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Automatic 40 Watt LED Solar Street Light Circuit Project – Part-1

Today solar panels and PV cells have become very popular and in the near future we would possibly see everyone of us using it in some or the other way in our life. One important use of these devices has been in the field of street lighting. The following article discusses one such interesting circuit which comprehensively explains the making of a 40 watt fully automatic solar street light system circuit (exclusively designed by me).

The circuit which has been discussed here has most of the standard specifications included with it, the following data explains it more elaborately:

LED Lamp Specifications

Voltage: 12 volts (12V/26AH Battery)

Current Consumption: 1.4 Amps @13 volts, and 1.2 Amps @12V

Power Consumption: 1.2 * 12 = 14.4 watts, (equivalent to light emitted by 39 watt LED lamp)

Light Intensity: Approximately around 2000 lm(lumens)

Charger/Controller Specification

Input: 32 volts from a solar panel specified with around 32 volts open circuit voltage, and short circuit current of 5 to 7 Amps.

Output: Max. 14.3 volts, current limited to 4.4 Amps

Battery Full – Cut OFF at 13.98 volts (set by P2).

Low Battery – Cut OFF at 11.04 volts (set by P1).

Battery charged at C/5 rate with float voltage restricted to 13.4 volts after “battery full cut OFF”.

Automatic Day/Night Switching with LDR Sensor (set by selecting R10 appropriately).

In this first part of the article we will study the solar charger/controller stage and the corresponding over/low voltage cut-off circuit, and also the automatic day/night cut-off section.

Parts List

R1, R3,R4, R12 = 10k
R5 = 240 OHMS
P1,P2 =10K preset
P3 = 10k pot or preset
R10 = 470K,
R9= 2M2
R11 = 100K
T1—-T4 = BC547
A1/A2 = 1/2 IC324
D1—D3,D6 = 1N4007
IC2 = IC555
IC1 = LM338

Solar Charger/Controller, High/Low Battery Cut OFF and Ambient Light Detector Circuit Stages:

Referring to the circuit diagram above, the panel voltage is regulated and stabilized to the required 14.4 volts by the IC LM 338.

P3 is used for setting the output voltage to exactly 14.3 volts or somewhere near to it.

R6 and R7 forms the current limiting components and must be calculated appropriately as discussed in this solar panel voltage regulator circuit.

The stabilized voltage is next applied to the voltage/charge control  and the associated stages.

Two opamps A1 and A2 are wired with converse configurations, meaning the output of A1 becomes high when a predetermined over voltage value is detected, while the output of A2 goes high on detection of a predetermined low voltage threshold.

The above high and low voltage thresholds are appropriately set by the preset P2 and P1 respectively.

Transistors T1 and T2 respond accordingly to the above outputs from the opamps and activates the respective relay for controlling the charge levels of the connected battery with respect to the given parameters.

The relay connected to T1 specifically controls the overcharge limit of the battery.

The relay connected to T3 is responsible for holding the voltage to the LED lamp stage. As long as the battery voltage is above the low voltage threshold and as long as no ambient light is present around the system, this relay keeps the lamp switched ON, the LED module is instantly switched OFF in case the stipulated conditions are not fulfilled.

IC1 along with the associated parts forms the light detector circuit, its output goes high in the presence of ambient light and vice versa.

Assume it’s day time and a partially discharged battery at 11.8V is connected to the relevant points, also assume the high voltage cut off to be set at 14.4V. On power switch ON (either from the solar panel or an external DC source), the battery starts charging via the N/C contacts of the relay.

Since it’s day, the output of IC1 is high, which switches ON T3. The relay connected to T3 holds the battery voltage and inhibits it from reaching the LED module and the lamp remains switched OFF.

Once the battery gets fully charged, A1’s output goes high switching ON T1 and the associated relay.

This disconnects the battery from the charging voltage.

The above situation latches ON with the help of the feedback voltage from the N/O contacts of the above relay to the base of T1.

