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Charging lifepo4 with solar. What is a Solar Charge Controller

Charging lifepo4 with solar. What is a Solar Charge Controller

    How To Charge Lithium Iron Phosphate (LiFePO4) Batteries

    If you’ve recently purchased or are researching lithium iron phosphate batteries (referred to lithium or LiFePO4 in this blog), you know they provide more cycles, an even distribution of power delivery, and weigh less than a comparable sealed lead acid (SLA) battery. Did you know they can also charge four times faster than SLA? But exactly how do you charge a lithium battery, anyway?

    Power Sonic recommends you select a charger designed for the chemistry of your battery. This means we recommend using a lithium charger, like the LiFe Charger Series from Power Sonic, when charging lithium batteries.


    As you will learn in this blog, there are many similarities in the charging profiles of SLA and lithium. However, extra caution should be exercised when using SLA chargers to charge lithium batteries as they can damage, under charge, or reduce the capacity of the lithium battery over time. There are many differences when comparing lithium and SLA batteries.

    Let’s go back to the basics of how to charge a sealed lead acid battery. The most common charging method is a three-stage approach: the initial charge (constant current), the saturation topping charge (constant voltage), and the float charge.

    In Stage 1, as shown above, the current is limited to avoid damage to the battery. The rate of change in voltage continually changes during Stage 1 eventually beginning to plateau when the full charge voltage limit is approached. The constant current/Stage 1 portion of the charge is crucial before moving onto the next stage. Stage 1 charging is typically done at 10%-30% (0.1C to 0.3C) current of the capacity rating of the battery or less.

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    Stage 2, constant voltage, begins when the voltage reaches the voltage limit (14.7V for fast charging SLA batteries, 14.4V for most others). During this stage, the current draw gradually decreases as the topping charge of the battery continues. This stage terminates when the current falls below 5% of the battery’s rated capacity. The last stage, the float charge, is necessary to keep the battery from self-discharging and losing capacity.

    Stage 3 is used if the battery is being used in a standby application, the float charge is necessary to ensure the battery is at full capacity when the battery is called upon to discharge. In an application where the battery is in storage, float charging keeps the SLA battery at 100% State of Charge (SOC), which is necessary to prevent sulfating of the battery that therefore prevents damage to the plates of the battery.


    A LiFePO4 battery uses the same constant current and constant voltage stages as the SLA battery. Even though these two stages are similar and perform the same function, the advantage of the LiFePO4 battery is that the rate of charge can be much higher, making the charge time much faster.

    Stage 1 battery charging is typically done at 30%-100% (0.3C to 1.0C) current of the capacity rating of the battery. Stage 1 of the SLA chart above takes four hours to complete. The Stage 1 of a lithium battery can take as little as one hour to complete, making a lithium battery available for use four times faster than SLA. Shown in the chart above, the Lithium battery is charged at only 0.5C and still charges almost 3 times as fast! As shown in the chart above, the Lithium battery is charged at only 0.5C and still charges almost 3 times as fast!

    Stage 2 is necessary in both chemistries to bring the battery to 100% SOC. The SLA battery takes 6 hours to complete Stage 2, whereas the lithium battery can take as little as 15 minutes. Overall, the lithium battery charges in four hours, and the SLA battery typically takes 10. In cyclic applications, the charge time is very critical. A lithium battery can be charged and discharged several times a day, whereas a lead acid battery can only be fully cycled once a day.

    Where they become different in charging profiles is Stage 3. A lithium battery does not need a float charge like lead acid. In long-term storage applications, a lithium battery should not be stored at 100% SOC, and therefore can be maintained with a full cycle (charged and discharged) once every 6 – 12 months and then storage charged to only 50% SoC.

    In standby applications, since the self-discharge rate of lithium is so low, the lithium battery will deliver close to full capacity even if it has not been charged for 6 – 12 months. For longer periods of time, a charge system that provides a topping charge based on voltage is recommended. This is especially important with our Bluetooth batteries where the Bluetooth module draws a very small current from the battery even when not in use.


    Voltage and current settings during charging

    The full charge open-circuit voltage (OCV) of a 12V SLA battery is nominally 13.1 and the full charge OCV of a 12V lithium battery is around 13.6. A battery will only sustain damage if the charging voltage applied is significantly higher than the full charge voltage of the battery.

