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9 Simple Solar Battery Charger Circuits. Solar cell battery charger

9 Simple Solar Battery Charger Circuits. Solar cell battery charger

    Solar Panel Charge Time Calculator

    Note: Use our peak sun hours calculator to find out how many peak sunlight hours your location gets per day.

    Tip: If you’re charging your battery with a battery charger rather than solar panels, check out our battery charge time calculator.

    How to Use This Calculator

    Enter your battery voltage. For instance, if you’re using a 12V battery, you’d enter the number 12.

    Enter your battery capacity in amp hours. If you have a 50Ah battery, you’d enter the number 50. (If you only know your battery’s capacity in watt hours, first convert watt hours to amp hours.)

    Select your battery type. Select “Lead acid” if you’re using a flooded or sealed (AGM or gel) lead acid battery. Select “Lithium (LiFePO4)” if you’re using a lithium iron phosphate battery.

    Optional: Enter your battery depth of discharge as a percentage. If your battery is 80% discharged, you’d enter the number 80. (If you have a lead acid battery, keep in mind that they should usually only be discharged 50%.)

    Enter the wattage of your solar panel or solar array. If you’re using a 100W solar panel, you’d enter the number 100. If you’re using a 400W solar array, you’d enter the number 400.

    Select your charge controller type.

    Click “Calculate” to get your results. Your estimated charge time is given in peak sun hours. You can use our peak sun hours map or calculator to find out how many peak sun hours your location gets. For example, let’s say your estimated charge time is 8 peak sun hours and your location gets on average 4 peak sun hours per day. In that case, you know it’ll take about 2 days for your solar panel(s) to charge your battery.

    How to Calculate Charging Time of a Battery By Solar Panels

    Besides using our calculator, here are 3 ways to estimate how long it’ll take to charge a battery with solar panels.

    I’ll run through each method step by step, starting with the simplest and ending with the most complex.

    Note: None of these methods is perfect. Each makes a number of assumptions that aren’t obvious to the untrained eye. I talk more about these assumptions at the end of this section.

    Method #1

    This is one of the more common ways you’ll see people estimate charge time. It’s simple but inaccurate. For this one, your battery and solar panel need to have the same nominal voltage.

    Accuracy: Lowest

    Complexity: Lowest


    Divide solar panel wattage by solar panel voltage to estimate solar panel current in amps. For example, here’s what you’d do if you had a 100W 12V solar panel.

    Solar panel current = 100W ÷ 12V = 8.33A

    Divide battery capacity in amp hours by solar panel current to get your estimated charge time. Let’s say you’re using your 100W panel to charge a 12V 50Ah battery.

    Charge time = 50Ah ÷ 8.33A = 6 hours

    If using a lead acid battery, multiply charge time by 50% to factor in the recommended max depth of discharge of lead acid batteries.

    Charge time for lead acid batteries = 6 hrs × 50% = 3 hours

    Method #2

    This way takes into account two important factors that the first method doesn’t: battery depth of discharge (DoD) and solar charge controller efficiency. Incorporating DoD adds flexibility. You can estimate charge time regardless of what state of charge your battery is at.

    Accuracy: Medium

    Complexity: Medium


    Multiply battery voltage by battery amp hours to get battery capacity in watt hours. For example, let’s say you have a 12V 100Ah battery.

    Battery capacity = 12V × 100Ah = 1200Wh

    Multiply battery watt hours by battery depth of discharge to estimate how much of the battery’s capacity has been discharged. Let’s say your battery is discharged 80%.

    Discharged battery capacity = 1200Wh × 80% = 960Wh

    Multiply solar panel wattage by rule-of-thumb charge controller efficiency (PWM: 75%; MPPT: 95%) to estimate solar output. Let’s say you’re using a 200W solar panel and an MPPT charge controller.

    Solar output = 200W × 95% = 190W

    Divide discharged battery capacity by solar output to get your estimated charge time.

    Charge time = 960Wh ÷ 190W = 5.1 hours

    Method #3

    This last method builds on the previous one. It takes into account system losses to give you an even more accurate estimate.

    Accuracy: Highest

    Complexity: Highest


    Multiply battery voltage by battery amp hours to get battery capacity in watt hours. For example, let’s say you have a 12V 200Ah battery.

    Battery capacity = 12V × 200Ah = 2400Wh

    Multiply battery watt hours by battery depth of discharge to estimate how much of the battery’s capacity has been discharged. Let’s say your battery is discharged 50%.

    Discharged battery capacity = 2400Wh × 50% = 1200Wh

    Divide discharged battery capacity by the battery’s rule-of-thumb charge efficiency factor (lead acid: 85%; lithium: 99%) to get the amount of energy required to fully charge the battery after factoring in losses during charging. Let’s say you’re using a lead acid battery.

    Energy required for full charge = 1200Wh ÷ 85% = 1412Wh

    Multiply solar panel wattage by rule-of-thumb charge controller efficiency (PWM: 75%; MPPT: 95%) to estimate solar output. Let’s say you’re using a 400W solar array and an MPPT charge controller.

    Solar output = 400W × 95% = 380W

    Multiply solar output by 100% minus a fixed percentage to take into account system losses. The National Renewable Energy Laboratory’s PVWatts Calculator uses 14.08% as its default value for system losses, so I’ll use that number here.

    Adjusted solar output = 380W × (100%. 14.08%) = 380W × 85.92% = 326W

    Divide the amount of energy required to fully charge the battery (in watt hours) by the adjusted solar output (in watts) to get your estimated charge time.

    Charge time = 1412Wh ÷ 326W = 4.3 hours

    Assumptions Shortcomings of All These Methods

    All these methods make assumptions. And they all leave out factors that affect solar charging time in the real world. Here are a handful of the main ones:

    • Assumption: The solar panels are outputting their rated power. A solar panel will only output its stated wattage under ideal conditions (called Standard Test Conditions, or STC). You’ll rarely see a 100W panel output 100 watts. Environmental factors such as weather, shading, and ambient temperature all affect solar output in ways that these calculation methods fail to capture.
    • Assumption: There are no loads connected to the battery. Your battery may be powering something while your solar panels are charging it. That device draws power from the battery, so your battery will need even more energy to reach full charge. Also, the solar charge controller itself is a load that will always be connected to the battery and using up a little power. The charge controller is usually a negligible load, but for some scenarios — particularly trickle charging a large battery with a small solar panel — leaving it out does have a material effect on charge time estimates.
    • Shortcoming: Rules of thumb don’t always hold true. The calculations use rules of thumb for simplicity’s sake. Reality is always much more complex. PWM and MPPT charge controller efficiency varies wildly based on factors such as temperature and the difference between PV voltage and battery voltage. A lead acid battery’s charge efficiency changes based on state of charge. And each system will have different sources and sizes of losses.
    • Shortcoming: Charge controllers often have a timed absorption stage. Once a battery reaches a certain voltage, charge controllers usually enter an “absorption” stage for the remainder of the charge cycle. This stage often lasts a fixed amount of time. For lead acid batteries, the absorption stage typically lasts 2 hours. Lithium batteries don’t need absorption, but charge controllers will often do a 20-30 minute absorption charge to balance the battery cells. This timed stage isn’t captured using these methods.

    Our charge time calculator takes into account a couple of these variables for a more precise estimate. But, alas, it can’t predict the weather…yet.

    How Do You Charge a Battery with a Solar Panel?

    Never connect a solar panel directly to a battery. Doing so can damage the battery.

    Instead, connect the battery then solar panel to a solar charge controller. Charge controllers regulate the current and voltage coming from solar panels to safely charge the battery.

    There are two main types of charge controllers: PWM and MPPT. Check out our recommendations and reviews for each type:

    Simple Solar Battery Charger Circuits

    Simple solar charger are small devices which allow you to charge a battery quickly and cheaply, through solar energy.

    A simple solar charger must have 3 basic features built-in:

    • It should be low cost.
    • Layman friendly, and easy to build.
    • Must be efficient enough to satisfy the fundamental battery charging needs.

