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.
How it Works
The circuit design is extremely straightforward and may be understood with the following points:
As can be seen in the given circuit diagram, the design basically consists of a solar panel, a PNP transistor, few LEDs, a battery and a few resistors.
The transistor is the only active component which is positioned as a switch for preventing the battery voltage from reaching the connected LEDs during day time.
During broad day light, the solar panel produces the required amount of voltage which is applied across the rechargeable battery via the 1N4007 diode and the resistor R*. This voltage charges the battery gradually from dawn to dusk.
Selecting the Current Limiter Resistor
The resistor R* value should be adjusted as per the specs of the battery for limiting excessive current to it.
The resistor also serves as the current limiting resistor for the connected LEDs when the transistor is switched ON.
Here it has been calculated as 10 Ohms.
As long as the solar panel generates the optimal amount of power, the positive potential at the base of the transistor keeps it switched OFF.
However when dusk sets in the solar voltage begins to drop, and when it drops below the zener diode rating, the transistor slowly starts conducting, illuminating the LEds gradually.
With complete absence of sun light or when its completely dark, the transistor conducts fully with the help of the 1K resistor, and produces full brightness over the LEDs.
The next morning, the cycle repeats all over again.
The circuit can be modified in many different ways.
Circuit Diagram
The above diagram may also be built in the following manner. It looks more sensible now as the resistor is removed from the emitter for facilitating efficient triggering of the transistor.
PCB Design
Parts List
The diagram shows an incorrect transistor number (8050), use 8550 instead.
Recommended Solar Panel Specs
6 to 8V/2 watt
Voltage - 6V
Current - 330 mA
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.
Sparjan says
Sir I not understand 8050transistor.pls explain 8050 and how its use in this ckt
Swag says
Please check any online datasheet of 8050 transistor for the pinouts and other details, you can also use 2N2222 instead of 8050
Vishwa mukh says
Sir,
Thanks a lot for your prompt help.
Thanking you for your time,
Swag says
you are welcome!!
Vishwa Mukh Bharadwaj says
Sir,
I have compiled the part list. May I request you to please confirm if any changes are required:
1. Solar Panel = 2V 380mA
2. R1 = 5K
3. T1 = BC547C
4. R2 = 100 Ohm
5. T3 = BC558B
6. R3 = 1.5K
7. T2 = BC547C
8. R4 = 20K
9. P1 = 20K
10. 1.2V rechargeable cell
11. R5 = 10K
12. R6 = 13.2K
13. R7 = 100k
14. R8 = 10K
15. T4 = BC547B
16. R9 = 200 Ohm
17. R10 = 10K
18. T5 = BC547C
19. R11 = 1K
20. T6 = 2N3904
21. R12 = 10K
22. T7 = BC547C
23. TR2 = 40
24. R13 = 200 Ohm
25. T8 = BC547C
26. Cluster of 9 white lights in series.
Can you please tell more about component at serial number 23. TR2 = 40?
Thanking you for your time,
Swag says
Vishwa, it looks OK to me.
TR2 is the boost coil. 40 is the number of turns for both primary and secondary using any super enameled copper wire which fits inside a torroid ring. For more on this you can refer to the following two articles:
https://homemade-circuits.com/8x-overunity-circuit-using-joule-thief/
https://homemade-circuits.com/1-watt-led-driver-using-joule-thief/
Ananta says
Sir,
I have a 3w ,6v solar panel.the maximum current = .34a as per the maufraturer & 6v/4.5ah SMF battery. I am new in electronics.pls suggest that can I go with the PCB which had provide you above without any changes.if need,what would be done.
Swag says
Ananta, your panel and battery are OK and can be used for the mentioned circuit, but I cannot guarantee the PCB layout because it was designed by somebody else…so please verify it by comparing it with the schematic
Ananta says
Sir
How much led (8mm straw head
.5w 20ma) can be used for 12 hour
Swag says
If the battery is 1 AH rated, you can use 5 LEDs in parallel, and illuminate for 10 hours approximately.
Bikash says
I have 6v 3watt solara panel,6v 4AH battery,5nos 8mm straw hat led fwd voLt 3.2 to 3.4 & 150 amp.
Please suggest for the both resistance value/ cicuit
Swag says
your solar panel voltage should be at least 8V to 9V otherwise the 6V battery will never get charged.
resistor value can be a 4 ohm / 2 watt
abba says
I want to ask again
1. do we have to worry about over-charge when using lithium battery even-though we provided voltage regulation?
Swag says
yes you have to worry about over charging if the output is set at the maximum charge level of the battery….if it is fixed at slightly lower than the full charge level then you can keep it connected forever, without worrying.
abba says
thanks a lot in advance.
Hi swagatam I have a couple of questions
1. do we have to care about overvoltage or current protection when using lead-acid battery ?
2. when the battery got full during the day time, wouldn’t it affect the battery’s health and life-span due to absence of auto-cutoff feature?
Swag says
Hi Abba, you must care about the over charging factor for all batteries and you must not keep it connected permanently with the source. In the above design we are assuming that the battery will not charge fully during the course of the entire day or rather we have to select the parameters in such a way that the battery is able to charge only upto 60 to 70% maximum during the daytime.
