How-to Choose a Solar Charge Controller for a DIY Camper Van ...

What is a Solar Charge Controller?

The Charge Controller takes the power made by the solar panels and transform the ‘solar panel power’ into a form of power that the batteries can use.

Link to KINGSUN

Quick note before we get started.  This is just one part of a overarching “How to Install a DIY Camper Van Electrical System” series.  If you’ve just stumbled on this article directly without seeing that, there are likely some things we’ve already covered.  If you want to check out that step by step guide, you can do that here: https://www.explorist.life/diy-campervan-solar

Also, we have interactive solar wiring diagrams that are a complete, A to Z solution for teaching you exactly what parts go where, what size wires to use, fuse size recommendations, wire lug sizes, and all kind of other stuff to help save you time and frustration.  You can check that out here: https://www.explorist.life/solarwiringdiagrams/

Finally, for this blog post you’re reading right now, we have a calculator that will help you choose a charge controller. I HIGHLY recommend reading this post to truly learn how a charge controller works, but if all you need is the calculator, here that is:

How does the Charge Controller Work?

Solar panels typically put out a voltage that is too high for batteries to use. If you have your solar panels wired in series like I recommend, you could possibly have over 100 volts coming out of the solar panels. If you connected your 100 volts from the solar panels directly to the battery, it’s not going to work. The Charge Controller regulates the voltage from the solar panels back down to the 12.6 – 14.6 volts that the batteries can store/use.

MPPT vs PWM CHARGE CONTROLLERS

There are two main types of charge controllers. They are MPPT and PWM. This blog post is a crash course in solar design and getting into the specifics of the differences is out of the scope of this blog post. Here’s what you need to know regarding MPPT vs PWM charge controllers MPPT is the newer, more efficient technology. From here on out, any time I talk about charge controllers, I will only be talking about MPPT charge controllers as I want to guide you to build a high-end, expandable solar setup.

HOW TO MATCH SOLAR PANELS TO A CHARGE CONTROLLER

One of my favorite series of charge controllers is the Victron BlueSolar MPPT Charge Controller. If you’ll notice, there are MANY different sizes of charge controllers:

• Victron SmartSolar MPPT 75 | 10
• Victron SmartSolar MPPT 75 | 15
• Victron SmartSolar MPPT 100 | 15
• Victron SmartSolar MPPT 100 | 20
• Victron SmartSolar MPPT 100 | 30
• Victron SmartSolar MPPT 100 | 50
• Victron SmartSolar MPPT 150 | 35
• Victron SmartSolar MPPT 150 | 45
• Victron SmartSolar MPPT 150 | 60
• Victron SmartSolar MPPT 150 | 70
• Victron SmartSolar MPPT 150 | 85
• Victron SmartSolar MPPT 150 | 100
• Victron SmartSolar MPPT 250 | 85
• Victron SmartSolar MPPT 250 | 100

WHAT DO THOSE NUMBERS MEAN?!?

Lets use the Victron SmartSolar MPPT 100 | 30 for example. The 1st number, 100 means the maximum input voltage the controller can handle. In other words, the Victron SmartSolar MPPT 100 | 30 can handle a max of 100 volts coming from the solar panels into the charge controller. The 2nd number, 30, represents the max amount of amps the controller can output going INTO THE BATTERIES.

*MATH ALERT*

Let’s say, for example, you have 4 x 100 watt solar panels with the following stats.

EACH 100w solar panel has an Open-Circuit Voltage (Voc) of 21.6 volts. and an Optimum Operating Current of 6.72 Amps. Those are the only two numbers we are concerned about for now. I generally recommend just wiring all of your solar panels in series for simplicity and efficiency sake. Which means: Those 4 x 100 watt solar panels get wired together like this:

Since they are wired in series, the voltages get ADDED together for a total of 86.4 volts. (Open-Circuit Voltage (Voc) of 21.6 x 4 panels) The amps on the “upstream” side of the 100w solar panels remains 6.72 since in series, the voltages get added and the amps stay the same.

So, the 86.4 volts is under the safe threshold of the 100 max volts of the Victron SmartSolar MPPT 100 | 30 solar controller.

100 is the first number. What about the 2nd number, 30?

The 30 in the Victron SmartSolar MPPT 100 | 30 is the MAX resulting amps AFTER the solar controller has worked it’s magic. We need to do some math to determine the amperage. Here are the things we know:

• We have 4×100 watts of solar panels totaling 400 watts of solar.
• Assume batteries are 12.6v
• Amps = Watts / Volts

This means, that at 400 watts and 12.6v we can expect up to 31.74 amps coming out of the solar controller.

Now, we are talking about that Victron SmartSolar MPPT 100 | 30, we have to compare that 2nd number, 30.

