Choosing a solar charge controller for a rv solar set up

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. To help you choose the right solar charger, we’re explaining what a solar charge controller does and the difference between the two main models of charge controllers MPPT and PWM.

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.

Some charge controllers have load control, where you connect the DC load directly to the charge controller instead of the battery. It will turn the DC load (like your lights or fans) on or off, based on the battery levels. This is optional, and you don’t have to connect or use this if you don’t want.

In simplified terms, a solar charge controller protects your batteries by regulating the levels (currents) sent from the solar panels to the batteries.

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

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 set ups 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

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 set up 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 up to 100 amps or more. The larger the solar array you have (like 420 Watts +) the larger you will want your charge controller to be. We have 360 watts of solar on our roof, and that works with a 30 amp solar charge controller. If we decide to build a portable solar panel to add to our set up it’s likely we will have that run through its own charge controller. The good news is you can have separate charge controllers going to the battery and they do not compete or interfere with each other.

how to select a solar charge controller

Once you’ve identified if you want an MPPT or PWM charge controller and determined the size you need, you have to choose a brand. There are dozens of companies making charge controllers. We ended up with an AIMS Power 30amp MPPT charge controller because we also got our (3) 120 watt flexible solar panel array from AIMS Power. So the compatibility was there and they helped us ensure the charge controller would fit for our solar array.

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: his 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.

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3 Comments

Raymond Moore on February 2, 2020 at 11:11 pm

How does using my generator in the RV affect my solar charge controller I have pwm charge controller and a 100 watt solar panel, I just want to use it to trickle charge my two deep well 12v acid type batteries. I just want to make sure i dont damage my set up when i start the generator. Thank you in advance Raymond Moore.
- EatSeeRV on February 16, 2020 at 4:09 pm
  
  You shouldn’t be doing damage when you use your generator, although you may have to adjust the charging rate on your inverter. The solar charge controller’s job is to protect the batteries from the solar, not necessarily the other components of your electrical system.
Dalton Bourne on August 21, 2021 at 8:50 am

Understanding what an MPPT or PWM solar charge controller does will help operate your RV appliances with clean, free, and efficient energy: An MPPT controller automatically adjusts the solar panels’ output voltage to recharge the deep cycle batteries. A PWM controller typically waits for the system voltage to stabilize and fall naturally before initiating the absorb charging state. I can say that the MPPT’s four-stage charging mechanism is better, safer, and healthier for your RV’s deep cycle batteries than a PWM’s three-stage design. A PWM charge controller is ideal for small-scale solar projects, generating less than 2,000 watts. The controller can accommodate up to 60 amperes and run on 12 and 24-volt systems. A MPPT is perfect for solar power systems that generate more than 2,000 watts. It can handle up to 100 amperes and operate on 36 and 48 volt systems.

Liz & Dennis

ESRV Team

We’re two travel-loving, real estate investing, foodies exploring North America as full-time RV’ers. This blog is where we share our lessons learned, tips and tricks, and favorite places to eat, see, and RV across North America! We hope it helps you find your wanderlust, plan and prepare for RV life, and get out on the road!

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