Mick Oude Engberink says
Does a 1 Ah battery mean that the battery will provide a current of 1A over the time span of 1 hour?
One of your earlier replies:
1watt LED x 12 hours = 12 watt hours will be the led consumption
12watt hours / 12V batt = 1ah battery will be sufficient, so 5ah is more than enough.
Here you say that for 12watt hours you will only need a 1Ah battery. I'm a noob so correct me if I'm wrong but doesn't this mean the battery will give an amount of 1/12=0,83A for 12 hours?
Swagatam says
yes that’s right, but in the most ideal conditions.
I meant to say 1ah is correct as per the calculations, and 5 AH battery will be sufficient, practically 1 ah will not be good, although technically it may look OK
Bryan Freed says
Verified Build, "Solar Garden Light Circuit with Constant Voltage". Work Great, Thank You!
If I'm using a LI-ion battery do I need to worry about a low voltage cut off?
Swagatam says
I am glad you could make it successfully.
yes you will have to worry about the over discharge,in that case you can build the following concept, with the above.
https://homemade-circuits.com/2016/05/solar-charger-circuit-using-transistors.html
maulik says
Hello Sir,
Please suggest me the complete circuit diagram of automatic garden solar led light for:
* Super Bright 8mm Straw Hat 0.5W/3.2V-3.6V (100-120mA) X 2 Nos.
* Lithium Battery 18650. : 3.7V/2600 mah
* SOLAR PANEL Cell: 5V/ 500mW
Thanks,
Swagatam says
Hi Maulik,
I'll update the circuit in the above article soon….
Swagatam says
Please see the updated diagram at the bottom of the article, you can use the concept for your application…
IT Computer says
dear i want make 20w LED with solar can you please describe me which circuit and parts i use
Swagatam says
please provide the voltage or the current specs of the LED, or both….
Albert Kravcov says
Could you please tell me how can I modify your circuit for my application? > wd-design.de/schaltung.png
Swagatam says
In my circuit remove the 10 ohm.
replace the battery points with your PCB's input (+)(-) points.
replace the LED points with your Arduino input supply points.
Ashok Dhenge says
Sir I assembled this circuit. But I assembled 3lights, providing 6volt 4.5ah battery at one place and connecting all light by cable approx 3meter distance. I used 3 no 8mm hat straw for one lights. My question is when I checked voltage at end off cable shows 3.2volt I don't get this reason. How to solve this? Because of voltage drop light illuminates very low.
Swagatam says
Ashok, please check the voltage across the collector/ground of the circuit without the LEDs connected, if you see correct battery voltage here, then the problem could be with the current consumption of the LeDs that may be causing the drop in voltage.
Swagatam says
…the wire resistance can also be the reason for the issue…
Navaneeth Nr says
Hi, Happy to see my garden light working!! Thanks a lot for the circuit.
one query ,what is the use of LHS diode connected directly to solar? Can the circuit function efficiently without it? Since my solar panel is only 5.5V ,battery charging is seeing 2 diode voltage drop 0.7+0.7=1.4v. Is there any modification I can do?
Swagatam says
I am glad too it's working for you!! you are welcome!!
the LHS diode is only to protect the circuit from accidental reversal of polarity, meaning if by mistake the solar panel is connected oppositely.
yes if you are sure you won't make the above mistake then you can definitely remove that diode…
Swagatam says
Navaneeth, TIP127 can handle upto 5 amps, so you can easily use it for your panned application, but make sure to put a large heatsing with it…
Bruno Viegas says
Hi, I have to do a similar project you make here, but I only have a 6v 140mah 0.6W solar panel, and absolutely no knowledge about how to choose components. Can you please help me out in order to make this work out with the panel I have if it's possible? Thanks in advance.
Swagatam says
Hi, you can try the second circuit from the above article with your panel, it will definitely work.
Bruno Viegas says
Sorry to bother again, but I showed the system to my teacher and He said that a on-off switch will suffice instead of the automatic day-night switch, can you modify this system for me with that in mind? The solar panel is still the same I said in the first comment.
As for the battery, I didn't find the one in your system to sell here. Do you have any suggestions for a more commom type?
Many thanks.
Swagatam says
In the second circuit, remove the right side diode, remove the transistor, remove the 1k resistor….now connect the switch terminals in series with the line which was going through the transistor to the positive.
that's all
the battery can be any battery whose voltage may be a few volts lower than the peak level of the panel…and the AH rating could be 3 or 4 times higher than the amp spec of the panel.
sunilsuth says
In this circuit the led starts glowing as soon as the SP voltage drops below 4.3v ,can u modify this and make the led glow when SP VOLTAGE drops below 3v or near to that
Swagatam says
you can add the following circuit with the panel for acquiring the mentioned feature
https://homemade-circuits.com/2013/05/low-battery-indicator-circuit-using-two.html
Tuan Sathiyan says
Thank you Sir.
chandraworld says
Thank-you,ihave tried 8550 and it works well.but led burns before it becomes dark.kindly suggest changes to be made.
