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9 Simple Solar Battery Charger Circuits. Solar charger module

9 Simple Solar Battery Charger Circuits. Solar charger module

    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.

    simple, solar, battery, charger, circuits, module

    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.

    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.

    simple, solar, battery, charger, circuits, module

    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.

    simple, solar, battery, charger, circuits, module

    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]

    DIY Solar Battery Charger for 18650 Li-Ion Batteries

    In this DIY project, I will show you how to design and build a simple but effective Solar Battery Charger for 18650 batteries. Using this project, you can charge two 18650 Li-Ion batteries directly from solar without any wall adapter.


    The need for sustainable living has led to the increased usage of renewable energy. Keeping aside the efficiency numbers, Solar Energy is one of the convenient alternatives (when compared to other renewable energy sources such as wind) to the grid supply.

    Now-a-days, large Solar Farms are being setup in acres of barren lands in many countries. But small-scale solar plants like on independent building rooftops and near small home communities are also becoming popular.

    The setup of a Solar Power Plant. whether large or small, is fairly simple. Setup an array of Solar Panels on rooftop, connect them to a Solar Charge Controller and charge the batteries. From the batteries, you can run any mains appliances using appropriate inverters.

    As a beginner’s solar project, I have designed a very simple Solar Battery Charger to charge 18650 Li-Ion batteries. Using these batteries, you can charge your mobile phones, tablets or use the batteries in LED Lamps, emergency lights etc.

    Circuit Diagram

    Let us dive into the project by taking a look at the circuit diagram or rather the connection diagram of this DIY Solar Battery Charger for 18650. All the components, which I will list out in the next section, are very easy to acquire and are easily available in local electronics stores (you can get them online as well).

    Components Required

    • 6V – 100mA Mini Solar Panel
    • 2 x 18650 Li-Ion Batteries
    • 18650 Battery Holders
    • TP4056 Li-Ion Battery Charger Module with protection
    • 1V to 5V Input to 5V Output Step-up Converter (Boost Converter)
    • 1N4007 PN Junction Diode
    • Switch (Push to ON and Push to OFF)
    • Connecting Wires

    How to Setup DIY Solar Battery Charger for 18650?

    First, I will explain the connections and the step by step setup of the Solar Battery Charger for 18650. Then we will understand the principle of operation.

    Coming to the connections, the Mini Solar Panel has two wires coming from it. One is Red, which is the positive wire and the other is black (or brown in my case), which is the negative wire.

    Now, take the TP4056 Li-Ion Battery Charger Module with battery protection. At the input side, it has two connections named IN and IN-. Take the Red wire from the solar panel and connect it to the anode of 1N4007 Diode.

    Connect the cathode of the diode to the IN terminal of the TP4056 Module and directly connect the black wire of the solar panel to the IN- terminal of TP4056. This completes the input section.

    On the output side of the TP4056, there are four connections named B, B-, OUT and OUT-. Take two 18650 Li-Ion batteries with holders and connect them in parallel i.e. both positive terminals of the batteries are common and both negative terminals are common.

    Connect the common positive terminal of the batteries to B of TP4056. You may have to solder the wires on to the Li-Ion Charger board. Similarly, connect the common negative terminal of the batteries to the B- of TP4056.

    The final step of the constriction is to connect the output of the TP4056 to the 5V Boost Converter Module. The Step-up converter module has two input terminals named IN and IN-. Connect the OUT of TP4056 to IN of Boost Converter module and OUT- to IN- respectively.

    You can use a switch between TP4056 and Boost converter so that you can turn ON or OFF the output. I have glued the entire setup on to the battery holder case with a switch in the center and the USB port on the edge.

    Principle of DIY Solar Battery Charger for 18650

    The solar panel used in this project is small 6V panel with a small output of 100mA. The output of this solar panel will not be a constant 6V but it might fluctuate between 5V and 7.5V (as per its data sheet).

    This voltage is given as input to the TP4056 Li-Ion Battery Charging Module, which in this scenario, acts as a Solar Charge Controller. The input to TP4056 can be in the range of 4V to 8V (which is the range of the output of the solar panel).

    TP4056 then charges the battery from the solar power itself. If you only want to charge the batteries, then this is sufficient. But since our project also needs to charge a Mobile Phone, we need to have a 5V output and the output of the 18650 Li-Ion batteries is only 3.7V.

    Here comes the Boost Converter to the rescue. The boost converter I have used is a 1V-5V input to 5V output step-up converter i.e. it takes an input anywhere between 1V and 5V and produces a constant 5V output. Also, this boost converter can support a current up to 1A, so the charging of mobile phone will not be that slow.

    I have used the project to charge my mobile phone as well as to power up an Arduino board.

    How to Build a Solar Powered Battery Charger

    Edmond Becquerel was the first to discover the photovoltaic effect, whereby electric current and voltage is generated by a material exposed to light. This discovery led to the invention of the first solar cell in 1893 by Charles Fritts.

    Today we have vastly improved solar panels capable of a wide variety of applications and power generating capacities. Today solar panels are used to power a range of devices from small calculators, to homes and even spacecraft.

    How a Solar Panel Works

    Inside a solar panel, a layer of N-type semiconductor material is in contact with a layer of P-type semiconductor material, forming a semiconductor junction at the point of contact. Conductive plates are attached to each side of the N and P layers, which are then connected to the power output leads. The diagram below shows how they are constructed:

    Check out our article on transistors for an in-depth explanation of how a semiconductor junction works.

    Free electrons in the N-type material bond with the electron holes in the P-type material at the junction, forming a charge layer. At this point, no current flows.

    When photons from the sun’s energy strike the junction, the bond breaks and the electrons and electron holes are forced back into their layers towards the terminals. If the terminals are connected to a circuit, an electrical current will flow.

    How to Build a Solar Powered Battery Charger

    In this project, we will build a solar powered battery charger that can provide remote power to any device powered by 5V USB cable, like a cell phone or Arduino project. Here is a diagram of the project:

    We will use two 3.7V 2600mAh lithium batteries to store the power generated by the solar panel. We will use the TP4056 battery charging module to take the power from the solar panel and charge the battery safely. The TP4056 battery charger accepts an input from 4.5V to 6V and regulates the output charge to the battery. All that remains is to choose a solar panel capable of outputting 6V.

