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How Does a Solar Charge Controller Work. Solar battery not charging

How Does a Solar Charge Controller Work. Solar battery not charging

    How to Charge a Battery with a Solar Panel

    This article was co-authored by wikiHow staff writer, Amy Bobinger. Amy Bobinger has been a writer and editor at wikiHow since 2017. She especially enjoys writing articles that help people overcome interpersonal hurdles but frequently covers a variety of subjects, including health and wellness, spirituality, gardening, and more. Amy graduated with a B.A. in English Lit from Mississippi College in 2011 and now lives in her hometown with her husband and two young sons.

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    Charging your batteries with a solar panel is a great way to use clean, renewable energy. However, before you can get started, you’ll need to install a charge controller, which regulates the voltage from the solar panel as it’s transferred to the battery. Otherwise, on sunny days, the solar panel may produce more energy than your battery can handle, which can damage the battery. Luckily, this is an easy process that will have you charging your batteries in no time!

    Purchasing a Charge Controller

    • If you don’t have one of those or you built your own solar array, use a multimeter to measure the wattage output of your solar panel when it’s in the full sun.
    • Solar panels are designed to produce more power than the voltage they’re rated for. For instance, a solar power designed for a 12V output might actually produce 17V of power. That’s because they’ll only produce their max voltage under ideal conditions. [2] X Research source
    • If the solar panel produces more power than the battery can handle, the battery can overcharge and be damaged. A charge controller helps prevent this from occurring.
    • For example, if your solar panel is 300W and you want to charge a 12V battery, you’d divide 300 by 12 to get 25 amps. In that case, you’d get a charge controller rated for 30 amps.
    • These options are more expensive than PWM models, but the increased energy efficiency can quickly make up for the price difference.

    Purchase a PWM charge controller for a budget-friendly option. If you’re just starting to experiment with solar power, a PWM charge controller can be a good point of entry. These controllers use pulses of energy to charge the battery, and they monitor the power in the battery to ensure it isn’t overcharged. [5] X Research source

    Tip: The process for installing these controllers is the same, so if you start off with a PWM model and decide you want to upgrade to an MPPT, they’ll be easy to switch out.

    Setting up the Controller

    • It’s always safest to mount electrical equipment to a non-conductive material, like a PVC panel or a piece of wood, rather than installing it on a metal surface.
    • For instance, you may want to use a red wire as your hot wire and a black one for the negative, or you could use solid black wire for your negative and a black wire with words printed on it for the positive side.
    • Of course, if your battery bank already has wires connected, you won’t need to attach new wires to the battery first.
    • Take care to match up the positive and negative cables with the appropriate ports, or you could short out your battery or controller.
    • If you’re connecting a 12V battery, use 10-gauge or 16-gauge wire. [9] X Research source
    • You can find these connectors wherever electrical or solar supplies are sold, and they should come with specific instructions on how to attach them to the wires.
    • Be sure to connect the male connector to a female connector and vice versa.
    • You can never be too careful when you’re working with electricity. Take the time to double-check that the positive and negative cables are matched up correctly!
    • Some charge connectors will even communicate with an app, so you can monitor the voltage from your smartphone or tablet!
    • Since the charge connector will stop the flow of energy to the battery once it’s charged, it’s fine to leave it on the charger until you need it!

    Community QA

    The easiest way to measure amperage is through the use of a digital multimeter. Make sure it is set to read amperage, you can then use a clamp on meter around the hot leg and record the actual amperage. If you do not have access to a ammeter clamp, you can open the circuit and insert the probes in series with the circuit. This will allow all electrons to pass through the meter and give you an accurate reading. Once you know your amperage, use the formula: Wattage = amperage x voltage.

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    A parallel connection avoids any change in the voltage level and is simple. Position your batteries side by side and run a separate pair of wires from the panel to each battery, connecting negative (-) to (-) and positive to

    Thanks! We’re glad this was helpful. Thank you for your feedback. As a small thank you, we’d like to offer you a 30 gift card (valid at Use it to try out great new products and services nationwide without paying full price—wine, food delivery, clothing and more. Enjoy! Claim Your Gift If wikiHow has helped you, please consider a small contribution to support us in helping more readers like you. We’re committed to providing the world with free how-to resources, and even 1 helps us in our mission. Support wikiHow

    I have a car which is not often used, and I would like to link a solar panel permanently when the car is unused. I am told a 20w panel is the right size but am unsure what size controller to buy.