Swagatam says
If you have used the series resistor correctly then the LED will never burn, please make sure you have connected a correctly calculated resistor.
Anonymous says
I have 5.5v,200ma solar panel,bc 547 transistor,3.5v power led.what are the values of resistances in circuit
Swagatam says
BC547 will not work, it should be a PNP and rated to handle 1 amp for the power LED, you can try 8550 or 2N2907 transistor with an identical set up as given above
you will also need a battery, preferably a 3.7 Li-ion
Navaneeth Nr says
Many Thanks. I agree. These type of special ICs also runs at particular frequency ( Even though the Leds blink , our eyes can't detect) there by reducing battery consumption. Can you help me in incorporating the circuit?
Swagatam says
Thanks, the frequency is used as a part of their buck or boost converter circuit which efficiently reduce or increase the voltage to the LED as per the LED specification….that's the only purpose of the involved frequency.
A LED will always require a constant DC with the correct V and I specs for illuminating at the optimal level…if its applied with a pulsed DC then its light will also dim or reduce proportionately
Navaneeth Nr says
Could you please try designing more efficient circuit like one using qx5252 (solar driver) , where it can light longer and has battery protection form discharge and overcharge?
Swagatam says
I already have many efficient and easy to build battery charger circuits posted in this site…you can find them under the "battery charger" category. I normally avoid using special ICs because they are mostly not available in all places and tend to get obsolete overtime.
Anonymous says
Thank you!
Anonymous says
How about rechargeable NiMH 3 batteries in series with 1800 mah each? Solar panel is as per specification. Any other changes needed ?
Swagatam says
no changes are required…
Anonymous says
Hello,
I can't find 4.5 V 1 amp battery in the market. Is there any other alternatives?
Swagatam says
you can use any other differently rated battery also, just make sure the panel and the LEDs are also appropriately matched with the battery specs
Anonymous says
Hi, I don't know much about electronics but this circuit looks great and I'm going to try and build it. Can you explain what is preventing the battery from overcharging? I don't understand that part.
thanks!
Swagatam says
sure you can try it out. there is no overcharge feature in this design for the sake of simplicity…
this is a cheap circuit so a charge controller cannot be expected for this design, although one can include it if it's felt important by the user.
here the charging current of the panel is matched with the batt specs such that it charges the batt to around 70% until it's dark…with this consideration the charger controller is eliminated for this design
Anonymous says
thanks for the explanation and fast response. nice, simple design.
Anonymous says
Hi,
I would like to use your circuit to run 20 x LED's in parallel (20mA – 0.4A total) with fwd voltage of 2.2v. Will the design above cope with this load? I assume it will as the battery would run the lights for approx 2 hours?? Would the resistor values have to change? Also, if I were to increase the amperage of the battery to make the LEDs stay on for longer what other components would need to change – lets say change the battery to 12v 4.5A.
Regards
Dan
Swagatam says
Hi, you can use the above circuit for your specific application without changing much….except the transistor which could be replaced with a TIP127…the resistor won't be critical with this transistor and anything between 1K and 22K would work satisfactorily.
you can use any battery as long as its voltage is compatible with the LED string voltage…nothing will need to be changed in the design….however the 10 ohm current limiter might require a recalculation for a given battery.
the following formula could be used for it
V = I/R where V is the supply voltage and I is specified safe charging current rate of the battery
Swagatam says
correction:
the formula should be as given under:
R = V/I
Anonymous says
Thanks for the reply. Also, if the LED's are in parallel will I have to have a current limiting resistor per LED or will 1 resistor cope with all of the LED's. Assuming the battery voltage is 6v I could have 10 parallel sets of 2 x LEDs in series with an 82 ohm current limiting resistor on each set of 2 LED's. Does this sound correct?
Regards
Dan
Swagatam says
the indicated resistor actually acts as a limiter for the battery, not for the LEDs, because LEDs are assumed to be having the forward voltage fixed in accordance with the battery voltage so no resistor would be required for the LEDs essentially.
But if the LED series FWD voltage is not calculated as per the battery voltage then the strings might require their own calculated limiting resistors
Unknown says
Hi Sir,
Thank you for sharing this circuit?
I have two questions
1) is it okay to continuously charge a battery. Normally for 12v batteries we have a charge controller. I didn't find too many for batteries below 12v. Why is that ?
2) is it possible to add a charging led indicator ?
Swagatam says
Hi,
this is a cheap circuit so a charge controller cannot be expected for this design, although one can include it if it's felt important by the user.
here the charging current of the panel is matched with the batt specs such that it charges the batt to around 70% until it's dark…with this consideration the charger controller is eliminated for this design
Rajkumar v says
Sir good day to you
May I use BD140 transister. What can I do to change this circuit ? My requirement one 3w led and battery type 6v4.5 amp
Thank you sir
Swagatam says
Hi Rajkumar, what is the voltage rating of the 3 watt LED?
BD140 might not work, use a TIP127 instead
Anonymous says
Hello,
Can we replace the battery with more commonly available 1.2V NiMH battery? Say 3 in series which gives a output of 3.6V?
Also can we add more LEDs so it will provide adequate brightness?