    I decided on a 6V 4.5W solar panel. The output current for this is 4.5W / 6V = 750mA. If we assume an efficiency of 85%, this will give us 640mA. As the two batteries in parallel have a total capacity of 5200mAH, we will need to charge them for 5200mAH / 640mA = 8.1 hours at least.

    The batteries operate at 3.7V, so we will need to step up the voltage to 5V to allow for USB charging. We can use a 3.7V to 5V step up converter module to do this. However, keep in mind that this module can draw 2A of current, but the maximum current of the TP4056 battery charger is only 1A. If you charge devices that can draw 2A, you risk burning out the TP4056 battery charger.

    Here’s the completed circuit:

    The red and black wires are connected to the solar panel. There is also a red slide switch at the top right to turn the module off when not in use.

    Home and Industrial Solar Installations

    The solar powered battery charger is nice, but what if we want to use solar power in bigger projects like supplying power to a home?

    If you connect solar panels in series, the voltage of each panel adds up to a higher voltage:

    If solar panels are connected in parallel, the voltage stays the same, but the current from each panel adds to a greater current:

    So it is clear that with clever use of series and parallel combinations, you can get the system voltage and current you require.

    Just like in the solar powered battery charger project above, you also have to consider the maximum voltage and current ratings for the charge controller and batteries.

    Calculating Solar Panel Size

    Let’s assume we want to add solar panels to a small holiday bungalow.

    First we need to calculate an estimated daily kWh usage. To do this, find the wattage rating for all of the appliances in the bungalow. Then estimate how many hours each appliance will be used on an average day. Now calculate the watt-hours (Wh) for each appliance using this formula:

    Watt-hours = watts hours used

    For example, the watt-hours of a 500W refrigerator that operates 12 hours per day is 500W 12 hours = 6,000Wh.

    Allowing for losses and an inefficiency of 30%, we should multiply the watt-hours by 1.3 to get 6000Wh 1.3 = 7,800 Wh.

    Now find the “average daily sun hours” for your location, which can be found by searching online. Now we can calculate the size of solar panel (in watts) that will be needed to provide the watt-hours calculated above.

    To do this, divide the daily watt-hours by the number of average daily sun hours. For example, with five sun hours per day in the example above, the size of the solar panel would need to be:

    So we need a 1,560W solar panel (or larger) to provide the required power. This can be split up into multiple panels though. For example, assuming we buy 100W solar panels, we would need at least 16 panels.

    Hope this article has helped you learn how to set up and use solar panels in your own projects! Be sure to leave a comment below if you have questions about anything.

    Introduction: Load Sharing || Use Solar Panel Safely With TP4056

    About: Make your life more lazy and awesome by the touch of electronics. Check out awesome projects and learn how to build them easily and cheaply. About Tesalex »

    Hi! Today I will show you why you should not use a solar panel directly with TP4056 Li-Ion battery charger, and how you can use solar panel with TP4056 Li-Ion battery charger.

    The problem. I wanted to use a float sensor to measure the level of water in my overhead tank. It has three wires coming out of it. It is basically a single pole double throw switch, which is controlled by the metal ball inside the sensor. The gravity pulls the metal ball up and down depending on the height on which sensor is floating and its counterweight. So, I wanted to make a circuit with LED to show low water level, buzzer to show high water level, a salvaged Li-Ion cell for power along with a boost converter and TP4056 charger. Originally, I planned to charge the Li-Ion cell with a 6V solar panel, but quickly realized the problem with it. The LED/buzzer will continue to draw current if the connection is not broken which would mean the TP4056 will not realize that the battery is full and continue to feed power to it. This can lead to overcharging of Li-Ion cell and in a worst-case scenario the battery can blow up. To avoid this, we can add a switch to cut off the power when battery is charging but that would require a manual intervention which in my case was not possible. The solution is to still add a switch, but in this case, it will be an automatic switch and will cut the power to the load whenever charger is connected and as an awesome bonus, will feed the load with its own power. Let’s see how we can achieve that.


    Please find the list of the parts I used below, along with some affiliate links.

    Step 1: Watch the Video

    Watch the video to get a visual understanding of how the circuit is working.

    Step 2: Load Sharing

    The solution, or rather the switching circuit is called load sharing and contains 3 components, a P-channel MOSFET, a Schottky diode and a pull-down resistor. Let’s understand its working. When charger is not connected, the gate of the MOSFET is pulled low, that means it is in conducting state and that means the load is connected to the output of TP4056 board. On the other hand, when the charger is turned on, the current chooses the lower resistance path to travel and hence the gate is pulled high, which means the MOSFET in not conducting anymore, disconnecting the load from TP4056. The diode is to make sure that current doesn’t flow from the battery to the charger when the MOSFET is conducting. Now that we understand the circuit, let’s move on to the next section.

    Step 3: Choosing the Parts

    Choosing the parts is as critical as designing the circuit right. You want to make the circuit as efficient as possible and choose the parts that offers the lowest power losses, especially if the load in your circuit is going to draw higher current. In the load sharing circuit, we can optimize two components to keep the losses to a minimum: the P-Channel MOSFET and the diode. You should choose the P-Channel MOSFET that has the lowest ON resistance. Same goes for the diode, it should have a minimum forward voltage drop. You can easily find the components using mouser website. Just search for what you want, add your requirements in the filter and there you go. It is really handy. I chose IRF4905 which has 20 mOhms of ON resistance and 1N5819 which has forward voltage drop of 0.4 Volts.

