A very simple automatic solar light system for illuminating your garden passages can be built using some LEDs, a rechargeable battery and a small solar panel. The system automatically switches ON the lamps at dusk and switches them OFF at dawn.
Main features
Although the following simple automatic solar LED garden light circuit looks simple, it includes a few interesting features which makes this design extremely adaptable, versatile, safe, efficient and long lasting.
The mains features are listed below:
- Automatic charging of battery during daytime with LEDs turned off, and automatic switching ON of the LEDs during nighttime.
- Proper current limiting for the battery to safeguard the battery from excessive charging.
- Current limiting for the LEDs which can be adjusted as per the required number of LEDs.
- Battery over-discharge protection ensures that the battery can never be overly discharged by the LEDs, which in turn ensures a longer life for the battery
How it Works
As can be seen in the following circuit diagram, the design basically consists of a solar panel, a couple of NPN transistors, LEDs, a battery, a few resistors and diodes.
Referring to the circuit diagram above, the working of each of the components can be understood with the following points:
The solar panel supplies the peak voltage of 6 V, at 500 ma during daytime, which charges the battery as long as this voltage is available from the solar panel.
The resistor Rx keeps the charging current to a safe lower level so that even after the battery is fully charged, the minimal current does not harm the battery.
The value of the charging current determining resistor can be calculated using the following formula:
Rx = (Vsolar(peak) - Vbattery(full)) / Icharge
Rx = (Solar peak voltage - Battery full charge voltage) / Battery charging current
Example:
Solar Panel Voltage = 6V
Battery Full Charge Spec = 4.2V
Battery Charging Current (optimal) = 500 mA
Rx = (Vsolar(peak) - Vbattery(full)) / Icharge
= (6 - 4.2) / 0.5
= 3.6 Ω
Rx Power = (Vsolar(peak) - Vbattery(full)) * Icharge
= (6 - 4.2) * 0.5
= 0.9 watts or simply a 1 Watt
However, if you want better protection than just a current limiting resistor, you can opt for a regulated charging system, as discussed in the next design after this explanation.
The BC547 transistor ensures that the LED driver transistor using 2N2222 remains turned off, as long as a base voltage of at least 0.6 volts is available from the solar panel.
Meaning, until the voltage from the solar panel has not dropped below 0.6 V, the BC547 transistor remains switched ON, causing the base of the 2N2222 to remain grounded, and turned off.
Therefore, until it is significantly dark or until the solar panel is able to supply at least 0.6 V to the BC547 base, the 2N2222 remains switched off, which in turn causes the LEDs to remain shut off.
Once the solar panel voltage drops below 0.6 V, the BC547 transistor slowly starts turning off, causing the 2N2222 to slowly start turning ON.
As the 2N2222 slowly turns ON, its collector LEDs also begin slowly getting illuminated, using the stored power from the battery which was charged during the daytime using solar energy.
Once it is completely dark and the BC547 is fully turned off, the 2N2222 BJT conducts fully causing a full illumination on the LEDs.
The LEDs now illuminate fully using the stored energy from the battery, and the battery slowly starts depleting its power through the LEDs.
The battery keeps the LEDs illuminated until the battery voltage has drained down to its lowest discharge level, which happens to be around 3 V for the 4.5 V battery shown in the diagram.
However, as we know that a BJT can conduct only until its base voltage is around 0.6 V higher than its emitter voltage.
But since the emitter of the 2N2222 is clamped with a 2.7 V zener diode, it means that the base voltage of the 2N2222 needs a minimum of 2.7 + 0.6 = 3.3 V to enable its proper conduction.
So, when the battery voltage drops to around 3 V, the base of the 2N2222 does not satisfy the minimum required base voltage of 3.3 V and thus it turns OFF.
In this situation the LEDs also shut off, preventing any further discharge of the battery, which protects the battery from over discharging.
A series resistor with the LED positive line ensures that the LEDs are protected from over current and are always safely illuminated without any possible harm or damage.
The limiting resistor can be calculated using the following formula:
R = (VBattery - VLED) / ILED
R = (Battery Voltage - LED forward voltage) / Total LED safe Current.
Example:
Battery Voltage = 4.2V
LED Voltage = 3.3 V
LED Current = 20 mA
Then,
R = (VBattery - VLED) / ILED
= (4.2 - 3.3) / 0.02
= 45 Ω
R (Power) = (4.2 - 3.3) * 0.02 = 0.018 watts or simply a 1/4 watt should work...
The next morning when sunlight falls on the solar panel, the BC547 yet again disables any conduction of the 2N2222 BJT and the LEDs, initiating a fresh charging cycle for the battery.
The above cycle now keeps repeating each day and night providing the required automatic illumination of the garden premise using this simple, versatile garden LED light circuit.
You may also like this PIR Controlled Solar Garden Light Circuit
Solar Garden Light with Regulated Battery Charging
The following diagram shows how the above simple design can be upgraded into an automatic solar garden light circuit with regulated battery charging.
The automatic operation of the LED lamp stage is actually exactly identical to our previous design, the only difference being the inclusion of the voltage regulator stage incorporating another 2N2222 BJT in an emitter follower configuration.
As we know that in an BJT emitter follower configuration, the emitter voltage of the BJT follows the base voltage, meaning the emitter terminal of the BJT replicates its base voltage.
However, due to the BJT's internal base/emitter voltage drop of 0.6 V, the emitter voltage is always around 0.6 Volts lower than the base voltage.
In the above regulated solar garden light circuit diagram, since the base of the left side 2N2222 emitter follower regulator BJT is clamped with a 5.1 V zener diode, means that its base voltage is fixed at 5.1 V, regardless of the solar panel voltage.
Therefore, the emitter voltage of this regulator 2N2222 BJT will be always fixed at around 5.1 - 0.6 = 4.5 V.
This 4.5 V fixed output is what we require for a safe charging of our 4.5 V battery, which means the 4.5V battery can be never charged above its full charge level of 4.5V, ensuring a safe regulated charging for the battery.
Parts List
- Resistor, 1k, 1/4 W CFR = 3
- Resistor, 10k 1/4 W CFR = 1
- LED limiting resistor and Battery limiting resistors as discussed previously.