The latch persists until the low voltage condition is reached, when T2 switches ON, grounding T1’s base biasing and reverting the top relay into the charging mode.

In the NEXT ARTICLE we will discuss the PWM controlled, simple LED lamp module and find out how the above circuit is integrated with it.


  1. i dont want the led driver as load i just want to use this design as solar charge controller so what should i eliminate ? please help me

    • dear sir , i am bala, i did the circuit without IC 555, iam not able to set the P1 and P2. please explain the alignment method. it will help to finish the project.

    • Dear Bala, For better indication replace the 1N4007 diodes a the outputs of A1 and A2 with LEDs.

      Now apply input voltage to the circuit, adjust P3 to generate 14.3V, and adjust P2 such that the LED at the output of A1 just lights up fully.

      Now reduce adjust P3 to get 11.2V and adjust P1 such that A2 LED now just lights up fully………..your circuit is set.

    • dear sir , As per your suggestions i did the alignment it is working fine and project is completed .but i cannot understand the battery full cut off area battery protection , T1 and its relay function. when i give 14.3 voltage to the circuit the charging voltage 13.3 comes to the battery . how the battery it is protected by over charging .

      with your help only i am doing all .

      please explain sir.

      thanks lot

  2. dear sir ,
    i have 230 vol a.c 600 va inverter and 12v/100 ah battery for my home to manage power cut. due to severe power cut iam planing to go for solar panels and charge controller. i want to charge my battery in solar panel at day time . here how i can change solar panel and a.c mains. i want to change my inverter ? please suggest me .

  3. dear sir ,
    iam going to make this circuit . please tell me where i want to place led for battery full(led green) and battery low (led red).

  4. I want to increase the power to 3KVA.I have got 24-0-24V transformer about 5kA. I am intending increasing the FET to 16pcs WITH A HEAT SINK, instead of 2.What other changes should l make to the circuit to achieve the power of 3kVA.Thanks for all your efforts.-Ladipo K.O ,fut, Akure, Nigeria.

  5. Its connected in parallel in output. Using above post I understand few something to avoid heating / short circuit by produced by the shaded cells.

    I had info about blocking diodes which we connect in series with battery. Thank you again

    • the shaded cells act more negatively compared to the unshaded cells, which generates heat inside the shaded cells due to the formation of negative current.

      A bypass diode nullifies the negativity of the cells by allowing current through it and thereby avoiding the heating of the shaded cells.

  6. sir , i did the circuit , it is working fine .sometimes the low voltage cut off relay giving vibration sound, i want to replace the relay ?

  7. sorry sir , i did a mistake with non-inverting(+)pin of A2 to R2 via a 10K resistor. now it is working well(there is no sound when the low cut off time). perfectly working. thanks for your valuable co-operation.


  8. sir how many hours its take to charge full battery and how many hours its lights and can we connect 60watt panel and above 12volt 26ah battery?? please help me?

  9. Res Sir,
    thanks for this precious circuit, I have made it using LM 338T (part no JM91BR) and gave an input of 17v from an solar panel of 12v 30 w rating. but when checking the volatge it is only 1.4v output, I think I've gone wrong some where, I've used a 5k preset intead of 4k7 preset, is it the problem, or else may be i've used a 220 ohms as R6 and 400 ohms R7, is my calculation wrong, can you tell me exactly what should be R6 and R7 to charge a 12v 26 Ah battery, because I am bad at calculation.Also can I use a LM317T for the same circuit to chagre a battery of 12v 7Ah x 2 in Parallel, please help me sir, thanking you once again
    Prem A

  10. I removed the 338 Ic and checked, it is giving an output equal to input, but back in the circuit it gives only 1.4 v do I ve check the BC 547 ic or the should I send the PCB Diagram I made for your consideration Sir, I designed it and asked one PCB Maker to etch it for me . Please … waiting for your reply and also sorry for troubling you so much