    Step 4: Making the Circuit

    I skipped prototyping and gathered the components to solder on a perfboard. I will use male headers to solder the TP4056 first. You can use a breadboard to hold the pins straight while soldering it. After individually soldering all the 6 headers to the board, I somehow managed to put it on the perfboard, as the pins were not aligning with holes on the perfboard. I had to bend some headers. After that, I soldered it in the perfboard. Again, to solder the boost converter I will make use of the male headers but the holes are a bit too big in the boost module. So, I will solder the headers first on the perfboard. The headers generally don’t easily fit in the perfboard, I use a hand drill to enlarge the holes a bit. After soldering the headers, I can now rest the boost converter on top of it and solder it to the headers. I will use male headers to connect everything that is not on the board, like the battery, LEDs and buzzer etc. I avoid using wires wherever possible. If the points are close enough, I use solder itself to make the connections. If it is far, I use leftover terminals from LEDs, diodes, or transistors to make connections. You can bend them at your will and are very easy to solder. The VIN of buck module connects to OUT of TP4056, and I connected OUT- of TP4056 to VOUT- of buck converter as VIN- and VOUT- as shorted making the connection length a little shorter. Now before making further connection, let’s first adjust the output of buck converter to 5 Volts. By the way DO NOT CONNECT wires to batteries like I did, it can be very dangerous. I disconnected one of the wires after the battery was not required anymore for safety. I finished the remaining circuit off-camera as it was a pretty normal soldering. I used jumpers when there was no place left in the bottom area. I also had to use one wire to connect the gate to 5V input. Doing a quick continuity test to make sure everything is connected correctly.

    Time to see if the circuit works. We are getting battery voltage and 5 Volts at correct places, so that’s good. I used an LED with a current limiting resistor to check the output. It is glowing that means the MOSFET is conducting. After that I connected a charger. I am using a power bank to imitate the charger. As soon as you connect it, nothing special happens except this blue LED glowing up showing the battery is full. Now I am disconnecting the positive pin of the LED from output leaving its negative pin there. The positive will connect to gate using an alligator clip to visualize the changes in gate voltage. I connected my battery again and the LED did not light up, meaning gate is pulled low as expected. When you connect a charger though, it lights up that means gate is pulled high and the MOSFET is not conducting. If I connect the LED back to output again, we can see it is glowing taking power from the power bank itself. That means our circuit is working fine.

    Step 5: Completing the Circuit

    I added some more female headers for the float sensor and the two loads it will control. Also, I soldered resistor for LED with the header itself so that the LED can be connected directly. I connected the pole of sensor to middle header and throws to either side and one LED. Let’s connect the power. The circuit is working perfectly fine with the sensor as well. I connected an LED to the other throw as well. The resistor for that is wrapped around its leg. Working just fine. Everything said, I plan not to use the solar panel for various reasons, and instead use a 5V adaptor to charge it, which only turns on when the water pump turns on. This load sharing circuit would still be required.

    Lastly, my plan is to use a buzzer instead of the green LED, but that can be a problem. When the tank is full, the sensor can stay in that position for a long time until the water level reduces, and I don’t want buzzer to keep buzzing until someone takes a bath. To solve that I connected positive of that throw to 5V input, which only turns on when the water pump is on. That means buzzer will only make noise until the pump is on. Once it is turned off buzzer will also turn off.

    Step 6: Done!

    Thanks for reading! If you enjoyed that Instructables, please consider subscribing and also take a look at our YouTube channel where we post more stuffs like this. Have a nice one!

    SparkFun Sunny Buddy. MPPT Solar Charger





    Creative Commons images are CC BY 2.0

    SparkFun Sunny Buddy. MPPT Solar Charger

    This is the Sunny Buddy, a maximum power point tracking (MPPT) solar charger for single-cell LiPo batteries. This MPPT solar charger provide you with the ability to get the most possible power out of your solar panel or other photovoltaic device and into a rechargable LiPo battery. Set-up is easy as well, just plug your solar panel into one side of the Sunny Buddy and your battery into the other and you are good to start charging!

    The output of the Sunny Buddy is intended to charge a single polymer lithium ion cell. The load should be connected in parallel with the battery. By default, the Sunny Buddy comes set to a maximum charge current of 450mA with a maximum recommended input of 20V (minimum 6V). It’s recommended that batteries not be charged at greater than their capacity rating; thus, the smallest battery that should be charged with the Sunny Buddy is 450mAh.

    Each Sunny Buddy comes equipped with a LT3652 power tracking 2A battery charging circuit and pre-installed barrel jack and 2-pin JST connectors with unpopulated areas to install your own personal 3.5mm screw terminals for added input/output options. This revision also adds a potentiometer to the input to set the holding voltage for MPPT and we’ve also tweeked the feedback resistors on the output to change the float voltage.

    October 10, 2016

    What does a baby elephant weigh? How much impact force does a jump have? Answer these questions and more by building your very own IoT industrial scale using the SparkFun OpenScale.

    Core Skill: Electrical Prototyping

    If it requires power, you need to know how much, what all the pins do, and how to hook it up. You may need to reference datasheets, schematics, and know the ins and outs of electronics.

    Skill Level: Competent. You will be required to reference a datasheet or schematic to know how to use a component. Your knowledge of a datasheet will only require basic features like power requirements, pinouts, or communications type. Also, you may need a power supply that?s greater than 12V or more than 1A worth of current. See all skill levels

    Комментарии и мнения владельцев

    Looking for answers to technical questions?

    We welcome your Комментарии и мнения владельцев and suggestions below. However, if you are looking for solutions to technical questions please see our Technical Assistance page.

    Are there any plans to make a version of this with a built in Battery Babysitter chip? (BQ27441-G1A from PRT-13777) Or perhaps a version or the Battery Babysitter that can handle the OC voltage of a solar panel? Or a breakout for the BQ27441-G1A (or similar) without the charger, that can be used in conjunction with the Sunny Buddy? I want to build a remote environmental sensor and I want to be able to monitor the battery health to 1) predict when the battery would need to be replaced 2) reduce reporting frequency (sensor power-up and/or uplink) if there’s not much sun for a while 3) whether to increase the size of the panel. How much current can the load traces handle in case I need to power a boost converter? Do you have a part # for a 2A inductor that will fit on this board to fully utilize the 2A capability of the LT3652?

