Are you thinking about a solar charging system for your RV? Whether it is a large “run the air conditioner” type system or just some simple panels to keep the batteries charged on a long weekend, there are a few simple steps that will help your get started in finding the best system to fit your needs. There are a lot of factors that need to be calculated before you can even think about how many watts of solar to put on the roof. Continue reading my multi-part series on the DIY solar install I did to our unit in our transition to full-time RV living. We are a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for us to earn fees by linking to Amazon.com and affiliated sites. We would appreciate if you find this information useful and are looking to purchase some of our recommended items that you would use our links provided.
So in my first blog I described some of the steps that I used to help me determine what my average/maximum usage was going to be. Now lets look at how we can take those numbers and start matching them to your equipment needs. Lets talk about some of the important background information for inverters.
Inverter vs Generator
There are times when one makes more sense than the other. It will depend on a few factors such as load and duration, time of day, and location to name a few. If you are going to be running a high load that is going to deplete your batteries and you will not be able to start the evening with full batteries, you may be better off running a generator. You may be limited to the duration of running your generator or to certain times of the day. You may need to supplement charging your battery bank anyway so it is best to do it at certain times.
If you are going to be running your air conditioner during the day, you might as well start up the generator instead of running it off your inverter and depleting your batteries. There are solar driven systems that can handle the power requirements but they are not common and are expensive. Another option to consider is to utilize an inverter to assist in providing power so it may be possible to use a smaller, quieter, and more fuel-efficient generator. On our trailer I originally installed
a 2000 watt Go Power inverter charger. It was capable in fulfilling our normal boondocking requirements.
There are going to be days that are going to be overcast and raining or you were able to score an epic camping spot that has partial shade. For the limited sunshine days, you are
better off charging your batteries with a generator first thing in the morning at the bulk rate and then let your solar panels take over to finish the absorb stage due to the lower amperage requirements of lead acid batteries.
Types of Power Inverters
Inverters come in two styles based on how they create the a/c current. They are known as modified sine wave and pure sine wave inverters. They both can produce 120v ac current by converting the 12v dc current from a battery bank. The modified sign wave inverters are cheaper and lower efficiency units that may not be able to run you modern electronic appliances the way they should be. Their sine wave looks like they are basically turning a switch on and off. The pure sine wave inverter produces a sine wave that is more like a household ac source. There are many inverters that produce power even cleaner then what you can get out the plugs in a house or RV park. They can however be more expensive than the modified sine wave inverters.
Note worthy options for Inverters
Automatic Transfer Switch. Inverters will sometimes include built-in transfer switches that will allow you to power a circuit when on a pedestal or generator, but transfer to the inverter automatically when the power is disconnected or lost. This is especially important when selecting an inverter to power a residential refrigerator. Some things to also pay attention to include transfer switch max pass through amperage. Some inverters will mention that they can pass through up to 60 amps of power. What they do no highlight is that it is via two 30 amp hot lines.
Hybrid technology or load assist. Different manufactures refer to the function a little different but the end is all the same. What it does is it allows you to be connected to an external source of power, but if the load was bigger then the source available the inverter would assist in providing the additional power required. When is this nice to have? Say you want to run a microwave. The microwave has a running current of 1800 watts. The 3000 watt inverter in the RV does have an automatic transfer switch but not load assist and shuts off the inverter when receiving power from an outside source. You are running a 1600 watt generator. When you start the microwave to heat dinner your generator is overloaded because it can not provide the current for the microwave and the inverter is turned off because there is power coming from your generator. If you had an inverter that had the power boost technology it would be able to add power to the 1600 watts of the generator and dinner would be served.
Built in battery chargers. A lot of the larger inverters are now coming with built-in battery chargers that are convenient when configuring your system so that they will charge your batteries when plugged in automatically. This will allow for the removal of the standard RV converter and allow for a more efficient charge when the unit is plugged into a pedestal or generator. Hybrid inverters will also be able to decrease the power to the chargers if the load assist feature is utilized.
How to choose an Inverter
If you started at my first blog you learned how to calculate your 120v ac wattage utilized. Your max usage will dictate you minimum inverter requirements. If you want to use your coffee maker in the morning to make a pot of coffee or your microwave to heat up a breakfast burrito, you will need to calculate how many watts those appliances draw and find an inverter that will supply enough power to carry that load. Now keep in mind at this stage you are only looking at maximum load at once. If you are going to make a piece of toast while your wife is blowdrying her hair, add the two wattages together. Also keep in mind any surge numbers of your items. Air Conditioning units surge pretty high. A lot of power tools like air compressors will also surge pretty high. Once you have calculated those numbers, look for an inverter that will handle them.
Wiring your inverter to the RV
I know in the decision to select an inverter it may seem premature to be discussing how the inverter will be wired to the trailer but it is for good reason. There are several ways to wire in your inverter and each installer will tell you their way is the best. Many will recommend the use of a sub-panel. A sub-panel is a secondary circuit breaker panel that is utilized to segregate all the circuits that are going to be powered by the inverter. The use of sub panels came about for a few reasons. They were utilized to keep owners from overloading the circuitry, only using certain circuits, and eliminating overuse of the battery bank.
When the first inverters were utilized, they often were used with transfer switches that had limited amperage capacity. Many would not be able to handle the power of the whole RV. So in order to supply inverters with pass through capability, often a circuit breaker would be placed in the main circuit panel that would power the inverter when connected to an outside power source which in turn would then power the sub-panel or direct to loads. Many manufactures still are using this method when installing residential refrigerators. It is still common to find modern inverters with internal transfer switches that have 30 amps max capacity. It may not be an issue if your RV only has 30 amp service but for RVs with 50 amp service it can be dangerous to install it any other way.
So the next step in the design phase would be to evaluate what size battery bank you need. It will need to be designed to be able to provide your maximum current to supply your inverter but also be able to give you lasting power to make it through the night if your furnace is running. For help with this be sure to come back and read the third installment dealing with the battery characteristics and how to set up your battery bank.
Come check out our RV Solar DIY Install Group site to get your questions answered, or to help find recommendations on a system for you.