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How to size an inverter to fit your needs

Are you trying to calculate the size of an inverter that will fit your needs? Maybe you are only looking to run a TV or instant pot. Perhaps you are wanting to power the air conditioners full time with the power you collect from the sun. In the following post, I will show you how we have come up with our inverter sizing to fit our needs. I will also show our system wiring.

Identifying an inverter based on your expected loads

There are several key factors that one needs to address when trying to properly size an inverter. What load you want the inverter to cover, are there other available sources of power available, and how long you want the inverter to power the load.

Knowing what your loads are and how they receive power is key to sizing your inverter to fit your needs.

The first key factor that you need to consider is the size of your expected load. To help calculate your needs check out our blog RV Appliance Power Consumption. It also helps to know what leg the power is fed through on a 50 amp power system. In some situations, a power outlet on a kitchen island may be different than an outlet on an external wall. This could be important if you are deciding which electrical circuits you would like to power.

We knew that we wanted to have the 5th wheel powered completely so that we would not need to change our habits. We wanted to function the same if we were off-grid or plugged in somewhere. Our desires are not to run a lot of high loads at once. We just did not want to compensate for our incoming power. Most of our loads, we found, are between 1100-1500 watts each. Calculating the max combined load was as easy as counting how many loads we wanted to run at the same time.

Are there going to be other power sources available that could change the size of your inverter to fit your needs?

Check out my post from last year dealing with inverters and some of their options. In that post, I write about the technology that most higher-end inverter/charges are coming with. It allows them to supplement other sources of AC power. It can be referred to as a hybrid boost or power assist by some manufactures. This feature may allow you to reduce the size of your inverter needs when running higher loads. Some of the other benefits of some inverters include the ability to pass through 50 amps of power on two separate legs.

In our first setup, we chose to go with a GoPower 2000 watt hybrid inverter. The benefit of that inverter was that it allowed easy wiring to our existing AC system. It would automatically power both legs of our 50 amp service when inverting. But it did not come without its flaws. You can see them in our YouTube Video here. Overall the GoPower worked well for us. However, in the end, it was not quite what we needed to fit our needs.

In our current setup, we wanted to be able to power both legs of service. We wanted to do it with the same power that we would see from an RV pedestal. Our loads are not consistently large for long durations. At the time of installation, that meant going with the only manufacture that could accomplish that. We chose to go with products from Victron Energy.

The third consideration for trying to size an inverter to fit your needs is duration of loads.

With knowing the size of your load, and any assistance that may be available to supplement, the final piece is how long is the load going to be carried. When sizing an inverter to fit your needs you do not want to expect your inverter to continuously carry its maximum load. Inverting 12v DC energy to 120v AC energy will create heat. There will also be some inefficiencies in the inverting process. Some ways to help counter these limitations are to use a larger inverter or change the battery voltage of the bank.

Victron Energy makes several choices of inverters. They rate their inverters by the measurement of Volt-Amps. The actual continuous wattage output is a little lower. A 3000VA unit rating on a Victron Energy inverter will continuously supply 2400 watts of power for 30 minutes. Each product specification sheet will define inverter capabilities. Victron Energy also makes inverters in 5000VA ratings if your intentions were to carry larger loads for longer durations.

The second option of changing the battery bank option will also help reduce heat. The increase of battery bank voltages also allows for the use of smaller sized wire. However, consideration needs to be given to the voltage requirement of the system already in the RV. For our loads, there was not enough benefit of choosing to go with a system other than 12 volts.

How did we wire our inverters to fit our needs?

Our dual Victron Inverter wiring to fit our needs.

Our current system consists of two Victron Energy 12/3000/120 50 inverter chargers that are the perfect size to fit our needs. Each inverter is capable of charging the battery bank at 120 amps per hour. They will provide 2400 watts of continuous power for 30 minutes. They are capable of surging to 6000 watts. The inverters are wired in split-phase to allow them to safely provide service to each leg of power going to my main circuit breakers.

Helping to feed split phase power to the inverters is a 100 amp autotransformer. Its purpose is to take a single phase of power and provide the second 180-degree leg of split-phase output. Single-phase could be from a generator of 30 amp or less shore power connection. The available current is split between the two inverters. The benefit is that each inverter will also pass-through power and charge the battery bank.

A 50 amp transfer switch is in use to switch between the standard 50 amp shore power connection and autotransformer outputs. This eliminates any kind of manual switching that will be a requirement to safely make the change. It will also ensure that no damage occurs if the wrong connection is made.

Still looking for some assistance?

If you would like a consultation to discuss your specific needs, send me a message at Justin@OptingOutofNormal.com. We can get a meeting scheduled. I do have a list of recommended vendors that do pay an affiliate fee. I could get credit based on people following links in my blogs or working with those vendors to quote packages for consultation projects. If you would like to source your own parts and equipment, consulting fees may apply depending on complexity and involvement. 

A complete list of parts and equipment that we utilize in our system can be seen at Kit.co/optingoutofnormal.

Check out our blog “How to size a battery bank to fit your needs“. We show how we get the most benefit out of our Battle Born battery setup. If you are boondocking in the National Forest or plugged into an outlet, you can harness the great features of the batteries. This allows you to maintain your energy loads while still living normally in an RV.

Check out some of our other blogs to see how we use our system.

Our Top 7 Free Camping Spots and Boondocking Tips
Bisti Badlands ~ New Mexico’s Most Hidden Gem
Living Full-Time in an RV for 3 years. Our 15 Tips

Are you in search of a like-minded group of solar enthusiasts? Maybe you are looking to find the latest tips and tricks for your install? Come check out my group on Facebook.

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