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What Is an RV Solar Charge Controller?

What Is an RV Solar Charge Controller?

Today’s post is all about the RV solar charge controller. “The what?”, you may ask. This essential component of an RV’s solar power system is seldom the focus when people talk about solar. Solar panels and battery banks seem to get top billing. But the solar charge controller is a critical element of any RV solar system, and today we’ll tell you why.

Harnessing the awesome power of the sun for your electrical needs is an amazing privilege. Because we live and run businesses from our RV full-time… mostly while boondocking off the grid… our power needs are considerable. So we went all out in building our solar array and electrical system. But some RVers only need a portable solar panel and a battery or solar generator to top off their electronics. Others need a little more than that to power their RV and a few small appliances.

Regardless of the size of your solar array and your battery bank, all you’ve gotta do is connect a solar panel to a battery and you’ve got power, right? Not so fast! Today’s post focuses on what’s missing in that scenario – the RV solar charge controller.

Let’s talk about what it is, what it does, how it works, and why you absolutely need it. If you’re thinking of powering your rig (or anything that requires power) with solar, then this information is critical to your plan.

Let’s dive in…

What Is an RV Solar Charge Controller?

With any solar power system, your energy source is the sun, and the component that harnesses that energy is your solar panel (or array of solar panels). Your battery bank is where the energy coming from your solar panels is stored.

Between the two – solar panel(s) and battery bank – you need a voltage regulator. Without it, your batteries could be damaged by excessive voltage and overcharging, and your solar panels won’t output their maximum power.

An RV solar charge controller is that voltage regulator. The rate of charge and the volume of energy going into your battery bank are regulated by your solar charge controller. Typically, it can be configured to provide the proper charging profile for your battery’s chemistry — typically flooded lead-acid, AGM (absorbed glass mat), or lithium. It’s an absolutely essential component of your RV’s solar system.

The solar panel and charge controller work together.

A solar charge controller sits between your solar panel(s) and your battery bank. It acts as a voltage regulator to prevent overcharging and stops the current from flowing back into the solar panels.

What Does an RV Solar Charge Controller Do?

In addition to protecting your battery bank from excessive voltage and overcharging, a solar charge controller stops the energy that’s stored in your batteries from flowing back out into the solar panel when the sun goes down.

So, it regulates the energy going into the battery bank, and it prevents the stored energy current from flowing in the other direction, (back to the solar panels), when darkness falls.

Your RV solar charge controller is the smallest, lightest component of your solar power system, but no less essential than solar panels and batteries.

What Is a PWM Charge Controller?

There are two types of solar charge controllers – PWM and MPPT. PWM stands for “Pulse Width Modulation.” In order to charge your battery bank, a PWM charge controller uses a series of short pulses (as opposed to a steady stream) of power.

A PWM charge controller is constantly checking the status of your batteries and uses that information to determine the timing and the size of the energy pulses it sends.

So, if your battery bank is significantly discharged, a PWM charge controller would send out long pulses of energy to your batteries continuously. But, if your battery bank was fully charged and there was no load on the system (i.e. you weren’t running anything requiring power), the PWM charge controller would send out only a very tiny pulse every few seconds.

As your battery bank becomes fully charged, a PWM solar charge controller will reduce the volume of power coming into the battery accordingly. Once your battery bank is fully charged, it will send out only a tiny trickle charge to keep your battery bank full. (This is often referred to as float charging.)

A solar charge controller.

There are two types of solar charge controllers – MPPT (Maximum Power Point Tracking) and PWM (Pulse Width Modulation).

What Is an MPPT Charge Controller?

MPPT stands for “Maximum Power Point Tracking”. An MPPT solar charge controller takes the high-voltage power output supplied by a solar panel and converts it to a lower, more acceptable voltage so that your battery bank charges safely and without damage, and your devices and appliances are charged efficiently.

So, an MPPT solar charge controller is an electronic DC-to-DC converter that takes the high-voltage DC output from your solar panel and converts it to the lower voltage required to charge your battery bank.