  11. I bought six solar garden lights from the store hoping they will illuminate my pathway and garden. However, these tiny chinese made solar lamps (it has one single 5mm led) produce only very little amount light like a firefly even with the full charge. Each lamp has only one 1.2v 600mah battery and the tiny solar cells are attached to the top of the lamp. On top of that I did not realize some parts of my garden get only 1 or 2 hours sunlight. Could you PLEASE help me to design a circuit that one solar panel (let say 3 to 5 watt) can safely (auto cut off when overcharges) charge some Li-ion 3.7v 3000maH (18650 type) or Sealed Lead Acid battery and then this power can be distributed to all 6 garden lamps to light high power LEDs (preferably 1W or 3W) in each lamp? I would greatly appreciate your invaluable time and effort to help me. My email address is mikbh@hotmail.com (please do NOT post my email address on this public domain, if you decide to publish this post). Thank you.
    With warmest regards,

  12. Also, I would like them to automatically turn on at dusk and turn off at dawn (like these tiny solar garden lamps do which have light sensor diodes but read somewhere that circuits made without these sensors to make dusk to dawn are better than with sensors, unfortunately, the author does not elaborate why).

  13. I don't understand how you derived "Current Consumption: 1.4 Amps @13 volts, and 1.2 Amps @12V" on top of the page under the title LED Lamp Specifications. My understanding was 1watt led has 350mA current rating, that doesn't add up just the 1.2 or 1.4Amp, please teach me correct way of calculating.

    • first of all here we are not driving the leds at full 350 mA, and is not recommended.

      the IC will generate pwm pulses which will keep the leds illuminated for only 50% of its total illumination period.

      therefore the effective consumption becomes 39/3(series) = 13 x 0.2(current) = 2.6amps/2(50%) = 1.3 amps.

      I hope you got it now.

  14. Just for the curiosity, can I use high power 3 watt leds instead of 1 watt in this circuit since the Vf for both 1 watt and 3 watts are within your calculation to arrange 3 leds on series and if this idea of PWM utilize very low current to illuminate the leds, it should not be the problem (despite the full current for 3 watt led is 700mA)? If I can use 3 watt leds, is there anything I need to modify on the circuit? Thanks.

    • Hi,

      You may try the above explained circuit, the IC1 stage along with the lower relay, D2,R4,and T3 won't be required, they all may be eliminated..

  15. Hello Sir
    I have a 40 watt solar panel and 12v,30AH battery and want to make this circuit, so can i used this ratings for this circuit.. looking forward for ua kind suggestion..

    • Thank you sir.
      Sir for the value of R6 the formula as u have given in other blog its 0.6/R6 = 1/10 battery AH

      That means for my 12v30Ah R6 will be 0.2ohm only? Sir i am a bit confused with it…

    • hello sir
      According to my battery AH i.e 30AH,after calculating R6=0.2ohm,since it s not availabe in the market, i tried 5 1ohm's in parallel also bt due to tolerance and all it used to cum around 0.6 ohm so i am so confused, is there any way to use R6??

    • Sir, I have connected everything as the above circuit except that instead of R6=0.2ohm(as i have mention in the above comment) i used R6=0.6ohm and when i try to make the output voltage to nearly 14.3volts by adjusting the P3 i can't make it less than 16volts or else p3 start burning, the input voltage from the panel is 19volts… Is that because of R6?
      please looking forward for your valuable sugestion….

    • that should not happen, there may be a big mistake somewhere, check the LM338 pinout connections.

      even without R6 (replaced with wire link)), the preset will never burn in any position.

      the voltage should vary right from 1.25 to the maximum level (19V)

    • Thank you sir, its coming. I think there was something wrong with the preset connection or preset itself, after i changed the preset with new one its coming as u said i.e from 1.25 to the maximum level (19V). I have some querry sir
      1) the o/p current is coming approx. 8Ampere, is it ok or it should be limit to 4 t0 5 Ampere, if so than how sir?
      2) As u have said "For better indication replace the 1N4007 diodes a the outputs of A1 and A2 with LEDs.Now apply input voltage to the circuit, adjust P3 to generate 14.3V, and adjust P2 such that the LED at the output of A1 just lights up fully", i did that sir but the Led doesn't light up at any point…
      3) The battery used to get charge from the charging circuit without connecting the other part i.e Ic724 part, but when i connect the battery does not charge at all…

  16. Hello sir, can you please tell me where to connect the led indication for knowing whether the battery is charging or not?