    The post comprehensively explains nine best yet simple solar battery charger circuits using the IC LM338, transistors, MOSFET, buck converter, etc which can be built and installed even by a layman for charging all types of batteries and operating other related equipment


    Solar panels are not new to us and today it’s being employed extensively in all sectors. The main property of this device to convert solar energy to electrical energy has made it very popular and now it’s being strongly considered as the future solution for all electrical power crisis or shortages.

    Solar energy may be used directly for powering an electrical equipment or simply stored in an appropriate storage device for later use.

    Normally there’s only one efficient way of storing electrical power, and it’s by using rechargeable batteries.

    Rechargeable batteries are probably the best and the most efficient way of collecting or storing electrical energy for later usage.

    The energy from a solar cell or a solar panel can also be effectively stored so that it can be used as per ones own preference, normally after the sun has set or when it’s dark and when the stored power becomes much needed for operating the lights.

    Though it might look quite simple, charging a battery from a solar panel is never easy, because of two reasons:

    The voltage from a solar panel can vary hugely, depending upon the incident sun rays, and

    The current also varies due to the same above reasons.

    The above two reason can make the charging parameters of a typical rechargeable battery very unpredictable and dangerous.

    Before delving into the following concepts you can probably try this super easy solar battery charger which will ensure safe and guaranteed charging of a small 12V 7 Ah battery through a small solar panel:

    • Solar Panel. 20V, 1 amp
    • IC 7812. 1no
    • 1N4007 Diodes. 3nos
    • 2k2 1/4 watt resistor. 1no

    That looks cool isn’t it. In fact the IC and the diodes could already resting in your electronic junk box, so need of buying them. Now let’s see how these can be configured for the final outcome.

    As we know the IC 7812 will produce a fixed 12V at the output which cannot be used for charging a 12V battery. The 3 diodes connected at its ground (GND) terminals is introduced specifically to counter this problem, and to upgrade the IC output to about 12 0.7 0.7 0.7 V = 14.1 V, which is exactly what is required for charging a 12 V battery fully.

    The drop of 0.7 V across each diodes raises the grounding threshold of the IC by stipulated level forcing the IC to regulate the output at 14.1 V instead of 12 V. The 2k2 resistor is used to activate or bias the diodes so that it can conduct and enforce the intended 2.1 V total drop.

    Making it Even Simpler

    If you are looking for an even simpler solar charger, then probably there cannot be anything more straightforward than connecting an appropriately rated solar panel directly with the matching battery via a blocking diode, as shown below:

    Although, the above design does not incorporate a regulator, it will still work since the panel current output is nominal, and this value will only show a deterioration as the sun changes its position.

    However, for a battery that is not fully discharged, the above simple set up may cause some harm to the battery, since the battery will tend to get charged quickly, and will continue to get charged to unsafe levels and for longer periods of time.

    You may also like this Highly Efficient 0-50V Solar Charger Circuit

    ) Using LM338 as Solar Controller

    But thanks to the modern highly versatile chips like the LM 338 and LM 317, which can handle the above situations very effectively, making the charging process of all rechargeable batteries through a solar panel very safe and desirable.

    The circuit of a simple LM338 solar battery charger is shown below, using the IC LM338:

    The circuit diagram shows a simple set up using the IC LM 338 which has been configured in its standard regulated power supply mode.

    Using a Current Control Feature

    The specialty of the design is that it incorporates a current control feature also.

    It means that, if the current tends to increase at the input, which might normally take place when the sun ray intensity increases proportionately, the voltage of the charger drops proportionately, pulling down the current back to the specified rating.

    As we can see in the diagram, the collector/emitter of the transistor BC547 is connected across the ADJ and the ground, it becomes responsible for initiating the current control actions.

    As the input current rises, the battery starts drawing more current, this build up a voltage across R3 which is translated into a corresponding base drive for the transistor.

    The transistor conducts and corrects the voltage via the C LM338, so that the current rate gets adjusted as per the safe requirements of the battery.

    Current Limit Formula:

    R3 may be calculated with the following formula

    PCB Design for the above explained simple solar battery charger circuit is given below:

    The meter and the input diode are not included in the PCB.

    ) 1 Solar Battery Charger Circuit

    The second design explains a cheap yet effective, less than 1 cheap yet effective solar charger circuit, which can be built even by a layman for harnessing efficient solar battery charging.

    You will need just a solar panel panel, a selector switch and some diodes for getting a reasonably effective solar charger set up.

    What is Maximum Power Point Solar Tracking?

    For a layman this would be something too complex and sophisticated to grasp and a system involving extreme electronics.

    In a way it may be true and surely MPPTs are sophisticated high end devices which are meant for optimizing the charging of the battery without altering the solar panel V/I curve.

    In simple words an MPPT tracks the instantaneous maximum available voltage from the solar panel and adjusts the charging rate of the battery such that the panel voltage remains unaffected or away from loading.

    Put simply, a solar panel would work most efficiently if its maximum instantaneous voltage is not dragged down close to the connected battery voltage, which is being charged.

    For example, if the open circuit voltage of your solar panel is 20V and the battery to be charged is rated at 12V, and if you connect the two directly would cause the panel voltage to drop to the battery voltage, which would make things too inefficient.

    Conversely if you could keep the panel voltage unaltered yet extract the best possible charging option from it, would make the system work with MPPT principle.

    So it’s all about charging the battery optimally without affecting or dropping the panel voltage.

    There’s one simple and zero cost method of implementing the above conditions.

    Choose a solar panel whose open circuit voltage matches the battery charging voltage. Meaning for a 12V battery you may choose a panel with 15V and that would produce maximum optimization of both the parameters.

    However practically the above conditions could be difficult to achieve because solar panels never produce constant outputs, and tend to generate deteriorating power levels in response to varying sun ray positions.

    That’s why always a much higher rated solar panel is recommended so that even under worse day time conditions it keeps the battery charging.

    Having said that, by no means it is necessary to go for expensive MPPT systems, you can get similar results by spending a few bucks for it. The following discussion will make the procedures clear.

    How the Circuit Works

    As discussed above, in order to avoid unnecessary loading of the panel we need to have conditions ideally matching the PV voltage with the battery voltage.

    This can be done by using a few diodes, a cheap voltmeter or your existing multimeter and a rotary switch. Ofcourse at around 1 you cannot expect it to be automatic, you may have to work with the switch quite a few times each day.

    We know that a rectifier diode’s forward voltage drop is around 0.6 volts, so by adding many diodes in series it can be possible to isolate the panel from getting dragged to the connected battery voltage.

    Referring to the circuit digaram given below, a cool little MPPT charger can be arranged using the shown cheap components.

    Let’s assume in the diagram, the panel open circuit voltage to be 20V and the battery to be rated at 12V.

    Connecting them directly would drag the panel voltage to the battery level making things inappropriate.

    By adding 9 diodes in series we effectively isolate the panel from getting loaded and dragged to the battery voltage and yet extract the Maximum charging current from it.

    The total forward drop of the combined diodes would be around 5V, plus battery charging voltage 14.4V gives around 20V, meaning once connected with all the diodes in series during peak sunshine, the panel voltage would drop marginally to may be around 19V resulting an efficient charging of the battery.

    Now suppose the sun begins dipping, causing the panel voltage to drop below the rated voltage, this can be monitored across the connected voltmeter, and a few diodes skipped until the battery is restored with receiving optimal power.

    The arrow symbol shown connected with the panel voltage positive can be replaced with a rotary switched for the recommended selection of the diodes in series.

    With the above situation implemented, a clear MPPT charging conditions can be simulated effectively without employing costly devices. You can do this for all types of panels and batteries just by including more number of diodes in series.

