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Charge Controllers: What The Heck Are They? The Definitive Guide [DIY Mini Course Part 3/6]

By SSK Admin November 24, 2021

Charge controllers

Charge Controllers: What The Heck Are They? The Definitive Guide [DIY Mini Course Part 3/6]

For many people beginning to assemble the parts of a DIY solar system, charge controllers are an unfamiliar piece of equipment.  Unlike the solar panels, the battery, and even the inverter, many first timers looking to install an off grid solar system have never even heard of a solar charge controller before.  In this lesson we will go in depth to explain the purpose, function, and types of charge controllers.

What are Solar Charge Controllers?

A charge controller, also known as a “solar charge controller'' or simply a “regulator”, is a very important part of an energy storage system in applications like wind, hydroelectricity, and solar.  As the energy is produced from the wind, water, or sunlight, a charge controller is used to regulate the amount of power that is sent to the battery. 

In a solar energy system, the charge controller is wired directly between the solar panels and the battery.  If you are using a solar power generator, it is likely the charge controller is built right into the system.  

Why & When We Need Solar Charge Controllers

Charge controllers are a necessary component in every off grid or portable solar system.  A charge controller is required to ensure the performance and longevity of any battery backed solar application.  

Without a charge controller, all of the energy produced by the solar panels is sent directly to the battery or battery bank.  If the storage is already full, adding extra power to the system will lead to overcharging, which can cause damage to the battery, reducing its performance and creating a potential safety risk.  To ensure the longevity of electricity production, the charge controller is critical in maximizing the life of your solar batteries.  

How Solar Charge Controllers Work

In an off grid solar system, the charge controller is placed between the solar panels and the battery bank.  In some arrays, there are module level charge controllers placed on the back of each solar panel.  More commonly in DIY setups, one large charge controller is installed near the battery. 

In order to prevent overcharging, charge controllers simply monitor the storage level of the battery or battery bank.  When the battery voltage rises to a certain level near capacity, the controller will momentarily stop or lower the supply of power going into the storage.  

Although they are built to serve the same purpose, it is this step in which it is important to know the differences between the two main types of modern solar charge controllers:  MPPT & PWM.    

PWM vs MPPT Solar Charge Controllers

In modern solar energy systems, charge controllers use two main kinds of technology to regulate the flow of power to the battery: Maximum Power Point Tracking (MPPT) and Pulse Width Modulation (PWM).  

The key difference between the two devices is that MPPT charge controllers have the ability to vary the amount of input voltage being sent to the battery to maximize the charging power, whereas PWM charge controllers are more like a simple switch that will slowly lower the amount of charge being sent to the battery as it approaches full capacity.

MPPT charge controllers are generally the more efficient and more expensive option.  PWM charge controllers have been used for decades, however, and work perfectly in smaller or budget conscious systems.  Grid tie solar panels must use an MPPT charge controller, whereas off grid or portable systems have the option of using either type.   

How to Size your Solar Charge Controller

Choosing the correct size for your charge controller is fairly easy and can be done with a simple formula.  Because wattage divided by voltage is equal to amps, to find the correct size charge controller, simply divide the wattage of the solar array by the voltage of the battery. 

If you have a 600 watt solar system, divided by a 12 volt battery, that leaves you with a 50 Amp charge controller. In sizing any component of your solar system, it is smart to err on the side of caution, so increasing the size to a 60 Amp charge controller is recommended.  More information about correctly sizing the parts of your solar energy system can be read in our sizing guide.  And for more info visit solar charge controllers sizing guide

Solar Charge Controller Conclusion

In conclusion, the charge controller is a critical part of any off grid solar system.  In order to maximize the efficiency and longevity of your system and its battery, it is important to choose the correct charge controller for your size and budget.  Ready to pick out your charge controller?  You can browse our selection of the best, handpicked solar charge controllers.

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