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How Does a Solar Charge Controller Work. Coleman solar charge controller

How Does a Solar Charge Controller Work. Coleman solar charge controller

    How Does a Solar Charge Controller Work?

    Solar charge controllers are an essential element to any solar electric panel system. At a most basic level, charge controllers prevent batteries from being overcharged and prevent the batteries from discharging through the solar panel array at night.

    Note: While the principles are largely the same regardless of the power source (solar panels, wind, hydro, fuel, generator, etc.), we’ll be speaking here in terms of solar electric systems and will be using the terms “charge controller” and “solar charge controller” interchangeably. Similarly, our term “battery” represents either a single battery or bank of batteries.

    What Is a Solar Charge Controller?

    An essential part of nearly all battery-based renewable energy systems, charge controllers serve as a current and/or voltage regulator to protect batteries from overcharging. Their purpose is to keep your deep cycle batteries properly fed and safe for the long term.

    Solar charge controllers are a necessity for the safe and efficient charging of solar batteries. Think of the charge controller as a strict regulator between your solar panels and solar battery. Without a charge controller, solar panels can continue to deliver power to a battery past the point of a full charge, resulting in damage to the battery and a potentially dangerous situation.

    Here’s why a charge controller is so critical: most 12-volt solar panels output anywhere from 16 to 20 volts, so it’s very easy for the batteries to overcharge without any regulation. Most 12-volt solar batteries require 14-14.5 volts to reach a full charge, so you can see how quickly an overcharging issue could occur.

    How Does a Solar Charge Controller Work?

    While you don’t necessarily need to understand the technical intricacies of a charge controller, being familiar with the basics is helpful – whether you’re doing a DIY solar installation or turning the job over to the professionals.

    The basic functions of a controller are quite simple. Charge controllers block reverse current and prevent battery overcharge. Some controllers also prevent battery over-discharge, protect from electrical overload, and/or display battery status and the flow of power. We’ll examine each function individually below.

    Modern solar charge controllers work by detecting and monitoring the battery’s voltage level and closely regulating the flow of current from the panels to the battery. Battery charging is best done in three stages: maximizing the current to charge the battery up to approximately 80% as quickly as possible (the “bulk charging” stage), then reducing the current as the battery approaches a full charge (the “absorb” stage), and finally maintaining a “float” or “trickle” charge to keep the battery topped off and ready for use. For more information about three-stage charging for solar batteries, check out the first video in our How to Charge a Deep Cycle Battery Properly video series.

    Types of Solar Charge Controllers

    When you begin searching for solar charge controllers for sale online, you’ll quickly realize that there are many different options. You can find a broad range of brands, sizes, price points, and features to choose from, which gives you the benefit of having great options – but it can also be overwhelming.

    Generally, the three primary charge controller types are 1- or 2-stage solar charge controllers, 3-stage and/or PWM solar charge controllers, and maximum power point tracking (MPPT). You’ll also find charge controllers for electric vehicles and golf carts. The most commonly used charge controllers range from 4 to 60 amps of charging current, but there are newer MPPT controllers that can achieve upwards of 80 amps.

    Simple 1- or 2-Stage Controllers

    These charge controllers use shunt transistors or relays to control voltage in either one or two steps (hence the names 1-stage or 2-stage controller). These are the oldest types and are extremely basic – and sometimes inefficient – in their components. However, their reliability and affordability do still attract some people.

    3-Stage and/or PWM Controllers

    Manufactured by well-known brands such as Xantrex, Morningstar, Steca, and Blue Sky, PWM charge controllers are inexpensive and reliable. Their drawback is that they should only be used when the nominal voltage of the solar panels matches the battery voltage – and even then, they have inefficiencies in larger systems.

    Maximum Power Point Tracking (MPPT) Controllers

    MPPT charge controllers are the highest-quality, most advanced option available, but they come with the high to match. Produced by brands like Victron Energy, OutBack Power, MidNite Solar, and others, MPPT controllers provide an impressive 94-98% efficiency level, delivering about 10-30% more power to the solar battery than other types. Unless your solar system is small (cabin-sized or smaller) and its battery voltage is no more than 24V, an MPPT controller is usually worth the extra initial investment. With larger, more advanced systems and 48V battery banks becoming much more common over the years, MPPT charge controllers are the new standard.

    Why Having a Solar Charge Controller Is Important

    Blocking Reverse Current

    Solar panels work by pumping current through your battery in one direction. At night, the panels may pass a bit of current in the reverse direction, causing a slight discharge from the battery. The potential loss is minor, but it is easy to prevent. Some types of wind and hydro generators also draw reverse current when they stop (most do not except under fault conditions).

    In most controllers, charge current passes through a semiconductor (a transistor) which acts like a valve to control the current. It is called a “semiconductor” because it passes current only in one direction. It prevents reverse current without any extra effort or cost.

    In some older controllers, an electromagnetic coil opens and closes a mechanical switch (called a relay – you can hear it click on and off.) The relay switches off at night, to block reverse current. These controllers are sometimes referred to as call shunt controllers.

