline cord that is wired directly to the distribution center. If you go with a portable generator, I do not see a good way to have an ATS as you would still need to plug a cord into the generator manually.
An ATS is simply a box that switches the power source. It is set on default to provide power when available from the generator line coming in and switches internally when it senses power from the shoreline cord, which then creates an open circuit from the generator.
If no ATS
If you did not have an ATS, you would physically plug the shoreline cord into a “J” box, that is an outlet wired directly from the generator.
Here you see the junction box with the shoreline cord wired into it on the left side, and then it is wired to the distribution center, which is similar to what you have now. The outlet to the right is the “J” box that has a line coming from the generator. When you plug the shoreline cord into the “J” box, power comes from the generator to the shoreline cord, through the junction box, and to the distribution center, just like if you were plugged into a campground source.
Maybe some of our readers have found something that automatically switches for a portable generator. However, as I stated earlier, you still need to remove the generator, start it up and plug some type of cord/line into it, so an ATS would not be needed.
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Dave Solberg is a leading expert in the RV industry and the author of the “RV Handbook.”
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RVDT2842
We have an 1800 watt (roughly 15A) dual fuel (only use propane) portable inverter (sinewave) generator. It has both 120AC and 12vdc charging ports. We have adapters for both our 30A and 50A TTs. The intended use is to keep our battery charged, recharge phones, and very important 🙂 , run the coffee maker in the morning. We are not typically boondockers, but can do so when necessary.