How To Select Solar Charge Controller

Anthony Joseph Lalonde

Last updated on April 13th, 2022 at 11:17 am

Table of Contents

    There are many important components that are needed to create a solar power system, the solar panel, the battery, the inverter, and finally, the solar charge controller you will be using. So, how to select a solar charge controller you might be wondering? The main purpose of a solar charge controller is to prevent batteries from being overcharged or damaged by too much power coming from the solar panels. 

    Solar charge controllers also help to prolong the life of batteries by preventing deep discharge. In this article, we will introduce you to the factors you need to consider and the information you should know when purchasing a solar charge controller for your needs.

    How Do Solar Charge Controllers Work?

    POWOXI Solar Panels Charge Controller, 8A Battery Regulator for 12V Solar Battery Charger, Solar Battery Maintainer and 12 Volt Batteries Power Kit

    A solar charge controller is an electronic device that regulates the flow of electricity from a solar panel to a battery. It is also known as a “charge regulator” or “solar charging regulator.” 

    When a charge current enters a semiconductor built into these controllers, it acts like a valve, regulating the flow. When the voltage is supplied to a battery reaches a certain threshold, the charging current is reduced by an auto controller to prevent overcharging. It’s worth noting that overcharging batteries can have a detrimental impact on the battery, hence charge controllers are particularly important.

    Overload protection: 

    If the amount of current flowing into your batteries is much greater than what the circuit can handle, your system may be destroyed. For example, your battery may overheat if it is put under a lot of strain. This can cause the battery to burst or catch fire, thus these gadgets are used to avoid such overloads from happening. We also recommend double safety protection with circuit breakers or fuses in larger systems.

    Low voltage disconnects: 

    When the voltage drops below a certain threshold, this technique automatically disables non-critical loads from the battery. The battery will reconnect to the power source automatically when it is being charged. This will prevent an over-discharge from occurring.

    Block Reverse Currents: 

    During the day, solar panels send electricity in one direction through your battery. At night, when the panels are presenting a lower voltage, they may briefly reverse some of the currents. This can result in a small charge drain and charge controllers serve as valves to prevent this.

    Two Types of Solar Charge Controllers

    The following are two main types of solar charge controllers:

    Pulse Width Modulation Charge Controllers (PWM)

    Morningstar - Tristar 60A PWM Solar Charge Controller for 12V/24V/48V Batteries, Lowest Fail Rate in The Industry, Built-in Diagnostics, (TS-60M)

    PWM charge controllers are the most common type of solar charge controllers on the market. They are also the least expensive.

    Pulse width modulation is a technique that regulates the amount of power going to your batteries by turning the solar panels on and off very quickly. The controller will send pulses of electricity to your battery, and by varying the length of these pulses, it can control the amount of power being delivered. 

    This type of controller is very effective at preventing overcharging and deep discharge are recommended for smaller systems.


    • For smaller systems, this is the best choice where efficiency isn’t as important

    • When the battery is nearly full, it performs best.

    • Cheaper than MPPT controllers

    • Because there are fewer components, it is more durable.

    • Ideal for warm and sunny weather


    • Efficiency is lower than MPPT controllers

    • Because solar panels and batteries must have matching voltages with these controllers, they are not appropriate for larger, more complicated systems.

    Maximum Power Point Tracking Controllers (MPPT)

    Renogy Rover 40 Amp 12V/24V DC Input MPPT Solar Charge Controller Auto Parameter Adjustable LCD Display Solar Panel Regulator fit for Gel Sealed Flooded and Lithium Battery

    Maximum power point tracking charge controllers are more expensive than PWM controllers, but they are more efficient at converting sunlight into electrical energy.

    MPPT charge controllers work by constantly monitoring the voltage and current output of your solar panels. They then adjust the resistance in the circuit to ensure that the maximum amount of power is being delivered to your batteries. 

    This results in increased efficiency and, in some cases, can increase the output of your system by up to 30%. They are recommended for larger systems where every bit of efficiency is important.


    • When the battery is on a reduced charge, it performs best

    • Extremely efficient

    • Ideal for circumstances where the solar array voltage is greater than the battery voltage.

    • It’s the best in colder, cloudier climates

    • Ideal for bigger systems that need more energy production.


    • Due to the many components, this type has a shorter lifespan

    • More costly than PWM controllers

    Also Read: PWM vs MPPT

    How To Select The Correct Solar Charge Controller

    When it comes to selecting a solar charge controller, there are a few things you need to take into account. Below are some considerations:

    1. The Size of Your Solar Array

    The first thing you will have to determine is the size of your solar array. This will help you to identify which type and size of controller you need. A small system will not require as much power and, therefore, a smaller controller will be fine. If you have a larger system, you will need a bigger and more powerful controller to manage all of the energy being produced.

    2. The Voltage of Your Solar Array

    Voltage is another important factor to consider when selecting a solar charge controller. Your array voltage must match the voltage of your controller in order to ensure proper operation. If they don’t match, the controller will not be able to properly function because it will not be able to draw enough power from the array.

    3. The Current Rating of Your Solar Charge Controller 

    If the current rating of your solar charge controller is too low, it will not be able to properly handle the amount of power being produced by your solar array. This can lead to damage or even complete failure of the controller. Conversely, if the current rating is too high, you will be wasting money on a controller that is more powerful than you need.

    4. Selecting between PWM and MPPT Charge Controllers

    Lastly, you need to decide between a PWM and MPPT charge controller. If you have a small system that is not going to produce a lot of power, a PWM controller will be just fine. However, if you have a larger system that needs to be very efficient, an MPPT controller is the way to go.

    Above all, make sure to do your research and select a solar charge controller that is the right size and has the features you need for your particular system.

    Also Read: Best Solar Charge Controller in 2022 (Reviews and Comparison)

    How to Size Your Charge Controller

    To size your charge controller, you need to know two things: the voltage of your solar array and the maximum current that your array can produce. Once you have this information, you can determine the size of charge controller you need:

    PWM Charge Controller Sizing 

    For a PWM charge controller, you need to know the volts and amps of your solar array. They are unable to limit their current output and simply use the array current. Once you have this information, you can use the following equation to determine the size of controller you need:

    Array volts x Array amps = Charge controller watts

    For example, if you have a 12-volt solar array that produces 6 amps, you would need a 72-watt charge controller.

    MPPT Charge Controller Sizing 

    For an MPPT charge controller, you need to know the volts and watts of your solar array. As these controllers can limit their output, you only need to make an array as large as you want and the controller will limit that output itself. 

    However, this implies that your system isn’t as efficient as it could be because you have panels that aren’t being utilized to the fullest extent. Once you have this information, you can use the following equation to determine the size of controller you need:

    Array volts x Array watts = Charge controller watts

    For example, if you have a 48-volt solar array that produces 1000 watts, you would need a 48000-watt charge controller.

    As you can see, the equations for sizing PWM and MPPT charge controllers are the same, but the information you need is slightly different. Make sure you have the right information before using the equation to size your controller.


    When it comes to choosing a solar charge controller, there are a few things you need to take into account. The size of your solar array, the voltage of your array, and the current rating of your controller are all important factors to consider. Additionally, you need to decide between a PWM or MPPT controller.

    Do your research and select the right solar charge controller for your needs to ensure that your system operates efficiently and safely.

    Thanks for reading! We hope this article was helpful in explaining how to select a solar charge controller.

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