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9 Simple Solar Battery Charger Circuits. Solar float charger

9 Simple Solar Battery Charger Circuits. Solar float charger

    Can I Leave A Solar Trickle Charger On All The Time?

    A solar trickle charger is a tool that uses solar power to charge various devices. These low-power charging devices are excellent for charging smartphones, laptops, or tablets.

    They can be left plugged in all the time, providing an outlet for these devices at home without using grid power.

    It’s also a great option for battery charging and can be used with or without overcharge protection, although it is generally recommended to use a solar trickle charger with overcharge protection.

    In general, a solar trickle charger can be left connected to a battery all the time. Most commercial chargers are designed to either generate very low power or incorporate over-charge protection. It’s always preferable to use a simple solar charge controller with any solar charging application.

    How does a solar trickle charger work?

    A solar trickle charger is powered by a solar panel, which is composed of multiple solar cells – panels used to charge 12 volt batteries have 35 cells and Voc (open circuit voltage) of 21 volts.

    A solar cell generates an electrical current from the sunlight and transfers it to the charging device, which then charges the devices connected to it. The typical power rating for a solar trickle charger is 0.5-10 watts.

    How many watts does it take to charge a battery with a solar panel?

    A solar panel output is measured in watts, and it can vary from product to product. Solar panels can generate up to 350 watts, but solar trickle chargers are very low power, just a few watts.

    In order to charge a battery, you will need a panel to generate more voltage than the battery, and also have a minimum power rating, which is determined by your battery size.

    The big factor affecting solar panel output, assuming it’s unshaded, is the irradiance which is a measure of the amount of the sun’s energy reaching the panel measured in kWh/m2/day or year.

    Incidentally, this value if also known as the peak-sun-hours for a particular location and is used by solar installers to assess solar panel output energy in kWh.

    Very low power solar panels can be left connected all the time

    How much energy does it take to charge a battery?

    Batteries are rated in ampere-hours (Ah). On the face of it, any calculation seems simple – if you have a battery of 50Ah, then you should be able to draw 25 amps for 2 hour. Unfortunately, this is wrong.

    A normal lead-acid car battery should only be discharged to 25% maximum, so it’s effective capacity is much less than its rated capacity in Ah. Even a deep-cycle marine battery should only be discharged between 50% and 80%.

    We need to express battery capacity in energy in Wh rather than Ah – this is done using the following formula:

    Chart showing Ah to Wh conversions 10 to 160 amp-hours

    See the chart below for conversions for various Ah ratings (assumes 12 volt battery):

    How much energy does a single solar panel produce?

    Energy produced in watts depends on irradiance, which is location dependent. A 10 watt solar panel based in Lexington, Kentucky would produce:

    10 x 4.05 peak sun hours = 40.5 Wh of energy per day

    If we had a battery with 20 Ah discharged, that would equal 240 watt-hours so it would take 240/40.5 days to fully recharge = 5.93 days.

    As you can see, trickle chargers are really just for maintaining a battery fully charged, not for recharging when it’s been heavily used.

    Do I need a charge controller?

    A charge controller is a tool that prevents overcharging. The controllers ensure that the battery does not exceed a safe charge current, therefore protecting it from overheating and damage. Charge controllers are generally recommended for charging batteries over 20Ah capacity.

    What is the difference between MPPT and PWM solar controller?

    MPPT stands for Maximum Power Point Tracking, while PWM stands for Pulse Width Modulation. Both of these solar controllers are designed to regulate battery charge current from solar panels.

    However, they do so in a different way. MPPT controllers have the ability to scan the internal resistance of a solar panel and determine which load resistance will result in maximum output from the panel.

    MPPT controller technology then matches it’s resistance to that of the panel to optimize the output. This is the Maximum Power Point of the panel.

    PWM controllers simply maximize this voltage by switching on and off to output as much power as possible using a momentary maximum voltage during on state. They are much less efficient, often delivering up to 30% less charging current than MPPT.

    Solar charge controllers – battery overcharge protection

    How to connect solar trickle charger to a battery?

    If using a solar trickle charge without a charge controller, connection is very simple. Place the solar panel in the sun and attach the crocodile clips to the battery terminals, black to negative and red to positive.

    A charge controller is generally recommended, and connection is not much more complicated. Simply connect the positive and negative solar panel leads to the controller and the controller red and black lead connect to the battery as previously described.

    What size solar trickle charger do I need for a battery?