In addition, “maximum power point tracking” means that an MPPT solar charge controller is constantly analyzing your solar panels and determining the exact voltage required to maximize the panels’ power output to your batteries. This changes constantly depending on the amount of light going into the panels, the ambient temperature, and other variable factors.

This is why MPPT charge controllers allow more efficient solar panel performance (by up to 30%) than PWM charge controllers. They allow the panels to operate at their optimal (higher) voltage for the conditions… and convert that extra voltage into additional charging amps.

Which Type of Charge Controller is Better – PWM or MPPT?

The answer to this question depends largely on your needs.

If you have low power needs and thus a low-power solar system, then a PWM solar charge controller would be a less expensive option and perfectly suitable. This would require that you have solar panels equalling no more than around 150 Watts and your power needs aren’t significant.

A PWM charge controller is also best for trickle-charging a battery for maintenance when it’s not being used.

Perhaps the greatest feature of a PWM charge controller is its very low voltage loss, which means that if your devices and appliances are turned off, your battery power is not being consumed.

But if your solar system is greater than 150 Watts and you have high power needs and multiple solar panels as we do, an MPPT solar charge controller is what you need.

Solar panels on RV roof.

If your RV’s solar system is greater than 150W, then you’ll want an MPPT controller. A PWM controller may be sufficient for smaller systems.

First, MPPT controllers allow for multiple solar panels to be wired together in series (increasing the voltage output), creating a very significant solar array. They also give us greater control with a large solar system and can utilize the maximum output from our solar panels (which a PWM charge controller would not be able to do). For anyone with a larger solar system, MPPT solar charge controllers provide up to 30% more efficient than PWM controllers.

So, while MPPT solar charge controllers are more expensive, they’re also more efficient in an application like ours, and thus the greater cost balances out with the greater efficiency.

Depending on the degree of sunlight and ambient temps, a PWM charge controller may produce anywhere from 65% to 85% efficiency (they’re actually best in sunny, warm climates) while an MPPT controller will provide maximum efficiency coming from a generous solar array, even in climates where ambient temperatures are cool.

To summarize this PWM vs MPPT discussion, if you’ve got a 100-150 Watt solar panel you’re using to keep your RV’s house battery topped off and you generally travel in fairly warm, sunny climates, a PWM solar charge controller may be perfectly sufficient for you, and they’re a simpler (fewer parts) and less costly option.

But, if you’re looking to supply more than around 150 Watts from your solar panels to your battery bank, or if you’re looking to connect multiple solar panels in series, you’ll want an MPPT controller to do the job.

What Are Amp Ratings on a Solar Charge Controller?

An amp is a unit of electrical current, and all solar charge controllers have a maximum amp rating. The current/amp rating is the maximum charging current that the solar charge controller can output to the attached battery bank.

However, the power rating for solar panels is stated in Watts and is determined by both the output current and the output voltage (for most RVs, the battery charging voltage will be either 12V or 24V).

An equation to bear in mind when trying to determine the appropriate amp rating for your RV’s solar charge controller is amps x volts = watts (and its corollary equation of amps = watts ÷ volts).

So, for example, a 30-amp (30A) charge controller with a 12V output will be able to handle up to 360 Watts (30A x 12V).

That same charge controller (30A) charging a battery bank with a 24V output will be capable of charging up to 720 Watts (30A x 24V).

Our Xantrex Inverter-Charger control panel.

Our Xantrex inverter-charger control panel.

What Amp Rating Do I Need For My RV’s Solar Charge Controller?

The general rule of thumb used in determining the appropriate amp rating for an RV solar charge controller is to select a solar charge controller with an amp rating that is 25% higher than the total peak power amperage of your solar array.

The reason for the additional 25% is that in certain conditions your solar panels may produce more than their rated output. Having room for 25% additional charging capacity will accommodate those conditions.

Remember that the amp rating is the maximum charging current (or maximum amperage output) to the batteries. Remember also that amps x watts = volts. This allows you to calculate the charging current of your solar panels in amps by using the equation watts ÷ volts = amps.

You can obtain the maximum rated power of a solar panel in watts by reading the back of the panel (or the spec sheet or manual that comes with the panel). You’ll also see the maximum power voltage expressed in volts.

