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What Is an RV Solar Charge Controller?

So, you’re thinking of setting up a solar system to power your RV? Harnessing the power of the sun and storing that energy for use on-demand is pretty awesome. But there are several components you need, in addition to solar panels, to make your solar system work. Today, we’ll look at one fundamental part: the RV solar charge controller. 

What Is an RV Solar Charge Controller?

Your RV solar charge controller is an essential component of your system. It’s what sits between the energy source (your panels) and the storage bank (your batteries). 

A charge controller is a voltage regulator that protects your batteries from damage due to overcharging and overvoltages. It regulates the volume and rate of charge to your batteries. 

lithium rv battery installation supplies

A solar charge controller acts as a valve of sorts to prevent current from flowing back out of the batteries and into the solar panels when the sun is gone.

Need a refresher on solar systems? Read this: The Beginner’s Complete Guide to RV Solar Battery Chargers

Types of RV Solar Charge Controllers

There are two types of solar charge controllers. Understanding the distinction will help you decide which to use. Let’s see how each type compares.

Pulse Width Modulation (PWM) Charge Controllers

Pulse width modulation (PWM) charge controllers send out a series of short pulses to charge the battery instead of a steady output. It continually checks the battery status and uses the data to send appropriately timed and sized energy pulses. These energy pulses essentially limit the amount of charge that is sent to the batteries

A PWM controller will send a minute pulse to the battery every few seconds in a fully charged battery with no load. But it would send long, continuous pulses to a discharged battery.

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As your battery approaches full charge, a PWM controller slowly reduces the power volume entering the battery. It will continue to supply a small trickle charge to keep the battery topped off after it’s full. 

A PWM charge controller is often used for float-charging.

Maximum Power Point Tracking (MPPT) Charge Controllers

Maximum Power Point Tracking (MPPT) charge controllers are more sophisticated. They convert the solar panel’s high-voltage power output to a lower voltage. Doing so means your batteries can charge safely, and your devices can access peak power. 

So MPPT controllers ensure the output meets the battery’s voltage requirements and that the charge is efficient.

victron energy mppt 100/50 solar charge controller

In addition to being a DC-DC voltage converter, the MPPT does something very special that its name is derived from, maximum power point tracking. What this means is that the MPPT device analyzes the solar panels and determines what the perfect operating voltage should be to maximize power output. It then holds the panels at that and thus increases that panel output. This technology can improve solar panel performance by 30% over a PWM controller.

The MPPT feature is not a single check of the solar panels either, it scans the panels many times through the day and anytime the power changes significantly. This is because the maximum power point of a solar panel will change depending on light and temperature conditions.

PWM vs. MPPT RV Solar Charge Controllers

PWM charge controllers are less expensive than MPPT controllers. They’re a more economical choice, but you would only use them with low-power systems. They’re also good for maintaining a battery near full charge when it’s not in use. 

PWM controllers’ most significant advantage (other than cost) is that the voltage loss is minimal. So when a device or appliance switch is off, you’re not using your battery charge.  

An MPPT charge controller is best in systems greater than 150W for RVers with high power needs. Here’s why:

MPPT charge controllers provide greater control in large systems. They’re as much as 30% more efficient than PWM controllers in these applications. They can use the maximum output from your solar panels, while PWM charge controllers cannot. 

PWM controllers’ efficiency rating is anywhere from 65-85% and often depends on weather conditions. On the other hand, MPPT controllers give you optimal efficiency from your solar array at all times, even in cooler climates. 

solar panels on rv roof

MPPT controllers also allow you to wire many solar panels together in series. So if you intend to have a more extensive solar system, you’ll need this device. While they’re the more expensive option, you’ll likely recoup the costs through efficiency.

When Do I Need an RV Solar Charge Controller?

If you have a solar panel system for your RV, you need a charge controller. Otherwise, you risk damaging your battery from overcharging because the panels alone cannot limit how much voltage your battery receives. 

Eliminating a charge controller from your RV solar system would not be sensible. The cost of replacing batteries would be far more than the cost of a charge controller.

Can I Connect Solar Panels without an RV Solar Charge Controller?

You can connect a very small solar panel without a charge controller. It shouldn’t be more than 5W to be safe. As mentioned previously, you might do this to trickle charge a battery for maintenance rather than for powering things in your RV. 

How Big of an RV Solar Charge Controller Do I Need?

It depends on the size of the solar array you’ll be using. The standard recommendation is 7.5A for every 100W of solar panels when using a 12V battery bank. So if you have a 200W system in series and are using a 12V battery bank, you’d need a 15A controller. 

Most charge controllers will specifications of what they are rated for when connecting to a solar system size. Refer to the manufacturers information when deciding how large of a unit you need.

Can I Use Multiple Solar Charge Controllers in the Same System?

Yes, and you might want to if you have high-power charging needs. 

rv solar electrical system with 3 solar charge controllers
This is our setup, we have 3 solar charge controllers running the system

You can connect solar controllers in parallel to a battery bank. Each controller should link to a separate solar panel array, so the MPPT controllers can track each collection and prevent voltage inconsistencies.