- BJT 2N2222 = 2
- BJT BC547 = 1
- Rectifier Diode 1N4007 = 1
- Zener Diode 5.1 V 1/2 watt = 1
- Zener diode 2.7 V 1/2 watt = 1
- LEDs as per requirement and battery capacity.
- Solar Panel = 9V to 12V, 500 mA
Using NPN Transistors
The above explained designs can be also replicated using two NPN transistors as shown in the following diagram:
Solar Pathway Light Circuit with Constant Voltage
If a Li-Ion battery is intended to be used for the above explained circuit, a constant voltage feature becomes crucial for safeguarding battery life and prolonging it.
The following circuit show how this may be done by adding a simple voltage follower regulator circuit:
If a 3.7V Li-Ion battery is used, make sure to adjust the 10K preset to achieve precisely 4V across the output points where the battery is supposed to be connected, do this adjustment without connecting the battery.
The 4V level ensures that the battery is never overcharged (at 4.2V) and this also allows the circuit charge the battery without a constant current supply.
1.5V Solar Garden Light with Enhanced Features
The following solar powered garden light was designed by Mr. Guido which includes additional features such over charge and low charge cut off for the battery and with a Schmidt trigger.
This ensures that the connected battery is never allowed to charge or discharge beyond unsafe levels.
The main attraction of the circuit is the use of a single rechargeable AAA penlight cell, which is able to light up a 3.3V high bright LED through an attached Joule thief circuit.
High Power 12V Garden Light Circuit
The following image shows a high power automatic garden porch light circuit using a 12V 7 Ah battery. The LEDs used are high power 1 watt LED each. Since 9 LEDs are used the total power output becomes 9 watt.
The circuit is designed to automatically switch ON the LEDs when the darkness level drops sufficiently and the solar panel voltage drops below 3 V.
The LED series resistor values can be calculated using the following formula:
R = Battery Supply - LED FWD V Drop / LED Current
= 13 - (3.3 x 3) / 0.3
= 2.1 / 0.3 = 7 Ohms
Resistor wattage = 2.1 x 0.3 = 0.63 watts or 1 watt.
The solar panel can be rated at 18V, 3 amp. The battery specification is 12V, 7 Ah. The solar panel output voltage is regulated using the LM338 voltage regulator.
Make sure that the 5K pot of the LM338 circuit is precisely adjusted to produce 14V for charging the 12V battery.
Have Questions? Please Leave a Comment. I have answered over 50,000. Kindly ensure the comments are related to the above topic.
Hello.
I am electronic engineer also. I am in Canada know but originally i am Iranian.
I look at your circuits . I don’t work in designing field but i work in repair and service field and i was in one Solar Farm installation in my country . 10 MW .
Best Regards.
Mohammad.
Thank you for your introduction, glad to know about you!
All the best to you…
Good afternoon i did email you previously and thank you for your reply but i am struggling to convert the 6v solar panel with a x3 1.5v rechargeable batteries onto a circuit board having never done this before so want to make sure when i do my first circuit board ad transfer you circuit diagram i will be a lot better infirmed. So is there anyway you can send me a overview of how i would transfer this onto a circuit board if you have the time please?
Hi Kevan,
You will have to connect the 3 cells in series to make them compatible with your 6V solar panel.
However, if this is your first circuit project then I am afraid you will have to first learn how to solder the parts on a PCB.
There are many good youtube videos which you can refer to, to learn how to put components on a PCB and assemble them by soldering.
Please let me know if you have any further doubts…
Hi. I haven’t successfully completed one of your previous circuits with the solar panel yet because the panel has a broken wire and the leds stayed on and flattened my battery.
I’ve now fixed the solar panel, however i wanted to ask whether and if the diodes actually are zenner in this first circuit. “However when dusk sets in the solar voltage begins to drop, and when it drops below the zener diode rating”. I looked up the data sheet for the 1N4007 diode and there wasn’t any mention of a specific reverse breakdown voltage or the name zenner anywhere. Thanks Tony
Hi, I am extremely sorry for the confusion. There’s actually no zener diode in the first circuit, I will do the necessary corrections in the explanation soon.
Also, please try the following diagram instead, because in the above first diagram the LEDs will start illuminating as soon the solar panel voltage starts dropping below 4V, which is not good. In the following diagram, the LEDs will illuminate only when the solar panel voltage has dropped below 1V.
Please let me know if you have any further questions…
That was an extremely fast reply. Thank you. I can see that this link to the 18v panel and 12v battery will be very useful in the future as mine and most other general use solar panels for boats, camper vans etc are either just under 20v output or 40v output….and in this linked diagram and circuit i assume the zennr breakdown voltage must be around 11.5v. I will probably try this one later….however, the first circuit was perfect for the little panel i had spare (6v), 4.5v battery from a broken tech piece and a set of led mushroom lights that i already had that were originally powered by 3 series button cell batteries. I’m pretty sure i should be able to tweak the circuit now I’m sure a zenner wasn’t required in this more simplistic circuit. Cheers, Tony
No problem at all, I am always happy to help!
Your are absolutely correct with your assumptions, regarding the previous circuit design.
For your 6V application you can try implementing the following design:
If you can tell me the mAh rating of your rechargeable battery, then I can provide you with the value of the Rx resistor…
Cheers!
Thanks for the new 2 npn resistor circuit, i think the amps coming out of the small solar are pathetic and this second circuit might be more sensitive to this. Two questions that probably come out of my lack of understanding of electronics..1. Could you explain why the first diode coming aways from the solar panel is necessary (i don’t want to lose any more volts than is absolutely necessary…. and 2. The final diode after the 2n22222 transistor looks like a throw back….or forward… to not depleting the battery too much…in which case would this be a 5v zener in reverse? Sorry if I’m seeming stupid now. Inexperience. Cheers
Thanks for the insights! You are absolutely correct, the diode which is connected to solar panel positive is simply not required, because the second diode can handle an accidental reverse polarity situation as well, and safeguard the components.
So you can safely eliminate the diode associated with the solar panel positive terminal.
Yes, the 2N2222 emitter diode can be replaced appropriately with a zener diode to prevent over discharge of the battery.
Let me know if you have any further doubts!