    Make sure the solar panel is getting enough sunlight first; if it is shaded, it will need more electricity to recharge the battery. Also, connect the solar panel’s positive lead to the battery’s positive terminal and the panel’s negative lead to the battery’s negative terminal.

    Thanks! We’re glad this was helpful. Thank you for your feedback. As a small thank you, we’d like to offer you a 30 gift card (valid at Use it to try out great new products and services nationwide without paying full price—wine, food delivery, clothing and more. Enjoy! Claim Your Gift If wikiHow has helped you, please consider a small contribution to support us in helping more readers like you. We’re committed to providing the world with free how-to resources, and even 1 helps us in our mission. Support wikiHow

    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 Charge LiFePO4 Batteries with Solar Panels

    Just so you know, this page contains affiliate links. If you make a purchase after clicking on one, at no extra cost to you I may earn a small commission.

    In this tutorial, I’ll show you 2 ways to charge lithium iron phosphate (LiFePO4) batteries with solar panels.

    (No solar experience necessary.)

    does, solar, charge, controller, work, battery

    In fact, I use both of these ways to solar charge my own LiFePO4 batteries.

    This tutorial will FOCUS on solar charging 12V LiFePO4 batteries, but I’ll also share some tips on how you can do it with lithium batteries of different voltages, such as 24V, 36V, and 48V.

    How to Solar Charge LiFePO4 Batteries with a Simple Charging Setup

    In my opinion, this is the easiest way to charge LiFePO4 batteries with solar panels.

    This method requires no tools or prior solar experience. It’s relatively cheap. And it’s as plug-and-play as it gets.

    does, solar, charge, controller, work, battery

    Video Walkthrough

    This method is so easy I made a 60-second video showing you how to do it. Check it out and consider subscribing to my YouTube channel if you like DIY solar videos like this!

    • 100W 12V solar panel — I’d recommend a 50 to 100 watt solar panel for this setup. The max solar panel size for this setup is 120 watts.
    • 12V LiFePO4 battery — I’m using a 100Ah battery, but you could use a smaller or bigger one as long as it’s still a 12V battery.
    • Allto Solar MPPT charge controller — This isn’t your traditional-looking MPPT charge controller, but it’s designed to be great at one thing: solar charging 12V batteries.
    • MC4 to SAE adapter cable — Most 12V solar panels have MC4 connectors. If yours does, you’ll need this adapter cable to connect the solar panel to the charge controller. You may also need the included polarity adapter.
    • SAE to battery alligator clips — This adapter cable lets you connect the charge controller to a battery. It even comes with an inline fuse which is an important safety practice when solar charging batteries.
    • SAE extension cable (optional) — This extension cable would make it easy to place your charge controller and battery inside while charging.

    Step 1: Connect the Solar Panel to the Charge Controller

    Connect the MPPT charge controller to the solar panel, using an MC4 to SAE adapter cable, if needed. Your charge controller should automatically turn on once you do. If it doesn’t, try using the included SAE polarity adapter to get the solar panel’s polarity to match the charge controller’s.

    Note: This charge controller is a bit of an exception, in the sense that connecting the solar panel first is not the normal order for most charge controllers. Most often, you’ll connect the battery to the charge controller first. It’s always important to read your charge controller’s product manual for its recommended connection order.

    Step 2: Select Your Battery Type

    Select your battery type using the charge controller’s MODE button. I’m using a lithium iron phosphate battery, so I pressed the MODE button until the “Lithium” battery setting was selected.

    If you’re using a different type of battery, such as an AGM or sealed lead acid battery, select that type.

    Step 3: Connect the LiFePO4 Battery to the Charge Controller

    Connect the battery to the charge controller using SAE to battery alligator clips. Connect the positive charge controller cable to the positive battery terminal and the negative cable to the negative battery terminal.

    Look at the charge controller’s screen to confirm that the solar panel is charging the battery. The charge controller’s screen should show you the charging amps and volts. (You may have to wait a minute for the charge controller to track the maximum power point.) Mine showed a current of 6.6 amps at 14.0 volts, which works out to 92.4 watts from my 100 watt solar panel.