31.74 amps is a bit over the 30 amp threshold. BUT…

Solar panels rarely put out their full wattage. AND…

In the Victron SmartSolar MPPT 100 | 30 manual, they say their controller is good for solar arrays up to 440 watts:

AND… If you happen to go ‘over’ on your Amperage, it’s not that big of a deal in terms of damage. It’ll just be lost power that the controller won’t convert.

So, basically, the Victron SmartSolar MPPT 100 | 30 is pretty perfect for those 4 x 100 solar panels.

But what if you like playing it safe? What if you want some wiggle room? Great! Size up to the Victron SmartSolar MPPT 100 | 50. Sure, it’s a little more money, but if it’s worth your piece of mind to have an extra 20 amps available to you, go for it.

Now, Why would you want wiggle room or safety margin? Let’s talk about temperature

Solar Controller vs Temperature

DID YOU KNOW… As temperatures drop, solar panels actually put out MORE power.

Totally honest though, the math gets messy, SO I made a calculator that you can input all of the values for your setup so YOU can see how temperature affects your solar panel setup AS WELL AS will give you a recommendation on what solar controller you need taking solar panel temperature into account.

There’s a video below the calculator you can check out if you need additional instructions on how to use it:

Now that you know what kind of charge controller is compatible with your solar panels, it’s time to learn how to choose an inverter for your DIY Camper setup.  Check that out here:

https://www.explorist.life/how-to-choose-an-inverter-for-your-diy-camper/

Everything that you are learning here is put to use in our FREE Interactive Solar Wiring Diagrams.  If you haven’t yet, check them out as they are a complete solution for a camper van electrical system.  Check them out here: https://www.explorist.life/solarwiringdiagrams/

Remember, this is just one part of a full camper van electrical educational series.  To see all of the individual guides, click here: https://www.explorist.life/diy-campervan-solar

To size a solar charge controller, take the total watts of your solar array and divide it by the voltage of your battery bank, then multiply by a safety factor of 1.25. This calculation will give you the output current of the charge controller. For example, a W solar array divided by a 24V battery bank equals 41.6A. Applying the safety factor, 41.6A x 1.25 = 52A. Therefore, you need a charge controller rated at least 52A.

Let’s dive deeper into the specifics of sizing a solar charge controller, addressing common questions and providing clear examples.

Understanding Solar Charge Controllers

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

Pulse Width Modulation (PWM) Controllers

PWM controllers are simpler and more affordable than MPPT controllers. They operate by gradually reducing the power flowing into the batteries as they near full charge, ensuring the batteries are maintained at a full charge without the risk of overcharging. 

However, this simplicity comes at a cost: PWM controllers are less efficient because they do not maximize the power extraction from the solar panels. This efficiency gap is particularly noticeable in systems where the solar panel voltage is much higher than the battery voltage.

Maximum Power Point Tracking (MPPT) Controllers

MPPT controllers are more advanced and efficient. They continuously monitor the output of the solar panels and the state of the battery to determine the optimal power point. This dynamic adjustment allows MPPT controllers to extract the maximum power from the solar panels, significantly improving system efficiency. 

MPPT controllers are especially advantageous in colder climates, where solar panel voltage can be significantly higher than battery voltage, and in systems with higher voltage panels. Despite their higher cost, the efficiency gains from MPPT controllers can lead to a faster return on investment through improved energy harvest.

Calculating the Capacity of a Solar Charge Controller

Sizing the capacity of a solar charge controller is crucial for the optimal performance and longevity of your solar power system. The capacity is primarily determined by two main factors: the system voltage and the maximum current that the solar panels can produce. Below is a step-by-step guide to accurately calculate the required capacity.

1. Determine the System Voltage

The system voltage is a key factor in sizing a charge controller and is typically dictated by the battery bank configuration. Common system voltages are 12V, 24V, or 48V. 

The voltage of the charge controller should match the voltage of the battery bank to ensure compatibility and efficient charging. For instance, if you have a 24V battery bank, you need a charge controller designed to work with 24V systems.

2. Calculate the Maximum Current

The maximum current that flows from the solar panels to the charge controller is a critical parameter. It can be calculated using the following formula:

Are you interested in learning more about 30 Amp Solar Controller? Contact us today to secure an expert consultation!

For example, if you have a solar array with a total wattage of W and your system voltage is 24V, the calculation would be:

This calculation gives you the base current that the charge controller needs to handle under standard conditions.

3. Add a Safety Margin

It is essential to incorporate a safety margin to account for variations in environmental conditions such as changes in sunlight intensity, temperature fluctuations, and potential surges in current. A typical safety margin is 25%, which provides a buffer to ensure the charge controller can handle unexpected increases in current without risk of damage or inefficiency.

To calculate the adjusted maximum current, you multiply the base maximum current by the safety margin factor:

By adding this safety margin, you ensure that the charge controller can manage the peak power conditions that might occur, thereby enhancing the reliability and durability of your solar power system.

