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9 Simple Solar Battery Charger Circuits

The post comprehensively explains nine best yet simple solar battery charger circuits using the IC LM338, transistors, mosfets, 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.

1) 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

R3 = 0.7/ Max Current Limit

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.

2) $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.

3) 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.

Sarfraz Ahmad

Rawalpindi, Pakistan

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.

4) 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.

Circuit Diagram

Relay Based Automatic Solar Light Circuit

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

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

5) 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

  1. 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.
  2. 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.
  3. 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

Transistor solar battery charger PCB Design

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.

6) Solar Pocket LED Light Circuit

The sixth design here explains a simple low cost solar pocket 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

  1. I want to make a SOLAR pocket 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].
  2. The battery should be replaceable when dead after use for 2/3 years/prescribed life by the rural/tribal user.
  3. 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].
  4. 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.
  5. 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.
  6. 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.
  7. 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.
  8. 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.
  9. You can see the lights we have made in google photos at https://goo.gl/photos/QyYU1v5Kaag8T1WWA Thanking you,

The Design

As per the request the solar pocket 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

solar pocket LED light circuit

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 pocket 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.

7) Simple Solar LED Highway Lighting System

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

Solar controller charger using 2N3055 Transistors

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
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:

8) 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.

1. Input voltage = 40 to 60 VDC

2. 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)

3. Output current capacity = 5-10A

4. Protection at output = Over current, short circuits etc.

5. Small LED indicator for unit operation would be an advantage.

Appreciate if you could help me designing the circuit.

Best regards,

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.

Circuit Diagram

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
D3 = 1N4007
L1 = 30 turns of 21 SWG super enameled copper wire wound over a 10mm dia ferrite rod.

9) 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. 

1. 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

R3, R4 = 15 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 her for the reading pleasure of our viewers.

Need personalized help? Please express your queries in the comment box below for initiating a discussion


About the Author

I am an electronic engineer (dipIETE ), hobbyist, inventor, schematic/PCB designer, manufacturer. I am also the founder of the website: https://www.homemade-circuits.com/, where I love sharing my innovative circuit ideas and tutorials. If you have any circuit related query, you may interact through comments, I'll be most happy to help!

161 thoughts on “9 Simple Solar Battery Charger Circuits”

  1. Howdy, Friend! Interested to Learn Circuit Designing? Let's Start Discussing below!
  2. Hello Swag, please how can I charge a 100ah and 7ah batteries with same 150w panel.the 7ah will be for emergence lighting. Thanks

  3. Hello Sir. Can you provide a modified circuit of this so that it can be serve both a power source will the battery is charging and the battery as power source when the solar panel is not supplying power? Thank you.

    • If you keep the full charge voltage level from the IC slightly lower than the actual value, then the cut-off action won’t be necessary and can be ignored

  4. Sir
    Can you just clarify. Using potentiometer P1, i set the output at 14V as measured by an ordinary multimeter. But when i connect a battery that voltage drops to 11.5 V. I am expecting the voltage reading to be maintained at 14V even when the battery is connected. Can you please help explain.
    Thanks very much.


    • Pyke, that is perfectly alright. As soon as you connect the battery the 14V must sink to the battery’s discharge level, and slowly as the battery charges the level would be seen slowly climbing until finally the 14V is reached…and then you can assume the battery to be fully charged, and disconnect it from the supply

      To implement the above procedure we always make sure that the charging current is significantly lower than the battery’s Ah rating….

  5. Sir I have to charge 24v 14ah battery by solar panel I have two 12v 20w solar panel can I charge the battery by them if I can what is the circuit

    • Sharath, put the panels in series and check if the output is around 29V at peak sunshine, if yes then you can charge the battery reasonably well with those panels.

  6. I read somewhere that the float voltage for lead acid battery is around 13.8 volts, and that with this voltage, the battery could be charged as long as possible, without causing any damage to the battery. What is your take on that sir?

  7. Sir,

    Thanks a million for your prompt help. May I use the schematic in my youtube video. I will mention the source and link to your website.
    Thanking you for your time,

    • You are welcome Vishwa, you can use my circuit diagram in your youtube video with a reference to my site, let me know when you have posted it.