If these are possible, what all changes we have to make to the circuit?
Thanks
satheesh k Nalluswamy says
Dear sir,
Good day to you May I use 4.5v 2A battery and 8 smd 5050 led (150ma) . what will be changes for this circuit .
Swagatam says
Dear Satheesh,
4.5V 2ah will not be able to support 8nos of 150mA LEDs for too long.
8 LEDs in parallel will consume 1.2 amps, which will drain the batt within 1 hour
Swagatam says
yes it will be harmful for the battery to use a higher rated panel….you can put a 7806 IC after the panel supply t0 drop the supply to 6V for the circuit and the battery
walker01 says
Does it matter how high the solar panel voltage is for recharging the batteries? Will using a 12v solar panel damage the batteries when charging them if the batteries only output at like 5v?
Thanks! awesome post
john kg says
good day sir
i made the solar garden lamp and it working well i just want to know how can i increase the sensitivity of the circuit so it will light up when sunlight really fade out
and i am using 3.7v li ion battery any problem realted to over charging since there is any control circuit
thanks
john
Swagatam says
Hi John, you mean you want the LEDs to illuminate when it is almost dark? to implement that you may have to add another transistor stage with the above shown design.
to avoid over charging we can dimension the 10 ohm resistor value such that it charges the battery almost fully by the time the sun is about to set….
john kg says
thankyou sir for the promt reply
can u help what vaule of resistor to put ( i am using 8v 200 mill amp solar panel and 4x 3.7v (18650)
in paralle)
john
Swagatam says
what is the mAH rating of the cells together or for each?
anyhow it seems the 200mA from the panel could be quite low for those cells, and no resistance should be used in order to allow some charging of the cells throughout the day….but a resistor should be included with the LEDs for safeguarding them, as per their rating
Pavel Dikov says
Hi, how can I modify this circuit with a timer so that the light turns on for about 3-6 hours after dusk? thanks
Swagatam says
you can use the same configuration that's shown above with the following modifications.
use a 4060 based timer circuit.
remove everything from the existing base of the 8550 and connect the base of the 8550 transistor via a 1K resistor to pin3 of the IC.
connect pin12 of the IC to ground via a 1M resistor, and connect a link from positive of the panel to pin12 of the IC.
set the R/C values of the 4060 to get 4 hours delay.
also connect a 1N4148 diode from pin3 to pin11..cathode to pin11
that's all
Pavel Dikov says
Can you also explain the exact flow of the current from the battery to the LED's, because I'm confused where the current goes after it passes through the LED's. Does it go through the transistor and back to the battery? If not, than what is the purpose of the transistor? Thank you.
Swagatam says
current from battery (+) enters the emitter of the transistor, comes out of the collector, enters the LEDs and returns back to the battery (-)
Unknown says
Hi, how can I modify this circuit so that the light turns on at dusk for about 3-6 hours? and where would I place the timer? thanks
Maruti patil says
Sir, This is exactly what I need except that I need to use a 15 watt 17 volt solar panel with an output of .89 amp. What components do I need to replace in order to run this solar panel? I'll be charging 2 or 3 18650 batteries in parallel with a 2500mah capacity each. thank you in advance.
Swagatam says
Maruti, for charging the mentioned cells you will need to eliminate the 10 ohm resistor and short it with a wire link.
make sure you connect the cells in series and not in parallel, since each cell is rated at 3.7V so 3 in series would require 12V to charge them fully and the 17V panel would work good since it's quite low in current compared to the required 2.5AH rating of the battery.
the transistor and the 1K resistor are related to the load not with battery charging…so will depend on the load specs,
Maruti patil says
Can you share the diagram
Unknown says
Hello Swagatam
Your site is of great help.
I have a query in above circuit.
What is purpose of 10Ohm,1/4W resistor? How does it act as current limiting resistor?
My understanding was resistor was added for voltage drop in battery voltage of 4.5V to LED spec voltage.
Can you provide the voltage/current/power of LED used?
Swagatam says
thanks unknown,
the 10 ohm resistor is for providing some sort of current limiting to the attached battery while the solar voltage is available, and it also acts like a current limiter for the LEDs while the solar panel voltage is absent and the LEds switched ON.
Swagatam says
the LEDs can be 5mm/ 20mA type white LeDs
Kancharla Nishanth says
Hello Swagatam,
Thanks for reply.
I am planning to use single 1 Watt LED (3.2 V, 350mA), so what should be resistance value and wattage of resistor?
Can i use 3.6V, 1000maH battery?
Swagatam says
Hello Nishanth,
3.6V/1000mAh will get drained very soon with a 1 watt LED, it should be at least a 2AH battery.
you can use a 2.5 ohm, 1/2 watt resistor
Kancharla Nishanth says
Hello Swagatam
Can you explain me on how you came up with 2.5 ohm, 1/2 watt resistor?
Swagatam says
hello Kancharla, it's calculated in this way:
R = 4 – 3.3 / 0.3 = 2.33 ohms
4 is the batt voltage, 3.3V is LED fwd V, 0.3 is the LED current
watt = 4 – 3.3 x 0.3 = 0.7 x 0.3 = 0.2 watts,
1/2 watt is selected for more safety
Swagatam says
.