4. Selecting the Right Size Controller

Based on the adjusted maximum current, you should select a charge controller with a current rating equal to or greater than this value. In the example above, you would choose a controller rated for at least 52.09A.

Other Factors to Consider

When selecting a solar charge controller, several additional factors can influence the performance and longevity of your solar power system. These include temperature compensation, load control, and efficiency.

Temperature Compensation

Temperature compensation is crucial for maintaining battery health, as the voltage requirements of batteries change with temperature fluctuations. 

If the temperature drops, the battery voltage needs to be higher to charge efficiently, and if the temperature rises, the voltage should be lower to prevent overcharging. Some charge controllers come with built-in temperature sensors and automatic compensation features, which adjust the charging voltage based on the ambient temperature. 

This feature is particularly important if your solar power system is located in an environment with significant temperature variations. Ensuring your controller has this capability can help extend the lifespan of your batteries and improve system performance.

Load Control

Some charge controllers offer load control functions, allowing you to power DC loads directly from the battery bank. This feature can be highly useful if you have devices or systems that you want to run directly from your solar setup. 

Load control functions help manage power distribution and prevent the battery from deep discharge by disconnecting loads when the battery voltage drops below a certain threshold. This protection is vital for maintaining battery health and ensuring that your essential loads are managed efficiently without risking battery damage.

Efficiency

MPPT controllers are generally more efficient than PWM controllers. MPPT controllers can significantly improve the energy harvest from your solar panels, especially in systems with higher voltage panels or in colder climates where panel voltage can be higher. 

The increased efficiency of MPPT controllers can often justify their higher cost by maximizing the overall energy production and improving the return on investment. 

For large or high-performance solar power systems, the efficiency gains provided by MPPT technology can be substantial, making them a preferred choice despite the initial higher expense.

Practical Considerations

When choosing and sizing a solar charge controller, it’s crucial to take into account various practical considerations to ensure your solar power system operates efficiently and has a long lifespan.

Compatibility with Solar Panels

Ensuring that the voltage and current ratings of the charge controller are compatible with your solar panels is crucial. 

For MPPT controllers, verify the maximum input voltage and current specifications to ensure they can handle the total output from your solar array. Mismatched ratings can lead to inefficiencies or damage to the controller and panels. 

Proper compatibility ensures that the charge controller operates within safe parameters and maximizes the energy harvest.

Installation Location

The installation location of the charge controller significantly affects its performance. It is vital to install the controller in a cool, ventilated area to prevent overheating, which can degrade its efficiency and shorten its lifespan. 

Avoid placing the controller in direct sunlight or near heat sources. Adequate ventilation helps dissipate heat, ensuring the controller functions efficiently and reliably over time.

User Interface and Monitoring

A user-friendly interface and robust monitoring capabilities can greatly enhance the management of your solar power system. Some charge controllers come equipped with LCD screens that provide real-time data on system performance. Others offer connectivity options for remote monitoring via mobile apps or web interfaces. 

These features allow you to track the status of your solar power system, detect issues early, and make necessary adjustments. Investing in a charge controller with advanced monitoring capabilities can provide peace of mind and help you optimize your system’s performance.

Conclusion

Sizing a solar charge controller involves understanding the types of controllers available, calculating the maximum current based on your solar array and system voltage, and considering additional factors such as temperature compensation and efficiency. 

By following the steps outlined in this article, you can ensure that you select a charge controller that meets the needs of your solar power system, enhances its efficiency, and ensures the longevity of your batteries. Properly sizing and selecting a charge controller is crucial for the overall performance and reliability of your solar power system.

FAQs

Q1: How many watts can a 30 amp charge controller handle?

To determine how many watts a 30 amp charge controller can handle, you need to consider the system voltage. For a typical 12V system, a 30A charge controller can handle:

• 30A * 12V = 360W

For a 24V system:

• 30A * 24V = 720W

For a 48V system:

• 30A * 48V = W

These calculations show that as the system voltage increases, the same charge controller can handle more watts.

Q2: What size charge controller for a W solar panel?

For larger solar arrays, such as a W system, the calculation follows the same principle. Let’s assume you have a 48V battery bank:

• W / 48V = 62.5A
• 62.5A x 1.25 = 78.13A

You would need a charge controller that can handle at least 78.13A. Most controllers come in standard sizes, so you would likely choose an 80A charge controller for this setup.

Q3: How many watts can a 70 amp charge controller handle?

High-capacity charge controllers, like a 70A model, are suitable for larger systems. For example, the Victron BlueSolar MPPT 150/70 can handle solar arrays up to 70A. If we consider different system voltages:

• For a 12V system: 70A * 12V = 840W
• For a 24V system: 70A * 24V = W
• For a 48V system: 70A * 48V = W

These calculations demonstrate the capacity of a 70A charge controller across various system voltages.

Q4: What size charge controller for various solar panel setups?

If you are looking for more details, kindly visit Amorphous Solar Panel.