    If you are using a solar panel array only to trickle-charge a battery (a very small array relative to the size of the battery), then you may not need a charge controller. This is a rare application. An example is a tiny maintenance module that prevents battery discharge in a parked vehicle but will not support significant loads. You can install a simple diode in that case, to block reverse current. A diode used for this purpose is called a “blocking diode.”

    Preventing Overcharge

    When a battery reaches full charge, it can no longer store incoming energy. If energy continues to be applied at the full rate, the battery voltage gets too high. Water separates into hydrogen and oxygen and bubbles out rapidly. (It looks like it’s boiling so we sometimes call it that, although it’s not actually hot.) There is excessive loss of water, and a chance that the gasses can ignite and cause a small explosion. The battery will also degrade rapidly and may possibly overheat. Excessive voltage can also stress your loads (lights, appliances, etc.) or cause your inverter to shut off.

    Preventing overcharge is simply a matter of reducing the flow of energy to the battery when the battery reaches a specific voltage. When the voltage drops due to lower sun intensity or an increase in electrical usage, the controller again allows the maximum possible charge. This is called “voltage regulating.”

    It is the most essential function of all charge controllers. The controller “looks at” the voltage, and regulates the battery charging in response. Some controllers regulate the flow of energy to the battery by switching the current fully on or fully off. This is called “on/off control.” Others reduce the current gradually. This is called “pulse width modulation” (PWM). Both methods work well when set properly for your type of battery.

    PWM solar charge controllers hold the voltage more constant. If a PWM controller has two-stage regulation, it will first hold the voltage to a safe maximum for the battery to reach full charge. Then, it will drop the voltage lower, to sustain a “finish” or “trickle” charge. Two-stage regulating is important for a system that may experience many days or weeks of excess energy (or little use of energy). It maintains a full charge but minimizes water loss and stress.

    The voltages at which the controller changes the charge rate are called set points. When determining the ideal set points, there is some compromise between charging quickly before the sun goes down, and mildly overcharging the battery.

    The determination of set points depends on the anticipated patterns of usage, the type of battery, and to some extent, the experience and philosophy of the system designer or operator. Some controllers have adjustable set points, while others do not.

    Understanding Control Set Points vs. Temperature

    The ideal voltage set points for charge control vary with a battery’s temperature. Some controllers have a feature called “temperature compensation.” When the controller senses a low battery temperature, it will raise the set points. Otherwise when the battery is cold, it will reduce the charge too soon. If your batteries are exposed to temperature swings greater than about 30° F (17° C), compensation is essential.

    Some controllers have a temperature sensor built in. Such a controller must be mounted in a place where the temperature is close to that of the batteries. Better controllers have a remote temperature probe, on a small cable. The probe should be attached directly to a battery in order to report its temperature to the controller.

    An alternative to automatic temperature compensation is to manually adjust the set points (if possible) according to the seasons. It may be sufficient to do this only twice a year, in spring and fall.

    Control Set Points vs. Battery Type

    The ideal set points for charge controlling depend on the design of the battery. Up until the mid-2010s, the vast majority of renewable energy systems used deep-cycle lead-acid batteries of either the flooded type or the sealed type. Flooded batteries are filled with liquid. These are the standard, economical deep cycle batteries.

    Sealed batteries use saturated pads between the plates. They are also called “valve-regulated” or “absorbed glass mat,” or simply “maintenance-free.” They need to be regulated to a slightly lower voltage than flooded batteries or they will dry out and be ruined. Some controllers have a means to select the type of battery. Never use a controller that is not intended for your type of battery.

    Typical set points for 12V lead-acid batteries at 77° F (25° C)

    (These are typical, presented here only for example.)

    High limit (flooded battery): 14.4V High limit (sealed battery): 14.0V Resume full charge: 13.0V

    Low voltage disconnect: 10.8V Reconnect: 12.5V

    Temperature compensation for 12V battery:

    -.03V per ° C deviation from standard 25° C

    What is Low Voltage Disconnect (LVD)?

    Lead acid deep-cycle batteries used in renewable energy systems are designed to be discharged only by about 50-80%. If they are discharged 100%, they are immediately damaged. Imagine a pot of water boiling on your kitchen stove. The moment it runs dry, the pot overheats. If you wait until the steaming stops, it is already too late!

    Similarly, if you wait until your lights look dim, some battery damage will have already occurred. Every time this happens, both the capacity and the life of the battery will be reduced by a small amount. If the battery sits in this over-discharged state for days or weeks at a time, it can be ruined quickly.

    The only way to prevent over-discharge when all else fails, is to disconnect loads (appliances, lights, etc.), and then to reconnect them only when the voltage has recovered due to some substantial charging. When over-discharge is approaching, a 12V battery drops below 11 volts (a 24V battery drops below 22 volts).

    A low voltage disconnect circuit will disconnect loads at that set point. It will reconnect the loads only when the battery voltage has substantially recovered due to the accumulation of some charge. A typical LVD reset point is 13 volts (26 volts on a 24V system).

    All modern inverters have LVD built in, even cheap.sized ones. The inverter will turn off to protect itself and your loads as well as your battery. Normally, an inverter is connected directly to the batteries, not through the charge controller, because its current draw can be very high, and because it does not require external LVD.