    …you’re charging your LiFePO4 battery with a solar panel!

    Now all you have to do is wait until your battery is fully charged. The charge controller will automatically stop charging the battery once it’s full.

    This setup is so easy to put up and take down that I just put the parts in in my shed when I’m not using it.

    Tip: If you want to keep your battery and charge controller out of the elements while charging, you can get an SAE extension cable and place it between the solar panel and charge controller. That way your solar panel can be outside while your battery and charge controller are safely inside.

    How to Build a Small DIY Solar Power System with LiFePO4 Batteries

    This second method isn’t nearly as easy to set up, but it’s the best route if you want a more permanent and expandable system with LiFePO4 batteries. It forms the basis of a basic DIY solar panel setup that you can use to power devices in a vehicle or off-grid system.

    Parts Tools

    Note: A lot of the solar components listed below are included in the Renogy 100 Watt Solar Panel Kit. Last I checked it’s cheaper to buy them as part of the kit rather than all separately.

    Here are the parts and tools I used for my setup. The wiring and equipment is sized for use with a 100 watt solar panel, with lots of room to grow in terms of current ratings in case you want to add more panels later on.

    • 12V LiFePO4 battery — I’m using a 100Ah battery, but this setup will work for nearly any size 12V battery
    • 100W 12V solar panel — I’m using a 100W solar panel, which is a good size for slowly charging a 100Ah battery over the course of a week (included in kit)
    • Lithium-compatible PWM charge controller — I’m using the Renogy Adventurer 30A, but a cheaper alternative is the Renogy Wanderer 30A (included in kit)
    • Solar adapter cables — for connecting the solar panel to the charge controller (included in kit)
    • Battery cables — for connecting the charge controller to the battery (included in kit)
    • 30A ANL fuse set — a 30 amp fuse is the right size for the charge controller linked above. If you’re using a different charge controller, look in its product manual for its recommended fuse size
    • Fuse cable — for adding the fuse between the battery and charge controller
    • Screwdriver
    • Optional: Wrench or ratchet — for tightening bolts

    Step 1: Understand the Wiring Diagram

    First, let’s quickly run through the wiring diagram and understand the important parts of it.

    does, solar, charge, controller, work, battery

    Here are the main things to understand about it:

    • Do not connect your solar panel directly to your LiFePO4 battery. Doing so can damage the battery.
    • Instead, connect the solar panel to the LFP battery via a solar charge controller. A charge controller regulates the voltage and current to safely charge the battery. It also stops charging once the battery is fully charged.
    • Use a charge controller that is compatible with lithium batteries. When shopping for a charge controller, look at the compatible battery types. Make sure the one you get is compatible with lithium batteries (sometimes listed as “Li” or “LFP”). Many cheap charge controllers only support lead acid batteries — such as sealed, gel, AGM, and flooded batteries.
    • Place a fuse on the positive cable between the battery and charge controller. This is a safety best practice in DIY solar setups. Look in your charge controller’s manual for the recommended fuse size.
    • You may need to fuse your solar panels. This will usually apply if you’re using multiple solar panels and decide to wire them in parallel. Watch this video to learn whether or not you need to fuse your solar array.
    • You almost always first connect the battery to the charge controller. Only once that’s done do you connect the solar panel(s) to the charge controller. Consult your charge controller’s manual for the manufacturer’s recommended connection order.

    Now that you understand the basics of how charging LiFePO4 batteries with solar panels works, it’s time to start building.

    Step 2: Connect the LiFePO4 Battery to the Charge Controller

    First, put the fuse in the fuse holder. Then connect the fuse cable to the fuse holder. Use a wrench or ratchet to tighten the bolts, if needed.

    Connect the positive battery cable to the other end of the fuse holder.

    Just like that, your positive battery cable is properly fused. Hooray for safety!

    Locate the battery terminals on your charge controller. They’ll usually be labeled with a battery icon or the word “BAT” or “BATT.”

    Connect the positive battery cable to the charge controller’s positive battery terminal. For most charge controllers, you use a screwdriver do this. Open the correct terminal on the charge controller with the screwdriver, insert the stripped end of the wire, then screw the terminal shut.