    ) Solar Charger and Driver Circuit for 10W/20W/30W/50W White High Power SMD LED

    The 3rd idea teaches us how to build a simple solar LED with battery charger circuit for illuminating high power LED (SMD) lights in the order of 10 watt to 50 watt. The SMD LEDs are fully safeguarded thermally and from over current using an inexpensive LM 338 current limiter stage. The idea was requested by Mr. Sarfraz Ahmad.

    Technical Specifications

    Basically I am a certified mechanical engineer from Germany 35 years ago and worked overseas for many years and left many years ago due to personal problems back home.Sorry to bother you but I know about your capabilities and expertise in electronics and sincerity to help and guide the beginnings like me.I have seen this circuit some where for 12 vdc.

    I have attached to SMD ,12v 10 watt, cap 1000uf,16 volt and a bridge rectifier you can see the part number on that.When I turn the lights on the rectifier starts to heat up and the both SMDs as well. I am afraid if these lights are left on for a long time it may damage the SMDs and rectifier. I don not know where the problem is. You may help me.

    I have a light in car porch which turns on at disk and off at dawn. Unfortunately due to load shedding when there is no electricity this light remains off till the electricity is back.

    I want to install at least two SMD (12 volt) with LDR so as soon the light turns off the SMD lights will turn on. I want to additional two similar light elsewhere in the car porch to keep the entire are lighted.I think that if I connect all these four SMD lights with 12 volt power supply which will get the power from UPS circuit.

    Of course it will put additional load on UPS battery which is hardly fully charged due to frequent load shedding. The other best solution is to install 12 volt solar panel and attach all these four SMD lights with it. It will charge the battery and will turn the lights On/OFF.

    This solar panel should be capable to keeps these lights all the night and will turn OFF at dawn.Please also help me and give details about this circuit/project.

    You may take your time to figure out how to do that.I am writing to you as unfortunately no electronics or solar product seller in our local market is willing to give me any help, None of them seems to be technical qualified and they just want to sell their parts.

    The Design

    In the shown 10 watt to 50 watt SMD solar LED light circuit with automatic charger above, we see the following stages:

    • A solar panel
    • A couple of current controlled LM338 regulator circuits
    • A changeover relay
    • A rechargeable battery
    • and a 40 watt LED SMD module

    The above stages are integrated in the following explained manner:

    The two LM 338 stages are configured in standard current regulator modes with using the respective current sensing resistances for ensuring a current controlled output for the relevant connected load.

    The load for the left LM338 is the battery which is charged from this LM338 stage and a solar panel input source. The resistor Rx is calculated such that the battery receives the stipulated amount of current and is not over driven or over charged.

    The right side LM 338 is loaded with the LED module and here too the Ry makes sure that module is supplied with the correct specified amount of current in order to safeguard the devices from a thermal runaway situation.

    The solar panel voltage specs may be anywhere between 18V and 24V.

    A relay is introduced in the circuit and is wired with the LED module such that it’s switched ON only during the night or when it’s dark below threshold for the solar panel to generate the required any power.

    As long as the solar voltage is available, the relay stays energized isolating the LED module from the battery and ensuring that the 40 watt LED module remains shut off during day time and while the battery is being charged.

    After dusk, when the solar voltage becomes sufficiently low, the relay is no longer able to hold its N/O position and flips to the N/C changeover, connecting the battery with the LED module, and illuminating the array through the available fully charged battery power.

    The LED module can be seen attached with a heatsink which must be sufficiently large in order to achieve an optimal outcome from the module and for ensuring longer life and brightness from the device.

    Calculating the Resistor Values

    The indicated limiting resistors may be calculated from the given formulas:

    Rx = 1.25/battery charging current

    Ry = 1.25/LED current rating.

    Assuming the battery to be a 40 AH lead acid battery, the preferred charging current should be 4 amps.

    therefore Rx = 1.25/4 = 0.31 ohms

    wattage = 1.25 x 4 = 5 watts

    The LED current can be found by dividing its total wattage by the voltage rating, that is 40/12 = 3.3amps

    therefore Ry = 1.25/3 = 0.4 ohms

    wattage = 1.25 x 3 = 3.75 watts or 4 watts.

    Limiting resistors are not employed for the 10 watt LEDs since the input voltage from the battery is on par with the specified 12V limit of the LED module and therefore cannot exceed the safe limits.

    The above explanation reveals how the IC LM338 can be simply used for making an useful solar LED light circuit with an automatic charger.

    ) Automatic Solar Light Circuit using a Relay

    In our 4rth automatic solar light circuit we incorporate a single relay as a switch for charging a battery during day time or as long as the solar panel is generating electricity, and for illuminating a connected LED while the panel is not active.

    Upgrading to a Relay Changeover

    In one of my previous article which explained a simple solar garden light circuit, we employed a single transistor for the switching operation.

    One disadvantage of the earlier circuit is, it does not provide a regulated charging for the battery, although it not might be strictly essential since the battery is never charged to its full potential, this aspect might require an improvement.

    Another associated disadvantage of the earlier circuit is its low power spec which restricts it from using high power batteries and LEDs.

    The following circuit effectively solves both the above two issues, with the help of a relay and a emitter follower transistor stage.

    How it Works

    During optimal sun shine, the relay gets sufficient power from the panel and remains switched ON with its N/O contacts activated.

    This enables the battery to get the charging voltage through a transistor emitter follower voltage regulator.

    The emitter follower design is configured using a TIP122, a resistor and a zener diode. The resistor provides the necessary biasing for the transistor to conduct, while the zener diode value clamps the emitter voltage is controlled at just below the zener voltage value.

    The zener value is therefore appropriately chosen to match the charging voltage of the connected battery.

    For a 6V battery the zener voltage could be selected as 7.5V, for 12V battery the zener voltage could be around 15V and so on.

    The emitter follower also makes sure that the battery is never allowed to get overcharged above the allocated charging limit.

    During evening, when a substantial drop in sunlight is detected, the relay is inhibited from the required minimum holding voltage, causing it to shift from its N/O to N/C contact.

    The above relay changeover instantly reverts the battery from charging mode to the LED mode, illuminating the LED through the battery voltage.

    Parts list for a 6V/4AH automatic solar light circuit using a relay changeover

    • Solar Panel = 9V, 1amp
    • Relay = 6V/200mA
    • Rx = 10 ohm/2 watt
    • zener diode = 7.5V, 1/2 watt

    ) Transistorized Solar Charger Controller Circuit

    The fifth idea presented below details a simple solar charger circuit with automatic cut-off using transistors only. The idea was requested by Mr. Mubarak Idris.

    Circuit Objectives and Requirements

    • Please sir can you make me a 12v, 28.8AH lithium ion battery,automatic charge controller using solar panel as a supply, which is 17v at 4.5A at max sun light.
    • The charge controller should be able to have over charge protection and low battery cut off and the circuit should be simple to do for beginner without ic or micro controller.
    • The circuit should use relay or bjt transistors as a switch and zener for voltage reference thanks sir hope to hear from you soon!

    The Design

    PCB Design (Component Side)

    Referring to the above simple solar charger circuit using transistors, the automatic cut off for the full charge charge level and the lower level is done through a couple of BJTs configured as comparators.

    Recall the earlier low battery indicator circuit using transistors, where the low battery level was indicated using just two transistors and a few other passive components.

    Here we employ an identical design for the sensing of the battery levels and for enforcing the required switching of the battery across the solar panel and the connected load.

    Let’s assume initially we have a partially discharged battery which causes the first BC547 from left to stop conducting (this is set by adjusting the base preset to this threshold limit), and allows the next BC547 to conduct.

    When this BC547 conducts it enable the TIP127 to switch ON, which in turn allows the solar panel voltage to reach the battery and begin charging it.

    The above situation conversely keeps the TIP122 switched OFF so that the load is unable to operate.

    As the battery begins getting charged, the voltage across the supply rails also begin rising until a point where the left side BC547 is just able to conduct, causing the right side BC547 to stop conducting any further.

    As soon as this happens, the TIP127 is inhibited from the negative base signals and it gradually stops conducting such that the battery gradually gets cut off from the solar panel voltage.