    Am I correct in assuming that this will NOT work with this battery, since that’s a 3-cell battery, and this is designed for a single-cell battery? Can anyone clarify? EDIT: Or maybe I can use that battery with this product, because it’s still 3.7V and the batteries are in parallel?

    You’re right, it’s still a low-voltage parallel cell pack that acts like a single cell (more or less), so you can charge it with this. HOWEVER, since the maximum charge rate of this charger is only 450mA, you’ll have a hard time fully charging that 6Ah cell with this during a single day. That’s not to say that you can’t use it, just that a smaller (cheaper) battery will likely give you as much as you can possibly get out of coupling that with the Sunny Buddy.

    If I understand the previous response, SFUptownMaker was specifying that due to the enormous charge capacity of the battery and the low charge rate, the time it takes to charge the battery to full capacity is essentially longer than there are hours of daylight in a day. Therefore, the battery is not ideal for this battery charger, but can still be used as all three cells are connected in parallel (i.e. it acts like a single cell battery). If I remember correctly, the charger can’t be used with multi-cell batteries like the 7.4V, 12.1V, etc. batteries. In applications with the larger capacity 6Ah battery, most users should probably be using a significantly smaller portion of the battery’s capacity for day to day use and relying on the battery’s capacity for days without sunlight (i.e. rain, cloudy days, etc.). Again, you would also need to be using less power that you would normally get throughout the day so that you can build the reserve power back up in the battery.

    I have an 18V 9W solar panel and 10000mAh battery. I’m looking to maximize the charging rate for this battery. If I go the full 2A is that a 0.05ohm resistor on RSEN? If not, what would you recommend in this configuration? If 0.05ohm is correct, any ideas where to source them, they seem a bit hard to find. Thanks!

    Otherwise, if you still need help, please use the link in the banner above to get help from our technical support team.

    Why is the inductor value so high (68μH)? Reviewing the data sheet, the Inductor Selection formula doesn’t seem call for anything near this much for a single cell lithium polymer.

    Hi there, it sounds like you are looking for technical assistance. Please use the link in the banner above, to get started with posting a topic in our forums. Our technical support team will do their best to assist you. That being said, there is a possibility that might have been what we had in our inventory that fit the design. (As opposed to the cost of sourcing and holding 5000 pcs. of another inductor value.) Unfortunately, the original engineer isn’t around for me to ask. If you post a topic on our forums, our TS team can look into it (maybe it was supposed to be 6.8µH. ).

    • Can I use this with a 14V 4S Lipo battery, or does it only output ~4V on the charge terminals? Previous people have asked this and it seems that one of the cells will overcharge and some will undercharge and then explode, right?
    • If only 4V output, can I use 4 of these in series to get a load of around 14V? I want to attach a 15W solar panel or 4 3.5W panels to this setup and output 12V to power a motor/redboard/other gear.
    • The max charging is only 450mA, what if my load is higher, like 1A 12V draw, will this work, or is it directly correlated to the charging power as well so I can only have a load of 4V @ 0.45A?
    • Member #647289 mentioned charging a lifenmpo4 battery instead. The diagram shows that it is possible to charge this type of battery, but what exact components would I need to change out?

    In other words, I absolutely need 12V output and a light weight solar/batt setup around 1-4AH. Everything else is negotiable. Is this the part I need, and if so, how can I make it work? Thank you!

    12- You can definitely attach four of these in series to charge multiple cells, but if you’re not absolutely sure what you’re doing, I’d steer clear of it, because you could easily start a fire doing it wrong. You want an individual solar cell for each Sunny Buddy in the system, as well. The loads should be in series but the cells should not. 3- if your load is higher than 450mA, the extra current will be drawn from the battery. If you don’t have a battery attached, you’ll brown out the system. 4- I have no experience with LiFe chemistry batteries. I’d refer you to the datasheet, which is linked above.

    Thank you for the quick reply, this is great to learn about! One quick last question, can I output 12V with this controller, or does it have to be 4V?

    It may be possible to change the circuit to charge 12V batteries; I’m not sure if that’s just a resistor change or if more is necessary for it. Again, I’d refer you to the datasheet to see what the circuit for SLA charging looks like.

    Since the solar panels you sell are rated at the minimum voltage for the Sunny Buddy, would hooking up super caps to the solar panel like the technique done in this tutorial be feasible or even work with the Sunny Buddy? Would that just mess up the power tracking?

    Advice on buying solar panels for this would be welcome, as a note in the Documentation section. I know enough to be confused. Many 12v panels on sale include a regulator, and are powered by panels which will generate up to 22v. more than recommended for the buddy, but using a Buddy downstream of another controller seems daft. And those controllers, it seems fail fairly often, anyway. The power a panel can generate is clearly a buying criterion. Easy to miss how little power some panels can produce. A 14v panel would seem perfect. Buddy spec’d for 6-20. I saw few if any of the common 10v panels. Hooking two 6v panels in series might work. What Could Possibly Go Wrong? Ah. some places on the internet say that if one is in shadow, it will effectively open the circuit, and you won’t get any volts rather than, say 8v. The same sources speak of bypass diodes. but the correct spec for such a diode. and which way to connect it. wasn’t clear to me. So. get the idea.

    I don’t see any reason why not. The charger may throttle the current in a way that’s suitable for a LiPo but unnecessary for a supercap, leading to longer charge times than strictly necessary, however.

    Cool, thanks 🙂 the application I’m looking at would have this outside during the Illinois summer and winter, so ambient air temps will vary from. 10 to 110F, which definitely won’t work for lithium batteries. I thought a high value supercap pair would fit the bill well though. Thought this would work for that, but wanted to ask to be sure 🙂

    Hello! SO the problem I have is the battery is not charging by itself without a load. I’ve measured the Load voltage and the Battery terminal voltage with the panel hooked up and its around 2.1 V and i know that’s not enough to charge the battery. So is there something i can do or is the unit faulty and i should order a new one? Btw my solar panel is an 18V 5W.