You’ll want to calculate the current that will be produced by your solar panel whenever it’s generating its maximum power. You can calculate the current in amps by dividing watts by volts.

Now let’s say, for example, you have two 100 Watt solar panels with a peak power of 6 amps each. Wired in parallel with each other, 6 amps x 2 panels means that your two solar panels will produce 12 total amps. In this case, you’ll want a solar charge controller rated for 25% more, so you’d want a minimum of a 15A controller.

(Note that in this particular scenario, buying a 20A charge controller would allow you to add another solar panel in the future, should you desire to do so.)

To make this easier, many solar panel kits come with the appropriate solar charge controller as determined by the manufacturer.

Can I Connect a Solar Panel to My RV Battery Without a Charge Controller?

If you want to use a solar system to power your RV, you will absolutely need a charge controller. Without it, you’re very likely to damage your battery bank due to the overcharging that’s likely to occur because the panels alone are not capable of limiting or regulating the voltage going into your batteries.

It should be noted that in theory, you can connect a very small solar panel (no more than 5 Watts) directly to a battery for the purpose of trickle charging the battery for maintenance purposes while in storage.

Small solar panel for trickle charging a battery.

Every RV solar system needs a solar charge controller. The only time you might be able to get away without a charge controller is when using a tiny solar panel to trickle charge a battery.

Can I Use My Batteries While They’re Being Charged With Solar?

You certainly can use your batteries while they’re being charged with your RV solar system.

You can use the power/electricity in your RV (taken from your battery bank) while the sun continues to send more energy to your solar panels, and your panels (through the solar charge controller!) continue to charge your battery bank.

What to Look For When Choosing an RV Solar Charge Controller

There are a number of features to look for when choosing an RV solar charge controller. We’ll take a look at those features, in brief, followed by five excellent choices of solar charge controllers on the market today.

Quality

The first thing you want to consider when shopping for an RV solar charge controller is quality. You want a charge controller made by a manufacturer recognized in the industry as a provider of quality solar components, with a good historical reputation for both product and customer service, and a warranty to back up the product.

Poorly made solar charge controllers can create electrical noise that interferes with the electronic frequencies of devices in your rig.

Be certain to only buy a charge controller that is UL-certified. UL (Underwriters Laboratory) is an independent non-profit organization that tests electrical components & equipment for potential hazards. UL-certified solar charge controllers have been tested by UL and have met their requirements for safety.

Remote Monitoring Ability

The ability to monitor your system remotely is a feature that can be very important. Some solar charge controllers come with a Bluetooth feature that will allow you to download an app that gives you the ability to monitor the system from your smartphone, from as much as 30 feet away.

Remote system monitoring via Bluetooth through a smartphone app.

Many RV solar charge controllers offer remote monitoring via Bluetooth through the manufacturer’s smartphone app.

This means that you can be sitting in the comfort of your RV, or even outside your RV, and you’ll be able to actually see the current flowing through your controller to your battery bank, check the voltage regulation, and take a look at how much power your solar panels are generating.

Some charge controllers provide a monitor panel to be installed in your RV so that you can check the activity of the controller from there. Some monitors allow you to log in remotely to check on the functioning of your system.

Adjustable Voltage Setpoints

Adjustable voltage setpoints allow you to adjust the charging voltage to align with the type of battery/batteries you have, whether they’re lead-acid, AGM, gel, or lithium-ion batteries. In some controllers, you simply select the appropriate battery type and it has the correct charging parameters pre-programmed. Other controllers may allow you to manually configure custom charging voltages for each charging stage. Either works.

On/Off Switch

An on-off switch is extremely handy to have because it allows you to turn off the charge controller anytime you want to stop charging your batteries.

Without this feature, you’ll need to remove the fuse of the battery bank anytime you want to turn off your RV solar charge controller, or wire in your own on/off switch.

Ability to Easily Switch from Shore Power to Dry Camp Mode

This is an interesting feature that allows you to change the set point of the battery charge based on how you’re camping. If you’re boondocking, you’ll want to be charging to maximum capacity. But when you’re connected to shore power you can switch to standby mode. You can also use stand-by mode to help maintain your batteries when your rig is in storage.