    If you have any DC loads, you should have an LVD. Some charge controllers have one built in. You can also obtain a separate LVD device. Some LVD systems have a “mercy switch” to let you draw a minimal amount of energy, at least long enough to find the candles and matches! DC refrigerators have LVD built in.

    If you purchase a charge controller with built-in LVD, make sure that it has enough capacity to handle your DC loads. For example, let’s say you need a charge controller to handle less than 10 amps of charge current, but you have a DC water pressurizing pump that draws 20 amps (for short periods) plus a 6 amp DC lighting load. A charge controller with a 30 amp LVD would be appropriate. Don’t buy a 10 amp charge controller that has only a 10 or 15 amp load capacity!

    Have Peace of Mind with Overload Protection

    A circuit is overloaded when the current flowing in it is higher than it can safely handle. This can cause overheating and can even be a fire hazard. Overload can be caused by a fault (short circuit) in the wiring, or by a faulty appliance (like a frozen water pump). Some charge controllers have overload protection built in, usually with a push-button reset.

    Built-in overload protection can be useful, but most systems require additional protection in the form of fuses or circuit breakers. If you have a circuit with a wire size for which the safe carrying capacity (ampacity) is less than the overload limit of the controller, then you must protect that circuit with a fuse or breaker of a suitably lower amp rating. In any case, follow the manufacturer’s requirements and the National Electrical Code for any external fuse or circuit breaker requirements.

    Why Displays and Metering are Important

    Charge controllers include a variety of possible displays, ranging from a single red light to digital displays of voltage and current. These indicators are important and useful. Imagine driving across the country with no instrument panel in your car! A display system can indicate the flow of power into and out of the system, the approximate state of charge of your battery, and when various limits are reached.

    If you want complete and accurate monitoring however, spend about 200 for a separate digital device that includes an amp-hour meter. It acts like an electronic accountant to keep track of the energy available in your battery. If you have a separate system monitor, then it is not important to have digital displays in the charge controller itself. Even the cheapest system should include a voltmeter as a bare minimum indicator of system function and status.

    Have it All with a Power Panel

    If you are installing a system to power a modern home, then you will need safety shutoffs and interconnections to handle high current. The electrical hardware can be bulky, expensive and laborious to install. To make things economical and compact, obtain a ready-built power panel. It can include a charge controller with LVD, the inverter and digital monitoring as options. This makes it easy for an electrician to tie in the major system components, and to meet the safety requirements of the National Electrical Code or your local authorities.

    Charge Controllers for Wind and Hydro

    A charge controller for a wind-electric or hydro-electric charging system must protect batteries from overcharge, just like a PV controller. However, a load must be kept on the generator at all times to prevent overspeed of the turbine. Instead of disconnecting the generator from the battery (like most PV controllers) it diverts excess energy to a special load that absorbs most of the power from the generator. That load is usually a heating element, which “burns off” excess energy as heat. If you can put the heat to good use, fine!

    Is a Solar Charge Controller Always Required?

    In most battery-based renewable energy systems, yes. However, a charge controller may not be necessary if you are using a small maintenance/trickle charge panel (such as panels rated 1-5 Watts). It is widely accepted that charge controllers aren’t a required component if your panel puts out no more than 2 Watts for each 50Ah (amp-hours).

    Is My Solar Charge Controller Working?

    How do you know if a controller is malfunctioning? Watch your voltmeter as the batteries reach full charge. Is the voltage reaching (but not exceeding) the appropriate set points for your type of battery? Use your ears and eyes-are the batteries bubbling severely? Is there a lot of moisture accumulation on the battery tops? These are signs of possible overcharge. Are you getting the capacity that you expect from your battery bank? If not, there may be a problem with your controller, and it may be damaging your batteries.


    A good charge controller is not expensive in relation to the total cost of a power system. Nor is it very mysterious. The control of battery charging is so important that most manufacturers of high quality batteries (with warranties of five years or longer) specify the requirements for voltage regulation, low voltage disconnect and temperature compensation. When these limits are not respected, it is common for batteries to fail after less than one quarter of their normal life expectancy, regardless of their quality or their cost.

    Shop the Best Solar Charge Controllers at the Lowest Prices

    Your unique needs, budget, and setup can help you determine the best charge controller options for your system – and whatever you choose, you can count on finding it at the best price from altE.

    Our selection of solar charge controllers features all the top-rated models from leading brands, saving you the hassle and time of having to check multiple stores to narrow down your options. And with altE, you can be confident that you’re getting the best possible price without sacrificing product authenticity or quality.

    How to Connect 2 100 Watt Solar Panels. Everything You Need to Know

    Connecting two 100 watt solar panels is an effective and simple way to increase the power output of your off-grid solar installation.

    Solar panels, like batteries, have negative and positive terminals. How these terminals are used to connect solar panels determines whether the connection is in series or parallel.

    Before teaching you how to connect two 100 watt solar panels in series and parallel, we will tell you about the difference between these circuits.

    We will cover the equipment needed to install and connect 100-watt solar panels. You will also find out more about the uses of series and parallel circuits, along with their advantages and disadvantages.