Hi Swagatam, i tried 12v high power garden light using lm338,but i cannot get it work.Please help me to get it work. Thank you.
Hi Vladimir, could you please tell me what exactly is happening with your circuit, I will try to solve it…
Hi Swagatam, Thank you for quick respond. Sorry, i forgot to put a diode like you mention. After this simple fix it is working now. Is it possible to put a diode in your on line site diagam circuit? Thanks again. God bless you!!!
Thank you Vladimir, Glad it is working now. Which diode are you referring to? Is it the zener diode at the base of the lower BC547 transistor?
Hi. the diode is not in circuit. it mention in red under circuit.
“Please remember to connect a Diode between R1 and the battery positive.”
So i did like you said
Ok thanks, understood, yes that diodes is important to make sure that the battery does not self-discharge through the 240 ohms and the potentiometer.
Hi Swagatam, without added diode led’s did not turn on at dark time, that was my problem. But i did not think about discharging battery also with out diode….
Thank you Vladimir,
The actual purpose of that diode is to prevent battery discharge through the LM338 resistors, but even without the diodes the LEDs should have illuminated?
Anyway, I am happy the circuit is now working for you.
Swagatam… I bought several landscape lights and these are 1.2v ni-cad units. They didn’t come with circuit diagrams and two have failed after a week or two. I suppose they could be faulty due to infant mortality and the store will exchange them for new units but it would be nice to tinker with them if I knew the parts layout and specs. Thanks for providing this webpage.
Thank you Ozzie, you can perhaps try the following design to revive the dead Ni-Cd cells and try experimenting with them:
Hi Swagatam,regarding 3.7V Li-ion voltage circuit. I am trying to make solar light powered with 6Ah Li-ion unprotected battery, which will turn on only at night, and only when PIR sensor detects movement. LEDs power should be about 0.5W and I expect ~60lm from them. What is the most efficient way to make this, as I need long last device without additional charging?
I saw all topics for solar lights and PIR sensors, but did not find any that I know how to modify for my requirements. Do you maybe have a PCB design that will fulfill those requirements?
Thank you in advance and best regards,
Tibor
Thanks Tibor,
To get accurate results you will need a two transistor circuit which will ensure that the LEDs do not turn ON until it is totally dark outside.
An additional LDR might not be required, we can manage with the solar panel voltage for the detection.
I have understood your requirement and will design the entire circuit soon and let you know, with all the part specifications.
Hi Tibor,
here is the complete circuit diagram that will fulfil all the specifications you need in your design:
Hi Swagatam,
this looks like something I need! Thank you very much for your help!
Also, I want to know why you choose 9V and 1A panel? Isn’t 1A not enough for 6Ah capacity?
And if I want to use 6V panel, whould it still work in this configuration?
Btw. I saw you wrote LED 1W, what will be the difference if I use 0.5W LED?
Thank you!
No problem Tibor, I am always happy to help!
In the shown diagram, the two diodes and the transistor combined will drop around 2.5V, so the panel voltage has to be at least 2 volt higher than this drop.
If your battery is 3.7V then its full charge level will be around 4.1V, that means the solar panel must be rated at 4.1 + 2.5 = 6.6V, but considering the sunlight fluctuations it is recommended to add 3V more to the panel, so it must be around 6.6 + 3 = 9.6V or higher.
Yes, for a 6Ah Li-ion battery 1 amp current is quite low, in that case you can consider adding more panels in parallel and upgrade the input current to 3 amps.
In that case the transistor will need to be replaced with a 2N3055 and the base resistor reduced to 50 ohms 1 watt.
The diodes can be 6A4 diodes each.
Also, there’s one mistake in the diagram. The 1K connected with the base of the 2N2222 must be removed because we want to activate the 2N2222 only through the PIR, and not from any other source.
For the LED, you can use any desired 3.3V LED, just make sure to change the series resistor accordingly.
Sir: where does one get all these components. Thanks
Hello Leon, you can search for the following phrase, you may find many good electronic stores for buying electronics spare parts:
buy electronic spare parts
Sir: need a circuit board for a LED lite string 3-5 volt dusk to dawn for a cross I am trying to light .Would like a board made in the USA. have a 12 volt solar panel on the cross. Need your recommend as I have failed many times because at 83 years old I have tremors bad and soldering is areal struggle. Thank you
Hello Leon,
According to me, the last circuit from the above article will be most suitable for your application. If you are having difficulty soldering, you can hire somebody to do it for you. Please let me know if you have any further questions.
I’d like to know how to convert a battery Operated garden stake globe into a solar powered garden stake globe (using a dollar store solar-lit garden stake). Is this possible? What should I do?
I do not know the voltage and current specifications of the units you have mentioned, so it is difficult for me to suggest.
EB, do you have a dc voltmeter? if yes then we need pictures of your project. if the original light uses two bateries that would be 3 vdc, if the dollar store uses one that is only 1.5 .
Hi swagatam
I need your help, for making a circuit of AUTOMATIC CUT OFF WHEN SOLAR CELL PLACE UNDER THE SUN AND TURN OFF LIGHT & CHARGE BATTERY. WHEN I PLACED THE SOLAR CELL UNDER THE SHADOW THEN AUTOMATIC LIGHT TURN ON, on battery
Hi Kartik,
Automatic cut off is not required. You can simply use a LM338 IC regulator and set it to provide a constant voltage to the battery which should be slightly lower than the extreme full charge level of the battery.
Here’s the design which you should build:
Thanks Swagatam, Let me try this solution…
Sure, no problem.
I have bought a 3W 6V solar panel what value of diode,resistor and transistor and led bulb should I use for a solar lighting system project. Can you please tell the assembling diagram too.thanks
You can try the following setup:
Adjust the zener diode so it creates around 4 V across the battery terminals (without connecting a battery)
The battery can be any 3.7 V Li-ion battery
Hi Swagatam, many thanks for the awesome website and content!
The wife bought some LED garden lights, but they don’t come with solar charging. I’ve decided to try and build the solar charging + automatic dusk toggling. These lights come with an IP44 3x AA enclosure, and I’m wondering if I can reuse them. The LED lights are 10x 0.3W. Based on this, am I correct in thinking I can use the second circuit listed under the “Circuit Diagram” title, without modification?
Cheers!