    What’s the open-circuit voltage, with no battery attached? That should be pretty close to 4.05V. If it’s not, you probably have a bad battery that’s dragging the voltage down. 2.1V is way low for even a depleted LiPo cell.

    Yep as i said the problem was that i wasnt in direct sunlight. When i moved it I saw the 4.04 V. Thanks for the help!

    I am looking to solar charge a 3.7V/7.8Ah battery pack ( and while searching for the LT3652 I found your SunnyBuddy. In the schematics, the load is connected in parallel to the battery, while on the Linear’s typical application it is through a schottky diode to separate the load from the battery charge. Could you please explain why you have connected the load parallel to the battery? My idea is to allow maximum charge to the battery, while the load is consuming from the actual power source directly without affecting the charge.

    The schottky stops the load from sourcing current into the battery; as that’s not usually a problem, we’ve omitted it, as it’s not without cost: it reduces by one diode drop (as much as 0.5V) the voltage range across which the battery can source current to the load, and that can represent a substantial portion of the battery’s total charge.

    Is it always set to 2.8V between the Set and GND? Does it depend on the Solar Panel used? I don’t see from the schematics and data sheet why 2.8V is required for MPPT. What is that 90% of?

    Yes, it’s always 2.8V. That’s the voltage the MPPT will attempt to keep on that pin, and it’s the scaled voltage of the solar cell’s output. When the cell is at peak efficiency, if you set that pin to 2.8V, the output will servo to attempt to KEEP that value at 2.8V and thus, to keep the cell’s operation at peak efficiency.

    Can I use secondary barrel jack to charge the battery using USB power? Can I do this parallel with solar charging?

    Not easily. You’d have to put some kind of diode inline with both supplies (the PV and the USB) to stop the higher voltage of the two backfeeding current into the lower voltage supply, and that would decrease the efficiency of the PV supply. There’s no easy provision for doing that on the board, so you’d have to hack it into the cable or cut traces on the PCB.

    Please remove references to MPPT, this chip does not actually do MPPT! The reference point is hardwired in, and assumes a maximum input voltage under full sun conditions. The only way to do true MPPT is to periodically let the solar panel voltage float open circuit (while running from battery) and then load the solar panel at ~80% of that open circuit voltage. Otherwise you are not getting maximum power from your solar panel. This is what the BQ25570 does, please use it instead!

    BQ25570 According to the data sheet it’s only got about a 200mA charge rate and an input voltage range of 0.1 to 5.1V so it wouldn’t be usable for 6V solar panels. It does seem like it would be amazing for smaller panels (down to a single cell), peltier (thermionic) devices, or even speakers. i.e. Energy harvesting applications. On the other hand, if the shut-down pin were broken out (on the LT3652) then you could shut down the charger and measure the OCV yourself and use a digital pot to trim the tracking voltage. But it isn’t.

    Should the charger work if powered by USB as opposed to solar? It only seems to be drawing 3mA from my power supply and I am confused as to why it isn’t higher?

    Okay, thanks for this. My solar panels seem to be giving open-circuit voltages between 4.5V and 6V. Do you have any recommendations of where I should look for preferable solar charger?

    If you have more than one solar panel, you can stack them by adding another barrel jack and adjusting the solder jumpers on the board.

    Not sure what the stacking idea is. is it more than a convenient way to connect two panels in parallel? Series? (From what you say, I guess series? Guess right?) Is there any advantage to using the two sockets/adjusting solder jumpers beyond mere mechanical considerations?

    If you follow the instructions I linked above, you’ll be adding a second panel in series with the first. I think that’s advantageous because a partially shaded panel won’t act as a load on the other panel, as would be the case with parallel panels.

    Why did you decide not to connect the NTC pin to some header? There is plenty of free space on the board.

    Does anyone know of any way to get the charge status? For my project I need to be able to know how charged to battery is and send that to a microcontroller.

    Hi, I’ve been running a couple of the v1.0 versions and the update adds some useful features. Just one query on the v1.0, however, I’d like to add a charging indicator (LED or even something I can measure) to the circuit. I can’t quite work out how the CHG and FAULT connections operate (I’ve had a look at the LT3652) but I’m struggling. Thanks

    CHG and FAULT are both open-drain active low devices, so they can’t drive an LED high. You’ll need to connect your LED anode to a supply voltage (say, VOUT), and then tie the cathode to the CHG or FAULT pin (through a resistor).

    Could I use CHG and FAULT somehow to set pins on an Arduino (specifically an Electric Imp) high or low, so I could get informed about the state?

    Yes; the outputs are open-drain, so you’ll need to either enable a pull-up resistor in the firmware of the target device or add an external pull-up resistor.

    Does the Sunny Buddy prevent the lipo from being run at too low of a voltage? and if so what is cutoff set to? Thanks!

    It does not. It is charge limited, and has a high-voltage cutoff, but for low voltage, it relies on the protection circuitry of the cell, if it has any.

    I’ve been looking for a nice, clean way to power some 5v gear with a LiPo and Solar. The best I’ve been able to come up with is the SunnyBuddy and a LiPower. Any better suggestions? Would SparkFun consider a version of the SunnyBuddy with integrated boost converter? That’d be awesome!

    That’s probably your best bet. As for the integrated 5V boost, that’s tough. There’s a large body of existing stuff that wants 5V, but things are also generally moving towards 3.3V, too.

    If the solar panel is producing zero voltage or is disconnected will the load pin draw from the battery?

    Hmm. I looked at the hook up guide and it said the load can’t be too heavy. I was going to make an iPad charger out of this. The only problem with that is for an iPad to not take a day to charge 😉 I need to supply the iPad with 2 amperes (roughly how much the wall adapter supplies). Is 2A too much for this board?

    I just realized that 2 Amperes is unrealistic as the charge rate of the board is 450mA shared between the battery and the load. I will have to figure out how to use transistors as current collectors or something.

    Hi, Thank you so much for sharing this awesome product ! I have two questions: 1. Is Sunny Buddy compatible with this 12V 10W solar panel ? 2. Can I use the default electronic design of Sunny Buddy for charge single Lithium ion polymer. 3.7v 2000mAh ? great thanks

    It should work fine for that panel. As for changing the charge current, you’ll need to adjust the inductor and possibly the diode, but generally it should be fairly easy to adjust.