    Series and Parallel: What does it mean?

    Why does it matter if your circuit is in series or parallel? How your solar panels are wired directly impacts your system’s performance. It also plays a role in which inverter to use.

    does, solar, charge, controller

    Ultimately, you want to wire your solar installation to give you a better return investment and the best possible savings. This is when knowing how to install 100-watt solar panel arrays becomes crucial.


    A series connection is created by connecting the positive terminal of one solar panel to the negative terminal of another solar panel. Connecting two or more panels like this creates a PV source circuit.

    A circuit in series has only a single path for current to flow along. A series circuit is a continuous, closed-loop where all the circuit’s current has to flow through all of the circuit’s loads.

    This is why your entire series circuit would stop working when a single panel is affected. Christmas lights are a great example of a series connection: when one bulb breaks, the entire string stops working.

    When panels are connected in series, the voltage of the panels adds up, but the amperage stays the same.


    A parallel connection is created by connecting the positive terminal of one panel to the positive terminal of another panel and connecting the negative terminals of the two panels.

    The positive wires are connected to the positive connector in the combiner box; the negative wires are connected to the negative connector in the combiner box. Multiple panels wired this way are called a PV output circuit.

    There are multiple paths for the current to travel along in a parallel circuit. When one panel in a parallel circuit is defective, the current will ignore the broken path and keep moving along other paths.

    Parallel connections are used for household electrical wiring. That is why you can turn your TV off, but your lights will stay on.

    When panels are connected in parallel the amperage increases, but the voltage stays the same. As the amperage increases, the thickness of your wires will increase too.

    Make sure you are clued up on what gauge wire for 100-watt solar panel installations would work best.


    Series-parallel circuits are not simple series or simple parallel circuits – they combine both elements.

    Two or more components in a series-parallel circuit may be connected in series to form one “group” of series components. There may be two or more “groups” of series components. These “groups” can be connected in parallel to each other.

    If one component in a series “group” fails, the other components in that series “group” also fail. But, the other “groups” of series components will keep working, because they form part of the larger parallel system.

    How to Connect Solar Panels in Series

    Assembling a series circuit is quite simple and no additional equipment is needed. When you wire solar panels in series, you only need a single wire to connect the panels.

    To set up your panels in series you must connect the positive terminal of the first solar panel to the negative terminal of your second solar panel.

    The wire runs from the negative terminal of one panel and is connected to the positive terminal of the next panel – this creates a string circuit.

    You would be left with one free positive terminal and one free negative terminal. These need to be connected to either the input of the inverter or the input of the charge controller.

    How do you know where to connect it? Off-grid solar systems and grid-tied systems with a battery backup need to be connected to the charge controller.

    Grid-tied solar systems without a battery backup need to be connected to the inverter.

    Power Output of Solar Panels in Series

    When two solar panels are wired in series, the voltage of the panels adds up, but the amperage remains the same.

    How to Connect Solar Panels in Parallel

    Wiring your solar panels in parallel is a bit more complicated since you need more than a single wire.

    To wire two solar panels in parallel you join the positive terminals of both panels together, and you join the negative terminals of both panels together.

    All the negative terminals need to be connected to each other, and all the positive terminals need to be connected to each other.

    In smaller systems, you can accomplish this in different ways, but a branch connector is usually used. Y-shaped branch connectors have two inputs for positive (that changes to one), and two inputs for negative (that changes to one).

    You will be left with one common negative terminal and one common positive terminal. This needs to be connected either to your charge controller or your inverter.

    How do you know where to connect it? Connect it to the charge controller if you have an off-grid system, or a grid-tied system with a battery backup.

    Connect it to the inverter if you have a grid-tied system without a battery backup.

    When installing a parallel circuit, you or your installer would need to install a combiner box. Combiner boxes transfer the combined output of multiple panels’ strings to an inverter

    Afterward, the charge controller can be installed.

    Power Output of Solar Panels in Parallel

    When solar panels are connected in parallel the amperage will increase, but the voltage will stay the same.

    If you have two 100 watt 12V solar panels and a 12V battery bank, your system needs to be parallel to keep the voltage the same.

    Apparatus and Equipment You May Need

    When you install solar panels and connect them either in series or parallel, there are some apparatuses that you may need.

    Make sure to check your 100-watt solar panel specifications to make sure these devices are compatible.

    Solar Charge Controller

    Solar charge controllers regulate the flow of current, charge batteries, and run electrical loads. They manage the flow of current between batteries and solar panels for optimal power output.

    You may be wondering: What size charge controller do I need for a 100-watt solar panel? A 10-amp charge controller would be suitable for a 100W solar panel with a 12V battery bank.

    Maximum Power Point Tracking (MPPT) charge controllers are used in series circuits, while Pulse Width Modulation (PWM) charge controllers are used in parallel.


    Inverters convert the current flowing from your battery from direct current (DC) into alternating current (AC).

    But what size inverter do I need for a 100-watt solar panel ? A 12V 200 Watt inverter would be suitable.


    Batteries store excess electricity. Without batteries, for your solar installation, you may find yourself without power on cloudy days or during the night.