    This means an SLA battery should be kept below 14.7V for Stage 2 charging and below 15V for lithium. Float charging is only required for an SLA battery, recommended around 13.8V. Based on this, a charge voltage range between 13.8V and 14.7V is sufficient to charge any battery without causing damage. When selecting a charger for either chemistry, it is important to chose one that will stay between the limits listed above.

    Chargers are selected to match the capacity of the battery to be charged, since the current used during charging is based on the capacity rating of the battery. A lithium battery can be charged as fast as 1C, whereas a lead acid battery should be kept below 0.3C. This means a 10AH lithium battery can typically be charged at 10A while a 10AH lead acid battery can be charged at 3A.

    The charge cut-off current is 5% of the capacity, so the cutoff for both batteries would be 0.5A. Typically, the terminal current setting is determined by the charger.

    Universal chargers will typically have a function to select the chemistry. This function chooses the optimal voltage charging range, and determines when the battery is fully charged. If it is charging a lithium battery, the charger should shut off automatically. If it is charging an SLA battery, it should switch to a float charge.

    Lithium batteries replacing sealed lead acid in float applications

    It is very common for lithium batteries to be placed in an application where an SLA battery used to be maintained on a float charge, such as a UPS system. There has been some concern, whether this is safe for lithium batteries. It is generally acceptable to use a standard constant voltage SLA charger with our lithium batteries, as long as it adheres to certain standards.

    If using a constant voltage SLA charger, the charger must meet the following conditions:– Charger must not contain a de-sulfating setting– Fast/Bulk charge voltage of 14.7V– Recommended float charge voltage of 13.8V

    As a side note, some Smart or multi-stage SLA chargers have a feature that detects open circuit voltage (As a side note, some Smart or multi-stage SLA chargers have a feature that detects open circuit voltage (OCV). An over-discharged lithium battery that is in protection mode will have an OCV of near 0V. This type of charger would assume this battery is dead and would not try to charge it. A charger with a lithium setting will try to recover or “wake up” an over-discharged lithium battery that is in protection mode.

    Long term storage

    If you need to keep your batteries in storage for an extended period, there are a few things to consider as the storage requirements are different for SLA and lithium batteries. There are two main reasons that storing an SLA versus a Lithium battery is different.

    charging, lifepo4, solar, charge, controller

    The first reason is that the chemistry of the battery determines the optimal SOC for storage. For an SLA battery, you want to store it as close to possible as 100% SOC to avoid sulfating, which causes a buildup of sulfate crystals on the plates. The buildup of sulfate crystals will diminish the capacity of the battery.

    For a lithium battery the structure of the positive terminal becomes unstable when depleted of electrons for long periods of time. The instability of the positive terminal can lead to permanent capacity loss. For this reason, a lithium battery should be stored near 50% SOC, which equally distributes the electrons on the positive and negative terminals. For detailed recommendations on long term Lithium storage, check out this guide regarding storage of Lithium batteries.

    The second influence on storage is the self-discharge rate. The high self-discharge rate of the SLA battery means that you should put it on a float charge or a trickle charge to maintain it as close as possible to 100% SOC to avoid permanent capacity loss. For a lithium battery, which has a much lower discharge rate and doesn’t need to be at 100% SOC, you may be able to get away with minimal maintenance charging.

    Recommended battery chargers

    It is always important to match your charger to deliver the correct current and voltage for the battery you are charging. For example, you wouldn’t use a 24V charger to charge a 12V battery. It is also recommended that you use a charger matched to your battery chemistry, barring the notes from above on how to use an SLA charger with a lithium battery. Additionally, when charging a lithium battery with a normal SLA charger, you would want to ensure that the charger does not have a desulfation mode or a dead battery mode.

    How to Charge Lifepo4 Battery? Everything You Need To know

    We’ll begin by covering some key points that you should be aware of before getting started with the charging process. These tips will help you charge your battery more effectively and with less risk.

    Overcharging can be dangerous

    LifePO4 batteries are absolutely safer and less flammable than traditional lead-acid models. But that doesn’t mean that you can do whatever you want with them and not worry about the repercussions.

    Extreme overcharging will lead to heating within the battery cells. This can eventually damage the LifePO4 battery and even cause a fire if the overcharging really gets out of hand.