What Are Some of the Best RV Solar Charge Controllers?

Let’s take a look at five excellent RV solar charge controllers in several budget ranges, and the features they offer.

Victron Energy SmartSolar MPPT 100V/50 amp 12/24-Volt Solar Charge Controller (Bluetooth)

The Victron Energy SmartSolar MPPT charge controllers are among the most popular RV solar charge controllers on the market. This particular model is a 100-volt, 50-amp charge controller for 12V and 24V battery banks, making it acceptable for up to 700 Watts of solar panels at 12V, or 1400 Watts of solar at 24V.

The SmartSolar feature allows your batteries to be charged to full capacity very quickly. (The manufacturer states that it can operate with a battery voltage as low as 0 volts, meaning that it could recharge a deeply discharged battery as long as the cells aren’t permanently sulfated or damaged in some other way.)

This charge controller has an internal sensor that gauges the ambient temperature and compensates accordingly.

It has built-in Bluetooth allowing you to configure and monitor the charge controller through the VictronConnect app on your smartphone or tablet.

Reviews for this Victron SmartSolar MPPT controller are stellar.

Victron SmartSolar MPPT 100/50 Charge Controller
  • SmartSolar MPPT 100/50 Charge Controller

Renogy 30A Adventurer 12V/24V PWM Solar Charge Controller with LCD Display Flush Mount Design Negative Ground, Compatible with Sealed, Gel, Flooded, and Lithium Batteries

The Renogy 30A Adventurer automatically detects whether your system is a 12V or 24V DC system, and offers Smart 4-stage PWM charging while protecting against overcharging, reverse current, reverse polarity, and short-circuiting.

This unit flush mounts on your RV’s wall, and the easy-to-read LCD screen displays solar charging and battery operation information and more, offering customizable parameters.

This is a negative ground controller with adaptability for AGM, gel, flooded, and lithium-ion batteries.

Sale
Renogy 30A 12V/24V PWM Solar Charge Controller with LCD Display Flush Mount Design Negative Ground, Compatible with Sealed, Gel, Flooded and Lithium Batteries, Adventurer 30A
  • 【12V/24V Automatically Detect】Automatically detects 12V or 24V DC system voltages (for non-lithium batteries). The LCD screen and multiple LED...
  • 【Smart 4-Stage PWM Charging】Smart 4-Stage PWM charging (Bulk, Boost, Float, and Equalization) increases battery life and improves system...

Xantrex 710-3024-01 Solar Charge Controller, MPPT, 30A

The Xantrex 710-3024-01 MPPT 30A solar charge controller offers an industry-leading 98% charging efficiency as well as dual-battery bank charging that allows you to simultaneously charge and maintain your house batteries and your rig’s starter battery.

A leader in the solar industry, Xantrex offers best-in-class protection for your batteries. This solar charge controller supports house batteries that are AGM, gel, flooded, or lithium-ion phosphate (LiFePO4).

Xantrex 710-3024-01 Solar Charge Controller, MPPT, 30A
  • Advanced Maximum Power Point Tracking (MPPT) technology increasing daily energy harvest by 20-30% compared to PWM technology
  • Dual-battery bank charging to simultaneously charge house and starter batteries

Renogy Wanderer Li 30A 12V PWM Negative Ground Solar Charge Controller Solar Panel Regulator w/ Temp Sensor Function Fit for Lithium, Sealed, Gel, and Flooded Batteries

Renogy’s Wanderer automatically detects your 12V or 24V DC system voltage and offers Smart 4-stage PWM charging (Bulk, Boost, Float, and Equalization). Like the Adventurer, it offers intelligent protection against overcharging, reverse current, reverse polarity, and short-circuiting.

Its simple interface is easy to use and offers multiple LED indicators of charge status and battery information.

The Wanderer is adaptable to AGM, gel, flooded, and lithium-ion batteries.