    What size battery for a 100-watt solar panel would be suitable? You would need a 100 Ah 12V battery for a 100-watt solar panel.

    When Are Series and Parallel Circuits Used?


    Series circuits are rarely found in common household electrical wiring. Usually, Christmas lights and landscape luminaries use series connections.

    Power strips and single ground-fault circuit interrupter (GFCI) receptacles which are found in electrical circuits also utilize series connections


    Parallel circuits are much more common than series circuits. Standard household circuits (120V) are parallel circuits.

    Your household branch circuit that runs your lights, appliances, and outlets is a parallel circuit.

    Advantages and Disadvantages of Series and Parallel Circuits


    • One defective branch of a parallel circuit will not affect the other branches or stop the flow of current in the system.
    • Appliances can be connected and disconnected without affecting the entire circuit.
    • The voltage remains constant across the entire circuit.
    • Constant voltage means that all the components function at the same capacity, regardless of the addition or removal of components. (i.e. light bulbs have the same brightness.)
    • Parallel circuits are safe and reliable.


    • It is difficult to transport energy over long distances with parallel circuits due to high amperage.
    • Parallel circuits are more expensive to build than series connections.
    • Parallel circuits require additional equipment and more wiring.
    • You cannot increase the voltage of a parallel circuit without decreasing the circuit’s resistance.


    • Series circuits act as current regulators.
    • Series circuits cost less than parallel circuits to build.
    • The voltage of the solar system increases.
    • It is easier to transfer energy over long distances with series circuits.


    • If one component fails, the entire circuit fails.
    • If more components are added the resistance decreases.
    • Less current flows through each component when resistance decreases. (i.e. bulbs burn less bright)

    Did you find our blog helpful? Then consider checking:

    • Solar Panels: Everything You Need To Know
    • Top 4 Portable Solar Panels
    • 300 Watt Solar Panels
    • 500 Watt Solar Panel System
    • DIY Solar Panel System Installation Guide
    • 1000 Watt Solar Panel Systems
    • What Equipment You Need for a Complete Solar Panel System?
    • 60-Cell vs 72-Cell Solar Panels
    • How Long Do Solar Panels Last?
    • Top 4 Grid-Tie Inverters Definitive Buyer’s Guide
    • Solar Power Inverters: Do I Need One?

    What Is An MPPT Charge Controller?

    The most basic functionality of a solar power system is solar panels collecting energy from the sun and storing it in batteries so that you can use it whenever you’d like. However, you can’t simply connect your solar panels directly to your batteries and expect them to charge. To get the most out of your solar panels, you’ll need a charge controller to charge your batteries efficiently. The most efficient type of charge controller is the maximum power point tracking or MPPT charge controller.

    Let’s take a look at how they work and what benefits they provide.

    What is Maximum Power Point Tracking?

    Before we dive into how MPPT charge controllers work, let’s explain how they get their name.

    The voltage at which a solar panel produces the most power is called the maximum power point voltage. The maximum power point voltage varies depending on environmental conditions and the time of day.

    MPPT charge controllers get their name because they monitor the solar panel and determine the maximum power point voltage for the current conditions. This function is called maximum power point tracking, or MPPT for short.

    Tip: Refresh on Amps, Volts, Watts and their differences.

    What Is An MPPT Charge Controller?

    Solar panels and batteries have different optimal operating voltages. Not only that, these voltages fluctuate. An MPPT charge controller is a DC-DC converter that maximizes the efficiency of a solar system. It does this by optimizing the voltage match between the solar panel array and the batteries.

    For example, depending on the state of charge, a 12-volt battery has a nominal voltage that ranges between just over 10 volts and just under 13 volts. Furthermore, the voltage required to charge a 12-volt battery ranges between 13.5 and 14.5 volts depending on the charging phase.

    On the other hand, the optimum output voltage of a solar panel varies depending on the panel’s temperature, time of day, how cloudy it is, and other environmental factors. For instance, under ideal conditions, a 250-watt solar panel may have an optimal operating voltage of 32 volts. As the panel heats up in the sun or on a hot day, the optimal voltage may drop to as low as 26 volts.

    The rated panel voltage must be higher than the battery voltage to accommodate for these voltage drops in the panel and the increased required battery charging voltage. Without an MPPT charge controller, this voltage differential leads to a lot of wasted power.

    What Is The Difference Between MPPT and PWM Charge Controllers?

    To better understand how this voltage difference causes inefficiencies, let’s first examine the other common type of solar charge controller. This controller is the pulse width modulation (PWM) charge controller.

    PWM controllers use a transistor switch that rapidly opens and closes as needed to regulate the charge current going into the battery. Since PWM controllers can’t modulate the voltage, they pull the output voltage of the solar panel down to match the battery voltage. Let’s look at an example.