Hi TJS,
yes you can use the second circuit, however if you find the 2N2907 heating up a bit then you can replace it with a BD140 or TIP32 transistor. If you find the brightness is not optimal, you can try reducing the a 10 ohm resistor or the 1K resistor with some trial and error.
Hi Swagatam, many thanks for the quick response. I’ve taken on board your suggestions for alternative components.
What changes would be needed to use a CL-SM3P cellevia power solar panel? Is it too powerful for this application?
Thank you TJS, can you please tell me the specifications of the solar panel in terms of its voltage and current? I will try to solve it for you.
Hi Swagatam, sure thing. Here goes:
Really appreciate your help!
Thank you TJS,
17V is a lot for a 3.7 V battery. If your battery is a 3.7 V rated then either you may have to use a step down regulator to control the voltage or use a 8 V solar panel instead.
Understood sir. I’ve found a 6V 2W panel. I believe this will work with the circuit we have been discussing.
yes, that should be OK, however if your 3.7 V battery would still require some kind of voltage regulation so that it is not overcharged beyond 4.2V. I would recommend the following type of simple regulator. The resistor can be a 1K resistor, the transistor can be BD139 and the zener diode can be selected such that the transistor emitter output generates around 4.2V. Check the 4.2V after putting a load resistor of 470 ohms across the emitter and ground of the circuit.
Hi Swagatam. Sorry, but I’m a little confused. Where do the lights go, in the diagram you’ve shared?
Hi TJS, here is the complete circuit diagram with the regulator. The zener diode value should be selected such that a full charge level of the battery is available across the points where the battery needs to be connected. This must be checked and set without the battery connected.
Hello, I made this system, but the LED lights up too early, where to insert the resistor to delay the LED lighting. Regards
Hi, thank you for trying this circuit….However If your solar voltage drops below 1V then the transistor will switch ON and the LEDs will light up, We cannot do anything about it.
Thank you for the quick reply. My problem is that the voltage is still 3 -5v and the LED is already starting to shine, I will add that the 1 Watt LED, 6v solar panel and 3.7v battery should the 1n4007 diode be only behind the 1k resistor or the 2n2222 transistor also give ?regards. Ps. very helpful site thank you very much!
At 3V you can check the base/emitter voltage of the transistor, if it is above 0.3V then the LEDs might start to shine a bit. To avoid this you can try adding a 1N4148 diode in series with the gate terminal of the transistor. Anode will go to the base and the cathode towards the 1K resistor.
The right side 1N4007 diode is important and cannot be removed. The left side 1N4007 transistor is only to protect the circuit from an accidental wrong polarity connection of the solar panel. If you are sure that the polarity connection is correct you can remove the left side 1N4007 diode
amazing to me your depth of knowledge, did you get most of your knowledge from a certain book? I am very interested in building resourceful projects. Maybe you have a suggested reading? please keep posting all your great ideas.
Thank you for your kind words. My knowledge of electronics has come from books and practical experience. Do let me know if you have any further doubts or questions.
Hi SwagatamRegarding your last circuit “High Power 12V Garden Light Circuit”, could you please advise as to where the best placement of a 12V Zener diode would be for low battery cut off? Would it be between Q2 base and battery +, or would it need to be in series with the 1K resistor and battery positive?
Many thanks for a very impressive site BTW
Thank you Duncan,
As correctly guessed by you, it must be in series with the 1K base resistor of TIP122
So I tried this insertion over the weekend, and it did not work as intended. When the 12V zener was connected, the lighting was illuminated, but very very dim. Even after removing the 1K resistor, the effect was the same.
Any ideas on this for a solution?
In that case you may have to reduce the value of the zener diode. You can try a 11V or 10V zener diode and check the response. However, first you may have to confirm whether the LEDs are illuminating brightly or not without the zener diode. If it does then the problem may be with the zener diode, and you can try using lower values.
Yes, my LED lights do illuminate fully without the diode. But, to give feedback, as you suggested I tried an 11V zener, and this seems to work. Although not 100% what I’d like, as it drops the battery down to ±10.8V which is not the best level to have your battery at.
But I guess it’s better than running the battery completely flat and into irreversible damage. What was interesting is that the diode starts to activate at around 12.2V and starts to put the lights into like a “limp mode”, at about ¾ brightness, then gradually dims until the zener voltage kicks in for total shut off.
Thank you for the feedback and update! It looks interesting, however I guess a simple zener network may be too basic to provide accurate cut-off results. So getting perfect results might not be possible using a zener diode only. Instead, a combination of an opamp and a zener diode might do the job to provide the desired accurate results.
Hi Swagatham,Thanks for the response and appreciate.As you asked me for specification of type of batteries and voltage and amperage. To myself clear I thought it would be more precise if I sent you pictures of the units I have. I have three varieties . Please have look . But it seems there is no way to send photos. 1.AAA 1.2V. 600mAh,NIMH BATTERY, one battery(2) AA 1.2V 600mAh,NIMH ,2 batteries.(3)AA1.2V 600Ah,Ni-Cd ,1 battery. All solar panels. I have AC to DCpower supplies of 5 V DC out put. Or any you may suggest.
Hi Ravi,
You can try two NiMH in series, and connect it with the following circuit:
You can replace the solar panel with your 5V DC input.
Then adjust the 10K preset such that battery points are set at exactly 3V. Do this without connecting the batteries initially. Once the preset is set then you can connect the batteries.