  8. Sir,

    As I am new to electronics I have listed steps to be doubly sure of the connection:

    1. Positive of solar panel to positive of D1.

    2. Negative of D1 to pin 3(IN) of LM338.

    3. Pin 2(OUT) of LM338 to positive of D2.

    4. Negative of D2 to positive of battery.

    5. Pin2(OUT) of LM338 to top terminal of R1.

    6. Pin 1(ADJ) of LM338 to pin 1 of BC547.

    7 Pin 1(ADJ) of LM338 to bottom terminal of R1.

    8. Pin 1(ADJ) of LM338 to base of P1.

    9.Pin 1(ADJ) of LM338 to top terminal of P1.

    10.Pin 2 (base) of BC547 to bottom terminal of P1.

    11.Pin 2 (base) of BC547 to top terminal of R3. .

    12. Negative of solar panel to pin 3(emitter) of BC547.

    13 Pin 3(emitter) of BC547 to bottom terminal of R3.

    14. Pin 2(base) of BC547, bottom terminal of P1 and top terminal of R3 to negative terminal of battery.

    Thanks for your help.

    • Vishwa, sorry I can’t verify this because I am not sure which pins of BC547 you are referring by saying pin#1, 2 etc.

      It is better if you could refer to the datasheets of the respective devices and check the pinouts yourself and then connect them by comparing with the diagram

  9. Sir,
    I want to charge a small Li ion 3.7V 2100 mh battery using 10W solar panel with following spec.Voc 10.43V, ISc 0.90A, Vmp 8.95V, Imp 0.82A. Will it work?
    Parts used:
    R1 = 120 ohm
    R3 = 1 ohm
    D1 = ?
    D2 = ?
    P1 = 10K
    Can you please help and tell me if LM337 will work? What are the values for diodes? Thanks

  10. hello Swag,
    i found this Solar, Wind, 2-Input Hybrid Battery Charger Circuit https://homemade-circuits.com/2015/09/solar-wind-2-input-hybrid-battery.html which is very simple not getting zener diodes in my area.

    moreover reading from the above the modern highly versatile chips like the LM 338 and LM 317 i can get all the parts for my personal project so i want to make a request from the above circuit.
    I have •Maximum Power: 265w •Maximum Voltage: 31.4v •Maximum Power Current: 8.44a
    •Open Circuit voltage: 38.6v •Short Circuit current: 9.03a solar panel with which i can modify and use
    but the other side is the shunt regulator from the wind mill if you could please add a circuit of Lm 338 and LM 317 with out zener diodes so i could use as a dual charger.


    • Hello Nito, a windmill should be ideally operated with a shunt regulator only, but if you are interested to have a LM338 circuit in its place you can easily do it by removing the entire opamp stage and replace it with a standard LM338 voltage regulator stage.

  11. Hello sir.
    First of all let me say thank you for your fast replays.
    The FSD ammeter and R3 are not available at the market. Suggest somthg instead sir?
    Best regard

    • Abubakar,

      you can connect a suitably selected automobile bulb in place of the meter, initially this bulb will glow brightly, and when the battery is fully charged this bulb will shut down….but this will happen gradually…so you can consistently get the idea regarding the battery charge level through the bulb’s intensity level.

    • yes you can use it for charging a 4V battery from a 6V panel, but preferably the panel voltage should be 3V higher than the battery voltage


    • yes the circuit can be used for charging the mentioned battery, but I am wondering how a 100 mAH battery could be used for operating an inverter

  13. sir, please also send schematic for 12v 2.2Ah lead acid battery charger using solar pannel and power rating of pannel.thankU

  14. Hello Sir,
    I have to charge 12v 2.2Ah Li-Ion battery using Solar pannel, will u suggest me what type of solar pannel should i use and what is the power, voltage, and current rating of pannel…

  15. Sir Swagatam can this circuit charge a lithium ion battery? Im looking for a solar charger that can charge a lithium ion battery pack with overcharge protection .. thank you very much for your help sir..