    Connect the negative battery cable to the charge controller’s negative battery terminal.

    Connect the positive battery cable to the positive terminal on your LiFePO4 battery. To do so, simply unscrew the bolt on the battery’s positive terminal, slide the cable’s ring terminal onto the bolt, then re-screw the bolt to the terminal.

    Connect the negative battery cable to the negative terminal on your LiFePO4 battery.

    Look at your charge controller for an indication that it’s powered on. Your lithium battery and charge controller are now connected, so your charge controller should automatically turn on. If it has a screen, the screen should turn on and start displaying system specs like battery voltage. If it doesn’t have a screen, it should have LED indicator lights that turn on or start blinking.

    If your charge controller has turned on, your battery and charge controller are now connected. Aww yeah!

    Here’s what my setup looked like at this point:

    If your charge controller doesn’t turn on, check for loose wires. Also double check that you inserted the battery cables into the correct terminals on the charge controller. If neither of these is the issue, your LFP battery may be in sleep mode, and I’d recommend following our tutorial on waking up LiFePO4 batteries.

    Step 3: Set the Battery Type as Lithium on the Charge Controller

    Note: Every charge controller has different steps for setting the battery type. Follow the instructions in your charge controller’s manual. These instructions are for the charge controller I’m using in this tutorial.

    Many charge controllers work with multiple battery types, so you need to tell yours which type of battery you’re using. This is an important step because different batteries have different charging parameters. If you’re using a lithium battery but your charge controller thinks you’re using a lead acid battery, it won’t charge it optimally.

    For my charge controller, the Renogy Adventurer 30A, I pressed SELECT until I got to the battery voltage screen. If using the Renogy Wanderer 30A, I run through the steps on setting battery type in my Renogy Wanderer review.

    Then I held ENTER until the battery type started flashing. As you can see, it was set to “Sld” which stands for sealed lead acid batteries. I pressed SELECT to cycle through the options until I got to the “Li” option, which indicates lithium batteries.

    I then held ENTER while the lithium battery option was on the screen to confirm my selection.

    That’s it! Your charge controller now knows it’s connected to a LiFePO4 battery, and it will charge it to the right voltage levels for that battery type.

    At this point, some charge controllers may ask you to set certain charging parameters, such as charging/absorption voltage and float voltage. Consult the charging parameters listed in your battery’s product manual or our article on LiFePO4 battery voltage charts for guidance.

    Step 4: Connect the Solar Panel to the Charge Controller

    Your charge controller and battery are properly connected. Your charge controller is properly programmed for LiFePO4 batteries. All that’s left to do now is connect your solar panel and start solar charging your LiFePO4 battery.

    Cover your solar panel with a towel, or flip it face down, to prevent it from generating power.

    Connect the positive and negative solar panel cables to the solar adapter cables. Make sure the exposed wire ends don’t touch! ⚡️

    Locate the solar terminals on the charge controller. They’ll usually be labeled with a solar panel icon or the word “PV.”

    Connect the positive solar cable to the positive solar terminal on the charge controller, and connect the negative solar cable to the negative solar terminal on the charge controller.

    Your solar panel and charge controller are now connected! And you’re so close to being done!

    Here’s what my setup looked like at this point:

    Just one little thing left to do…

    Step 5: Place the Solar Panel in Direct Sunlight

    Uncover or flip over your solar panel and place it in direct sunlight. For best results, angle it towards the sun.

    Look at your charge controller for an indication that the solar panel is charging the LiFePO4 battery. The indication is usually in the form of a blinking LED light, a battery charging icon, or a positive number on the PV/solar current screen. On mine, I confirmed by going to the PV current screen, which displayed the number 5.1A. That means my solar panel is charging my LiFePO4 battery at a rate of 5.1 amps.

    You’re now charging your LiFePO4 battery with solar power!

    Now you just need to wait for the solar panel to fully charge the battery. Charge controllers automatically stop charging once the battery is full. Your charge time will vary considerably based on factors like weather, battery capacity, and solar panel wattage.