    This is why you want to try to avoid overcharging your LIfePO4 battery. If you leave it on the charger overnight once or twice, that’s fine. But try to avoid leaving the LifePO4 battery on the charger for days, weeks, or months at a time, as this can get dangerous and damage your investment.

    You don’t have to charge them fully after every use

    Unlike lead batteries, LifePO4 batteries don’t sustain any damage if you leave them in a partially charged state. That means you don’t have to charge the battery to its full capacity each time that you use it.

    It’s perfectly fine to use some of the LifePO4’s battery charge on one day and some more on the next day without worrying about charging it in-between uses. This is another big advantage that this kind of battery has over lead-acid alternatives.

    Venting is not needed

    Another nice advantage of LifePO4 batteries is that you don’t have to worry about ensuring they have enough ventilation while you charge them.

    The chemistry featured in this kind of battery is much safer and more stable than other options. This means it’s able to charge in a low-ventilation environment, such as a tackle box in your fishing boat, without seeing a higher risk of damage.

    That being said, venting is good to provide during the charging process if you can do so just because it may improve charging times by regulating the temperature more effectively. But it’s not dangerous if you don’t do so.

    You can typically charge and discharge at the same time

    Finally, it’s also worth keeping in mind that you can charge your LifePO4 battery while using it at the same time.

    For example, if you forget to charge the battery before leaving for a trip, you can use the charge that’s left in it while also refilling the battery by using one of the methods we’ll cover in the next section.

    Four Ways to Charge Your LifePO4 Battery

    Okay, now that we’ve covered some LifePO4 charging basics, let’s get down to business and look at the four different ways you can charge one of these batteries.

    Use a Smart Charger

    The best way to charge a LifePO4 battery is with a Smart charger that’s designed for the specific battery that you own. This is because every battery has its own unique chemistry. So if you can charge your battery with a charger made for its specific chemistry, you’re always going to get the results.

    Smart chargers are able to adjust the current they provide as your battery refills. During the first so-called “bulk stage,” the battery charge will gradually increase over a period of 1-2 hours.

    After that, the “absorption stage” begins. This happens when the LifePO4 battery has reached a charge of about 90%. Here, the voltage reaches a constant, and the current decreases to about 5%. 10% of the battery’s overall rating.

    The bottom line is that this method will give you the best results because Smart chargers are specifically created to deliver those results for your battery. No other charging method for LifePO4 batteries can say the same.

    Use Solar Panels

    Solar panels are another fantastic method for charging your LifePO4 battery. They’re also more cost-effective since you won’t have to purchase a stand-alone Smart charger or pay for energy that you’re pulling from the grid.

    The charging process with solar panels begins when the panels convert the sunlight they receive into usable electrical energy.

    After that, the system’s charge controller will take the energy and regulate it to match the specific charging requirements of your battery. This ensures that your LifePO4 battery doesn’t overcharge or waste any energy.

    Your LifePO4 battery will receive its energy through the solar charge controller. The system also features an inverter, which basically converts this energy into usable electricity that can be fed directly to your appliances.

    Use a Lead-Acid Battery Charger

    You might be surprised to hear that you can actually use a lead-acid battery charge on some LifePO4 batteries. You just have to make sure that the charging settings on your lead-acid charger are within the acceptable parameters for your LifePO4 battery.

    You’ll typically want to turn the float charge option off, if possible. If that’s not possible, then try to set the floating voltage under 13.6V to avoid wasting energy and potentially decreasing the efficiency of your battery.

    Use an Alternator

    Finally, you also have the option of using an alternator. This is a generator that takes mechanical energy and turns it into electrical energy. These aren’t specifically made to charge LifePO4 batteries, though, and should only be used as a backup option because of the reduced efficiency they offer.


    How often should I charge my LifePO4 battery?

    You only need to charge your LifePO4 battery when you need to refill it for use. With this type of battery, there’s no need to worry about recharging it just to maintain the unit’s long-term efficiency.

    Should you leave your LifePO4 battery on full charge?

    No, there’s no need to worry about keeping your LifePO4 battery on a full charge. You can if you want. But don’t waste power trying to reach full charge just for the sake of doing so.

    What’s the best way to charge a LifePO4 battery?

    The two best options for charging a LifePO4 battery are with either a Smart charger or solar panels. Both can provide optimal energy flow for the specific kind of battery that you have.