    The size of the solar trickle charger you need depends on the size of the battery, its state of discharge and how much power you can get from your solar panel.

    It is important to know that it will take longer to charge larger batteries. So, if you have a battery with a larger capacity (more Ah), make sure that your solar trickle charger can match its power requirements.

    Lead acid battery state of charge chart

    The battery terminal voltage is a pretty good indicator of depth of discharge (DoD) for lead acid cells. The battery should be left with no activity for a few hours before. See the chart below for details:

    State Of Charge % (12 V Lead-Acid)

    Battery terminal voltage

    Simple Solar Battery Charger Circuits

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

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

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

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


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

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

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

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

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

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

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

    The current also varies due to the same above reasons.

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

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

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

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

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

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

    Making it Even Simpler

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

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

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

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

    ) Using LM338 as Solar Controller

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

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

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

    Using a Current Control Feature

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

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

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

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

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

    Current Limit Formula:

    R3 may be calculated with the following formula

    simple, solar, battery, charger, circuits, float

    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.

    simple, solar, battery, charger, circuits, float

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

    ) Simple Solar Charger for Street Lights

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

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

    Main Features of this system are:

    1) Voltage controlled Charging

    2) Current Controlled LED Operation

    3) No Relays used, all Solid-State Design

    4) Low Critical Voltage Load Cut-off

    5) Low Voltage and Critical Voltage Indicators

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

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

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

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

    Circuit Diagram

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

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

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

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

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

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

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

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

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

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

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

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

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

    How to Build

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

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

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

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

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

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

    Parts List

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

    Making th 24 watt LED Module

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

    ) Solar Panel Buck Converter Circuit with Over Load Protection

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

    Technical Specifications

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

    Input voltage = 40 to 60 VDC

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

    Output current capacity = 5-10A

    Protection at output = Over current, short circuits etc.

    Small LED indicator for unit operation would be an advantage.

    Appreciate if you could help me designing the circuit.

    Best regards, Deepak

    The Design

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

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

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

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

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

    The above action generates the required bucked voltage across C4,

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

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

    The output may be used for charging the intended battery.

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

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

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

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

    Technical Specifications

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

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

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

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

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

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

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

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

    The Design

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

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

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

    Total intended consumption is = 80 watts.

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

    Multiplying 80 by 12 gives = 960 watt hour.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

    T1, T2 = TIP35 on heatsinks

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

    simple, solar, battery, charger, circuits, float

    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. nbsp3 Terminal Fixed Voltage Regulators – Working and Application Circuits
    • 2. nbspEasy Two Transistor Circuit Projects for School Students
    • 3. nbsp4 Universal Electronic Thermometer Circuits
    • 4. nbsp4 Simple Power Bank Circuits for Mobile Phones
    • 5. nbspTemperature Controlled Relay Switch Circuit
    • 6. nbspHigh Voltage, High Current DC Regulator Circuit

    Soak up the Sun: The 5 Best Solar Battery Chargers for Boats

    It’s a tale as old as (modern) time. You’re in the middle of a favorite show and you get that low-battery warning. We’ve all been there.

    It’s no fun when your electronic devices lose power. It’s bad enough when you’re at home and have to stay attached to the wall. It’s a different story when you’re off-the-grid and anchored out on your boat.

    From chartplotters, GPS, VHF radios and cell phones to fish finders, stereos and blenders (can’t leave out the blender), you need electronic devices on a boat for safety, information, entertainment and what-not. And that means a power source of some sort.

    This is where solar panels and solar battery chargers for boats come into play.

    Charging everything up at home or in the marina is always a great idea. But what if you’re out on the high seas? Or high lake, for that matter.

    Read on to find out how handy and efficient boat solar battery chargers can be.

    What Is a Solar Battery Charger for a Boat?

    A solar battery charger for a boat has two basic parts that work together. The solar panel collects energy from the sun. This energy then goes to the charge controller, which regulates, stores and distributes it.

    All of that collected energy is then deposited into your battery bank (think of it as your very own bank teller, of sorts). Then, when you need it, you simply attach it to your electronic device.

    If the battery is completely empty, the charge controller puts as much energy as possible into it until it reaches a full charge. At this point, it goes into float mode, which maintains the power level automatically.

    The charge controller is a great piece of gear as it improves the charge quality and prevents the battery from overcharging and from loose connections.