  16. Sir what's the meaning of the ground symbol between battery negative and R3.

    should we connect it to pv negative by a separate connection?

  17. hi sir,
    im having a 12v 1 Ah battery(3*4v) and series pannel 6v+6v+3v = 15 v>

    is it possible to charge the same with this circuit ??

  18. sir could you please suggest any circuit for 1Hp single phase induction motor speed control, using PWM or variable frequency method.

  19. Hello Sir. I want to know if it is possible to charge a 12V 7A battery using a 9 V 3w solar cell using your circuit.

    Thanks in advance.

  20. sir do you know any current amplifier circuit that i can use because the output current from the circuit is very low, i recorded 200mA as the highest current that the circuit can supply so far which is not enought to fully charge the 40Ah battery. The panel is rated 100W and current peak is at 5.61A but it only supplies about 400mA input current to the LM338.

    • Nine, a current amplifier is out of question here….if your 100 watt panel is producing 400mA simply means it's faulty or something may be wrong with the connections….or if this happening after the LM338 IC stage would indicate a faulty or incorrectly wired LM338 IC….please check all these individually to confirm the results.

  21. sir i'm still thinking if I should remove the relay in the circuit.. the setup now is that the relay serves as a switch for the sensor circuit, if the battery is in charging process the relay trips and the sensor is disconnected from the circuit so the charging current is divided to the battery amd relay.. if I do remove the relay the charging current will be divided to the battery and sensor circuit, however, the sensor circuit is composed of a voltage regulator, ATtiny mmicrocontroller, op amp, and a power mosfet for the LED.. I know the sensor circuit is quite large so it will really require a sufficient amount of current than the relay I think.. what would you do here sir?

    • Nine, the sensor circuit is not supposed to consume more than 5 to 7mA and the relay not more than 30mA….so it's your wish now whether to use the circuit or not as per the application needs.

  22. also sir is it ok if I connected a dark sensor circuit parallel to the battery so the led lamp will automatically switch on at dusk? If yes, will it affect the charging process because the output current from the above circuit will be divided for the battery and sensor circuit?

  23. sir is that why the battery is dropping so quickly? also we also connected a regulator ic which is 7805 to bring down the voltage to 5V for our microcontroller, is 7805 also a factor why the battery is dropping? thank you sir

  24. hello again sir! i finally implemented the above circuit. I used a 100W solar panel to charge the 40Ah battery. First I used the battery to power the lamp and it dropped to 8V. I think the charging works fine because from 8V, the circuit was able to charge the battery to 13V. The problem now is that the battery is quickly draining, dropping to 8V after 2 hrs of supplying power to the 24W led lamp. The lamp still stays on but I think that should not happen to the battery dropping off too quickly. What would be the problem here?

    • Hello Nine, you must charge the battery up to 14.3V, for ensuring 90% charging….13v is not the optimal level for a 12V batt.

  25. sir i'm a bit confused.. i followed all the calculations and it said I need at least a solar panel of 30W and a battery of 20Ah.. but you said before for a 24W lamp I will need a panel of greater than 50W and a battery of more than 40Ah.. sir please explain thank you

    • you might have calculated wrongly….a simple way is to divide 30 by 12, it gives 2,5A, how can a 2.5A charge a 40AH battery within 6 hours, it would take about 18 hours at that rate.

      a 24 watt lamp will consume 24/12 = 2amps…so with a 40AH batt we get 40/2 = 20hours ideally but it would be just approx 12 hours practically

      so you will have to charge a 40AH battery fully for sustaining a 24watt lamp for about 12hours

  26. ok now I understand thank you sir.. anyways sir can I request for your insight on how to calculate the approriate battery and solar panel for our 12V 24W LED Lamp that should stay on for a whole night.. I just wanna have a concrete basis for picking the battery and panel..

  27. then it makes sense when the output voltage changes because the input voltage gets lower from the solar panel.. sir do you have any more circuit that can produce constant output regardless of the changes in the input?