    Hi, I connected two solar cells of respectively 4V and 44mA@pmpp in serie to obtain 8V in order to plug them in the sunny buddy, to charge a 850mAh 3.7V battery. But when I set Vset at 2.8V in full sun (the solar cells then deliver ~9V), I only observe a charge current of 7mA (battery is at 3.9V so not entirely charged). Can someone please explain me why I only have 20% of the th. pmpp current at sunny buddy output? Thanks

    The part dials back the charge current based on the cell voltage, and attempts to keep the cell voltage at around 4.0V (derating the upper limit improves battery life). That may be why you’re seeing that. Try with a more deeply discharged battery.

    I just measured and my solar panel actually delivers 22V on a real sunny day. Is that too much for this Buddy? If so, what would be the easiest way to bring it down?

    Most likely not. I doubt it’s got the efficiency and the impulse handling capability for that. Have you looked at our energy harvester board?

    Hi there, I have purchased 2 sunny buddy’s as I have a 2 cell Li-po battery and I was told I could use 2 sunny buddy’s in series to charge the battery. I am a little confused to how the circuit would go, as there is not a diagram for this on the data sheet. My 2 cell battery has a balance charging lead consisting of 3 wires, and a discharge lead consisting of 2 wires. I have 2 solar panels each for one MPPT, but would i connect each MPPT to the batteries balance lead with a shared ground? And then how would I go about taking to load from the battery? Would it come from the batteries discharge lead or would it go through the MPPT’s load port? The load is a single motor, the need for 2 cells is due to the 7.4V needed for the motor to operate at the correct conditions. Many thanks, Sacha.

    Neither the panels nor the Sunny Buddies share a ground. Connect the solar panels independently of one another to the sunny buddies, then tie the ground of one Sunny Buddy to the V output of the other. That connected node then gets tied to the connected node between the two batteries, and the unconnected ground of the low side sunny buddy gets connected to the black discharge wire. The red discharge wire should be connected to the V on the high side sunny buddy. Given that you have a 2S battery, I’m not sure that the center wire on the balance connector is, in fact, just connected to the middle of the battery stack. If there’s something else in there, this isn’t going to work. A far better way is to get two individual LiPo cells and connect them up.

    Hello, I’ve bought this product and I’m wondering if I can charge a lithium ion battery 4.2V with Sunny buddy? I know that it is design to charge lithium-ion polymer battery type not lithium ion(Li-ion). If so, should I change R2,R3 and R6 resistors to get 4.2V? Thanks, Reno

    It should. The 4.0V float voltage was selected because that prolongs the life of the battery; you can change those resistors to get to 4.2V if you really think it’s important, but it gains you very little extra energy.

    Hola, I have a sunny buddy and plan to regulate the output voltage of three 12V 5W panels in parallel (0.125 A) to 5V 3A to charge two power banks. Is it possible to INCREASE the output current of the sunny buddy to 3 A? If so, how?

    Guys, great product! I have 4 of them working perfectly! Just a question, what can I do in order to set the charging voltage from 4V to 4.2V? Which resistor in the eagle file should I change? Tnx a lot!

    R2, R6, and R7 all need to be adjusted, and the directions for setting those values is in the datasheet.

    hi there, in the data sheet, it says this can be used to charge a 2s liFePo4 and has a circuit diagram with a solar panel inputting the voltage. I apologise I only have basic knowledge with electronics, so is that diagram showing what resistors, capacitors etc which would be needed to make this work with a 2 cell battery? Cheers, Leon.

    Yes. Take a look at our schematic and change out the components to match what’s in the datasheet and you’ll have it. I’m not a big fan of that sort of charging, though, because the cells can become unbalanced, resulting in overcharging of some cells and undercharging of others.

    Brilliant, thanks for your quick reply, ideally I would like to charge a 2 cell lipo battery, but there is no diagram for that modification. Would that be possible? I would of thought the cells just need a higher charging voltage supplied. This setup would only be charging the battery occasionally, it would be balanced charged the majority of the time. Thanks, Leon.

    There’s a diagram for a 2-cell LiPo from 12V wall adapter that will work; the only difference is the set voltage of the input side divider. That you’ll need to figure out based on the solar cells you’re using. Raising the voltage is one part of the equation; however, for best results you want to balance the cells continuously. Charging is really a current-mode operation, rather than voltage mode: you push a certain current into the cells until the voltage of the cells reaches a defined set point. Say the set point you want is 4.0V per cell (a decent target; below 100% but it’ll give you a bit more life). That’s 8.0V when you have two cells. Without some extra circuitry, you have no way of knowing whether that 8.0V is 4.0V and 4.0V or 3.95V and 4.05V or whatever. It’s a guarantee that one of the cells will charge more slowly (or less efficiently, if you prefer) than the other. Even a small difference will add up over time, and eventually, you’ll have one cell well ahead of the other. At some point, one of them will be at the maximum healthy level for a LiPo (4.2V) while the other is still low enough that the sum will be less than the set point of 8.0V we chose earlier (i.e., 3.8V or less). The charger will still be pushing the current in, trying to get the sum voltage up to the set point, and then you can have trouble. Either the safety cut-off trips and you get a partial charge, or the good cell (the more efficient one) pops. Either way, it’s not what you’re after.

    Nice, I am going to go with the 2 cell lifepo4 setup. I have been looking over the diagram for that and I am a little confused, I apologise I am a aero engineering student and my electronics skills aren’t great. The diagram for the 2 cell lifepo4 shows the resistors and diodes etc, do they need to be on the circuit board in place of some existing original components? Or are they connected outside of the board. I’m confused if the pin diagram represents the chip on the board or the board itself. I cannot see the wiring diagram for the original board on the data sheet. Also I’m finding it quite difficult to find some of the really specific resisters like 542k 459k and 0.05k. Thanks Leon.