    However, the above situation permits the TIP122 to slowly receive a base biasing trigger and it begins conducting. which ensures that the load now is able to get the required supply for its operations.

    The above explained solar charger circuit using transistors and with auto cut-offs can be used for any small scale solar controller applications such as for charging cellphone batteries or other forms of Li-ion batteries safely.

    For getting a Regulated Charging Supply

    The following design shows how to convert or upgrade the above circuit diagram into a regulated charger, so that the battery is supplied with a fixed and a stabilized output regardless of a rising voltage from the solar panel.

    simple, solar, battery, charger, circuits

    The above designs can be further simplified, as shown in the following over-charge, over-discharge solar battery controller circuit:

    Here, the zener ZX decides the full charge battery cut off, and can be calculated using the following formula:

    ZX = Battery full charge value 0.6

    For example, if the full-charge battery level is 14.2V, then the ZX can be 14 0.6 = 14.6V zener which can be built by adding a few zener diodes in series, along with a few 1N4148 diodes, if required.

    The zener diode ZY decides the battery over-discharge cut off point, and can be simply equal to the value of the desired low battery value.

    For example if the minimum low battery level is 11V, then the ZY can be selected to be a 11V zener.

    The above design can be also integrated with an LM338 charger circuit as shown below:

    ) Solar LED Light Circuit

    The sixth design here explains a simple low cost solar LED light circuit which could be used by the needy and, underprivileged section of the society for illuminating their houses at night cheaply.

    The idea was requested by Mr. R.K. Rao

    Circuit Objectives and Requirements

    • I want to make a SOLAR LED light using a 9cm x 5cm x 3cm transparent plastic box [available in the market for Rs.3/-] using a one watt LED/20mA LEDS powered by a 4v 1A rechargeable sealed lead-acid battery [SUNCA/VICTARI] also with a provision for charging with a cell phone charger [where grid current is available].
    • The battery should be replaceable when dead after use for 2/3 years/prescribed life by the rural/tribal user.
    • This is meant for use by tribal/rural children to light up a book; there are better led lights in the market for around Rs.500 [d.light],for Rs.200 [Thrive].
    • These lights are good except that they have a mini solar panel and a bright LED with a life of ten years if not more ,but with a rechargeable battery without a provision for its replacement when dead after two or three years of use.It is a waste of resource and unethical.
    • The project i am envisaging is one in which the battery can be replaced. be locally available at low cost. The price of the light should not exceed Rs.100/150.
    • It will be marketed on not for profit basis through NGOs in tribal areas and ultimately supply kits to tribal/rural youth to make them in the village.
    • I along with a colleague have made some lights with 7V EW high power batteries and 2x20mA pirahna Leds and tested them-they lasted for over 30 hours of continuous lighting adequate to light up a book from half-meter distance; and another with a 4v sunce battery and 1watt 350A LED giving enough light for cooking in a hut.
    • Can you suggest a circuit with a one AA/AAA rechargeable battery,mini solar panel to fit on the box cover of 9x5cm and a DC-DC booster and 20mA leds. If you want me to come over to your place for discussions i can.
    • You can see the lights we have made in google photos at Thanking you,

    The Design

    As per the request the solar LED light circuits needs to be compact, work with a single 1.5AAA cell using a DC-DC converter and equipped with a self regulating solar charger circuit.

    The circuit diagram shown below probably satisfies all the above specifications and yet stays within the affordable limit.

    Circuit Diagram

    The design is a basic joule thief circuit using a single penlight cell, a BJT and an inductor for powering any standard 3.3V LED.

    In the design a 1 watt LeD is shown although a smaller 30mA high bright LED could be used.

    The solar LED circuit is capable squeezing out the last drop of joule or the charge from the cell and hence the name joule thief, which also implies that the LED would keep illuminated until there’s virtually nothing left inside the cell. However the cell here being a rechargeable type is not recommended to be discharged below 1V.

    The 1.5V battery charger in the design is built using another low power BJT configured in its emitter follower configuration, which allows it to produce an emitter voltage output that’s exactly equal to the potential at its base, set by the 1K preset. This must be precisely set such that the emitter produces not more than 1.8V with a DC input of above 3V.

    The DC input source is a solar panel which may be capable of producing an excess of 3V during optimal sunlight, and allow the charger to charge the battery with a maximum of 1.8V output.

    Once this level is reached the emitter follower simply inhibits any further charging of the cell thus preventing any possibility of an over charge.

    The inductor for the solar LED light circuit consists of a small ferrite ring transformer having 20:20 turns which could be appropriately altered and optimized for enabling the most favorable voltage for the connected LED which may last even until the voltage has fallen below 1.2V.

    ) Simple Solar Charger for Street Lights

    The seventh solar charger discussed here is best suited as a solar LED street light system is specifically designed for the new hobbyist who can build it simply by referring to the pictorial schematic presented here.

    Due to its straightforward and relatively cheaper design the system can be suitably used for village street lighting or in other similar remote areas, nonetheless this by no means restricts it from being used in cities also.

    Main Features of this system are:

    1) Voltage controlled Charging

    2) Current Controlled LED Operation

    3) No Relays used, all Solid-State Design

    4) Low Critical Voltage Load Cut-off

    5) Low Voltage and Critical Voltage Indicators

    6) Full Charge cut-off is not included for simplicity sake and because the charging is restricted to a controlled level which will never allow the battery to over-charge.

    7) Use of popular ICs like LM338 and transistors like BC547 ensure hassle free procurement

    8) Day night sensing stage ensuring automatic switch OFF at dusk and switch ON at dawn.

    The entire circuit design of the proposed simple LED street light system is illustrated below:

    Circuit Diagram

    The circuit stage comprising T1, T2, and P1 are configured into a simple low battery sensor, indicator circuit

    An exactly identical stage can also be seen just below, using T3, T4 and the associated parts, which form another low voltage detector stage.

    The T1, T2 stage detects the battery voltage when it drops to 13V by illuminating the attached LED at the collector of T2, while the T3, T4 stage detects the battery voltage when it reaches below 11V, and indicates the situation by illuminating the LED associated with the collector of T4.

    P1 is used for adjusting the T1/T2 stage such that the T2 LED just illuminates at 12V, similarly P2 is adjusted to make the T4 LED begin illuminating at voltages below 11V.

    IC1 LM338 is configured as a simple regulated voltage power supply for regulating the solar panel voltage to a precise 14V, this is done by adjusting the preset P3 appropriately.

    This output from IC1 is used for charging the street lamp battery during day time and peak sunshine.

    IC2 is another LM338 IC, wired in a current controller mode, its input pin is connected with the battery positive while the output is connected with the LED module.

    IC2 restricts the current level from the battery and supplies the right amount of current to the LED module so that it is able operate safely during night time back up mode.

    T5 is a power transistor which acts like a switch and is triggered by the critical low battery stage, whenever the battery voltage tends to reach the critical level.

    Whenever this happens the base of T5 is instantly grounded by T4, shutting it off instantly. With T5 shut off, the LED module is enable to illuminate and therefore it is also shut off.

    This condition prevents and safeguards the battery from getting overly discharged and damaged. In such situations the battery might need an external charging from mains using a 24V, power supply applied across the solar panel supply lines, across the cathode of D1 and ground.

    The current from this supply could be specified at around 20% of battery AH, and the battery may be charged until both the LEDs stop glowing.

    The T6 transistor along with its base resistors is positioned to detect the supply from the solar panel and ensure that the LED module remains disabled as long as a reasonable amount of supply is available from the panel, or in other words T6 keeps the LED module shut off until its dark enough for the LED module and then is switched ON. The opposite happen at dawn when the LED module is automatically switched OFF. R12, R13 should be carefully adjusted or selected to determine the desired thresholds for the LED module’s ON/OFF cycles

    How to Build

    To complete this simple street light system successfully, the explained stages must be built separately and verified separately before integrating them together.