John Dougherty says
Ahh thank you I though it was a pnp transistor. But since it's not is there a way to know just by the label number if it is?
Swagatam says
The label will not inform regarding its polarity, you may have to refer to its datasheet online to learn the details….
John Dougherty says
I should also be able to include a picture if you think that would be helpful
John Dougherty says
Hello, I liked your schematic because it appeared to be very straight forward, however when i went to make it for myself the LED lit up but would not turn off when light was exposed to the solar panel. when looking for transistors i could not find the exact transistor you call for but i did get a 2n2923 transistor i thought would work. since this is the only active component I'm not sure if the problem could be there or somewhere else. since we are using a battery pack for 8 double A's that should cause it to act as a 12v battery we are using a 750 resistor along with the 1K resistor. currently there is only one LED connected and I believe everything else follows the schematic exactly. Any ideas or suggestion what could be causing this problem would be greatly appreciated.
Swagatam says
Hello, 2N2923 is an NPN transistor, so it will simply not work, it has to be a PNP, or may be you can use two 2N2923 for getting the same results.
Vikirthi......... says
Hi, Can you provide a solar lamp with LDR circuit details ?, Something similar to A LTTER OF LIGHT Program.
Swagatam says
LDR won't be required, the solar panel will itself work like a light sensor…… the concept explained in the above article is a good example
Kancharla Nishanth says
But on cloudy day without sun light, LED will start glowing as current is zero from panel. But we may not need LED light as it is day. Will LDR help here?
Swagatam says
Yes, it will start glowing at a proportionately dim level depending on how much overcast it may be…LDR will not help…. you will need a relay changeover instead of a battery changeover, as shown in the following circuit:
https://homemade-circuits.com/2015/03/solar-led-lights-with-charger.html
Lorenzo Chow says
Sir, This is exactly what I need except that I need to use a 15 watt 17 volt solar panel with an output of .89 amp. What components do I need to replace in order to run this solar panel? I'll be charging 2 or 3 18650 batteries in parallel with a 2500mah capacity each. thank you in advance.
Swagatam says
Lorenzo, you'll need to change the transistor with a BD140, and reduce the 1K resistor value to may be 220 ohms 1 watt
also you'll need to connect the 3.7V batts in series for making its voltage compatible with the panel output…. for more safety you can think of using a LM338 variable regulator IC at the input…..
Basavaraj Bijjal says
Sir
I want one circuit diagram.and I want automatically ON & OFF the street lights by using L.D.R's and lanp which is connected to solar energy
Swagatam says
Basavraj, you can try the following design:
https://homemade-circuits.com/2012/10/automatic-40-watt-led-solar-street.html
Jit Lee says
Sir, is it ok if I use 6V battery?
Swagatam says
yes it's OK
Shiraz rizvi says
Ye jo aap ne 4.5 1h ki battery use ki diagram me ager ye bttery ki jagha 12v26ah ki battery lagau to transistor kitne no ka use karu ?
Swagatam says
use TIP127
azra says
hi, i used 4.5 v solar panel, and i used 3,7 A li-ion battery. Do i have to change anything to the circuit? thanks.
Swagatam says
Hi, 4.5V will not do, you will need at least a 6v panel for the above circuit.
Shiraz rizvi says
Hi swagatam bhai ty for help
Maine soler automatic circuit banai ager mujhe 10 watt soler 12v 7ah or 4.5v led h uske liye mujhe kya krna chahiyye help me
Swagatam says
Hi Shiraz bhai you can use the circuit that's shown in the above article.
just replace the shown transistor with TIP127, connect the LED across collector/ground and battery at the given position
please mention the LEd wattage and voltage also so that I can calculate and provide you the series resistor value for the LED
Shiraz rizvi says
Thanx you so much mere bhai
Swagatam says
my pleasure bhai.
Anonymous says
Hi!
I want to use a 12volts 2 watts Solar Panel as a main battery charger and supply for my soil Humidity circuit in one body.
So I want basically to make the Solar panel as a charger for the 4.5v battery that will supply the garden light at night and in daytime the Solar panel will also serve as a supply for the soil Humidity Circuit. So simply on night time the Solar panel switches off along with the Soil humidity circuit.
My question is.. Will the solar panel affect Ur original circuit along with its parts. If so what steps should I make to prevent it?
PS: my soil humidity circuit will just be hooked up on the end of the transistor and ground pole.
Swagatam says
Please refer to the previous comment posted just above this comment..
Anonymous says
Sir I want to make this circuit but I only have a 12volt 2watt Solar panel available. Will it Overload the batteries or damage the other parts? If so. What steps should i take to make my Solar panel be usable for this project. I Have all the parts my only problem is my Solar panel and its possible effect to the entire circuit. Please reply as soon as u can. Thank you!
Swagatam says
If you are using the configuration that's shown in the above article then you may have to first step down the solar panel voltage to 6V to safeguard the battery.
You can use a 7806 IC at the input of the circuit such that the panel voltage passes through the IC and then reaches the above circuit.