    A 250-watt solar panel may have an optimal or max power voltage (Vmp) of 32 volts and a max power current (Imp) of 7.8 amps. (32 volts x 7.8 amps = 250 watts)

    Using a PWM controller, your panel will still produce 7.8 amps. But the voltage will drop to match the battery at 12 volts. Now, your panel is only providing 94 watts instead of 250 watts. (12 volts x 7.8 amps = 94 watts)

    How MPPT Charge Controllers Work

    As we mentioned before, MPPT charge controllers are DC-DC converters. This means they regulate the charge current into the battery like a PWM controller. But, they also convert the voltage coming out of the panel to match what the battery needs. Let’s look at an example of how this drastically improves efficiency.

    Using the same 250-watt panel, the MPPT controller allows the panel to operate at the max power voltage (Vmp). Now the power going into the controller is the full rated 250 watts.

    The output from the controller to the battery still needs to match the battery at 12 volts. But the current increases to 20.8 amps allowing you to utilize the full 250 watt potential of your panel. (12 volts x 20.8 amps = 250 watts)

    For simplicity, these examples assumed a 100% efficient conversion in the charge controllers. In reality, a small amount of power is lost as heat during the conversion.

    Benefits of an MPPT Charge Controller

    Efficient at Using Power

    On a properly sized solar power system, it’s not uncommon to see up to a 30% increase in efficiency by switching to an MPPT controller. This efficiency increase is even more significant on systems where the solar panel voltage is much higher than the battery voltage, like our example above.

    Best for Large Systems

    Utilizing an additional 20-30% of power out of your system becomes more advantageous as the size of your system grows. For this reason, MPPT controllers are often best used on large systems and may not be worth it on smaller, simpler setups.

    Better in Cloudier Environments

    The maximum power point tracking feature of MPPT controllers is a huge benefit in cloudy environments where the max power point of the solar panels will be fluctuating all day.

    Are MPPT Solar Charge Controllers Worth It?

    MPPT charge controllers are more expensive than PWM controllers. The added cost of upgrading your controller may not be worth it on small, basic systems. However, on larger systems or in locations with unstable weather conditions, the increased power and efficiency gained by using an MPPT controller will likely more than makeup for the added cost of the controller.

    does, solar, charge, controller

    Nobody likes to waste power. MPPT charge controllers help you get the most out of your solar panels without worrying about changing weather conditions or making sure you perfectly sized your solar panels to your battery voltage.

    What size solar panel do I need to charge a 12v battery?

    Jul 16th 2020

    Authors Note: This has been updated on Feb 9, 2022 with updated information, links, and resources.

    • What to know about using 6 volt batteries in your solar installation
    • What are deep cycle batteries?
    • How do you charge batteries with solar panels?
    • How to charge 12v battery?
    • What are amp hours?
    • How many amps does a 100 watt panel produce?
    • How many panels would I need to charge a 200ah battery?
    • How long will it take to charge a battery?
    • How many solar panels does it take to charge a 100ah battery?
    • What are the best conditions to charge a battery?
    • Does it matter what kind of battery you use?
    • Do lithium batteries charge faster than flooded lead acid batteries?
    • How do I size my battery bank and why is it important?
    • What should a 12 volt battery read when fully charged?
    • Battery Capacity
    • Expected Discharge Rate
    • Sizing Your Solar Panels
    • Combining Solar Panels for 12-Volt Battery Systems

    What to know about using 6 volt batteries in your solar installation

    If you live in an RV, van, or cabin, solar with battery storage is a great way to meet your energy needs. Once you’ve selected your solar panel kit, you’ll need to purchase a battery to store that energy produced from your panels. But how do you make sure that battery gives you the power you need and how do you know that solar panel will charge that battery effectively? Let’s break it down.

    What are deep cycle batteries?

    Deep cycle batteries may look similar to the batteries used in your car, but they are actually very different. In contrast to car batteries which only provide short bursts of energy, deep cycle batteries are designed to provide sustained energy over a longer period of time. Deep cycle batteries can be discharged up to 80%, but most manufacturers recommend not discharging below 45%. Regularly going beyond that point will shorten the life of the battery.

    How do you charge batteries with solar panels?

    Using solar panels to charge a battery, you’ll still need a charge controller. The wiring diagram below can offer you an easy understanding.

    how to charge a battery from solar panel

    Can you charge solar batteries without charge controllers? The answer is necessary and obvious, solar panels with batteries need a charge regulator which will be responsible for maintaining the charge of the batteries and keeping them in good condition. Solar batteries store the energy that is collected from your solar panels. The higher your battery’s capacity, the more solar energy it can store. In order to use batteries as part of your solar installation, you need solar panels, a charge controller, and an inverter.

    When using batteries for solar panels as part of a home solar system, you’re able to store the excess electricity your panels produce instead of sending that energy back into the grid. Electricity will be sent to the grid if your batteries are fully charged and your panels are still producing energy.

    Your solar panels will first need to be connected to a charge controller which will help monitor how much energy is stored in the batteries to prevent overcharging. Charge controllers will also shut down a system if the batteries become too depleted. Before powering your appliances, your batteries will need to be connected to an inverter to convert the DC energy collected from solar panels and converted to AC energy.

    How to charge 12v battery?

    In addition to solar panels, you can also charge your 12V battery through grid power and alternators. But the other two ways will not be as economical as solar panels which offer access to clean and free solar power.

    What are amp hours?