    First assemble the T1, T2 stage along with R1, R2, R3, R4, P1 and the LED.

    Next, using a variable power supply, apply a precise 13V to this T1, T2 stage, and adjust P1 such that the LED just illuminates, increase the supply a bit to say 13.5V and the LED should shut off. This test will confirm the correct working of this low voltage indicator stage.

    Identically make the T3/T4 stage and set P2 in a similar fashion to enable the LED to glow at 11V which becomes the critical level setting for the stage.

    After this you can go ahead with the IC1 stage, and adjust the voltage across its body and ground to 14V by adjusting P3 to the correct extent. This should be again done by feeding a 20V or 24V supply across its input pin and ground line.

    The IC2 stage can be built as shown and will not require any setting up procedure except the selection of R11 which may be done using the formula as expressed in this universal current limiter article

    Parts List

    • R1, R2, R3 R4, R5, R6, R7 R8, R9, R12 = 10k, 1/4 WATT
    • P1, P2, P3 = 10K PRESETS
    • R10 = 240 OHMS 1/4 WATT
    • R13 = 22K
    • D1, D3 = 6A4 DIODE
    • D2, D4 = 1N4007
    • T1, T2, T3, T4 = BC547
    • T5 = TIP142
    • R11 = SEE TEXT
    • IC1, IC2 = LM338 IC TO3 package
    • LED Module = Made by connecting 24nos 1 WATT LEDs in series and parallel connections
    • Battery = 12V SMF, 40 AH
    • Solar Panel = 20/24V, 7 Amp

    Making th 24 watt LED Module

    The 24 watt LED module for the above simple solar street light system could be built simply by joining 24 nos 1 watt LEDs as shown in the following image:

    ) Solar Panel Buck Converter Circuit with Over Load Protection

    The 8th solar concept discussed below talks about a simple solar panel buck converter circuit which can be used to obtain any desired low bucked voltage from 40 to 60V inputs. The circuit ensures a very efficient voltage conversions. The idea was requested by Mr. Deepak.

    Technical Specifications

    I am looking for DC. DC buck converter with following features.

    Input voltage = 40 to 60 VDC

    Output voltage = Regulated 12, 18 and 24 VDC (multiple output from the same circuit is not required. Separate circuit for each o/p voltage is also fine)

    Output current capacity = 5-10A

    Protection at output = Over current, short circuits etc.

    Small LED indicator for unit operation would be an advantage.

    Appreciate if you could help me designing the circuit.

    Best regards, Deepak

    The Design

    The proposed 60V to 12V, 24V buck converter circuit is shown in the figure below, the details may be understood as explained below:

    The configuration could be divided into stages, viz. the astable multivibrator stage and the mosfet controlled buck converter stage.

    BJT T1, T2 along with its associated parts forms a standard AMV circuit wired to generate a frequency at the rate of about 20 to 50kHz.

    Mosfet Q1 along with L1 and D1 forms a standard buck converter topology for implementing the required buck voltage across C4.

    The AMV is operated by the input 40V and the generated frequency is fed to the gate of the attached mosfet which instantly begins oscillating at the available current from the input driving L1, D1 network.

    The above action generates the required bucked voltage across C4,

    D2 makes sure that this voltage never exceeds the rated mark which may be fixed 30V.

    This 30V max limit bucked voltage is further fed to a LM396 voltage regulator which may be set for getting the final desired voltage at the output at the rate of 10amps maximum.

    The output may be used for charging the intended battery.

    Parts List for the above 60V input, 12V, 24V output buck converter solar for the panels.

    • R1-R5 = 10K
    • R6 = 240 OHMS
    • R7 = 10K POT
    • C1, C2 = 2nF
    • C3 = 100uF/100V
    • C4 = 100uF/50V
    • Q1 = ANY 100V, 20AMP P-channel MOSFET
    • T1,T2 = BC546
    • D2 = 30V ZENER 1 WATT
    • D3 = 1N4007
    • L1 = 30 turns of 21 SWG super enameled copper wire wound over a 10mm dia ferrite rod.

    ) Home Solar Electricity Set up for an Off-the-grid Living

    The ninth unique design explained here illustrates a simple calculated configuration which may be used for implementing any desired sized solar panel electricity set up for remotely located houses or for achieving an off the grid electricity system from solar panels.

    Technical Specifications

    I am very sure you must have this kind of circuit diagram ready. While going through your blog I got lost and could not really choose one best fitting to my requirements.

    I am just trying to put my requirement here and make sure I understood it correctly.

    (This is a pilot project for me to venture into this field. You can count me to be a big zero in electrical knowledge. )

    My basic goal is to maximize use of Solar power and reduce my electrical bill to minimum. ( I stay at Thane. So, you can imagine electricity bills. ) So you can consider as if I am completely making a solar powered lighting system for my home.

    Whenever there is enough sunlight, I do not need any artificial light.2. Whenever intensity of sunlight drops below acceptable norms, I wish my lights will turn on automatically.

    I would like to switch them off during bedtime, though.3. My current lighting system (which I wish to illuminate) consists of two regular bright light Tube lights ( 36W/880 8000K ) and four 8W CFLs.

    Would like to replicate the whole setup with Solar-powered LED based lighting.

    As I said, I am a big zero in field of electricity. So, please help me with the expected setup cost also.

    The Design

    36 watts x 2 plus 8 watt gives a total of around 80 watts which is the total required consumption level here.

    Now since the lights are specified to work at mains voltage levels which is 220 V in India, an inverter becomes necessary for converting the solar panel voltage to the required specs for the lights to illuminate.

    Also since the inverter needs a battery to operate which can be assumed to be a 12 V battery, all the parameters essential for the set up may be calculated in the following manner:

    Total intended consumption is = 80 watts.

    The above power may be consumed from 6 am to 6 pm which becomes the maximum period one can estimate, and that’s approximately 12 hours.

    Multiplying 80 by 12 gives = 960 watt hour.

    It implies that the solar panel will need to produce this much watt hour for the desired period of 12 hours during the entire day.

    However since we don’t expect to receive optimum sunlight through the year, we can assume the average period of optimum daylight to be around 8 hours.

    Dividing 960 by 8 gives = 120 watts, meaning the required solar panel will need to be at least 120 watt rated.

    If the panel voltage is selected to be around 18 V, the current specs would be 120/18 = 6.66 amps or simply 7 amps.

    Now let’s calculate the battery size which may be employed for the inverter and which may be required to be charged with the above solar panel.

    Again since the total watt hour fr the entire day is calculated to be around 960 watts, dividing this with the battery voltage (which is assumed to be 12 V) we get 960/12 = 80, that’s around 80 or simply 100 AH, therefore the required battery needs to be rated at 12 V, 100 AH for getting an an optimal performance throughout the day (12 hours period).

    We’ll also need a solar charge controller for charging the battery, and since the battery would be charged for the period of around 8 hours, the charging rate will need to be around 8% of the rated AH, that amounts to 80 x 8% = 6.4 amps, therefore the charge controller will need to be specified to handle at least 7 amp comfortably for the required safe charging of the battery.

    That concludes the entire solar panel, battery, inverter calculations which could be successfully implemented for any similar kind of set up intended for an off the grid living purpose in rural areas or other remote area.

    For other V, I specs, the figures may be changed in the above explained calculation for achieving the appropriate results.

    In case the battery is felt unnecessary and the solar panel could also be directly used for operating inverter.

    A simple solar panel voltage regulator circuit may be witnessed in the following diagram, the given switch may be used for selecting a battery charging option or directly driving the inverter through the panel.

    In the above case, the regulator needs to produce around 7 to 10amps of current therefore an LM396 or LM196 must be used in the charger stage.

    The above solar panel regulator may be configured with the following simple inverter circuit which will be quite adequate for powering the requested lamps through the connected solar panel or the battery.