How to Choose an RV Solar Charge Controller

Most importantly, use the criteria above to decide between a PWM or MPPT controller. Then, choose a solar charge controller rated for your solar panel array’s total peak power (amps). Keep in mind that if using an MPPT charge controller the Amp rating they have is for the lower voltage side. This means that if you use higher voltage panels and a lower voltage battery bank, the amperage on the battery side is the limit.

Also, consider that if you use a charge controller that is too small it won’t hurt anything. The charge controller will just limit itself and the power that it can push through. However, using a unit that is too small may make it work much harder and shorten its lifespan. Usually, we like to oversize our charge controllers by 25%.

Beyond that, you want to choose a good-quality controller that will last. After all, your power supply depends on it! Here are a few criteria to consider. 

Avoid Cheaply-Made Controllers

Cheaply-made charge controllers could create substantial electrical noise. This means that they can interfere with certain electronic frequencies of televisions, radios, stereos, etc.

For this reason, it’s best to buy a charge controller that’s UL-certified. UL is a company that tests, inspects, and certifies products for safety, efficiency, and reliability. They only put their stamp of approval on great products. 

Extra Features

RV solar charge controllers may come with many extra features, including the following:

Bluetooth: Download an app on your phone so that you can monitor your solar system from 20-30 feet away. You can see how much energy your solar panels generate, voltage regulation, the current flowing through the controller, and much more.

External Reporting: Use a monitor inside your RV to read the charge controller’s impact. We use an Octo GX to monitor our system. This computer collects data and sends it to an online portal, so we can log in remotely and see how our system is functioning.

victron energy octo gx

Adjustable Voltage Setpoint: Adjust the charging voltage setpoint to the type of battery you have (flooded lead-acid, gel, AGM, lithium-ion). You can identify the proper charging voltage from your battery’s manufacturer or owner’s manual.

On/Off Switch: Turn off the RV solar charge controller to stop charging the battery without removing the battery bank’s fuse.

Dry Camp/Shore Power Switch: You might want to change the battery charge set point depending on whether you are boondocking or using shore power. You can switch to maximum capacity if you’re boondocking and then to stand-by mode when on shore power. It also helps you maintain your batteries when your RV is in storage.

What Is the Best RV Solar Charge Controller?

Today’s top RV solar charge controller is the Victron 100/50 SmartSolar MPPT Charge Controller. It’s suitable for up to 700W of solar at 12V or 1400W at 24V. 

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The device is a 100V, 50A charge controller for 12V and 24V battery banks. Victron products like this are known for voltage regulation and battery protection. This unit also has built-in BlueTooth for monitoring and configuring your system through the VictronConnect app.

It uses SmartSolar, which lets your batteries reach full charge as quickly as possible. It can even recharge a working battery that’s fully depleted. SmartSolar also features an internal sensor that compensates for ambient temperatures. If you purchase the optional Smart Battery Sensor, you can monitor the battery temperature too.

Reviews are outstanding for this Victron product! One Amazon customer wrote:

“Victron components are incredible. I already had the BMV-712, and just added the SmartSolar 100/50 to add solar power to my RV. Used with two 100w Renogy mono panels, with the plans to add two more soon. The build quality of this solar controller is incredible, it feels like you’re getting what you’re paying for.”

accessing the battery monitor information via blue tooth

Other reviewers noted that the VictronConnect mobile app connects seamlessly over Bluetooth to simplify data observation and settings management. The app automatically scans for systems within range, so you don’t have to worry about pairing. 

Along with real-time monitoring in the app, you can make adjustments to the system as necessary. You can also configure settings dependent on your battery type and mark low-temperature cutoffs. There’s the option to view and export your system’s performance via email as well. 

Which Charge Controller Is Right for Your Solar System?

This Victron charge controller is a sophisticated and refined technology that exists to manage any RV solar system optimally. In fact, we use three Victron charge controllers in our Ultimate Off-Grid RV Solar Power System Build.

Ultimate RV Off-Grid Solar System Build - 2760 Watts of Solar ☀️ 11Kwh Battery, on a 32' Fifth wheel

But don’t just take our word for it. Now that you understand an RV charge controller’s function and significance, you can determine which RV solar charge controller will best suit your solar application.

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About Tom Morton

Tom, a Pacific Northwest native, is our technical genius. Born in Washington and raised in Alaska before settling in Michigan. He's the man who keeps our operation running, both figuratively and literally.

With a background in Electrical Engineering, Tom specializes in RV solar systems and lithium batteries. He made history as the first documented individual to use a Tesla battery module as an RV battery. Tom has personally assisted countless RVers with system installations and has educated thousands more through his videos and articles.

Cinematography is another of Tom's passions, showcased in his work on the Go North series. You can see his camera skills on display in The RVers TV show on Discovery Channel and PBS where he also stars as a co-host.

Tom's mechanical expertise extends beyond RVs to boats, planes, and all things mechanical. He's renowned for taking on maintenance and repair projects single-handedly and is often spotted underneath RVs, making him the technical backbone of our endeavors.

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Dalton Bourne

Saturday 21st of August 2021

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.

Dalton Bourne

Sunday 29th of August 2021

Understanding what an MPPT or PWM solar charge controller does will help you create the most efficient energy system for your motorhome.

john urbas

Sunday 25th of April 2021

Good information to know. When using a portable solar unit with its own built-in controller, could there be an issue between the controllers and is there a proper proper way to incorporate the portable source into the system?