    If your solar panel doesn’t start charging your battery, here are some common issues:

    • Your solar panel may not be receiving enough sunlight. Make sure it’s in direct sunlight and no part of the panel is shaded or covered. You can also mount it at the optimal tilt angle and azimuth angle for your location.
    • Your system may have loose connections. Double check all your wiring connections, especially the terminals of your charge controller, to make sure no wires have come loose.
    • Your battery may be fully charged. Charge controllers automatically stop charging once a battery is 100% charged. Discharge the battery a bit and retry.

    How Long Does It Take to Charge a LiFePO4 Battery with Solar Panels?

    A 100 watt solar panel produces around 300-500 watt hours per day, so it usually takes about 3-4 sunny days for one to fully charge a 12V 100Ah LiFePO4 battery. Though the exact number will vary quite a bit based on weather, location, and time of year. (For instance, on very cloudy days a 100W panel can produce less than 100 watt hours.) Try out our solar panel charge time calculator to get an estimate of your particular setup.

    If you’re wondering how that charge time compares to a standard LiFePO4 battery charger, you can estimate your charger’s charge time using our battery charge time calculator.

    Of course, you can always speed up or slow down the charging rate by picking a different size solar panel. Our solar panel size calculator can help you estimate what size solar panel is right for your desired charge time.

    Charging Multiple LiFePO4 Batteries with Solar Panels

    To solar charge multiple LiFePO4 batteries at the same time, you need to first connect the batteries in series or parallel.

    Batteries connected together should be identical with the same age, BMS, voltage, and capacity. They should also have been purchased from the same brand around the same time. If your batteries aren’t identical, I recommend solar charging them separately.

    Solar Charging LiFePO4 Batteries Wired in Series

    Wiring batteries in series sums their voltages and keeps their amp hours the same. So two 12V 100Ah LiFePO4 batteries connected in series will produce a 24V 100Ah LiFePO4 battery bank.

    In this case, in order to solar charge your LFP battery bank, you’ll need to make sure your solar panel or solar array has a nominal voltage of 24 volts or higher.

    You achieve a 24V solar array by using a 24V solar panel or wiring two 12V solar panels in series.

    Solar Charging LiFePO4 Batteries Wired in Parallel

    Wiring batteries in parallel sums their amp hours and keeps their voltages the same. So two 12V 100Ah LiFePO4 batteries connected in parallel will make a 12V 200Ah LiFePO4 battery bank.

    In this case, you can continue charging your battery bank with the setup I built in this tutorial. It will just take longer for it to fully charge.

    If you have an MPPT charge controller, you can speed up the charging process by connecting more solar panels in series or parallel. If you have a PWM charge controller, you can speed up the charging process by connecting more panels in parallel.

    Tips for Charging LiFePO4 Batteries with Solar Panels

    • Don’t charge a LiFePO4 battery below freezing (32°F or 0°C). Doing so can reduce your battery’s capacity and even cause it to develop internal shorts which cause irreparable damage. The exception to this rule is if you have a LiFePO4 battery with low-temperature charging protection.
    • Don’t exceed the battery’s maximum charge rate. The recommended max charge rate in amps is usually listed on the battery label or in its product manual. Most often it’s a 0.5C rate, meaning the number of amps is equal to half of the battery’s capacity in amp hours. For example, a 50Ah LiFePO4 battery will likely have a recommended max charge rate of 25 amps. For a 200Ah LiFePO4 battery, it’ll likely be 100 amps.
    • When disconnecting the battery from your solar charging setup, you almost always disconnect the solar panels first. Most charge controllers recommend disconnecting the solar panels first, then disconnecting the battery. As always, consult your charge controller’s manual for its specific recommendations.
    • Place or mount your battery and charge controller inside. I took pictures with all my equipment outside because of the better lighting. But batteries and charge controllers aren’t usually waterproof like solar panels are, so you’ll definitely want to bring those inside when raining.

    What are the Solar Battery Charging Stages?

    Home » FAQ » What are the Solar Battery Charging Stages?

    Solar charge controllers put batteries through 4 charging stages:

    What are the 4 Solar Battery Charging Stages?

    Bulk Charging Voltage

    For lead-acid batteries, the initial bulk charging stage delivers the maximum allowable current into the solar battery to bring it up to a state of charge of approximately 80 to 90%. During bulk charging for solar, the battery’s voltage increases to about 14.5 volts for a nominal 12-volt battery.