  17. hi, i have a few questons.

    1. how many hours will the battery take to discharge completely if 40 LED's are used as in your circuit.
    2.Is R10 min LDR circuit a preset or fixed. if fixed can a preset be used and of what value???
    3. where are full/low battery and ambient light indicators are connected in schematic???

    • apply 14V to the circuit adjust p1 such that the top relay just activates.

      Now reduce voltage to 11V and adjust P2 such that the above relay just deactivates.

    • adjust P3 to get 11v across D5 cathode and ground. then adjust P2 to activate the upper relay.

      then adjust P3 to increase voltage to 14V, then adjust P1 to deactivate the upper relay and activate the lower relay.

  18. Dada
    Ic 324 consists of 4 gates and 14 pin so in the circuit can we use a single IC 324 for the complete purpose of the circuit.

  19. lm 338 was not available so i used lm7815 with transistor d1047 (connecting input of 7815 to collector, output to base)for current more than just 1 A(output from 7815). is this arrangement ok???
    secondly how much max current can bc547 can pass??? can i use d1047 in place of bc547 if bc547 cannot supply current upto 2.5 A? if yes then what other changes do i need to make.

  20. Hello dada,
    I want to make this circuit as a emergency light for my village house because of huge power cuts.
    I had also made a semi automatic solar charger Iam uploading its image on facebook.
    and how can we modify this circuit to so that is charges the battery via the solar panel and it switch on the LED bank when the grid power supply fails and the sun goes down.
    (I think the concept which I used in my LED Emergency light transistor BD140,can work and power it by Transformer less power supply ).
    Can You explain how the IC 324 works?
    please help

    • Hello Tanmoy,

      You can use the above circuit for your application with the following modifications:

      Remove the IC2 section entirely and connect the D6 anode with D5 cathode.

      That's all is required rest all will be as is, the circuit will start functioning as per your specifications.

  21. I want to use this circuit as a college project but i need to finish it and put it in a reasonable cover and hence its a street light i was wondering if it will be possible to put the battery somewhere in the head of the street light

    Also is it possible to get a small solar panel that will give me the required 14.4V i need to charge the battery

    Thank you

    • The battery can be installed anywhere around the light box, but should be appropriately enclosed and protected from water and direct sunlight.

      The desired soar panel can be easily procured from your nearby electronic market.

  22. my ratings are 12v 5 watts solar pannel and battery is 12v 1.3 ah will this circuit can be made with this ratings? if not suggest me the appropriate ratings for low power (5-10 watts)

  23. hi.
    there is some problem with this circuit. when i set A1 it works normally when i move voltage level up and down from P3. but when i adjust A2 for low cuttoff then although A1 changes its output indicated by empty and full led but relay doesnot deactivates. it seems as it creats some latching with relay of A2. again when i adjust A2 preset to zero value the A1 relay works properly. any suggestions???

    • Hi, the above design is absolutely correct, there could be some problem with your assembly or parts.

      Or the slight delay may be happening due to the zener diodes in series with the transistor bases, which is not a big issue.

      For exact confirmation you can replace these zeners with LEDs, and remove the existing LEDs across the opamp outputs.

  24. I am using a 12volt, 10 watt solar panel, and a battery of 12 v nd led light of 12v, what are the values of resistors of r2,r6,r7, nd what should be the output of battery,…plz rply fast i need to attach only these 3 on pcb, ty

  25. hi swagatam
    can i use this circuit for home light systems. there is some questions:
    1: There is no R6 & R2 right?
    2: As led 12v bulb light used as gives low light as length of wire increase what should we do for loss of power?
    3: What is max watt of panel & Ah of battery is used?