    • ….the output should be perfectly constant even if the input fluctuates widely but it should not be very close or lower than the intended load voltage

  28. sir what should be the minimum input voltage from the panel so I can constantly produce 7V from the circuit using lm317? and what should be the minimum input voltage from the panel so I can achieve 14V from the circuit once I used the lm338?

    • It should just 1V higher than the required output, meaning for 7V output the input could be 8V…and for 14V output it needs to be 15V minimum

  29. it's okay sir.. I just tried to put the panel under outdoor light even if it's cloudy.. now i'm getting up to 12V from the circuit.. I guess it makes a huge difference when you're testing it indoor.. now the problem is the output voltage keeps changing whenever I move the panel from different locations.. I adjusted the circuit to produce 7V but it keeps changing when I move the panel.. I thought this circuit will produce constant voltage once I adjusted the potentiometer regardless of the varying input voltage from the panel.. sir what is wrong here?

    • Yes the IC must produce a perfectly constant voltage regardless of a changing input.

      Check and confirm the circuit first with a variable DC power supply and see the response.

  30. sir i'm having problems with the circuit.. I tried. to construct this circuit in smaller scale so I bought a 12V 10W solar panel to charge s 6V 4.5ah battery. I used lm317 and I eliminated the transistor part because I want to see the output voltage first. But then the output voltage i'm getting is only up to 1volt. I checked the output voltage from the solar panel alone and its 7V. sir what am I doing wrong here? I haven't tried to put the panel under sunlight because it is cloudy here so i'm just testing it under indoor light.

  31. Hello sir. I would like to use the above circuit to charge a 3.7V 1500mAh mobile phone battery, with a 12V 5W panel. Can you please let me know the changes needed to be done to the circuit?

  32. i'm determined to use your circuit so what should be the input voltage and current for lm338? and is there anyway to adjust the output current?

    • input voltage is 32 max, current doesn't matter it can be anything as long as volatge is within 32V.

      the max output current can be set anywhere from 0 to 5amps by selecting different values for R3 as per the calculations

    • yes will do but a 50 ah battery will need a higher wattage solar panel for fast charging, it will charge very slowly with the existing 50watt panel

    • There's no way to increase the back up time, unless another battery in parallel is used…. but that will require upgrading the panel to 100 watts.

  33. for the current rating of the solar panel (12V 50W), what do you suggest I use sir? a 12V 40Ah lead acid battery or a deep cycle battery?

    note: the battery should be able to supply enough power to the LED lamp for the whole night (12 hours at most). thank you sir

    • deep cycle batteries are also lead acid batteries, so you can use a 40AH lead acid battery for the said purpose.

      The mentioned 24W lamp can be operated for not more than 6/7 hours at stretch with a fully charged 40AH batt.

  34. sir this is the current setup of the project..
    12V 50W solar panel to charge a 12V 40Ah lead acid battery, the load will be 12V 24W LED lamp
    what are your thoughts about these adjustments? and can the circuit above can charge a deep cycle battery? thank you so much sir for answering my questions

    • yes a 12V 50 watt panel can be used for charging a 12V 40AH deep cycle battery, but will require around 10 hours to get fully charged.

      a 12V panel during peak should be producing 15 to 16V, so according to me you can connect it directly with the battery through a 6A4 diode…the above circuit may not be required.

    • for a 12V battery a 50 watt panel can be used, but the panel peak voltage should not be above 15/16V for an optimal response,

      yes the above circuit will just fit in.

  35. ok sir i'll research more on that.. anyways can I use a 24V 50W panel to charge a 55Ah 22V battery, by the way the battery will supply a 12V 45W LED Lamp.. what's your opinion about this sir?

  36. correct me if I'm wrong sir, but you're assuming that the battery is rated @10 hr. I will be using a battery that will be rated @20 hr, so i can use a maximum of 100Ah because 100/20= 5A, which is the maximum output current of LM338..

    • I don't know if a lead acid battery can be charged at AH/20 or C/20 rate, so I can't say much about this calculation…C/10 is considered as the minimum optimal range for charging lead acid batts.