    Hi there, I am partaking in a solar powered model aircraft project for my dissertation. Basically I am using a 3s lipo, but i do not need to charge it as my motors draw will be more than the power produced by the solar array. Therefore I need to draw all the current from the solar array and some from the battery. Does this device allow to do this if I had a 1s lipo? What could I do to allow this configuration on a 3s lipo? Many thanks, Sacha.

    You could use three chargers and three solar cells, one across each cell. It’s possible to redesign the circuit on the SunnyBuddy to charge up to 3 cells in series but that would require changing a number of components. See the datasheet for more details on that option.

    Is the V_set adjustment to do with the Vin Regulation and why are we setting it to 2.8V? Do I need to adjust this to 2.8V first and then adjust pot to get maximum current at JP3 current monitor? Thanks!

    The SunnyBuddy will servo the output current in an attempt to keep the input current at a level where the value at that pin is 2.8V. It will never, however, source more than about 400mA to the load. Your best bet is to put a depleted LiPo on the SunnyBuddy, to max the charge current, then go out in full sun and tweak the pot until the sense voltage is at 2.8V.

    I have a 11.1 v lipo battery that I need to connect to the mppt but the battery has a 4 pin lead instead of a two pin one so I can’t connect it. Is there a way I can make this happen?

    Probably not. The SunnyBuddy only puts out up to 4.0V, so it can only charge a single LiPo cell. What you have is a pack of three cells in series.

    Hi there, is it possible to charge a 1s lipo battery with this whilst discharging it? If so how would it be connected? Many thanks, Sacha.

    Does anyone have any idea why the float voltage for the board is set to 4.0V instead of 4.2V?? With this setting you can never fully charge a single cell lithium ion or polymer battery.

    I would like to use the sunny buddy with a 5v Nano. Is it possible to solar charge two Polymer Lithium Ion Batteries. 3.7v 2000mAh in series, so that I can get the output voltage I need for the Nano and the 5v sensors and accessories I will be using? This will be a remote setup and unfortunately I have several accessories that require a mandatory 5v. Thanks

    Not easily. If you use two solar panels and two Sunny Buddies and connect them only at the batteries, you can charge the two batteries independently of one another. Another possibility you may want to consider is using something like the LiPower boost converter to achieve your 5V. It’ll sting you a bit on efficiency but if you’re careful you may well be able to handle it.

    I’ve built a power bank (solar buddy battery USB power boost) but I can’t take much power out of it because of the small battery I have. Is it worth putting a Polymer Lithium Ion Battery. 3.7v 4000mAh on the solar buddy? If so is there a single cell battery with even bigger capacity?

    Yes and no. We have a 6Ah battery pack which has the cells in parallel, so they can be used with the Sunny Buddy. Bear in mind, however, that under ideal circumstances, the Sunny Buddy only pushes out about half an amp. You can boost that a bit with a new current sense resistor but you’re unlikely to be able to fully charge the 6Ah battery in one day, unless you’re in the extreme north or south during summer.

    Thanks for the quick answer. Of course I was not expecting to charge a 6Ah battery in one day. But at least it would use as much energy as possible through 1 / 2 days and I would be able to charge more power hungry devices with it, right?

    There’s a ceiling to the amount of energy you can burn in one 24 hour period- there’s no point in putting a battery larger than that on your system. 4000mAh is about at that limit.

    Can I use a battery like this one with the solar buddy? BATTERY-LIPO4400mAh. The Seller says it has the cells in parallel.

    Does the sunny buddy normally make a high pitched whine while charging? I just hooked mine up to a 2000mah battery, a 2w panel (~6v, 333mah) with a spark core as the load and the SB board is pretty loud. I have tried different, smaller panels and the whine is about the same.

    We’ve noticed this; it’s harmonics from the switching regulator causing either the coil in the inductor to vibrate or the ceramic element in one of the capacitors to act as a piezo element. It’s annoying but harmless. You could try dampening the vibrations of either element with a little epoxy.

    Thanks for the reply, it is a bit annoying, but glad to hear it’s not anything bad happening. I tuned the voltage set potentiometer a bit and it immediately went away.

    After chatting with Allison (who was very helpful) I should make a point on this item: Yes, you can use an 18650 BUT It will discharge into oblivion if you don’t have a protection circuit for the cell! And there is the potential for over-discharge-current (over 1C)! This is intended to be used with a cell that HAS PROTECTION CIRCUITRY ALREADY ON-BOARD, or you have to provide it yourself! What I would like to see is a version of this board that has a cell holder for an 18650 and that has the protection circuitry built into it for that kind of cell (not to replace this item, but as an alternative).

    A few questions: 1) What are the specs of supported solar panels? The hookup guide says the SF small panel will work but that’s listed as only having a 4.5V / 100mA output. How will that work if the minimum voltage rating for this board is 6V? 2) Since the maximum charge current is 450mA, does that mean that only panels supplying less than 450mA of power should be used? 3) Is it possible to use this as a general LiPo charging circuit, if the solar input is switched out for a wal-wart supplying 6V? If this would work, what would be the maximum current that could be supplied?

    • The specs of the supported solar panels are 6-20V. You can stack the small Solar Cells (make sure to reconfigure the jumpers as directed), and be good to go.
    • You can use panels that have a supply greater than 450mA, but the Sunny Buddy will only pull 450mA. As long as you keep it under 20V it should be good to go.
    • Yup, if you plug a wall-wart into the sunny buddy, it will charge your battery. Maximum current should be kept under 20V. I can confirm this, because I have a 9V wallwart plugged into my Sunnybuddy charging the battery on my desk at this moment. 🙂

    I am using the sunny buddy regulate the output voltage of two 12W 5V panels in parallel to charge a 3000 mAH powerbank. Does it make sense to replace the Rsense value with 0.22 ohm so that I get a output charge current of 0.9 amp?

    You may find that at 900mA your power inductor starts to saturate. That’s dangerously close to the 1.05A spec limit of the part. Also, 5V is too low a voltage; the SunnyBuddy won’t start up below ~6V. Put the panels in series, and you’ll probably be okay; in a step-down system, the inductor current shouldn’t be too much higher (if at all) than the output current.