You can take the help of the following post for knowing the 7806 connection details, it will exactly same as shown in the following circuit:
https://homemade-circuits.com/2012/03/how-to-make-simple-dc-to-dc-cell-phone.html
Lucky Day says
Just built this and tested it out and it works great.
I'm curious though if maybe the 1k resistor can be lowered and what kind of value would be safe to make the LEDs brighter.
I would like them extremely bright, but don't want to blow them obviously.
At the moment they light up, and they are fairly bright, but not as bright as I've seen these LEDs get before (I'm using 8mm standard 20ma LEDs that you can get from Radioshack)
Swagatam says
Thank you Lucky Day,
reducing iK resistor wouldn't be a good idea, rather you can try inserting a resistor in series with each LED and remove the common 10 ohm resistor.
the value for the individual resistors could be around 2 ohm, 1/4 watt
Anonymous says
Doesn't the 1k resistor makes a short-circuit on the solar panel, because it is connected from + to – ?
Swagatam says
It would hardly dissipate anything, you may try increasing it to 2k2.
John Merten says
Hello. I hope I'm not to late for this question period. I am a total newbie but non the less find this fascinating and confusing. What is the purpose of connecting the line with the 1K resistor from negative to the positive in the first place?? even if "It would hardly dissipate anything" How can that help anything?
Swagatam says
It's for biasing the transistor…so that the transistor is able to sense the voltage level from the panel and switch the LEDs ON or OFF?
John Merten says
Ahhh ok. Light bulb just came on. thank you.
Anonymous says
Hello Swagatam,
I was wondering what voltage the solar panel has to turn the LEDs on. In your diagram, the battery has a voltage of 4.5v, does this mean that the LEDs will turn on when the solar panel has a voltage of 4.4v (or lower)?
I am asking because I am building a small solar charger for 3x AA batteries and want to incorporate a flashing LED indicator which turns on when the solar panel hasn't enough voltage to charge the batteries. So let's say the 3x AA have a combined voltage of 4.0v, I want the flasing LED to turn on when the solar panel gives 3.9v so that you know you have to move the panel into more sunlight.
Thanks, I love your simple circuits.
Swagatam says
Hello friend,
With the transistor as a switch there won't be well defined switching rather the transition would be in a gradual manner.
As long as the solar voltage is above 4.5V, the LEDs would be completely shut off, as the panel voltage begins dropping downward, the LEds would begin illuminating dimly and start getting bigger as the voltage drops further, finally when the solar voltage becomes almost zero, the LEDs would glow at their maximum rated intensity.
2ea5c024-ebf9-11e2-95c4-000f20980440 says
hello SM,
is there any chance you can work on a circuit similiar to the following ebay link? www.ebay.com/itm/LED-Solar-Power-Motion-Sensor-PIR-Wall-Mount-Garden-Path-Yard-Door-Light-Lamp-/310657821723
its PIR solar light running off 3x 1.2v rechargeable batteries? Ive looks around google for a similiar circuit but no luck, so i decided to try my luck with you! plmk.
Thanks
G.
Swagatam says
Hello G,
The above circuit and the second last design presented in the following link can be easily combined to produce identical results:
https://homemade-circuits.com/2012/09/pir-controlled-led-driver-circuit.html
Some tweaking would be required to make the design perfect, though.
Anonymous says
Thanks, I appreciate your fast reply. I made a solar battery charger for 3xAA batteries with a build in USB 5v DC DC booster to charge mobile phones. I was looking for a very simple circuit for a 'battery fully charged' indicator so not to have the charger in the sun for too long and stumbled upon your website.
I'll bookmark this website.
Swagatam says
you are most welcome!
Anonymous says
Hello!
You write: "However when dusk sets in the solar voltage begins to drop, and when it drops below the zener diode rating, the transistor slowly starts conducting, illuminating the LEds gradually."
…but I don't see zener diode in the diagram. Does that mean it can be without?
Thanks!
Swagatam says
The initial diagram had a zener diode at the base of the transistor which I removed later on for making the circuit more responsive and efficient.
Anonymous says
Transistor symbol indicates it is a PNP type on your circuit, but I am confused if you can simply replace a NPN transistor with PNP without changing anything in the circuit? Google search tells me 8050 is a NPN transistor, but 2N2907 is a PNP transistor.
Swagatam says
may be you did not notice the message written in BOLD letters just under the diagram
Anonymous says
You are right, sometimes you don't see the forest but only the tree:) Thank you for pointing it out. I hadn't imagined the correction would written instead of correcting the diagram after the discovery of mistake.
Swagatam says
Go and check the cached impression in Google you would know it was done a long time ago.
Swagatam says
Check the previous comments dated May14, June7, it's always wise to check the facts before criticizing.
Anonymous says
I was NOT criticizing you at all, not even thought about it. The first time I read only the article (not the comments underneath) and of course not after the two circuit diagrams where you wrote the corrections. I simply thought you would have corrected the diagram, if any mistake was discovered on the diagram. It was not a criticism, just what I thought with my simple mind. My apology!