    • Hi Ashok,

      1.R6/R2 have been removed so it's not there in the present diagram.

      2.You can connect the Ac/DC adapter or the battery very close to the LED circuit and install them as one module over the desired location, this will solve the issue.

      3.It's not limited to any value, only the voltage of the two must not exceed above 24V.

  26. thanks for reply.
    As you stated 2 comment what i do for all light grid in home in all room.
    and my first question can i use above circuit for home light system as charger & power supply.

  27. Can we use computer UPS with 12v/ 45AH battery as a INVERTER for home use?
    I have one UPS with inbuilt 7 AH battery i want to use above circuit to charge 45 AH battery and UPS as inverter. Can we do it?

  28. I assemble the circuit i observe following:
    1: voltage at solar input 18.9 volt
    2: voltage at D5 is 13.02 volt
    3: Voltage at battery connection 13.02 volt
    is this ok? how to chk LED point? Actually i print the pcb at a time & assemble & chhk the circuit

    • voltage should be 14.3V after D5 without any battery connected, this must be adjusted with the help of P3.

      the LEDs will respond when P1 and P2 are set at their respective cut-of thresholds

  29. I assemble he circuit but i chk voltage at battery connector & D5 voltage is 14.4volt as in put from solar is 20.8 volt i adjust but thr is no changes in voltage. How to make cut off by adjusting P1 & P2 that means from which point 14.2 volt & 11.01 volt has to put?

    please help me….

    • don't connect the battery while setting up, I mentioned this in the previous comment also.

      initially use a 15 or 24V AC/DC adapter for supplying to the circuit, don't use solar panel

      without any battery adjust P3 to get 14.4V at the cathode of D5.

      Now adjust P2 so that the upper relay just activates, if it's already activated, adjust P2 to deactivate it and again adjust the same to activate it and seal P2.

      Now adjust P3 to reduce the voltage at D5 to 11.1V, and adjust P1 so that the upper relay just deactivates again, seal P1

      confirm the above actions by adjusting p3 back to 14.3V and 11.1V two three times.

    • Hi sir for long time i replied, actually i did not have variable voltage supply, now i assembled for the above circuit use. As you stated in above comment steps are as follow,
      1: disconnect battery supply at solar point 21-22volt dc using supply.
      2: adjust P3 to get 14.3 volt at battery point.( i do at this point)
      after that i rotate both preset but nothing happen with relay.
      3: adjust P3 to get 11.13 volt rotate P1 & P2 but nothing happen

      please guide me…

    • It means you might have done something wrong with the connections.
      Initially keep the collector of T2 disconnected from the base of T1.
      Now adjust P2 to activate the relay at 14.4V.
      Reconnect T2 collector to T2 base and apply 11V.
      Now adjust P1 to switch OFF the relay.

  30. sir actually i m confused can u explain my question answer. without battery connect, When i apply 21 volt supply at solar panel point, at battery point voltage is 14.3 v by adjusting P3 ok. Next at this point adjust P2 for battery full cut out without disturbing setup. next again without disturbing setup adjust P3 to 11.3 v output of battery point now adjust p1 for low cutout.
    is this battery point open right that is no connect battery just open those point. so without load at battery point how we can adjust low & full cutout?

    • yes it should be without any battery connected, the variable inputs simulate the battery threshold levels and is used for setting the relevant presets.

  31. Ya I will take aluminium PCB to place LEDs as required. Pls. provide charge controller and LED driver with dusk to dawn operation that should be common PCB for many LED loads with little bit modifications. The LEDs I will connect in series mode only.
    Thank u very much…

  32. Hello Sir, the coil configuration of third relay(at extreme right side of the circuit diagram which is connected to LED lamp module) is no shown in the diagram.