    From wind generators and solar panels to boat solar battery chargers, renewable energy is a free (after the initial purchase of the capturing equipment) and a Smart way to go about boating.

    Let’s discuss more about solar battery chargers and how they can provide power and peace of mind for days (and nights) out on the sailboat, liveaboard trawler, pontoon boat or sport fishing boat. Even kayakers can benefit from small solar panel battery chargers.

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    Features of Solar Battery Charger Systems

    Charge Controller

    Also known as a regulator, the charge controller is what puts the energy into your battery. It’s very possible to have a solar panel without one. But you’ll want to make sure you choose a panel that comes with a charge controller.

    Charge controllers are necessary if the panel is more than five watts. The best thing about the charge controller is that it can store the energy for later use. A solar panel alone needs sunlight to work.

    Solar Panels

    The solar panel is the part that collects the energy from the sun. You’ve likely seen them on house rooftops. They’re becoming more and more prevalent on boats.

    Pulse Width Modulation

    Pulse width modulation (PWM) is the temperature compensation that protects the battery from things like overcharging and frequent charging. This is a must-have safety and efficiency feature. You don’t want to have to go out and buy new batteries every Monday.


    Self-regulating boat solar battery chargers don’t have a built-in controller. Every boater is different, of course, but anything built-in is a positive feature in my opinion.

    Plastic and Aluminum Construction

    Plastic and aluminum mean less breakage and more weather resistance. Wind, sun and saltwater (and water in general) can be rough on any piece of boating gear as well as anchors, ratchet straps and dock lines.

    Types of Solar Battery Chargers for Boats

    • Trickle Chargers provide a very low level of output by continuously releasing a small amount of power to charge the battery as you use it
    • Float Chargers are similar to the trickle charger, but they prevent overcharging (this type is my pick for the best all-around solar battery charger)

    The 5 Best Solar Battery Chargers for Boats

    So, we’ve come to the conclusion that solar battery chargers are a great investment for liveaboards, recreational boat and even fishing kayaks and jet skis.

    Let’s take a look at some examples for purchasing options.

    Eco Worthy Portable Folding Solar Charger and Panel

    The Eco Worthy Folding Solar Panel comes pre-wired and pre-installed with a 15 Amp PWM solar charge controller that protects from overcharging and reverse connections. The high-efficiency monocrystalline solar cell is made of lightweight aluminum.

    Its suitcase-style design makes it easy to transport. When you get where you’re going, just unfold and set it up.

    The charge controller has waterproof integrated junction boxes, and there’s a corrosion-resistant frame on the panel.

    This is a nice mid-sized panel and solar battery charger. Best part? All that pre-wiring and pre-installing makes it ready to use right out of the box.

    • Size: 30.7 x 22.1 x 5.1
    • Charger Type: Float Charger
    • Panel Type: Monocrystalline

    HQST Solar Battery Charger and Panel

    The HQST provides quiet power production for 12 and 24-volts in marine and other outdoor and off-the-grid environments. It has a 30A PWM LCD charge controller with LCD display, 20-foot adapter cables and a set of Z-brackets for mounting.

    It can charge a 50Ah battery from 50% in three hours (depending on the sunlight, of course). Pre-drilled holes make the panel easy to install. You can expand your solar system by connecting other panels for even more energy output.

    • Size: 40 x 27 x 1.5
    • Charger Type: Trickle Charger
    • Panel Type: Polycrystalline

    POWISER Solar Battery Charger and Panel

    The POWISER 3.3W is an easy-to-connect and use trickle charger. It has polycrystalline high-efficiency solar cells with thin amorphous panels that allow it to be used in any weather.

    Compact in size, it’s perfect for jet skis and small boats. It even comes with suction cups to attach to your boat’s window. I really like the compact size and shape of this solar panel and battery charger.

    • Size: 14 x 8.5 x 0.8
    • Charger Type: Trickle Charger
    • Panel Type: Polycrystalline

    SOLPERK 12V Solar Battery Charger and Panel

    The SOLPERK 12V Solar Panel is a trickle charger. It charges and maintains 12V batteries like Wet, Gel, MF and many more. The automatic charging and maintenance controller provides protection against short circuits, open circuits, reverse and overcharging.

    It’s lightweight and easy to install on jet skis and small boats. The best thing about the SOLPERK? It has thin film amorphous solar cells that allow it to work on cloudy days. Win/Win!

