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.
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.
https://www.homemade-circuits.com/wp-content/uploads/2013/03/solar-led-lamp.png
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.
https://www.homemade-circuits.com/wp-content/uploads/2024/08/simplest-solar-garden-light-circuit.jpg
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:
https://www.homemade-circuits.com/wp-content/uploads/2024/08/simplest-6V-solar-garden-light-circuit.jpg
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?
https://www.homemade-circuits.com/wp-content/uploads/2022/08/12V-high-power-garden-poch-light-circuit.jpg
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:
https://www.homemade-circuits.com/wp-content/uploads/2022/09/Ni-Cd-zapper-circuit.jpg
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:
https://www.homemade-circuits.com/wp-content/uploads/2023/12/simple-12V-solar-garden-liight-circuit.jpg
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!
https://www.homemade-circuits.com/wp-content/uploads/2023/12/simple-12V-solar-garden-liight-circuit.jpg
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:
https://www.homemade-circuits.com/wp-content/uploads/2022/08/12V-high-power-garden-poch-light-circuit.jpg
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:
https://www.homemade-circuits.com/wp-content/uploads/2023/05/solar-garden-light-circuit-diagram-with-regulated-input-supply.jpg
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.
https://www.homemade-circuits.com/wp-content/uploads/2022/09/solar-regulator-emitter-follower.jpg
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.
https://www.homemade-circuits.com/wp-content/uploads/2023/05/solar-garden-light-circuit-diagram-with-regulated-input-supply.jpg
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:
https://www.homemade-circuits.com/wp-content/uploads/2013/03/garden-2.png
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