For the LEDs you can use 6 nos of high bright 20mA LEDs in parallel
Hi, My name is Ravi and I am in UK. I USED TO LIVE IN USA ALSO. I have accumulated lot of solar path lights and others. Here in UK climate does not offer sun shire consistently. Hence can charge the solar panels fully. So I now decided to use DC power. I have combination of 1.2 V and 1.5 V battery models. What modification I need to add appropriate resisters/ and some thing else.I WOULD BE GREATFUL IF YOU COULD PROVIDE ME A CIRCUIT DIAGRAMS AND RESISTER VALUES, I WILL SOLDER THEM ON TO THE CIRCUIT BOARD. I AM REASONABLY HANDY TO THIS IF I KNOW WHAT TO DO. IF you feel some other details you need to help me, I will provide. Kind regards. Ravi
Hi Ravi,
Can you please tell me the specifications of the battery. Are they rechargeable type, such as NiCd or NiMH type? If they are rechargeable type then you may need a charger circuit also to charge them from an AC to DC adapter.
i have a solar panel which used to runasmall water fearute the circit got smashed at a house move time the remains suggest it was a simple 1fuse 1 diode system the remains cannot be identified correctly need fuse and diode identified or suitable substitutes solar working ok
What is the voltage and current specifications of the solar panel?
no idea it was bought as a working unit by my son all i can say is the water fountain was a 12 volt unit worked ok in his garden then he moved to oz hence i ended up with it the solar panel has no information on physically its 17 by 12 ins that’s actual solar panel measured inside its housing i have a voltmeter panel shows over18 volts in full sun,thanks for answering
OK, in that case, the fuse amp rating will depend on the amp rating of the load. For example if the max current of the load consumption is 2 amps then the fuse can be rated at 2 amps.
And the diode can be a 1N5402 assuming your panel current is less than 3 amps.
new problem fan not working still works of 12 volt battery solar panel still giving 17 volts as soon as you switch fan on voltage from solar panel drops to almost nothing
It means that the solar panel current delivering capacity is far too less compared to the fan’s current rating….you can confirm the panel’s AMP output capacity by connecting an ammeter across its terminals at peak sunshine.
We’re due to move into a new house in the Spring of 2023 for which I am preparing my “Charlie Dimmock” design for the back garden.
I need to include lighting for the said design, ideally not using power from the grid, i.e. instead using solar power. However, rather than having individual solar lights, I need advice on perhaps having a single solar collector, placed in the best possible position for the sun and a battery storage system from which the garden lights will be fed when the sun goes down.
However, to compound things, we are also considering PV panels to hopefully reduce our reliance on the grid house power consumption, so would it be best to combine the two systems?
Whilst I shall print off the content of your web article, any early advice on the aforementioned would be mush appreciated.
It may be possible to extract the power from the PV panels for the garden lights so separate solar panels may not be necessary for the garden lights.
If you tell me the total wattage of the LED lights and the number of LEDs, I will try to figure out the automatic system and the controller for the LEDs.
Hi Swagatam. i’m EN
I have a question.
For example, if I think I use 50W of a solar cell, is there a way to calculate the specifications of the battery or how many W of LED can be used?
Hi EN,
Can you please tell me the voltage rating of the solar cell, I will try to figure it out for you!
solar Power 30W
Max power voltage 18V
Max power current 1.66A
open circuit voltage 21.6V
Let me know if you need any further information. Thank you
You can use a 12V 7 Ah battery with a LM338 solar voltage regulator set to control the max voltage to the battery at 14V.
For the LEDs you can use 3.3 V 1 watt LEDs. Make 3 LEDs in series and connect 5 of these strings in parallel. Each string must have a individual series resistor rated at 7 ohms 1 watt
The maximum voltage of the solar cell is 18V, but is there a reason why the battery uses 12V?
Also, I wonder why LEDs are used in a combination of series and parallel.
How many hours is the LED light based on this connection?
Using a 12V battery leaves a good margin for the battery to charge even while the sunshine is not at its peak. For LED total forward voltage must be lower than the battery lowest voltage level. With 3 in series, the total forward voltage of the string becomes 9.9V which means even if the battery voltage drops to 11V the LEDs will still remain illuminated. The LEDs will not illuminate if the series forward voltage of the LEDs become higher than the battery voltage. With a fully charged battery the backup time should be around 4 to 5 hours.
The battery should be charged through a LM338 regulator
Hi. swagatam.
Do you have a sample circuit for your explanation?
And I hope to be lit for more than 10 hours using 10 LEDs.
Hi EN,
I have updated the diagram for you at the end of the above post. It will last for 10 hours, using 9 nos LEDs, 1 watt each
Thank you for your answer. I’ll test it.
Previously, the LED was said to operate for 5 hours, but the circuit is a circuit that operates for 10 hours. What’s the difference?
And if I change the specifications of solar cells and batteries, do I just change the resistance in the circuit?
Sure, you can build it and let us know the results.
Previously 15 LEDs were used, and now only 9 LEDs are used, therefore the backup time has increased. These are only approximate values, the actual value can be found only by testing it practically.
You don’t have to change anything in the circuit upto 30 V input. But as the solar voltage is increased, the heat on the LM338 will increase proportionately.
Thank you for all the circuits you proved with your emails, I always look forward to receiving your emails to see what circuit ideas you have.
Many thanks, keep going you should do a YouTube channel I would join.
Thank you so much, I appreciate your kind response.
I have a video channel, you can view it here: https://www.youtube.com/c/SwagatamMajumdar/videos
hie.i would like to design the above solar light cct.can i connect two batteries 3,7 v in series to increase power stored and lighting time
How long does the above light ís on before switching offf
Hi, yes you can use two batteries in series and configure the LED series connection accordingly.
How long it stays ON will depend on the battery capacity and charging conditions
Hi Swagatam.
There’s a question in your circuit.
“a simple voltage follower regulator circuit”
What does 10K preset mean in this circuit?
Regulator? resistance?
Additionally, I don’t have 8050 or 2N222. 135D was used. No problem?
I’ll be waiting for your response. Thank you.
Hi EN, the 10K is a variable resistor preset or a trimpot.
I could not find the datasheet of 135D transistor, so I am unable to suggest whether it can be used or not.
Thank you for answering.
It’s BD135 from Onsemiconductor.
In the above quesiton circuit, do i have to use tow 1N4007? Tow letters were written, so a circuit was created, but the battery does not charge even when exposed to sunlight.
BD135 can be used, You must adjust the 10K preset accurately so that the emitter voltage reaches the full battery charge level across the battery terminals. Measure this without connecting battery. I did not understand what you meant by “tow 1N4007”
The solar panel current must be correctly rated as per the battery specification, only then the battery will charge.
solar panel 6V, 0.35A, Battery 4.2V, 2550mA
Is there a way to send pictures? Mail or another?
Thank you
Additionally, how do you adjust the 10K preset?
I want to know the formula
You can use voltage divider formula to get the base voltage…
and then add 0.6 to the result….this will be the emitter voltage.