  37. sir what is the maximum Ah that this circuit can handle? and can you teach me how to add an overcharge protection circuit to this one because i need the circuit to automatically stop the charging when battery is full.. thank you

  38. sir can you explain the role of each component in the circuit? i wanna understand how each of them function.. and how did you come up with the computation R3=0.7/chg. current? thank you so much sir!

    • The upper resistors are as per the IC datasheet…the BC547 is responsible for grounding ADJ pin of the IC and disabling it when an over current is sensed, and this happens when the potential across R3 exceeds 0.7V which is the switch ON (saturation) voltage of the transistor

  39. Hi sir
    I wanna ask if i can use this circuit to charge a 12v 40W lead acid battery ti powerup an LED lamp during the night. I'm planning to use this for a streetlight.

    • Hi Nine, did you mean a 40 AH battery? Yes you can use the above circuit for charging a 40AH batt, make sure to put the IC LM338 on an adequately large heatsink

  40. Hi sir,
    I realised the circuit of this article but I can manage only the voltage at the output with the potentiometer, not the current. What could it be wrong? I didn't put the R4 and I switched the multimeter as ammeter and connected it in series the output of circuit with the battery.

    • Thanks, I really appreciate your help, the circuit works, finally! 😉 I have just one more question: there is any ways to evaluate the charging current? I have two batteries in parallel, one is 10Ah e another one 4.5Ah. The solar panel produce 1,7A and the R3 is 0.47ohm. I guess I made the correct calculation but I would check the real current that pass on the circuit. Any suggestions? Thanks in advance for any answer 🙂

    • Thanks Daniele,

      Usually it's AH/10 for lead acid batteries and AH/1 for Li-ion batts, but if you have two batts in parallel with different AH rating in that in case you may have incorporate separate current limiting circuits for each batts.

      You may have to make two of the above circuits, and calculate R3 separately in order to feed the respective batts…the ground will be common for both the circuits.

  41. actually i want to make charging my 24 volt 1.5 Ah battery to supply 24 volt, 600 mA STEPPER MOTOR…..
    is this possible from 12 volt 250 mA solar panel using 12-24 volt boost converter???

  42. ok… so according to you i should connect two 6 volt, 250 ma panels in series… then i will get 12volt 250ma…. am i true sir??

  43. have a good day sir!!!
    plz help me about my question that, is it possible to charge 12 volt 1.5A battery from 6 volt 250 mA solar panel?????

  44. Sir, i have 70Ah 12volt battary and i'm about to buy 100Ah solar panel to charge it. there need to be solar charging system(circuit)? could i connect battary directlly from solar panel for charging? it will harmfull for battary?

    • Dev, solar panel current is not rated with AH, its rated with amps….a controller can be avoided by selecting a correctly rated solar panel for the battery.

      for a 12V 70ah battery use a 18 V, 10amp solar panel….18v is the peak rating of the panel and 10amp is the short circuit current of the panel

  45. hii sir,
    Is there any single chip IC for dust sensor and sound sensor??? If no please suggest me a simple circuit… thanks

  46. Thanks sir i have assembled all the components except this resistor…. taking your suggestion i will progress the circuit and tell you about the output ….
    Sir do you have a of DC 12v to 18v or 24v DC converter circuit i am not not getting this in your site…can you please help me…once again thank u …

  47. Sir me bhanu can u plese tell me how to calculate charging current easily….
    You have given a formula i.e 0.6/Charging current
    Can i use 0.6/ battery Ah or i will take 1/10th of battery Ah

  48. sir, what is the charging current of 12v 7Ah battery? what is the diode use in here?and what is the watt of resistor to be use?..thanks

    • Erns, R4 is not needed, you can remove it.
      the ideal charging current of a 12V 7ah battery is around 1amp.
      the diode is for preventing accidental polarity reverse conditions at the input.

  49. sir,
    I want to design a solar battery charger,all components should be SMD type and my aim is to reduce PCB size as much as possible…pls help me…

  50. sir,
    I have to drive robot which require 12 v,1.5 amp to operate .So,please help me to decide which solar panel and rechargeable battery i have to use.

  51. sir,
    i want to charge a 12 volt 5 amp battery using this circiut in your blog..what would be the specification of the solar pannel..plz help.

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