    Absorption Charging

    When Bulk Charging is complete and the battery is about 80% to 90% charged, absorption charging is applied. During Absorption Charging, constant-voltage regulation is applied but the current is reduced as the solar batteries approach a full state of charge. This prevents heating and excessive battery gassing. At the end of Absorption Charging, the battery is typically at a 98% state of charge or greater.

    Float Charging

    Float charging, sometimes referred to as “trickle” charging occurs after Absorption Charging when the battery has about 98% state of charge. Then, the charging current is reduced further so the battery voltage drops down to the Float voltage.

    The Float charge of a battery keeps the battery at maximum capacity throughout the day.

    Equalization Charging

    For flooded open vent batteries, an Equalization charge is applied once every 2 to 4 weeks to maintain consistent specific gravities among individual battery cells. The more deeply a battery is discharged on a daily basis, the more often equalization charging is required. Solar Charge Controller Equalization is for flooded, not for sealed, GEL, or valve-regulated batteries which can be damaged by equalization.

    Figure 3: Multi-Stage Battery Charging Diagram

    Although lead-acid batteries are the most common type of battery regulated by solar charge controllers, lithium batteries are starting to gain traction. Morningstar launched an Energy Storage Partner program that involves working with many lithium iron phosphate battery manufacturers to maintain the highest state of charge for their batteries and to help maximize battery life.

    The integration guides you can download provide custom solar charge controller voltage and time settings for absorption and float charging, and other information that you will need to charge your batteries safely and to increase their longevity. In addition to lead-acid and lithium, Morningstar solar charge controllers can also charge nickel, aqueous hybrid ion, and flow or redox flow batteries.

    Why Your Solar Battery Bank is Not Holding Charge

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    The “battery not charging” indicator is the last thing you want to see on a solar power system. Batteries are the most expensive part of the setup, and realizing it is not charging can be stressful. Fortunately, we can identify the most likely causes and try different ways to fix them.

    The most likely reasons a battery doesn’t hold a charge are a defective charge controller, faulty wiring, or the battery is damaged. The battery will not charge if the solar panel, charge controller or battery is not properly configured.

    How to Diagnose a Solar Battery Bank Problem

    If the battery bank is suddenly unable to hold a charge, perform the following procedures. These steps are necessary to narrow down the possible causes. At the same time you can check the entire system’s health status. If the solar panel is not producing power, the battery will not charge as well.

    You will need a multimeter to perform this test. we recommend he AstroAI digital multimeter for its simplicity and versaility.

    • Test the solar panel. Disconnect the solar panel from the system. Use a multimeter to check the panel voltage. There should be a voltage on the solar panels as long as there is sunlight. If there none, the panel is defective and needs to be repaired.
    • Test the battery. Use a multimeter tool here. If the voltage is 0 or under 10.5V, the battery is defective and needs to be replaced.
    • Test the charge controller. All charge controllers have a specific output range. if the multimeter shows the voltage is not close to this value, the controller is damaged.

    When you have performed the three tests, you will know which component is at fault. Let us take a look at each one in detail.

    Safety Tips First

    • Do not forget to turn the system off before doing any inspection.
    • Also make sure to wear safety glasses and gloves. Remember that solar batteries, especially lead acid, can be dangerous so exercise caution when handling them.
    • Some of the steps below require you to handle wires and cables. If you are not comfortable with these or don’t know how, consult a professional solar installer.

    Why is My Charge Controller Not Charging the Battery?

    If you suspect the charge controller is preventing the battery from holding a charge, check for the following.

    Loose or disconnected wiring. Check the battery solar cable wire if it is still connected to the controller. Give it a gentle tug to see if it is loose. Tighten the connection and turn on the controller. The display should show a voltage reading.

    Low battery bank voltage. Some controllers will stop charging if the battery VDC falls below a certain value. Refer to your battery manual for the value. Use a volt meter to check the value, and if it is too low, recharge the battery. That should fix the problem.

    Blown fuse. The battery fuse may be defective or blown. Replace it immediately with a new one. If your RV solar panel system uses a side wall port, check for signs of a blown fuse too. While you are it, check the rest of the system too.