    Parts list for the above inverter circuit: R1, R2 = 100 ohm, 10 watt

    T1, T2 = TIP35 on heatsinks

    The last line in the request suggests an LED version to be designed for replacing and upgrading the existing CFL fluorescent lamps. The same may be implemented by simply eliminating the battery and the inverter and integrating the LEDs with the solar regulator output, as shown below:

    The negative of the adapter must be connected and made common with the negative of the solar panel

    Final Thoughts

    So friends these were 9 basic solar battery charger designs, which were hand picked from this website.

    You will find many more such enhanced solar based designs in the blog for further reading. And yes, if you have any additional idea you may definitely submit it to me, I’ll make sure to introduce it here for the reading pleasure of our viewers.

    Feedback from one of the Avid Readers

    I have come across your site and find your work very inspiring. I am currently working on a Science, Technology, Engineering and Math (STEM) program for year 4-5 students in Australia. The project focuses on increasing children’s curiosity about science and how it connects to real-world applications.

    The program also introduces empathy in the engineering design process where young learners are introduced to a real project (context) and engages with their fellow school peers to solve a worldly problem. For the next three years, our FOCUS is on introducing children to the science behind electricity and the real-world application of electrical engineering. An introduction to how engineers solve real-world problems for the greater good of society.

    I am currently working on online content for the program, which will FOCUS on young learners(Grade 4-6) learning the basics of electricity, in particular, renewable energy, i.e. solar in this instance. Through a self-directed learning program, children learn and explore about electricity and energy, as they are introduced to a real-world project, i.e. providing lighting to children sheltered in the refugee camps around the world. On completion of a five-week program, children are grouped in teams to construct solar lights, which are then sent to the disadvantaged children around the world.

    As a not 4 profit educational foundation we are seeking your assistance to layout a simple circuit diagram, which could be used for the construction of a 1 watt solar light as practical activity in class. We have also procured 800 solar light kits from a manufacturer, which the children will assemble, however, we need someone to simplify the circuit diagram of these light kits, which will be used for simple lessons on electricity, circuits, and calculation of power, volts, current and conversion of solar energy to electrical energy.

    I look forward to hearing from you and keep on with your inspiring work.

    Solving the Request

    I appreciate your interest and your sincerely efforts to enlighten the new generation regarding solar energy.I have attached the most simple yet efficient LED driver circuit which can be used for illuminating a 1 watt LED from a solar panel safely with minimum parts.Make sure to attach a heatsink on the LED, otherwise it may burn quickly due to overheating.The circuit is voltage controlled and current controlled for ensuring optimum safety to the LED.Let me know if you have any further doubts.

    Request from one of the avid readers of this blog:

    Hi, thank you for everything you do to help people out! My son would like to create a science fair experiment where he can show an electric car running on a solar panel only during the day while charging a battery and running on battery only during the night. For this, we planned to have a small solar panel connected to a battery and motor in parallel (see the attached drawing).

    • Will this work?
    • Can you recommend a size of solar panel, battery and motor?
    • As to not overcharge the battery, should a resistor be added? What size would you recommend?
    • Should a diode be added? What size would you recommend?
    • yes, it will work.
    • Use a 6 to 8V 1-amp solar panel.
    • The switch in series with the battery is not required. The remaining two switches are fine. This switch can be replaced with a 4 ohm 2 watt, or simply a 6 V flashlight bulb.
    • This bulb will illuminate while charging and will slowly shut off as the battery gets fully charged.
    • You can add a diode in series with the positive wire of the solar panel. It can be a 1N5402 diode
    • The battery can be any 3.7V 1200mAh Li-ion battery.
    • Motor can be any 3.7V DC motor.


    Couple more questions, I cannot find a solar panel with those specs, do you think you could send me one on the internet so I can find something similar? Great idea on the flashlight bulb, I assume this would need to be an incandescent light? Do you think this would properly protect the battery or would an additional resistor be needed?

    For the solar panel, you can search for a 6V 5 watt solar panel.Yes, the flashlight bulb will need to be an incandescent type, so that the filament can be used to control the current.The bulb should be enough to control the current, no additional resistor will be required.Please find the attached diagram for the detailed schematic.

    You’ll also like:

    • 1. nbspHow to Generate Electricity from Road Speed Breakers
    • 2. nbsp3 Smart Li-Ion Battery Chargers using TP4056, IC LP2951, IC LM3622
    • 3. nbspSimple Peltier Refrigerator Circuit
    • 4. nbspLoudspeaker Thump Sound Eliminator Circuit
    • 5. nbspSimple Car Shock Alarm Circuit
    • 6. nbsp12V Battery Charger Circuits [using LM317, LM338, L200, Transistors]

    Best Solar Chargers for Backpacking in 2023

    A solar charger is a very useful gadget for long backpacking trips because it allows you to easily recharge your electronic devices such as a handheld GPS device, hiking watch or a smartphone. Since many backpackers rely on these devices for navigation along the trails, solar chargers have become very popular. Especially those who use smartphones for navigation on trails (check out our test of the best hiking apps) appreciate solar chargers, because no smartphone with GPS turned on constantly runs for more than a day without being recharged.

    Solar chargers absorb sunlight and convert it to electricity which charges your devices or the battery pack. Unlike regular power banks which get drained sooner or later, solar chargers are suitable for very long trips because they allow you to recharge your devices as long as you have sunlight available.

    In the following we listed the best solar chargers currently available to make your buying decision a little easier. We only listed high-quality solar chargers that come for a good price and provide good durability.

    We regularly update our reviews and selections to always recommend you the best products on the market.

    We only list top-tier products. Read how our selections of best hiking products differ from others here.

    We use affiliate links and may receive a small commission on purchases at no extra cost to you.

    Our Picks of Solar Chargers for Backpacking

    Best Solar Chargers for Backpacking

    The Selection

    Goal Zero Nomad 10

    Suitable for:

    The Goal Zero Nomad 10 solar panel features built-in kickstand which clicks into place at multiple angles and allows you to position the solar panel perfectly towards the sun. It is made of rugged and durable materials, and can be strapped to your backpack, tent or other gear. The solar panel has an output of 10 watts and works perfectly with power banks from Goal Zero. The Goal Zero Nomad 10 solar panel is often combined with the Goal Zero Venture 30 power bank which has a capacity of 7800 mAh. The solar panel recharges this power bank in 4.5 to 9 hours. Nevertheless, the solar panel can also charge various devices such as cell phones, cameras etc. directly. The Goal Zero Nomad 10 is a powerful solar panel that is perfect for backpacking and other lengthy activities in the outdoors.

    Where to buy?

    BigBlue SolarPowa 28

    Suitable for:

    The BigBlue SolarPowa 28 is a panels-only solar charger and thus it is a good option if you already have a battery pack/power bank. However, it is also suitable for charging electronic devices such as smartphones, headlamps etc. directly. The Big Blue SolarPowa 28 solar charger features advanced technology which discovers and replicates your device’s original charging protocol to provide the fastest possible charging speed via 3 USB ports. However, be aware that the solar panels will not generate enough electricity to match the device’s original charging protocol in case of cloudy or rainy weather. This BigBlue solar charger has attachment points, so you can easily attach it on a backpack. It is also water and dust resistant for good performance on hiking trails.

    Where to buy?

    Choosing a Solar Battery Trickle Charger Maintainer

    Jan 26th 2022

    When you think about solar panels, what is the first thing that comes to mind? The chances are that you pictured massive fields of industrial-use panels or rooftop-mounted residential units. While these are some of the most commonly used types of solar panels, the technology has advanced substantially in recent years.

    Solar panel manufacturers are able to create smaller and more efficient panels. This improvement has allowed them to use scaled-down panels for a variety of purposes, including in solar battery trickle chargers, which allow you to charge your car battery with solar. These devices are a great way of keeping the batteries on certain pieces of equipment charged and ready for use.

    What is trickle charge?

