If you are installing your own DIY solar set up on your RV you’re going to have to choose a solar charge controller. With the broad range of charge controllers out there with different sizes, types, manufacturers, and price range it can be difficult to determine which one is right for your solar setup.
This blog explains what a solar charge controller does and the difference between the two main models of charge controllers MPPT and PWM. Let’s dive in!
What is a solar charge controller?
A solar charge controller is a component that regulates the amount of voltage and current that is sent from your solar panels or solar array to your batteries. It plays an important role in a full solar set up as it keeps your batteries from overcharging by monitoring the battery voltage, opening the circuit, and stopping the charging when the battery voltage rises to a certain level.
In simplified terms, a solar charge controller protects your batteries by regulating the levels (currents) sent from the solar panels to the batteries.
Some charge controllers have load control. This allows you to send the DC (direct current) load to the charge controller instead of your batteries. It will turn the DC load (like your lights or fans) on or off, based on the battery levels. This is optional feature that you don’t have to connect or use if you don’t want.
Types of charge controllers
There are two modern types of charge controllers, MPPT and PWM. While most people opt for the MPPT charge controllers, a PWM can do the job depending on the type of batteries you have and the output voltage of your solar array. There are a ton of technical sites out there with graphs showing you difference in performance between the two – but for the ease of this blog post I’ll keep it simple as we compare charge controllers.
PWM charge controller
PWM stands for “Pulse Width Modulation” because it pulsates the power that is supplied to the batteries pulling the voltage down to near the voltage of the batteries. It also keeps the batteries in a “float” state or fully charged states and prevents them from overcharging.
PWM charge controllers are often less expensive, but it’s important to note they are only good to use with smaller solar setups as it cannot be used with higher voltage solar panels. You can check to see if this will work by looking at your solar arrays output voltage.
Make sure it doesn’t exceed the maximum input voltage of your charge controller. Also important to note that the voltage of the PWM charge controller must match the battery bank voltage for example (12v output from you panel to a 12 volt battery system).
MPPT charge controller
MPPT stands for “Maximum Power Point Tracking”. This charge controller is considered more advanced and efficient than a PWM because it is able to convert excess voltage into amperage. This means your batteries are able to charge more efficiently, using less power, and battery charge often lasts longer.
Because MPPT charge controllers can handle higher voltage solar arrays you can typically add to your current system at a later time without having to increase your charge controller. MPPT charge controllers are the more expensive option but depending on your setup may be the only option.
With an MPPT controller, you do not need the voltage to match the battery bank. For example, 24v output from your charge controller can still be paired with a 12v battery bank. If you have a large solar array, chances are you will need an MPPT charge controller.
In summary, MPPT charge controllers are typically the way to go. They are newer technology and regulate the charging current of your batteries more efficiently. They are more expensive, but they also do not require the voltage outputs from the panels to match the voltage of the batteries.
What size charge controller do I need?
Regardless of the type of charge controller you choose. It’s imperative that the maximum input voltage and current rating of the charge controller is higher than the maximum output voltage and current (amps) of your solar array.
There are charge controllers as small as 10 amps. And charge controllers up to 100 amps or more. We have 400 watts of solar power on our roof and have a 30 amp solar charge controller. This is sufficient for the power we bring in. However an RV solar array with 800 watts for example, would require a 50 amp charge controller or possibly more.
You can set up separate charge controllers to the batteries. They will not complete or interfere with each other. This is how many people are able to use a portable solar panel (with its own charge controller built in) in conjunction with a full solar array on the roof of the RV.
How to select a solar charge controller
Once you’ve identified the type and size of charge controller you need, you can choose a brand. There are dozens of companies making charge controllers. We’ve used Renogy’s MPPT charge controller on 2 of our RVs. We also tried AIMS Power 30-amp MPPT charge controller. Both brands worked well with our solar panels and batteries.
We found a great video on Youtube that compares different brands and types of charge controllers to show efficiency to see if one brand really is better than others. Spoiler alert: the video confirms that cost and size have very little do with effectiveness. You do, however, want a well built solar charge controller that allows for heat to circulate and vent with wide input terminals.
It’s also helpful if the charge controller has a temperature compensation sensor (especially important with lead acid batteries) and a screen to change the data of the charging rate or voltage of the controller. Ours has all of these things so to us, it checks all the boxes!
Hopefully this post help you understand the main differences between the various types of charge controllers and made the process of choosing a solar charge controller for your DIY RV solar set up a little bit easier.