Swagatam says
I regret it if I misunderstood you, I thought you were saying that the written corrections were made immediately after listening to your suggestion.
Correcting the image is time consuming and involves more effort therefore I put in the text form.
Anyway, cheers!
Anonymous says
Can you show how to make a smaller version for a single garden light?
Swagatam says
you can modify the above circuit simply by calculating the resistor as per the given formula.
Bharat says
Hi,
I want to use 12V 7.5Ah battery with 12V 10Watts solar panel. what changes I require to do, so that battery is not over charged as panel is giving 18v in open circuit. Thank You.
Swagatam says
dividing 10 by 18 gives 0.55A, or 500mA, that's quite OK, so you may directly connect the panel output with the battery, the voltage will automatically drop to the required level.
But be sure to remove the battery from charging when the voltage reaches 14.4V.
having said that, you may a;so try connecting a couple 1N4007 diodes in series with the panel positive for dropping some voltage to the battery.
Bharat says
Hi,used the above circuit and connected the Solar Panel 10Watts 12v for battery charging, so LED's would come ON when no sunlight. But 1K resistance at the transistor base is getting heated up during charging. Do i require to change the resistance value?. Thank you
Swagatam says
yes, change it to 4k7 or little more.
Anonymous says
Greetings, I would like to ask about the transistor.. What would be its effect to the entire circuit.. and what part is possible to replace it to enhance the capability of the circuit.
Swagatam says
Greetings, The transistor acts like a switch here, nothing can be replaced in it's place for the present configuration.
Anonymous says
Hi,
Do I need to change 1N4007 and 8550 to other number if I would like to use 5v solar panel to charge 3.7v battery. Thank you.
Swagatam says
No you don't have to change them, they would be fine with 5v also.
Anonymous says
greetings Swagatam, can I use 1w 350mA LED and 3.6/3.7 battery? What will be the illumination of 1w led, will be bright or very bright? I made a similar scheme and it works but I'm not satisfied with the illumination od 1w LED.
Sorry for my english.
Tnx
Swagatam says
Greetings to you!
The illumination would be great no doubt if the cell is optimally charged.
Swagatam says
yes you can use it!
Anonymous says
i want to put a water level alarm circuit but it uses the solar panel as its day time supply and turns off at dusk. should i put a regulator? and whats the name of the part should I input?
Swagatam says
yes it would be a safe idea.
Anonymous says
Sir, What is the circle in the middle of the circuit? and what is 8050 or 2N2907?
Swagatam says
it's a transistor
scotty says
Eventually, I made some modifications to the circuit and work properly, your quote and plan
Thanks
scottyfjr.files.wordpress.com/2013/05/simple-solar-lamp-circuitdoyleyei-1.jpg
Swagatam says
absolutely bizarre….anyway, thanks and congrats!
Swagatam says
OK you were correct, i am sorry, there was indeed a small mistake in the circuit, very silly of me.
it was the missing second diode. this diode will now prevent the battery voltage from going to the base of the transistor and will allow the illumination of the LEDs.
without the right hand side diode the battery voltage could reach the base of the transistor and that was creating all the problem.
the second diagram is even better which makes the circuit work more efficiently.
cheers;D
scotty says
There is no problem nor wrong, humans are wrongs do, so we say here in GREECE.
Thus continue the very good work you do and offered in all of us
Thanks
Anonymous says
Sir Swagatam can i use a 6v, 2.5 watt solar panel to replace the solar panel u used?
Swagatam says
yes will do.
Anonymous says
So Swagatam can u post the list of parts to be used in this Circuit? and also their usable specs..
Swagatam says
i have provided it in the diagram itself, you can see it there.
scotty says
not all of this happening to me .. I changed 6 transistor pnp ,difference Led , and I have made the circuit 10times, but nothing again.
The construction is very simple but does not seem to work.
If your plan is right .. what I am wrong;;
scottyfjr.files.wordpress.com/2013/05/2013-05-11-13-22-29.jpg
Swagatam says
just by doing things blindly won't help….check and correct the base voltage as explained in the above comment.
scotty says
I did the test by connecting collector emitter, and the lamp illuminate, changed the transistor with an identical model new, but again the lamp does not illuminate. will try with other types npn to finally see what's wrong.
Thanks for the tips and hints
Swagatam says
check the voltage at the base of the transistor, it should be 0.6V
touch negative prod to base and positive prod to the positive line.
Swagatam says
NPN transistors will not work here.
scotty says
with 2N2905A the circuit is not working, I'll try to find it 2N2907 and I'll tell you ..
There is easy to try and you are doing it 2N2905A tell me if it works;;
Thanks anyway
Swagatam says
the circuit will work with any appropriately rated PNP transistor, doesn't matter whether it's 2905, 2907, 8550 or any other similar type…
short the transistor emitter collector points with a wire link, check if the LED lights up or not.
If "yes" means the transistor is faulty, if "no" means the LED is faulty or connected the wrong way.
scotty says
Can I use the 2Ν2222 or BC547 instead of 2N 2907
Swagatam says
2n2222 and bc547 are NPN transistors….
scotty says
I tested the 2Ν2905 instead 2N2907.. but unfortunately the construction does not work..any idea??