Sale
Renogy Wanderer Li 30A 12V PWM Negative Ground Solar Charge Controller Solar Panel Regulator w/ Temp Sensor Function Fit for Lithium, Sealed, Gel, and Flooded Batteries, Wanderer Li 30A
  • 【Optimized for 12V Batteries】Compatible with 12V battery banks on the market, including lithium batteries. The LED indicators allow you to set...
  • 【Smart 4-Stage PWM Charging】Smart 4-Stage PWM charging (Bulk, Boost, Float, and Equalization) increases battery life and improves system...

Victron Energy SmartSolar MPPT 75V 15 amp 12/24-Volt Solar Charge Controller (Bluetooth)

Victron’s SmartSolar MPPT 75V, 15A solar charge controller is another feature-rich Victron product that’s very similar to the Victron SmartSolar charge controller noted above, though this product is a 75-volt, 15-amp charge controller.

This charge controller also has built-in Bluetooth for remote configuration and monitoring via the VictronConnect app on a smartphone or tablet.

Victron uses a sophisticated 3-stage charging method that includes a float charge. This charge controller comes highly recommended by a full 93% of 4-and 5-star Amazon reviewers.

Do I Need a Solar Charge Controller for My RV?

If you intend to harness the power of the sun using solar panels to store energy in your RV’s battery bank, then yes, you will need an RV solar charge controller that is consistent with your system.

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Rich Fulton

Tuesday 4th of January 2022

Thanks for the great info. I don't understand when you said "But when you’re connected to shore power you can switch to standby mode". Is this required or just desirable? Is there damage if you don't? How is this done? I have 400W of Zamp solar on my trailer and a Victron Smart 150/35 solar controller installed last year. They did not say anything about the need to manually switch to "standby mode" when I'm plugged into shore power. I assumed it's all fine and automatic regardless of whether I'm on solar or shore power. They did install a manual solar panel cutoff switch to do this if needed....is that what you mean by "standby" mode?

TheRVgeeks

Tuesday 4th of January 2022

Hi Rich. That "Standby" feature is available on some charge controllers... but not all (our Xantrex doesn't have it... and probably not Victron, either). But you don't need it... even plugged in and the converter/charger running, the solar charge controller will adapt. When the battery is full, both charge controllers should shut off.

On the plus side... when staying in a park for a long-term stay (where you might be paying for separate, metered electric), having the solar on can help to offset your electric bill.

Don't worry about it... you'll be just fine.

Vic

Monday 3rd of January 2022

Any thoughts on the GoPower charge controllers and solar arrays? They appear to be conspicuously missing from your list of reviewed products. Thanks.

TheRVgeeks

Tuesday 4th of January 2022

Hi Vic. GoPower would've been next on the list (but we had to cut it off somewhere, right?). Nikki & Jason Wynn had GoPower solar on their RVs and had very good experiences with it.

Brad Wartman

Friday 31st of December 2021

My rig has 3 sets of solar panels, 2 portable panels:

1-ZAMP 120W, PWM controller 1-Dokio 300W, MPPT controller

and 1 fixed array:

350 watts, Blue Sky MPPT solar controller.

Our battery bank is 2 SOK 206 Ah batteries connected in parallel (12V, 412 Ah).

Can I connect all 3 sets of panels at the same time to charge the batteries? So far the fixed array (with occasional generator use) has been good enough to keep the batteries charged but I'd like to have the option to add the portable panel(s) if needed (for cloudy days, when parked in shade, etc.). Thanks!

TheRVgeeks

Friday 31st of December 2021

P.S... that is assuming that all three solar charge controllers can be set/configured to use a Lithium-compatible charge cycle, since your SOKs are LiFePO4. If not, don't connect that charger to the system, as it could over-charge the lithium batteries.

TheRVgeeks

Friday 31st of December 2021

Hi Brad. Good question! Technically, yes... there shouldn't be any problem connecting all three charge controllers to the batteries and letting 'em run. They should all see the same voltage at the batteries and run their charging cycles. But... you may notice that one or more of them cut out a bit sooner, depending on slight variations in the voltage they "see" the battery being at (i.e. the output from one charge controller could make one/both other controller think the voltage is high enough for it to stop charging), differences in their electronics, and/or the actual point they're connecting to in the electrical system. But, honestly, even if it happens, it shouldn't be an issue. It's likely to only occur when the battery is very near fully charged.

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