    • Size: 21.3 x 18.2 x 1.2
    • Charger Type: Trickle Charger
    • Panel Type: Amorphous solar cells

    Sunway Solar Solar Battery Charger

    Small and compact, the Sunway Solar Battery Trickle Charger slowly charges and maintains battery power levels in Wet, Gel, Deep Cycle and AGM batteries. A built-in diode protects against reverse charging.

    Crystalline panels have clear PV glass and ABS plastic housing for efficiency and durability. The long rectangular shape of the Sunway makes it a good choice for mounting on a dash or bow of the boat.

    The charger maintainer has a cigarette lighter adapter and alligator battery terminal clips.

    Cleaning Solar Panels

    As with any boating accessory, cleaning and general maintenance are needed for solar panels. Luckily, it’s not too hard. Rainfall is a handy thing to have in this case. For more in-depth cleaning, here are a few tips.

    • Use a soft brush to swipe away any caked-on dirt, grime and the inevitable bird droppings. You may need an extension rod for this job.
    • Next, get out that garden hose and spray away. A boat hose nozzle with an adjustable water stream is an excellent tool to have. You don’t want to shoot your panels with a heavy stream of water.
    • A microfiber sponge or cloth is helpful if there are still stains and dirt to scrap away.
    • Using soap is not suggested as it can leave a residue that will attract dirt. Try a small amount of Better Boat Boat Soap to see how it does with your particular solar panels. It’s 100% biodegradable and designed to rinse clean and residue free.

    As you can see, you have a lot of choices when it comes to keeping batteries charged out on the water. Hopefully, this has shed some light (pun intended) on your boat solar battery charger questions.

    May the wind be at your back and your batteries always be full.

    Solar Battery Charger

    Option 1: Plug it into your vehicle’s cigarette lighter.

    Option 2: Connect it to your battery directly with clips.


    It’s Rain-Proof, so do not drop it into the water. Dry it up immediately if you dropped. If the moisture goes inside, the circuit and chip could be damaged.

    How to use and maintain?

    • Extremely high temperatures could damage your solar panel, do not leave the solar panel working in any sealed and windless place, always place it outside of your vehicles.
    • Most cars can be charged with a cigarette lighter when the engine is turned off. Some new models may have a power-off setup, when you found your cigarette lighter can not be used to recharge the battery. You can use alligator clips and cables to connect directly to the battery.

    Shipping and Warranty

    • Free shipping
    • One-year standard warranty
    • Extra one-year warranty for Powoxi members. Make a Powoxi account to have your Powoxi membership!

    Customer Reviews

    I left it on my motorcycle two months ago. I came back this spring, the battery is fully charged.

    I had never seen that before. I have held a small panel like this, under a 30,000 candle power LED flashlight, and it would not make power. The 60 watt LED kitchen bulb, made enough power to make the red light glow, on the solar panel. 7.5 watts also, I was expecting only 5. These are the good monocrystal, not the disposable polycrystal panel.

    This unit is compact and really works to keep the battery charged on my vehicle when it sits for a long time. The only problem is the suction cup feet don’t work very well. But for me it doesn’t matter since I just sit it on top of the windshield wiper. This is very well made and will probably last for many years. 7.5 watts per hour when the sun is out. Works on any battery.

    I bought the unit in Feb,2021, and it worked great until just recently. It keep the battery at its peak, and the truck would start up quickly after sitting for weeks. Just recently I noticed the red light was on, which means it wasn’t working. After fidgeting with it. I found it had a bad cigarette lighter adapter. I contacted the company, and after verification of purchase they sent out a replacement adapter. The whole problem was resolved in a matter of a few days. The charger is working great again. My experience was excellent with Powoxi, and I will make them a preferred choice for future business. All companies should be this reputable.

    Got 7.5W, It’s good for small appliances and low wattage products. It helps also with car battery maintenance, but I would prefer higher wattage after the results post trials.

    Solar Battery Charging

    This instructable will show you how to make your own solar battery charger from very simple components. It is taken from my documentation provided with a kit I supply. you should easily be able to source the same components yourself of course.

    If you have any Комментарии и мнения владельцев on how to improve the documentation then please do not hesitate to say 🙂

    Step 1: The Components Needed

    The items shown in the image are contained in your kit. This page explains their uses. Your kit may have a smaller/larger copper stripboard than this and may contain extra wire. I try to beef up the kit as time goes on.

    The Copper Stripboard contains rows of copper tracks. Each track is electrically separate from its neighbour. It contains holes for your components. The boards I supply are larger than needed, this will allow you to expand the system at some future date.