    Deep cycle batteries have a specific amp hour rating. This refers to the amount of current that is supplied from the battery over a certain period of time. If you have a 200ah battery, it can supply 20 continuous amps for 10 hours or 10 amps for over 20 hours.

    How many amps does a 100 watt panel produce?

    Calculate the current in amps by dividing power in watts by the voltage in volts. When a 12V solar panel is rated at 100W, that is an instantaneous voltage rating. So if all of the test conditions are met, when you measure the output, the voltage will be about 18 volts. Since watts equals volts times amps, amperage will be equal to 5.5 amps (100 watts divided by 18 volts). So your panel will produce 5.5 amps per hour.

    How many panels would I need to charge a 200ah battery?

    If you have a 200ah battery, only 80% of that is usable due to depletion limitations, so you really only have 160 amp-hours of energy to draw on. If you learn that you typically can last two days with energy from that battery, that means you consume 80 amp hours a day.

    Based on the earlier calculation, a 100 watt panel will produce an average of about 30 amp-hours per day (based on an average sunny day). This means you would need three 100 watt solar panels or one 300 watt panel to fully recharge your battery on the average day.

    How long will it take to charge a battery?

    Total charging time depends on the weather, as well as state and type of battery. If a battery is completely drained, a panel can typically charge the battery within five to eight hours.

    The total charging time will vary depending on the state of a battery. If a battery is totally drained, a solar panel can energize the cells within five to eight hours. The position of the sun in the sky can impact a panel’s charging speed. When sunlight shines directly on a panel in the middle of summer, the charging speed will be faster. Charging cycles are slower on cloudy days.

    How many solar panels does it take to charge a 100ah battery?

    Again we use the same calculation dividing power in watts by the voltage in volts to find amps. Charging your battery at 12 volts and 20 amps will take five hours to charge a 100 amp hour battery. By multiplying 20 amps by 12 volts, 240 watts is how big of a panel you would need, so we’d recommend using a 300w solar panel or 3 100 watt solar panels.

    What are the best conditions to charge a battery?

    You’ll find that all of Renogy’s deep cycle batteries have a normal operating temperature, storage temperature, and operating charge temperature specifications listed. Most batteries have a normal operating temperature of 77°F plus or minus 5.4°F. Most batteries have an ideal operating temperature between 50°F and 85°F. Batteries typically lose about 10% of their capacity for every 15°F to 20°F below 80°F. Their internal chemistries slow down, resistance increases and capacity and charge acceptance drop. This reduced capacity is temporary.

    Does it matter what kind of battery you use?

    Yes! Different batteries can have a huge impact on how your solar installation operates. There are three main types of deep cycle batteries used in solar systems: flooded lead acid, sealed lead acid, and lithium iron phosphate batteries. Each of these batteries vary in price, battery capacity, voltage, and cycle life.

    For example, battery capacity is important because it measures the amount of energy you can store. If you need to power certain appliances for long periods of time, you’ll need more batteries to carry a bigger load. Capacity is measured in total amp hours. Look at cycle life to learn about the number of discharge and charge cycles a battery can provide before the capacity drops below the rated capacity. This varies sharply from technology to technology and is measured in a number of cycles. For more information about battery types and how to choose the best battery for your system, refer to our blog post.

    Do lithium batteries charge faster than flooded lead acid batteries?

    Lithium iron phosphate batteries are more efficient than sealed and flooded lead acid batteries. They also have a faster rate of charge. This is because they can typically handle a higher amperage, which means they can be recharged much faster than flooded lead acid batteries. Lead-acid batteries are limited in how much charge current they can handle, mainly because they will overheat if you charge them too quickly. In addition, the charge rate gets significantly slower as you approach full capacity.

    How do I size my battery bank and why is it important?

    It’s very important to properly size your deep cycle battery bank. The amount of battery storage you need is based on your energy usage. Energy usage is measured in kilowatt hours. For example, if you need 500 watts for 8 hours per day, then your energy usage is 4kWh per day. A battery capacity of 4 to 8 kWh is usually sufficient for an average four-person home. Your energy needs may greatly differ from that depending on what you’re powering in your household.

    What size battery do I need?

    As the average power consumption for the US households ranges between 3kWh to 6kWh, you can find the suitable size and number of batteries in the table below.

    To size a system that will best fit your needs, we recommend making a list of all the devices you plan on running. Get the wattage information, or the amps and volts of the product, and provide an average run time per device. The Renogy solar power calculator is a great tool that makes it a quick and easy process to help determine your specific needs.

    What should a 12 volt battery read when fully charged?

    Batteries usually come with voltage range on their product package or somewhere on their selling page. For example, a Renogy 12V 200Ah Lithium Iron Phosphate Battery has a nominal voltage of 12.8V, and its voltage range is 10 to 14.8V. When the battery is fully charged, the voltage will read a little higher than 12.8V, which means the voltage value of 12.8 to 14.8 can indicate the battery has been topped off.

    Battery Capacity

    Sizing your solar panels to charge a 12v battery depends on several factors. You must consider your battery capacity and your expected discharge rate before sizing your solar panels to suit your needs. After you’ve determined these two factors, you can determine what size solar panel will be sufficient to charge your 12v battery.