Base voltage = Vin (R2 / R1 + R2)
R1 = 1k or 1000 ohms
R2 = preset adjustment value
Vin = 6V
Emitter voltage = Base voltage + 0.6
Did you confirm the 0.35 A and 6 V with meter? Check it with meter it might be less than that. By the way 0.35 amps will not charge a 2550 mAh battery efficiently…it should be minimum 0.5 amps to 1 amp. Pictures are not required, values are enough.
In fact, solar panels are measured lower than 6V.
I don’t know how to approach it,,, but I should study again while looking at the circuit diagram.
Thank you.
The minimum voltage can be 5V, but the current should be between 500 mA and 1 amp.
When the actual test was conducted, the panel was measured at 4.4V and turned on only 3 hours after charging for 3 hours.
I have a question. Why do you use two 1N4007 diodes in the first circuit?
Because of the principle of operation of the transistor?
I ask questions because I lack a lot of knowledge.
The left side diode is actually not required, it is placed to safeguard the circuit from an accidental reversing of the solar panel polarity. If you are sure you will always connect the panel polarity correctly, then you can remove the left side diode.
Thank you for your answer.
If I have any questions, I’ll ask you more!
Have a good day.
Sure, no problem.
Would appreciate if you add costing of components used in the circuit.
I tried adapting these ideas to understand how 200 blue LEDs ((3.2V, 20mA each)) can be lit from one single 1.2V NiMH battery slow-charged from a small solar cell, but I remain mystified. It’s not for any class ((I graduated college in 1979, LOL!)) but I’m wondering, because I’d like to repair 2 light strings if that’s possible. I simply haven’t been able to get from here, to there…
Many thanks in advance for any information or links!
Thank you for your interest in this concept. 200 nos are too many LEDs, and a NiMH might not have sufficient current to handle this. However a Li-ion cell with along with a joule thief circuit might be perhaps able to handle this load
Thank you for your reply!
That must be why the string never worked from the start. Now that I know to not keep struggling to make the original thing work, I’ll start from the ground up so to speak.
Sure, no problem!
Hi SM. I work for a maritime museum and we have a lighthouse which was fitted with a 120v incandescent lamp. I would like to convert this to a pulsating/breathing LED lamp. I have did some research and came across you forum. Thank you for the diagrams. My question is using a 6v agm battery what size of solar panel would be needed? I have read that to charge a 6v battery you should use a 7-9V solar cell. Also any ideas on the pulsating/blinking/breathing feature to simulate an actual lighthouse?
Hi Dennis, for a 6V battery you can try a 9 to 12V solar panel, and use a constant current and constant voltage charger. The current rating of the solar panel can be 7 to 10 times lower than the battery Ah value.
for the rotating light effect you can probably try the following circuit
https://www.homemade-circuits.com/police-ambulance-siren-circuit-with-rotating-beacon-light/
hello, I found this site & followed all the steps but the LED lights could not turn off even during the day. what could be the problem
Hello, connect the transistor base with its emitter manually and check if the LEDs shuts off, if not then your transistor is faulty.
do I basically need to use specifically the transistor indicated on the diagram
It just needs to be a PNP transistor, that’s all
In the picture whose Pictorial Diagram is given, how many volts/amperes is the panel and is the battery 9V ni-cd? Can 9V ni-mh or lithium be used instead of 9V ni-cd battery?
In what range should the mah value of the battery be? thanks
I have updated the diagram with more details, and also provided the relevant calculations.
The battery shown in the diagram is NiCd, Li-Ion or NiMh can be also used. For Li-Ion and NiMh batteries the 10% figure indicated in the R3 formula will change to 50%
Hey, 7.4Volt 2600mah (2 serial 3.7V li-on batteries), how do I set up a circuit for a battery? Can you help me build the circuit? For example, how many volts should the panel be? can you draw a circuit diagram. Thank you
You can use a 12V 1 amp solar panel, and adjust the output voltage using a LM317 circuit to precisely 8.2V and then you can charge your series battery safely.
Hello, I’m trying to design a solar dusk to dawn light using a 3.7v 18650 2400mah battery, a single bright white 60-80lumen light with the smallest solar cell that charges on cloudy days. The light must maintain light atleast 10 hrs at night. The led possibly could pulse at 50 cycles as to save on power and not notice blinking by the naked eye. Thank you.
Hello, you can use a 100 mA or 50 mA straw hat type LED, and use with your battery for a 10 hour back up. The solar panel must e rated at 6V, 1 amp. You will need an auto cut off circuit for charging the battery with this solar panel.
Thank you, would you have an existing circuit diagram?
You can try the last circuit from the following article:
You may replace the P mosfet with a 2N2907 transistor, and replace the 2N6284 transistor with 2N2222
https://www.homemade-circuits.com/battery-deep-discharge-protection-circuit/
How can the pcb pictorial be done on a copper clad board? I have only an inkjet printer and want to build this circuit?
You can refer to this article for the details:
How to Make PCB at Home
dear sir; the above constant voltage circuit designed with 6v battery and 6-8v/2w solar panel, 2 transistors and few resisters and load of (24) .5w high power leds is really great. my question is if I increase the load to (44) .5w and select the a/h of battery to 20a/h also double the the amperage of solar panel would circuit work properly? I thank you very much..
Dear Vj, yes you can definitely upgrade the circuit by suitably modifying the parts, and the battery. You will have to use a TIP127 for the transistor, 10k resistor for the base, the charging current limiter must be adjusted to a value which allows only 1 .5 amp to 2 amp current for the battery charging.
I’m a 75yo woman and have no electrical background, but am willing to learn new things. I have purchased a commercial solar powered pump package with a fixed solar cell. The pump turns on with a manual pushbutton switch. The small electrical storage battery (12v) does not hold enough electricity to power the pump through the hours after the solar cell loses sunlight until the next day. Once the power supply is exhausted, the pump switches off and remains off until the manual switch is pushed again. It is in a remote area, so the pump might be off for several days until I can get back to switch it on. I am making a solar tracking unit to extend the hours that it is in sunlight, which will hopefully extend the battery service also.
Here is my question: Is there a way to use a small solar cell to power a switch that will bypass the manual switch and turn the pump back on when the sunlight is available the next day? If one of your examples above will do that, please tell me which one to use.