    The Batter Holder. errrr holds your batteries. and comes with two pins, one for the positive and one for the negative ends, they will be soldered into the stripboard.

    100 Ohm resister. at one point this was needful in the kit as the LED couldn’t cope with some of the voltages in the experiments. however the new LEDs do and the resistor is simply in there because it is advertised as such! Maybe you will have need of it when you expand the system.

    LED. this is a high intensity light emitting diode. 3.2-3.6V forward voltage, with 10000mcd at 20ma. A LED must be placed in the circuit the correct way around. The longer leg should receive current from the positive terminal/direction.

    1N5817 DIODE. this diode allows current to flow in only one direction. this prevents battery power discharging through the solar panel at night. It drops about 0.2V from the system. This blocking diode also needs placing in the circuit in the correct orientation. The diode has a circular Band across its barrel at one end of the diode. This should be closest to the negative/ground.

    Wires. Usually I include at least 4 wires. a black and red wire for the solar panel, a brown wire as a jumper and another wire for use in unsoldered testing.

    Solar Panel. This image shows the back of the solar panel. On your solar panel in the centre of the left side and the right side you will see a small panel of smooth metal. this is the negative/positive terminals. I have marked the positive side by adding black dots on that side. This solar panel will output a max of 3V at 150ma.

    Warning. I suggest you read the whole document before making any experiments. information is contained throughout the document which will improve your understanding of charging batteries using solar power.

    HINT. you should probably purchase a multimeter and learn how to use it. this will tell you important information on typical voltages and currents you solar panel will produce in varying weather situations.

    It is quite possible to use this kit without having to do any soldering at all. however at some point you will need to so I include both soldered and non soldered options.

    Step 2: The Solar Panel. Attaching Wires

    Attaching the black and red wires to the solar panel

    To attach the wire one can use the soldered or the non-soldered method. Soldered is the best way to go and I show you pictures of both. if you plan on using more panels or using the single panel a lot you will find it best to mount the panel onto a piece of sheet wood or plastic. This will keep the wire in place and prevent strain on the contacts wires.

    You can see an example of the solderless method. Yes that is cellotape! The red squares indicate where the contacts are. The wire ends were stripped and then flattened onto the contacts and firmly taped in place. I don’t suggest using glue! you wont get the wire staying in touch with the contacts as the glue gets in the way. Allow some tape to move round to the solar side to ensure a firm placement.

    Also shown is the soldered method. Not the most fantastic job in the world but it is held securely. Always make sure the contact points are clean and free from grease.

    Step 3: Main Experiment

    Place a full charged 1.2V rechargeable Nimh battery into the battery holder. I assume you know the right way round to insert it. The 1.2V battery on its own will not be enough to light the LED. The 2-3V solar panel will also have a lot of trouble lighting the LED by itself. We can attempt to use the voltage of the battery PLUS the voltage of the solar panel to operate the LED. Below is the solderless version.

    Connect the RED POSITIVE terminal of the solar panel to the NEGATIVE leg of the battery holder. Use the extra wire supplied to connect the POSITIVE end of the battery holder to the longer of the two legs of the LED. The longer leg of an LED is always connected to the positive side of the circuit. Then connect the NEGATIVE wire of the solar panel to the other LED leg. If the battery is fully charged and you have a sunny day the LED should light up. You can even power the solar panel from a powerful torch or lamp by shining it onto the panel. Try experimenting by attempting to light the LED with the battery alone, or with the solar panel alone.

    Step 4: Charging Your Battery. Part 1A

    And now we come to making your own battery charger. Below is the circuit diagram for it.

    The solar cells positive terminal is connected through the diode to the positive terminal of the 1.2V battery. If the voltage of the solar cell drops below 1.4 volts then with the 0.2V the blocking diode takes there wont be enough potential to charge the 1.2V battery. The purpose of the diode is to disallow current dissipating out from the battery to the solar cell when this low voltage situation occurs in the solar cell.

    Step 5: Charging Your Battery. Part 1B

    The next photo shows the front of the completed and soldered circuit.

    The red lines at the bottom show how the copper tracks are aligned on the other side of the board. The blue lines show how the circuit completes through its electrical common points ( i.e. the tracks ). See how the small silver Band at the top of the diode is toward the positive terminal of the battery. It allows flow towards the battery but not from it.