    Trickle charge is used to compensate for the capacity loss of the battery due to self-discharge after a full charge. To compensate for self-discharge, the battery is kept in a continuous low-current charge that approximates a fully charged state, also known as maintenance charging. Generally, Battery Maintainer is the same as Battery Trickle Charger on Renogy, There are types of battery trickle chargers available for sale here.

    Below, we discuss what a solar battery trickle charger is, how they work, and what they are best used for. If you are looking to take advantage of this convenient technology, keep on reading.

    What Is a Solar Battery Trickle Charger Maintainer?

    As the name implies, a “solar battery trickle charger maintainer” is a solar-powered device that is used to charge batteries. Trickle charges have been in use for decades. However, solar-powered variants are a relatively new technology.

    A trickle charger is a safe and effective way to ensure that your battery keeps a charge, even if the device that it is installed in has not run for a long time.

    Typically, you may hear before the trickle charger for cars, but there are more on that below. Traditional trickle charges must always remain plugged into a power source, which makes them a bit tedious to use.

    Conversely, a solar battery trickle charger only needs to be connected to the battery. This flexibility makes them much more versatile than standard trickle chargers.

    As long as the trickle charger’s flexible solar panels are in direct sunlight, the device will keep operating as designed. The solar panels allow you to trickle charge batteries, even if you are not anywhere near a power outlet.

    How Do Solar Panel Trickle Chargers Really Work?

    Operating a solar battery trickle charger is incredibly easy. The typical charger has three components, which include the following:

    In order to set up your solar battery maintainer, simply connect the alligator clips to the positive and negative poles of the battery that you want to charge. One clip should be attached to each pole. Next, place the flexible solar panel in a location that is in direct sunlight.

    Depending on which model of trickle charger you purchase, there may be a small “on/off” switch on the inverter box. If so, make sure that the switch is turned to the “on” position.

    simple, solar, battery, charger, circuits

    Keep in mind that not all solar battery trickle chargers have these switches. If yours does not, it will automatically begin working once the clips are connected, and the panel starts producing electricity.

    Before we discuss the difference between standard battery chargers and solar battery chargers, let’s cover a few frequently asked questions regarding solar trickle charger maintainers:

    Can I Leave a Solar Trickle Charger On All the Time?

    Yes, the most convenient aspect of using a solar battery trickle charger is that you can leave it on all of the time. Trickle chargers deliver a small, steady stream of electricity to the battery. The amount of electricity is so negligible that the device will not overcharge your battery, no matter how long you leave the device connected.

    The only time you should disconnect your trickle charger is when operating your piece of equipment. For instance, if your solar battery trickle charger is connected to your boat, remove the alligator clips and secure the portable solar panel before starting the motor.

    With that being said, it is important to note that trickle chargers are not suitable for “jump-starting” a battery that is completely drained. While a solar battery trickle charger will eventually recharge the battery, this process takes hours.

    Trickle charger maintainers are designed for preventing batteries from going dead. They are also useful for recharging batteries that you do not need to use immediately. If you need to start a piece of equipment quickly, then you will need to use jumper cables, a standard battery charger, or a jump box.

    Do Solar Car Battery Chargers Work?

    Do solar car battery chargers work? Yes, solar battery trickle chargers work as well as, if not better than, standard trickle chargers. They are particularly useful if you are in a rural area and are not near a standard power outlet. These devices will steadily charge the battery that they are attached to as long as they are exposed to sunlight.

    Can a Car Trickle Charger Ruin a Battery?

    No, solar battery trickle chargers will not ruin a battery. However, a standard battery charger may. This discrepancy exists because a regular power battery charger is designed to rapidly recharge the device it is connected to. If it is left on too long, then it will diminish the capacity of the battery.

    There is no risk of ruining a battery’s capacity when using a solar trickle charger maintainer. That is why these devices are becoming much more popular than traditional battery chargers.

    What Size Solar Panel Do I Need to Trickle Charge a Battery?

    The size of the solar panel you need to trickle charge a battery will depend on its capacity. For instance, let’s say that you need to charge a 100ah battery. The average device charges a battery at 12 volts and 20 amps per hour. Therefore, it would take approximately five hours to fully charge your 100ah battery.

    In order to calculate the wattage you will need, multiply the amps by volts. Using the information from our scenario, 20 amps times 12 volts equals 240 watts. Portable solar panels are available in increments of 100 watts. In this scenario, you would need either one 300w solar panel or three 100w solar panels.

    Want to skip all that math? If so, then check out our solar panel calculator. All you will need is some basic information about your battery, and our handy tool will do the rest.

    What is the Difference Between a Battery Charger and a Battery Maintainer?

    On occasion, the phrases “trickle charger maintainer” and “battery charger” are used interchangeably. While both devices are designed to charge a battery, they are not the same.

    A battery charger is designed to recharge a battery as rapidly and safely as possible. These devices do this by delivering a large amount of amperage and voltage to the battery so that you can get your equipment running quickly.

    While using a battery charger is an effective way of cranking a piece of equipment that has a dead battery, these devices cannot be left plugged in all of the time. If you do, then the device will seriously diminish the capacity of your battery.

    On the other hand, solar battery trickle chargers take a “slow and steady” approach to charging batteries. They deliver an incremental amount of electricity over several hours in order to recharge a battery or keep it from dying when not in use.

    Solar Battery Trickle Charger Uses

    Solar battery trickle chargers are versatile pieces of equipment that can be used for many different applications. If you need to charge a small battery and have access to plenty of sunlight, solar trickle charger maintainers present a great option. Some of the most common use cases for solar trickle chargers include:

    Most lead-acid batteries have warranties of five years or fewer. You can expect to see warranties of ten years or more for lithium-ion batteries.

    Solar Battery Temperature

    Like anything using electricity, temperature is a constantly important consideration. Batteries won’t do well in either extreme heat or extreme cold. The best place for a solar battery is in a temperature-controlled space where it won’t be exposed to the elements.

    Trickle Battery Charger for Car/RV

    Typically, you use your car often enough that the battery does not have a chance to lose its charge. However, batteries in cars that have not been driven for days or weeks will eventually go dead. In order to prevent this, you can attach a solar battery trickle charger for car battery to your vehicle’s starter battery.

    Car trickle charger maintainers are also excellent for RVs and campers. Unlike cars, RVs frequently sit around for weeks or even months. During that time, the battery will likely go dead if it is not charged.

    Remember, your RV does not have to be parked in direct sunlight. Only the flexible solar panel needs sun exposure to work. If your RV is stored in the shade or within a building, simply run wires from the panel to the battery. The flexible solar panel can be attached to the roof of your storage building so that it gets maximum sunlight.


    If you own a boat or other marine equipment, you know just how frustrating a dead battery can be. You carefully plan a trip to the lake or bay, only to find that your boat’s battery is dead. Keeping your boat battery charged is often a challenge, especially if you store it at a marina, as there is little to no access to power outlets.

    Fortunately, solar battery trickle chargers present the perfect solution. The solar panel can be placed on the deck of your boat, and the alligator clips can easily be connected to the battery. This setup ensures that your boat is ready to use all year round.

    Outdoor Equipment

    Solar battery trickle chargers are a great way of keeping all of your outdoor equipment charged and ready to go. This coverage includes four-wheelers, ATVs, side by sides, tractors, riding lawn mowers, and more.

    You can quickly connect a trickle charger maintainer to any of these devices without having to break out the hundred-foot extension cords.

    Trickle charger maintainers are a true “set it and forget it” way of charging equipment batteries. You never have to worry about ruining your battery or going out to mow the lawn only to find out that your equipment will not start.


    That’s right; solar battery trickle chargers can be used to charge cell phones as well. The inverter boxes on many trickle charger maintainers include USB ports so that you can quickly connect the charging cord of your cellular device.

    Solar-powered trickle charger maintainers have become hugely popular among avid outdoors fans, campers, and hikers. Small flexible solar panels can easily be deployed at a campsite or attached to a backpack.