    Your 12v battery capacity should be listed on your battery’s specification sheets or printed on the outside of your unit. Typically, capacity is listed in amp-hours (Ah).

    A battery that has a 100Ah capacity will be able to provide 100 amps of power for one hour or 10 amps for 10 hours. If you have multiple batteries working together in a system, you may need to do some calculations to determine your battery bank’s total capacity and voltage.

    If you have multiple battery banks wired together in parallel, you simply add the Ah ratings together to determine your total capacity and keep the voltage the same. For example, if you have three 100Ah 12v batteries wired in parallel, you would have a total battery bank capacity of 300Ah at 12 volts.

    If your batteries are wired together in series, you are instead adding the voltages of the battery together while capacity remains the same. In the same example, with three 100Ah 12v batteries, if they are wired together in parallel, you would have a battery bank with 100Ah capacity at 36 volts.

    Expected Discharge Rate

    Calculating your discharge rate is important if you intend to continue using your batteries while they are charging.

    If you have appliances that run around the clock — such as a refrigerator, air conditioner, or lights — determining their expected power draw will help you to ensure that your solar panels are powerful enough to both keep your appliances operating and charge your battery banks.

    Power draw is typically expressed in watts, just like solar panel production capacity. It may be easier to understand how your battery capacity can handle power draw by converting amp-hours to watt-hours.

    Using a 300Ah 12v battery system as an example, multiply the amp hours by the voltage to determine your capacity in watt-hours; in this case, 3600 watt-hours (Wh). A battery bank of this size can operate an appliance that consumes 300 watts for approximately 12 hours.

    Determining the draw of your appliances can be done similarly. Most appliances will give you some indication of their expected power consumption.

    Look at the charging cord, the bottom or back of your appliance, or the charging block — it should indicate either wattage or show you a voltage and amperage rating. If given the latter, convert it into watts by multiplying the voltage and amperage together. For example, a 120-volt appliance that draws 3 amps will use 360 watts.

    Once you have your appliances’ power consumption ratings, you can determine your expected draw in a few steps.

    • Refrigerator: 150 Watts x 4 Hours = 600 Wh
    • Six LED Lights: 6 x 5 Watts x 6 Hours = 180Wh
    • Air Conditioner: 1000 Watts x 2 Hours = 2000 Wh
    • Total Expected Daily Discharge: 6001802000 = 2780Wh

    Now that we have our expected discharge rate of 2780Wh, we can determine the size needed for our solar panels.

    Sizing Your Solar Panels

    Continuing with our example of a 300Ah 12v battery (with a 3600Wh capacity) and an expected daily discharge of 2780Wh, we can determine what size solar panels we need to both keep our appliances operating and fully charge our battery banks.

    To operate these devices alone, you will need 2780Wh of power. Ideally, your solar panels will provide more than enough power to the system than needed to meet your daily needs alone, allowing your batteries to charge to maximum capacity for overnight use or periods in the shade.

    If you add your total battery capacity to your expected daily usage for a total of 6380Wh, you can fully charge your 12v batteries from empty while simultaneously running all of your appliances.

    Working with the 6380Wh estimate, we can calculate the power required from the solar panels. Solar panels are sold by watt, so this calculation is relatively straightforward, but there are certain components to keep in mind.

    The main consideration is that solar panels don’t always operate at their peak efficiency, so estimating a 70% power production from each panel will give you a more accurate representation of their power production in typical use.

    To reach 6380Wh in a typical 12 hour day, we follow a simple calculation: 6380Wh (desired energy production) / 12 hours (average hours of daily sunlight) = 531.67 Watts. In this example, we need the solar panels to produce 532 watts per hour for 12 hours to meet our energy goals.

    Using our 70% power production estimate from earlier, we can further calculate: 531.67 Watts / 0.7 = 759.52 watts. This calculation brings us to the size of the solar power system we would need to appropriately power our 12v battery system while including daily consumption.

    Combining Solar Panels for 12-Volt Battery Systems

    If there isn’t a single solar panel that meets your energy needs, you can combine multiple panels to reach the desired wattage. For our above example, you could combine four 200 watt solar panels into an 800-watt system to exceed the desired output of 759.52 watts, or you could combine two 400 watt panels.

    When connecting solar panels in parallel or series, you need to consider what the total output voltage and amperage are so that you can select an appropriate solar charge controller.

    If connecting solar panels in series, the total system voltage is the sum of each individual panel’s voltage, while the amperage remains the same. In parallel, the total amperage is the sum of each panel’s, while voltage remains the same.


    It can be intimidating when you first start navigating the solar and battery options out there. From deciphering amp hours from volts, sealed lead acid from flooded lead acid, there’s definitely a lot to consider. But by doing some simple math, properly calculating your energy needs, and learning a bit about the different battery options available to you, you’ll be well on your way to a battery bank to fit you and your household’s needs.

    Now it’s time to select your own solar storage system. Whether you want a 12v lithium battery, 12 volt deep cycle battery. 24v battery. 48v battery. or other type of batteries, you can find a suitable one at Renogy store!

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