Thanks
Swagatam says
tell me what's happening with your circuit I will try to troubleshoot it.
Swagatam says
remove the zener and then check…
scotty says
I tested without the zener but again unfortunately nothing ….
Lists and 2 photo of circuit
scottyfjr.files.wordpress.com/2013/05/2013-05-11-13-22-29.jpg
scottyfjr.files.wordpress.com/2013/05/2013-05-11-13-20-26.jpg
Swagatam says
what exactly is happening to your circuit, is the LED not illuminating or the transistor not switching off the LED when solar power is connected??
scotty says
the Led not illuminated in any case, connecting the battery and solar panel.
Probably something is not right in the circuit
Swagatam says
the led will illuminate only when there's no supply from the solar panel.
There'e nothing wrong in the above design.
Anonymous says
Sir Swagatam Majumdar. I would like to ask if you can use this circuit to add a soil temperature circuit that alarms when the ground is too dry and uses the solar panels as its direct supply in the day. then deactivates at the night. please help.
Swagatam says
Yes surely it can be implemented using the above circuit and a soil humidity monitor circuit. If possible I'll try to address the topic in this site.
Anonymous says
Thanks sir..
Vivek Palekar says
Dear Swagatam,
1. This is simply a greatest idea because the solar panel can be mounted where there is plenty of sunlight throughout the day keeping the lamp even at the shaded garden unlike in store bought garden light having its solar panel on top of the light so that lamp can not be place in the shaded area.
2. This is simply a smart idea because it is a smart lamp that automatically switches ON the lamps at dusk and switches them OFF at dawn.
3. This is the brightest idea because this model has 6 leds (though staw hat leds come in typical 5mm 10000-16000mcd and 0.5W 100kmcd and it is not mentioned which one was used in this model) and should be much brighter than that of store bought wimpy firefly model with only one (or 2 at the most) led(s).
However, it seems to me this model needs a make over (aka some modification) to be cost effective IMHO because:
1. Choice of the solar panel seems to be little uncommon size here and that is making it expensive (about US$ 11 per piece in the US market) and battery size seems to be odd as my search could not find any 4.5V 1AH battery (unless it is meant to be 3x 1.2V Ni-mh/Ni-Cd type battery).
2. A typical house pathway or backyard garden requires 6 to 8 solar lamps to light well and decorate well. Unless this model is modified using a single solar panel of higher output to cover all 6 to 8 lamps (connecting in series, maybe), buying one 6V 2W panel at $11 for each lamp seems to be very cost ineffecient in my humble opinion.
3. Battery type for this model should be fairly common type (3.6V Li-ion; the most advanced type these days, or typical 4V, 6V, or higher voltage SLA battery should be used.
Your time and effort for a simple modiciation to make your great idea the greatest will be greatly appreciated by all your valued readers.
Swagatam says
Thanks very much Vivek!
That was a good in-depth analysis…keep it up!
I'll try to update the design as per your suggestions…
Vaibhao Ingle says
hi sir,
sir can we use 12v battery and 4nos of 1watt power led for this combination.
Swagatam says
yes, but you might have to connect them in series.
Monica says
What should be the specification of solar panel if we want to charge a 12V battery (5Ah or 2.5 Ah) for using 4-5 power LEDs ? What changes are to be made in the above circuit so that LEDs can glow for atleast 8-9 hours?
Thanks.
Monica says
Thanks for the reply sir.,actually LEDs will not be used simultaneously,I want that the battery gets charged during day time and used at night. Whether a 12V(5AH) battery is sufficient or not? Also,what should be the 'Wattage' rating of the solar panel?These power LEDs are connected in series and as far as I know the 1 watt i.e. power LED requires 350 ma current.What is the value of resistance that is needed to be connected for this 5 Watt LED circuit?
Thanks..
Swagatam says
An 18V, 1 amp solar panel would be OK, if only battery is charged, if LEds are also simultaneously used then you would require a 3 amp solar panel.
the backup time will entirely depend on the battery AH and the led current, led current should be approx 1/10th of battery AH for 9hrs operation.
Swagatam says
Here are the calculations:
1watt LED x 12 hours = 12 watt hours will be the led consumption
12watt hours / 12V batt = 1ah battery will be sufficient, so 5ah is more than enough.
12/5 hours sunlight = 2.5 watt solar panel will do
2.5/battery V = 2.5/12 = 0.208amp solar panel will be required
the above calculations was done as per the following article:
https://homemade-circuits.com/2013/05/how-to-calculate-and-match-solar-panel.html
Swagatam says
refer to the formula given at the bottom of the following article for calculating the resistance value:
https://homemade-circuits.com/2013/06/universal-high-watt-led-current-limiter.html
Ram says
What is the use of 6V 400mW led (is this normal led) ?
Swagatam says
It's not an LED, it's a zener diode, it switches ON the transistor as soon as the panel voltage drops below 6 or 7V.
old-engineer says
What zener diode are you referring to? The 1N4007 is a general purpose diode.
Swagatam says
it was there at the base of the transistor in the previous diagram, it has been removed in the present updated diagram.