    What are the best LifePO4 charge settings?

    Most manufacturers recommend a charge voltage of between 14 and 14.6V. Keeping your charge settings here and regulating the temperature of your battery can help to give it more charge cycles.

    BougeRV Can Help You Charge Your LifePO4 Battery with Solar Panels

    Solar panels are an extremely cost-effective way to keep your LifePO4 battery charged while you’re using it. BougeRV sells a wide variety of affordable solar panels for on-the-go use.

    Whether you’ve got an RV, you love camping, or you enjoy taking your boat out on the lake, we’ve got solar panels, batteries, and more to give you the best experience possible while generating energy on the go.

    Take a look at our product page to learn more about what we have to offer.

    How LiFePO4 Batteries Work

    The LiFePO4 battery is a new type of lithium-ion battery that uses lithium iron phosphate as the cathode material.

    LiFePO4 batteries have many advantages over regular lithium batteries: they are lighter, more durable and have higher discharge power.

    LFP batteries function differently than traditional lithium-ion batteries and when charge with solar charge controller, the parameter setting must specified.

    Solar Charge Controller Settings for Lifepo4 Batteries

    Solar controller settings include battery type selection, battery voltage selection, charge voltage and disconnect voltage parameters setting.

    Battery type selection: Lifepo4 batteries can be charged with solar systems using charge controllers designed for lithium ion (Li-ion) batteries.

    There are different codes for different battery types and voltages, choose the correct LFP code.

    Battery voltage selection: The battery voltage must match the battery voltage.

    if is a 12V battery, choose the 12V mode, and 24V system, choose 24V mode.

    charging, lifepo4, solar, charge, controller

    Charge voltage: This is the maximum charger output voltage that will be allowed to charge your Lifepo4 battery pack.

    if is a 12v lifepo4 battery, set the boost charge voltage to 14.4V.

    24V system, multiplied by two.

    Disconnect voltage: This is the voltage at which your controller will disconnect power from your solar panels.

    if is a 12v lifepo4 battery, set the overvoltage Disconnect setpoint to 16.0V.

    same as lead acid and gel batteries.

    Frequently Asked Questions

    What is the charging voltage of a 12V LiFePO4 battery?

    The charging voltage of a 12V LiFePO4 battery is around 13.8-14.4 volts, depending on the charge controller you are using.

    charging, lifepo4, solar, charge, controller

    What voltage should I charge my LiFePO4 battery?

    The voltage you should charge your LiFePO4 battery depends on the solar controller you are using and the voltage of battery pack.

    Some solar controllers allow for charging at 14.4 volts or higher for a LifePo4 Battery

    Always check with your solar controller manufacturer to make sure that they are compatible with your Lifepo4 battery pack before setting any parameters.

    What is the best charger setting for LiFePO4?

    The best charger setting for LiFePO4 batteries is usually around 13.8-14.4 volts with a charge current of 50-100 mA.

    What should battery settings be on solar charge controller?

    The battery voltage should match the battery voltage of solar PV output voltage. charge current should be set according to solar controllers’ parameters.

    LiFePO4 Depth Discharge

    The following is the depth discharge for a typical 12V battery. Double the values if your battery is 24 volts and running a 4kw solar system.

    • 13.6 to 14.4V – 100%
    • 13.4V – 99%
    • 13.3V – 90%
    • 13.2V – 70%
    • 13.1V – 40%
    • 13.0V – 30%
    • 12.9 – 20%
    • 12.8V – 17%
    • 12.5V – 14%
    • 12V – 9%
    • 10V – 0%

    Some solar charge controllers may not have options for lithium iron phospate. in that case, look for a “user” or custom configuration mode. Adjust the settings similar to the ones given here.

    If you are a seasoned solar power user, you might want to tinker with the settings to get the results you want. Even at the default however, lithium batteries will outperform lead acid, AGM and gel.

    Lithium batteries charge faster and have a longer depth discharge rate. For heavy duty applications it is better to invest in lithium batteries than lead acid. Of course you must have an MPPT charge controller to take full advantage of it.

    Most of these batteries need at least 13.6V to charge. Anything under that and charging will take too long, if at all. Above 13.6V and the battery will get to 95%. At 14V the controller needs only a few hours to recharge the battery up to 95%.