    Defective charge controller. If the multimeter still shows an incorrect value for the controller, the unit is probably damaged and needs replacement. Try any troubleshooting tips in your charge controller manual, and if they don’t work, a replacement is due.

    Charge controller protection mode triggered. The main purpose of a charge controller is to protect the battery. There are built in values in the controller uses during charge, and if the voltage goes above these values, it might stop charging.

    The battery terminal voltage cannot be more than the charge controller protection value. This is usually not a problem if the controller is compatible with the battery, so make sure the controller amps can match that of the battery bank.

    If you suspect a damaged charge controller, it is better to buy a new one that have it fixed. We suggest getting an MPPT charge controller since they can handle different battery and solar panel voltages. Our favorite is the EPEVER MPPT 40A because it has all the features necessary to run a solar battery

    Battery Wiring Problems and Solutions

    The larger the solar array, the bigger the battery bank. This also means thicker, more numerous wires that are vulnerable to problems.

    Loose controller and battery wiring. Check the wire that connects the charge controller and battery. Tighten if necessary and replace if it is frayed or worn out. Use only the manufacturer recommended wire sizes for each component.

    Incorrect wiring. If the battery wires are reversed or installed incorrectly, the charge could stop altogether. Correct the wiring and the battery should run again.

    Faulty solar panel wiring. The battery, charge controller and solar panels are interconnected. If the solar panel cables are incorrectly installed or damaged, it will reduce energy output and affect battery charge.

    Overcharge protection. in rare instances, the controller overcharge mode may get triggered and stop the charge. This will only happen if the panel supplies more current than the battery can handle. As long as the batteries and solar panels match, this will not be a cause for concern.

    Battery Charging Problems and Solutions

    If the charge controller is working properly, the problem could lie in the battery or batteries. Here are the most common issues and how to resolve them.

    Old battery. The older a battery gets, the faster it loses power. The battery will also take longer to charge and have trouble keeping charge. If your solar battery is showing signs of old age, it is time to get a replacement.

    Capacity. if the battery capacity is too small, it will not be able to sustain a charge for long. If you are running a solar washing machine or a fridge, these require a lot of batteries. If the bank is too small the internal circuits won’t last and charging becomes a problem.

    Damaged battery. The easiest way to check the battery status is a volt meter or multimeter. If the reading is zero, the battery is dead. Check its health status regularly and do not wait for the battery to die out before replacing it.

    Left idle for long periods. Batteries left discharged for long periods gradually lose power. This makes it harder to recharge them. Even if it does charge the unit will not be able to hold the current. If recharging the battery does not work, you have to replace it.

    Solar Panel Problems and Solutions

    Sometimes the problem has nothing to do with the battery or the charge controller, but the soar panel. Remember, everything starts with the solar panels converting the sun’s energy into current, so if there is a problem here, the rest of the system is affected.

    Damaged panels. Look for signs of hot spots, cracks, snail tracks etc. These are common solar panel problems that could disrupt or halt energy output. These have to be remedied right away to avoid more problems.

    Weather. If is raining, snowy or just overcast, solar panel production will be minimal. So do not expect the battery to charge as fast as it does during the summer.

    Shading. is there something blocking your panels? Maybe some foliage or tree branch? Did birds make a nest on one of the cells? Any of these could cause a big issue with solar output. A single blocked cell can significantly reduce solar energy production.

    Compare Past Battery Performance

    Keeping a record of your solar system’s performance makes it easy to check for potential problems. If the battery was able to last for a specific number of hours running an inverter. but then suddenly drops, you know something is amiss.

    If you have not increased the inverter load and the weather is very much the same, the problem is likely due to the charge controller or the battery. But if you did increase the watt load, the battery bank capacity has to be increased as well.

    The same goes for the charge controller and solar panel. If your system produces 500W a month and is sufficient, no problem. But if you use more solar accessories and appliances, power consumption might exceed 500W. You will need to upgrade the batteries and controller.


    Usually solar batteries run without a hitch, but if there are problems you should always be prepared. Seeing that your battery bank does not hold charge can be alarming, but the possible causes – wiring issues, charge controller or battery defects, etc. – can be remedied and fixed with the right knowledge.

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