    Hi! I want to charge a 6V Lead acid battery using these, I was thinking on changing the voltage divider values to get the one required. Do you think I can desolder this resistors and put instead a trim pot with a higher resistance value?

    It’s not quite that simple. Please refer to the datasheet on circuitry changes needed to adopt this to charge a lead-acid battery. I think it can be done but you may need to change more than just the feedback resistors.

    Customer Reviews

    4.2 out of 5

    6 of 6 found this helpful:

    Exceeded Expectations in Emergency Situation

    about 6 years ago by Member #984253 verified purchaser

    A little introduction is in order;

    This part was used in a company project in Cheyenne, Wyoming. For the month prior to its installation, we’d been having trouble with power outages of the project, a solar-driven sensor, and finally a decision was made to massively boost the power supply by a factor of 10x to provide enough electricity. However, that meant using solar panels with a nominal voltage of 25 volts and a maximum current of 6 amps.

    The datasheet on the driving chip mentioned a max input voltage of 40V and a nominal input voltage of no more than 32, so all good there. It also mentioned that the charger only allowed switching current until the voltage on the SENSE pin was reached. I’d soldered a 0.075 9W resistor into R_SEN, limiting its current output to a max of 4.5454 amps (exceeding the output current) and proceeded with the assumption that the IC would automatically limit its output current even if it could produce more.

    I was correct. Though the current output reached the inductor’s saturation levels and thus stopped it behaving like a true inductor, the Sunny Buddy caught the passed-through voltage and cut off the power supply (thus preventing the 25 volts from hurting anything on the output side). It’s exceeded my expectations in performing and, to give all those out there an idea of how robust it is, is currently connected to a 100W solar panel display and a 6600mAh battery (along with the load).

    So long as you don’t exceed the maximum recommended voltage input don’t worry about the current drawn; the Sunny Buddy automatically limits that. It’s much better than the current Adafruit solar charger and will be my go-to from here on out.

    4 of 4 found this helpful:

    Neat little board!

    about 8 years ago by Member #529167 verified purchaser

    I bought this board to use with the Large Solar Panel from this site. It’s been really interesting to experiment with. The flexibility of the footprints on the board is really nice because it allowed me to attach terminal blocks to the inputs so I could connect the panel voltage to one and a current sensor to the other. Great!

    One suggestion for this board: consider adding an independent voltage input to the set pin so that the MPPT can be managed by a controller.

    4 of 4 found this helpful:

    Keeps output below 4v, but I wish the NTC pin went somewhere.

    about 6 years ago by Member #90144 verified purchaser

    This charger was great for me. one feature not described in many chargers is whether the charger will always output 3 volts even if the solar panel voltage goes above that. I tried a few other chips which all listed passing through the panel voltage as a feature. This is actually big design annoyance for 3v devices. However, the sunny buddy will always output max 4v even without the battery plugged in, even when charging. even when the solar panel voltage goes to 15v. Great!

    The big issue for me with this device is the NTC pin for the thermistor is NOT broken out. For weather stations and things which are outside (where you would use this device) you should not charge below 0C. The chip has a pin deticated to reading a 10K thermistor to prevent charging above 50C? and below 0C. Even if this pin went to a small via it would be great, but it is actually just a pad. TL;DR; if you want to connect a thermistor be prepared to solder some small stuff.

    9 of 9 found this helpful:

    Neat board, works well.

    about 8 years ago by Member #496446 verified purchaser

    simple, solar, battery, charger, circuits, module

    1 of 2 found this helpful:

    Neat All-in-One Solution to Power Your Circuit from Solar Panels

    about 7 years ago by fratti verified purchaser

    While I haven’t used it extensively so far, preliminary testing seems to confirm that it does what it says it does, and quite well.

    There are a few minor inconveniences though. The first one being that the jumpers for configuring the amount of panels attached aren’t actual jumpers, but pads that are solder-bridged. While it certainly keeps the cost down this way, it makes it somewhat of a hassle to change the setup quickly (unless you’re the kind of person who always has a hot soldering iron nearby).

    The second minor annoyance is that for tuning it right, you have to hold the multimeter probes onto the SET and GND pads, but the pads are so small it’s easy to slip off with the probes in one hand while trying to tweak the little knob with the other. Though this could also be the fault of my probes, or my hands.

    While a bit bare on the side of soldered-on components, it definitely does what you want it to do.


    about 2 years ago by Member #308887 verified purchaser

    I bought this because I wanted an off-the-shelf solution. I didn’t want to read the LT3652 datasheet. I didn’t want to look at schematics. Of course I ended up doing just that. I feel like if the documentation were just a little better, everything could have been a lot easier. Most of my problems revolved around the set voltage. The directions said to set it to 2.8V with the panel in direct sunlight. The cutoff is around 2.7V which pretty much guarantees it will ONLY charge in direct sunlight. For whatever reason (insert lawyers name here), the float voltage was set to 4.0V. I’m not sure why it wasn’t set to 4.2V for LiPo, effectively robbing you of about 40% of your battery capacity. Since I did have to look at the schematics, please allow me to make the following suggestion. Reference designators are only useful if you put them on the board. On this board there is ample room for reference designators on every part. Makes debugging a lot easier. LED’s on the charge and fault pins would have been a nice touch.

    Very helpful for our students

    about 7 years ago by Member #853814 verified purchaser

    In the education, how the use solar energy in consumer applications it a very compact device with excellent instructions

    Best product available, but no NTC pin

    about 4 years ago by Member #1467674 verified purchaser

    Sunny Buddy is really the best product of its kind available on the market today. But there is a problem. The LT3652 chip supports battery temperature monitoring using NTC, which is important for LiOn battery safety, but the Sunny Buddy for some unknown reason has this pin inaccessible, no track connected to it.

    Regardless of this minor flaw, the product is amazing and worth it.

    Good but could be better

    about 3 years ago by Member #273747 verified purchaser

    It would be better if it had a fuel gage with an I2C interface.

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