    How to Choose the Best Solar Battery Trickle Charger for a Solar Energy System

    As you can see, solar battery trickle chargers are extremely versatile and user-friendly devices that can be connected to just about any type of battery. However, not all trickle charger maintainers are created equal. That is why it is vital that you do your research and carefully choose the right solution for your solar energy system.

    There is no one-size-fits-all option when it comes to solar battery trickle chargers. You should consider several factors when selecting your equipment, including:

    Number of Charging Ports Needed

    Some trickle chargers and power banks include multiple USB ports. If you go camping with multiple people and want everyone to be able to charge their devices, then select a battery with more than one USB port.

    On the other hand, if you are a solitary person who likes to venture out on your own, then a smaller device with only one port will work just fine.

    Capacity of the Device

    Another major consideration is the capacity of the device that you need to charge. For example, a deep cycle battery used for a large boat will have a higher capacity than your cell phone. If you are purchasing a solar battery trickle charger for your boat, then you need to select an option with large panels.

    Whether or Not You Want to Charge Devices After Hours

    The only real downside of solar battery trickle chargers is that they only work during daylight hours when they are exposed to direct sunlight. Fortunately, there is a way to remedy this shortcoming. You can supplement your trickle charger maintainer with a portable battery pack power bank.

    If you are using your solar battery trickle charger with large equipment, such as an RV or boat, you may want to incorporate a power box into your system. These devices work like portable power banks, but they store much more energy.

    Before selecting a solar battery trickle charger, make sure to consider all of the ways you plan on using it. You can also connect with our experts if you need additional guidance.

    Quality Trickle Charger Maintainers from Renogy

    If you want to charge your car battery with solar, Renogy can help. We are the premier provider of trickle charger maintainers, home solar panel kits, solar panel monitoring equipment, and more. You can check the following video to learn about Renogy’s 5W, 8W, 16W Solar Battery Trickle Charger. Renogy’s Solar Battery Maintainer can help you maintain a healthy battery, which can convert solar power into a usable 12V DC current to keep your battery topped off at a stable level.

    No matter what type of home or vehicle solar equipment you need — car, boat, whatever — we have the perfect trickle charging solutions in our massive online inventory. Check out our learning center to find out more or contact us for support.

    See our other related articles to learn more:

    What is a Solar Battery Charger for Boats?

    Solar battery chargers are incredibly useful for boats out in the sun all day without access to shore power. Being able to harness the sun’s energy to fuel our tech-heavy lives is a fantastic feat. From the smallest fishing boat to the largest yacht, solar charging offers convenience and peace of mind when your battery is running low.

    What Is a Solar Battery Charger for Boats?

    A solar battery charger generates electricity for your boat’s battery system no matter where you are, so long as you have sunshine. Solar chargers range from small trickle chargers for a trolling motor or some lights, up to thousands of watts that can power all your boat’s electrical needs.

    What Types of Solar Battery Chargers Are There?

    A solar battery charger is not a single component but rather a combination of various components with different capacities for different applications. A solar battery charger consists of a solar panel (or multiple), a solar charge controller, and wiring to connect to the system together. In general, there are a few main applications ideal for the various sizes of solar battery chargers.

    Trickle Charging

    Trickle charging is optimal for lead-acid starting batteries and provides a very small amount of power to keep them healthy and ready to use. If shore power is not available, a small solar battery charger that can keep the batteries topped off and ready to start the engines is beneficial. These systems are also very cost-effective.

    Light-Use Charging

    A small solar battery charger system that consists of around 100 watts can provide enough power for small electronics, fish finders, stereos, and charging phones during the day. These systems can be used on boats with one battery or connected to a house battery bank. Small solar battery charging systems are perfect for light use on boats that may not have other charging means while operating, such as small fishing boats, day-use sailboats, or speedboats.

    Heavy Power-Use Charging

    Liveaboard yachts and sailboats require significant amounts of power and, consequently, heavy-use solar battery charging systems. Liveaboard vessels have a separate battery system used exclusively for lights, electronics, and large household appliances such as microwaves, TVs, and computers. These solar charging systems may consist of thousands of watts of solar collection to provide all of the day-to-day power needs for living on a boat.

    Benefits of Solar Battery Chargers for Boats

    Regardless of the size of the solar battery charging system, solar chargers on boats provide some excellent benefits when it comes to helping maintain your battery’s charge.

    Harnesses the Sun’s Energy

    For liveaboard or cruising boats, you may not be near fuel or power sources regularly. Luckily, the sun’s energy is delivered to your boat free of charge every day. All you need to do is harness it. A solar electric system collects this energy anywhere the sun shines for your use whenever you need it.

    Little to No Maintenance

    Rugged solar boat battery charging systems can withstand harsh weather and marine applications. After the initial purchase, there are rarely other expenses or maintenance required.

    Silent and Fuel Free

    Traditional gas generators are noisy and require continuous refueling. Even wind generators can be loud and cause vibration interrupting a peaceful day on the water. Solar battery chargers are silent and don’t require anything other than the sun to provide clean energy for your boat.

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    How Solar Boat Battery Chargers Work

    A solar boat charger consists of three parts: solar panels, a charge controller, and wiring.

    The solar panels collect energy from the sun and convert them to electricity. However, the electricity from the solar panels is not conditioned for the batteries and could damage them if connected directly.

    The solar charge controller ensures safe charging conditions by regulating the current and voltage flowing to the batteries.

    Wiring and fuses connect the solar panels, charge controller, and batteries to complete the solar battery charging system.

    MPPT vs PWM Battery Charging for Boats

    When selecting a charge controller for the solar panels, you will see two primary options: PWM and MPPT charge controllers. PWM stands for pulse width modulation, and MPPT stands for maximum power point tracking.

    A PWM charge controller uses electronics to rapidly pulse the current flow. The pulsing prevents the battery from overcharging by limiting the amount of current flowing to it. However, PWM controllers do not have any control over the charge voltage. This means that you need to select solar panels near or slightly above your battery system voltage.

    MPPT charge controllers are also known as DC-to-DC converters and regulate both voltage and current. MPPT controllers can control the power on the solar panel side of the controller and the battery side. This enables the charge controller to find the maximum operating efficiency of the solar panels by holding the correct voltage.

    MPPT charge controllers cost more than PWM controllers, but they’re also up to 30% more efficient. Additionally, MPPT controllers allow you to use much higher voltage solar panels, giving you more options.

    Should You Leave a Boat Battery Charger Plugged In All The Time?

    The solar charge controller regulates the charging making it safe to leave the system plugged in without damaging the battery. In fact, with lead-acid batteries, keeping the solar charger on continuously can help maintain them and prolong their life. With lithium batteries, the solar charger will keep them full and ready to use.

    What Size Solar Panel Do You Need To Charge Your Boat Battery?

    The size of the solar panel depends on the amount of power you need. If you have a liveaboard boat with large household appliances, then you’ll need a higher wattage system. If you’re keeping a battery maintained for your radio and some lights, then you can get away with a smaller system.

    You also need to consider how sunny it’s going to be, the time of year, and your latitude to get a reasonable expectation on how much power you’ll make. It varies a lot, but a good rule of thumb is that a 100-watt solar panel will generate around 350 watt-hours per day.

    The size of your solar system will also depend on how much battery capacity you have installed. If you have a large battery bank and plan to use a lot of power at night, you need enough solar to recharge your battery bank, plus meet your energy needs during the day.

    Are Solar Battery Chargers for Boats Worth It?

    Solar panels can have a high upfront cost, but they’ll start paying for themselves and saving you money after the initial purchase. They’re eco-friendly, silent, and eliminate the need to refuel a generator. For many, the benefits of having solar power on a boat far outweigh the costs and drawbacks, making solar chargers for boats a great option.

    Being out in nature is all about utilizing what resources you have. No one wants to be worried about running out of gas or not having enough power for appliances, especially when you’re out at sea. While you soak up some sunshine, let your solar battery charger for your boat do the same.

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