You can build and implement the following concept:
Please note that the relay of the circuit will activate ON and OFF momentarily only when the sun light has reached a reasonable peak level. If you want the circuit to activate at a lower peak level of the sun light then you can reduce the relay value to 5V, and also replace the 12V zener to a 5V zener.
Hello Swagatam,
Firstly, top notch support for your ccts. You really are very patient with everyone. Can I ask please, I have a very low power 5v solar cell, how much current loss is caused by the simple single transistor circuit? I presume this one would be the least hungry of the ccts. At the moment I use a switch to feed the leds and automated is definitely the way forward.
Thank you for your time and I hope you have remained healthy through the pandemic.
Neill
Thank you very much Neil for your kind words!
No current would be wasted by the transistor circuit, since the transistor circuit would remain switched OFF. However, a slight current would be lost through the base resistor of the transistor, which would be in a couple of mA may be. You can definitely think of replacing the mechanical switch with a transistorized circuit, with minimal current drain.
Figure 1 & 2 I can’t seem to make it work at all, the same is true for the similar circuit using the 2 transistor version, 2222 & 2907, the mail issues is I can make it light with the battery but it will not shut off the led during the day / charging cycle… Checked and double checked… Help…
Please check the circuit first with a bench power supply, not with solar panel.
With the input DC connected check the voltage across base/emitter of the transistor, it must be 0V, and it should be around 0.6V when the input supply is removed!
With 0V across B/E, the LEDs should be switched OFF, and with 0.6V the LEDs must switch ON
Good morning Sir,
1) What is the advantage of the circuit with the two npn transistor ? Does doubling the transistor increase brightness ?
2) I want to use 14 LEDs (4mm leds) to run for 12hrs with good brightens, using 3.7v li-ion battery;-
a) what should be the capacity of the battery?
b) if I have 2watts 6v solar panels how many can I parallel to charge the battery.?
c) which circuit can I use for this to serve as an automatic solar outdoor(landscape) security light?
Thanks
Hi Ngang, slight advantage is there due to better ON/OFF switching of the LEDs, and better transfer of power to the LEDs.
A 2 watt solar panel will produce 2 / 6 = 0.33 amps or 300 mA current, which means a 4.5 V battery or a 3 V battery can be used having 2 Ah rating
LEDs can be 3.3 V 1 watt single, or 3.3 V 20 mA up to 10 in parallel.
Hello, I have 4 garden lights each one has two 8mm white leds I would like to use only one solar panel,two service all four lamps,but dont know what
size or wattage or voltage to use.
I hope you can help…………Frank
Hi, assuming your LEDs are 50 mA each, and the two LEDs are in series in each of the modules, then for 4 lights the total current required will be 200 mA. Now to illuminate this 200 mA lamp for 10 hours will require a battery rated at 2 Ah or 2000 mAh.
Your solar panel must be around 3 amps and voltage equal to 10 V, with a 7V controller
Thank You..
Frank.
Hi Namaste Swagatham
I just beginning to learn and do some hobby during Covid-19. I have solar powered pedestal light on long post. The switch failed due to water leakage. I am trying to replace the switch. But I need to replace the resister to reconnect the wires. I cannot recognise the resister. It is tiny blue resister connected to terminals. This is because the switch has three positions. Semi / Off / Full. The switch has six terminals three on each side.The resister is connected semi and off terminals. Perhaps I I could send photo, but do not know how to include in this comment. Please help. I have also other small hobby projects which I will let you know. Thank you very much. I am from UK, SENIOR CITIZEN. RAVI
Hi Ravi, without seeing the image it can be difficult for me to understand the fault. What you can do is, upload the image on any free image hosting site online, and provide me the link, I will quickly check it out and try to solve it for you….
Hi Swagatam,
I have found several of your articles very interesting and delightful. However, I have a project that is VERY unusual and have not been able to find a circuit to solve my problem.
I am attempting to back light a lithographed photo that is mounted on an outdoor plaque. I want to use a single white LED (or a single 5050 RGB strip light LED) to backlight the lithograph. Normally, I could use a solar powered Garden light circuit, however I need it to stay lit during the daytime AND night time and still charge a battery (1.2V NI-CD) for the nighttime use. I can use 2 solar cells, one for daylight use and the other to charge the battery for nighttime use, However, I am not sure of the best way to isolate the two solar cells so one powers the LED during the day while the other charges the battery and then at night switches to the battery. Any help would be appreciated. I am an electronics tech with some engineering (self taught) background, but this seems to be eluding me for some reason. I hope you can help. Thanks in advance.
Thank you Tony, glad you found them interesting!
I think two alternating cells may not be necessary, instead multiple cells could be attached in parallel which may be rated to keep the LEDs lit up for 24 hours with each charge. Similarly the solar panel may be rated to ensure both the cells are optimally charged each day.
If you provide me the LED current and voltage specifications I can provide the estimates for the solar panel and charge control specifications
Alternatively, if you think two alternating cells would be a better choice, I can suggest an appropriate design for that also….
Thanks for that it’s really worth to query the designer appreciate it very much
It’s wonderful finding you on Pinterest
Rgrds,
Eduardo
It’s my pleasure and happy to help!
After reading I’m trying to find that zener diode describe but not available in anypart of the schematic diagram pls give details
Thank you for sharing
In the second last diagram, the 10k preset was not included in the original initial diagram, instead a zener was put in that area for getting a fixed output at the emitter side. If you don’t want the preset for customized adjustment you can replace it with an appropriately rated zener diode
I’m new to this website. It appears to be exactly what I need.
Home / Mini Projects / Simple Solar Garden Light Circuit – With Automatic Cut Off
This is a genius little circuit and would be perfect for my Japanese lantern. Is the PCB board available?
Hi, Thanks, and Glad you liked this website and the circuit! However, sorry I do not have ready made PCB for this project, but since the design requires very little parts you can easily assemble them over a small veroboard or a strip board.