    It is of course possible to do away with the brown wire and connect the black/negative wire the same track as the negative end of the battery. We simply wanted to show a more ‘closed’ circuit form.

    Step 6: Charging Your Battery. Part 1C

    From below you can see the soldered connections and how they run along the copper tracks. I have added in the brown wire as a brown line and the diode as a blue line, I have also added in the positive and negative makers for the battery. Remember the position is flipped from the previous photo.


    The maximum output of the solar cell is 150ma. This is with the best conditions. A high capacity rechargeable Nimh can hold 2000mAH. This means that it would take ( 2000/150 ) hrs to fully charge it. This is about 13hrs!

    When choosing solar cell arrangements one needs to work out

    a) How many batteries do you want to charge at once b) How fast do you want them to charge.

    By adding extra solar panels one can charge more batteries, charge batteries faster or even both at the same time.

    Step 8: I Want Voltage!

    In order to double the voltage you need to join two solar panels in series. i.e. you need to connect the negative terminal of one solar panel to a positive terminal of the other solar panel. This will then leave you with a positive terminal from one panel and a negative terminal from the other to connect your wires to. In this case you would then have a solar panel rated at a maximum of 6V at 150ma ( the maximum voltage of a single panel is 3V ). voltage would allow you to charge more batteries at one time. just remember that although 3V is the maximum rating of the solar panel you need to get an idea of the typical output for your climate. The batteries would also need to be connected in series ( negative to positive like in most multi-battery devices ). The circuit diagram shows below the solar cells in series and their accumulative voltage

    Step 9: I Want Current!

    current would allow you to charge your batteries faster. To double the current output you need to connect the solar panels in parallel. Connect the positive terminal of one panel to the positive terminal of the other panel and also connect the negative of one to the negative of the other. This will give you a max rating of 3V at 300ma. The circuit diagram below shows the solar cells connected in parallel. You can see that the voltage is the same at 3V but now the current will be doubled.

    Step 10: Gotchas

    Just a few gotchas to help you avoid any errors or misconceptions.

    1) Get a multimeter and get a good feel for how your solar panel operates in various weather conditions and at various times of the day. Maximum ratings are all well and good but we don’t all live in sunny Florida.

    2) Be careful about how much current you pass through your battery. Most modern batteries can be charged at quite a high current. For example you could charge a 2000mAH battery with a 500mA current for just over 4hrs and it would be fully charged. keep on charging it beyond that 4hrs and you could seriously damage the battery ( or even cause an explosion). Nimh batteries have a protective mechanism when they get overcharged and attempt to dissipate the excess current as heat. However they can usually only managed to discharge one tenth of their total current as heat. What this means in practical terms is that if you charge a 2000mAH battery with 200mA then it will survive without a problem if you overcharge it for a while. However if you are charging it with a 500mA current and then overcharge it things get more serious.

    I will attempt to expand this tutorial further. if you have any suggestions, additions, corrections then please contact me at

    To purchase this kit or any extra solar panels please go to

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    9 Комментарии и мнения владельцев

    Do I took apart some dollar store solar garden lights, but on a few there wires came completely off. Is there a way to tell which side is positively charged and which is negative? Or is it not important?

    it does matter, try connecting a multimeter to the positive/negative wires. it should read a voltage. if you have the connection backwards (e.g. positive multimeter to the garden light negative, etc), it will read the voltage but with a negative number instead of positive. simply switch the connection and then you know which is positive/negative.

    Hi as well as charging the 1.2v Nmh with s solar panel, I would like to run the led after dark.what, if any modifications to your charging circuit do Ineed to make.I wan to wake a 2 cell outdoor garden light.

    nice and easy to follow.even a beginner can follow it.but i want to see something like putting a voltage limiter or a zener diode to cut-off the supply if the battery is already full/max.and it will supply again once the battery is at low/min(15%).anyone with this diagram or arcticle please send me link.credits to this owner well done.

    Good Afternoon. I am working on a project that will function exactly like those stick-in-the-ground solar garden lights you see. The differences are the battery and solar cell need to be extremely thin, and extremely light, e.g. cell = 50-80mm diam and 2-3mmt thick, battery = 2032 Li-Ion rechargeable coin/button battery. The LED bulb will be remote from the other components 15-18cm connected by filament wire.I’m having a hard time finding the proper cell to provide the charge and still be small enough to fit within my confines.Any suggestions? Thank you for your time and expertise! Glakes1

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