  33. Hello, i would like to build this circuit but was wondering if you have a stripboard layout for it because it will be easier to construct and instead of me spending time making one i thought to ask you..please help it will be really appreciated

    Thank You

    • sampath, it's clearly shown in the diagram, only N/C and the pole are used the N/O is unused for RL2…the coil is connected across the positive and the T3 collector

  34. sir i wanna make project same as this in small scale plz help me . I wanna glow a LED with solar power. I have also sold 3v solar panel but my circuit is not completed due to non availability of components (0.47mH 4R9 and 10R)

  35. Dear sir, can you please mention the specs for capacitor C1, Resistor R7, LDR and power wattage for the solar panel. Also min and max LED output power that this circuit can support. Thanks

  36. Dear sir, can you please provide more details on the LED lamp module. Orientation of the LEDs in that module. Are they connected in parallel or in series to each other. Also, what is the value of the current limiting resistors for each LED. Thanks

  37. I want to make Automatic 80 Watt LED Solar Street Light Circuit Project so can u plz tell me how many volts & amperes of solar panel is required…??? Should I double it compared to 40 watt…???? Please reply as soon as possible…. Please

  38. Dear Mr. Majumdar. I am interested in 15-34 watt LED street light project without battery at Haridwar, Uttrakhand
    Would like to be dealer for same.
    Also is there any solution for automatic invertor battery charger when the light goes off.
    Also it is seen that qhen the light is on the use of battery is nil. Can there be a design which when invertor battery is full it should cut mains and go on battery backup upto letus say 50% or it can be adjustable as per requirement. This way use of battery will be at maximum and electricity bill be reduced. Kindly reply if u feel it a good idea.

    • Dear Nauty,

      I already have the required battery charger design in my website, you can easily find the required from the "categories" list however the idea of having 50% supply from the battery during the mains presence will not do any good….because while the battery is supplying current to the load it is simultaneously acquiring it from the mains…so that would not help in saving mains power in any manner.

  39. Hi sir, I spoke to you before about the strip board layout if you could help me with a strip board layout of this circuit i hope you remember and I would like to follow up to see if you have had a chance to make one for me. Thanks

  40. Hello sir,
    I have one problem in my street light
    Panel 75w,20V
    Battery 75Ah , 12v

    O/p of controller to charge battery is 2.3volts
    O/p of panel is 20v
    Lamp is 15w 12v led

    Sometime operate and sometime don't opetate

    What can be reason

    • Hello Umesh, it would be difficult to understand the fault without a practical check up, but it appears that the unit is malfunctioning…

      yes you can connect the specified panel with the specified battery directly for the time being…it will still charge the battery, although not quickly.

  41. Hello sir,
    I want to make this project but with some modification.. I want solar panel to follow the direction of sun.. something like solar tracker… so can you please help me with the circuit diagram…. I would wait for your reply….

    • all components are 1/4 watt except R8.

      All reputed online stores are good, you can google "buy online electronic parts" for the list of main vendors.

  42. Sir!i have some problem to understand the "Ambient Light Detector Circuit"part.which mode is it?There is "R" B/n pin 5 and pin 7.Is it because to prevent pin 7 being damaged as it shorts to 0v ?why at all pin 5 connects to pin 7 and why pin 6 too connects to Vcc?would you mind giveing me more explanation?
    Thanks in advance.

    • The IC is used simply as a comparator here, only the pin#2 opamp is utilized while the pin#7 opamp is kept unused….pin#5 connection with pin#7 helps to provide some degree hysteresis to the triggering.

  43. Sir i have 74 watt solar panel, and 75AH battery. How to design a solar charge controller with LDR sensor and INDICATION LED of charging, discharging and low battery..

    • Arindam, I have published many automatic charger circuits in this website you can select any of them for your purpose….no issues, if you have any further problems you can always consult me here…

    • Hi Arndam, I would request you to kindly express your thoughts under the articles…because attending my readers personally would be difficult for me.

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