Hi. Found this site about 2 weeks ago and built the circuit. First time I have done anything similar for maybe 50 years!! I was a bit apprehensive. However the circuit works well. I am quite happy with it. One problem the LEDs light up too early. It is still light. I am using 4×1.2v Li-ion batteries. I reduced the 10 ohm resistance to 5 ohms. Is there away to prevent the LEDs lighting up before it gets dark? Thank you for firstly the circuit and secondly the time you spend answering queries
That sounds amazing and Glad you could make it successfully. The early switch ON could probably be prevented by upgrading the circuit through a couple of more transistors as shown in the following image:
Hi Swag,
In this circuit, can I replace the 6 LED’s by a single of high Power, say 1W, 3W or 5W?
If so, which changes can I made?
Best Regards.
Nelio.
Hi Nelio, yes that’s possible, the formula for the series resistor is:
R = (Battery Voltage – LED Fwd voltage) / LED Current
Hi,
You are refering the first circuit.
I was considering this one :
Solar Pathway Light Circuit with Constant Voltage
Nelio
Yes I was referring to the first circuit, in the pathway circuit you may have to connect a resistor in series with the collector of the LED transistor. This resistor should be calculated using the previous formula
Ok.
Thanks.
Best Regards.
Nelio
Glad to help!
https://drive.google.com/drive/folders/1oCAPL9J53O0QZP7SXJnlNtnkq8NQ9QoY?usp=sharing
I have reverse modeled the board. If you are curious to see it, you can find it here as .jpeg file. Most of the elements I was able to read, but not all.
It is difficult to understand the diagram in this form, please draw it in proper schematic form with correct symbol and pin direction, I will try to figure it out.
Hello Swagatan,
I found your site by accident a week ago and I`m completely hooked up.
I have an old solar lamp that uses 1.2V Ni-CD battery and 1 piranha LED. It has an LDR to turn it ON/OFF, however I notice that even without it, it turns ON/OFF if the Solar Panel is illuminated.
Can you reverse engineer this board, if I provide you pictures of it, as I want to make myself more of these DIY. It says 3033 on one of the elements, has SGL0047-3033 printed on it. I could not find anything on the internet about it.
Thanks for your answer in advance.
Thanks Dimitar, I am glad I found my sire useful.
I think an LDR is not necessary for a solar automatic LED circuit. The first circuit from the above article will also do the same. When sufficient light applied on the solar panel, the LEDs will remain OFF, and they will switch ON when the light becomes weaker.
Thank you for your fast reply, Swagatam.
Is the first circuit going to work at 1.2V, or must it be 4.5V, 3 NiCD/NiMH batteries in series?
Yes it should be 4.5V. At 1.2 V the LEDs will not light up.
I understand.
The solar lamps I have use 1x 600mAh 1.2V NiCD battery and powers a 1W warm white COB LED. I believe they are rated at 3.2V. It lasts about 5-7 hours, depending on the amount of sun during the day.
Can you propose a way to achieve this? Do you want me to send pictures of the board? If yes, how?
Images won’t be required since it will be difficult to identify the parts and the layout from the images.
Instead you can try the following version which uses a joule thief circuit for boosting the 1.2 V to 3 V for the LED:
If the LED doesn’t light up with a 1.5 V cell, you can try swapping the terminals of the winding between the transistor base and the 1K resistor.
Thank you for the great advice, Swagatam!
I found the joule thief circuit on your site, but what was interesting to me is that this solar lamp uses no coil, only a couple of resistors, diodes and transistors.
P.S. My bad, it does have an inductor, it does use a joule thief.
OK, so in that case you can use the diagram which I suggested in my earlier comment. It has a feedback loop which will switch OFF the LED during day and switch ON during night at 1.2 V supply
Sounds like great systems. I am not however looking to build a system but buy a ready made system for a large garden area where I can plug in various low voltage garden lights or Christmas lights. Any suggestions? Getting tired of the cheap solar lights from the hardware store and too far to run 120V. thanks.
Thanks, please provide the LED specifications and the connection details that you wish to use, I’ll try to figure out the required set up accordingly
I have made 40 W street light solar circuit I m working in offline solar inverter manf company I m not getting desired output 2 V instead of 12V but cut off low & high is working properly.
I could not understand your question.
Sir I have made a circuit with help of your diagram for 40 W solar street light circuit I m able to adjust low & high cut off but sir I m not getting Required output when solar voltage is given I m getting only 1.9 V max
Dweep, please show me your exact schematic so that I can understand it…upload it to any free image hosting site and provide the link here….
Hi Swagatam –
thank you for all the information here! I’ve made some simple LED circuits before, but I’m new to solar. I am making a night light for indoors – the LED doesn’t need to be very bright, but there won’t be as much sunlight to charge it. Can I increase the size of the solar panel to maximize the charge? Would I need to worry then about overcharging the batteries if the panel got direct sunlight?
Thank you Hannah, yes you can increase the solar panel size for maximizing the output, but stronger sunlight may harm the battery in that case. If you can provide the battery specifications, I can suggest the controller circuit for you.
Thank you! I haven’t bought my batteries yet, but I was thinking about using 2 Kentli Li-on rechargeable AAs – – they output 1.5v 2000mA. I have some flexibility in my design so I could use larger batteries, but I’m not powering much – just one standard brightness white LED. I’m mostly interested in longevity – if possible, I’d like to set things up so the light runs for at least 5 hours even if it’s not charged in direct sunlight.
As per the given specs the battery seems to be quite powerful and has a built-in over charge cut off system so it cannot be harmed by the panel anyway.
You can use a 6V 5 watt panel and connect its output directly to the battery for charging. Since the current is only 5 / 6 = 830 mA and will continue to drop as the sun goes down, the voltage will effectively therefore drop to the desired battery level and keep the battery topped up always.
I have a garden PV light PCB but it does not have any visible ICs, transistors, or non-LED diodes unless these components are hiding under a hard circular mound of dried adhesive or maybe heat sink material that is on the side opposite the components. I wish to understand where the conductor tracings connect but this is hidden under the mound. (I would send my photos.) I have minimal circuit analysis skills and hope this simple PCB will be instructive.
You can upload the pics to your google drive and share the link with me here, I’ll try to figure it out
Wanted to say thanks! Will an 18v panel be too high of a voltage (at really low current) for the base of the pnp? I assume the higher (than 12.8v battery) voltage is what turns it off during the day.
Thanks!