    Speed wise there is not much of a difference beyond 14.2V. So you can set absorb at 14V to 14.6V and the charge should run fine.

    LiFePO4 Battery Charge Settings Explained

    The following are some of the most common specifications you will find in charge controllers. Check your controller instructions for more detailed information.

    Boost charge mode. The controller charges at the highest power level until the boost mode value is attained. The controller will attempt to draw max power until it reaches the target voltage. The duration can be adjusted.

    Boost reconnect voltage. When the system is at float, the voltage can change due to solar output. The system goes back into boost if the voltage drops below the boost reconnect voltage value

    Charge limit voltage. The controller stops charging the battery if the battery voltage is higher than the charge limit voltage.

    Discharging limit voltage. Sends a warning at the given voltage set.

    Equalize charge voltage. Refers to the voltage used over a specific period. This is applied after the boosttarget voltage has been attained.

    Equalize duration. This is the absorption phase. When the boost period is reached, voltage is now constant.

    Float charge voltage. Once the boost stage is finished, the controller adjusts the power search. The panels are set to generate a constant voltage float.

    Low voltage disconnect. When this voltage is reached, the battery load output is disconnected.

    Low voltage reconnect. This is turned on if the load is disconnected because of low battery power.

    Over voltage disconnect. The load output gets disconnected if the battery voltage goes over this value.

    Over voltage reconnect. If the load is disconnected because the battery goes over voltage, the system will reconnect at the given value.

    Under voltage warning. This is where warnings are set.

    Under voltage warning reconnect. The warning is turned off at this value.

    Boost, Bulk Charging and Other Settings

    Some charge controllers use the terms boost and bulk interchangeably. Others consider them two different settings.

    In some charge controllers, the bulk is the first part of the charge cycle. A controller remains in this phase until constant charge voltage is attained.

    Constant charging follows and consists of boost and equalize. During the equalize cycle, the battery electrolytes are stirred and gassed. The boost cycle prevents too much gassing and overheating.

    You can think of it this way. When you charge a LiFePO4 battery, the controller commences with the highest setting the solar panel can generate. The voltage will remain constant when the boost level is reached. The boost period can be any duration but usually it is two hours.

    Boost duration is the same as the absorption phase, and absorption voltage is the same as boost charging voltage.

    After the charge reaches the float phase, the controller will try to keep the voltage constant. The voltage will drop to boost reconnect under certain conditions. For instance, unfavorable weather might affect solar performance, or the load might be too much for the system. If it drops to boost reconnect the charging process will restart.

    The equalization duration period is usually at zero for LiFePO4 batteries. The equalization voltage must be lower than boost or equal to it. in most cases it is better to have the equalization voltage lower.

    Important Reminders for Charging LiFePO4 Batteries

    • Avoid 100% SOC charging whenever possible.
    • Avoid a 100% SOC float.
    • Cycling under 10%-15% SOC is not recommended.
    • The battery temperature should be kept above 0 C / 32 F when you discharge.
    • Discharge and charge currents has to be below 0.5 C / 32.9 F
    • The battery temperature has to be under 30 C / 86 F

    Majority of charge controllers will have no problems charging a LiFePO4 battery. its voltages are similar to AGM, gel and other lead acid batteries. All high quality LiFePO4 batteries including the BTRPower 100ah also have a BMS (battery management system) that protects it from overheating and overloading. The BMS also makes sure the battery operates at the ideal temperature and the cells are properly balanced.

    To recap: when aLiFePO4 battery is charged, the system tries to maintain the current. If you are using a solar array, that means the system tries to send as much current as the solar system can deliver (without overcharging the battery).

    The voltage then starts to rise until the absorb phase is reached. At the absorb level the battery is around 90% filled. For the rest of the charge the battery current tapers while the voltage remains the same. The battery reaches 100% SOC (state of charge) at 10% to 5% of its ah rating.

    Compared to lead acid, v batteries are simpler to charge. Just make sure the voltage is high enough and the charge will proceed. There is no equalizing or sulphating to worry about. You do no even have to charge the battery 100%.

    Lastly, do not purchase a LiFePO4 battery without a BMS. This is very important as it can mean the difference between a long lasting battery and one that dies off quickly. Buying from a reputable manufacturer is always a good thing as well.

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