LED Emergency Light With Battery Over Charge Protection

The following LED emergency light with battery over charge protection feature circuit was designed by me in response to the request sent by PP.

Main Features

The article describes an LED emergency light circuit with advanced features such as,

  1. over charge battery cut off,

  2. day time auto-disable,

  3. and need less to say that the circuit switches ON the LEDs automatically when AC mains fails and reverts to charging mode when power is restored.

  4. The good thing about this circuit is that it incorporates ordinary, cheap components which can be easily procured from the local market.

Simulation and Working


Let's try to understand the circuit functioning with the help of the following points:

IC1 which is our very own IC555 has been set as a comparator. During day time, the light over LDR keeps the LDR resistance low such that the potential at pin #2 of the IC is kept well over 1/3Vcc. This situation ensures that the output of the IC at pin #3 stays at logic high.

The logic high at pin#3 of the IC keeps T1 switched ON, which consequently keeps T2 switched OFF.

With T2  switched OFF, the LED array remains inhibited from the ground connection and therefore the whole white LED array also stays shut off.

Another factor that keeps T1 switched ON and T2 switched OFF, is the voltage from the transformer power supply stage.

This function is implemented via the resistor R9. This also means that as long as mains AC is available, T2 is restricted from conducting and therefore the LEDs cannot light up.

Now suppose the mains power to the transformer fails, and assume that this happens during night or complete darkness, pin#3 of IC555 reverts to zero and also there's no voltage from the power supply, means T1 has absolutely no base bias and therefore has to switch OFF.

This instantly prompts T2 to switch ON and consequently the entire LED array also switches ON, providing the required emergency illumination to the surrounding.

MAKE SURE THAT THE LIGHT FROM THE LED DOES NOT FALL OVER THE LDR, WHICH MIGHT TRIGGER A RAPID UNDESIRABLE SWITCHING OF THE LEDS.

The battery charging section consists of T3, T4 and the associated parts. P1 is set such that it switches ON T3 when the battery voltage reaches just above 14 volts.

The moment this happens, T4 switches OFF, cutting of the negative supply to the battery and restricting any further charging of the battery.

Diode D2 ensures that the battery receives the negative supply during the charging process only through T4 and also provides a normal negative path to to T2 and the LED array when they conduct.

The left side LED indicates, mains power ON or presence of day light.

The LED at the right side indicates, battery is charging.


Parts List


R1 = 2M2
R2 = 1M
R3, R4, R5, R9, R6, R7, R8 = 4K7
ALL LED RESISTORS = 330 OHMS
D1, D2, D3 = 1N4007
D4----D7 = 1N5402
C1 = 1000uF/25V
C2 = 1uF/25V
T1, T3 = BC547
T4, T2 = BD139
Z1, Z2 = 3V/400mW
P1 = 10K PRESET
IC1 = IC 555
TRANSFORMER = 12V, CURRENT = 1/10 OF BATTERY AH
LEDS = WHITE 5mm, OR AS PER CHOICE.
BATTERY = 12V, AH = AS PER LED POWER AND BACK-UP REQUIREMENTS.


Using a Single PNP BJT


The above circuit can be much simplified by eliminating the IC555, and by using just a  single PNP transistor instead of two NPN in the battery auto-battery cut of section.



P1 is used for adjusting the ambient light threshold at which the LEDs stop illuminating.

P2 is set such that at 14.6V (across the battery terminals) the base LED becomes very dim, hardly visible, and at 12.5V it's brightly lit.

Adding a Solar Panel


The above circuit can be also coupled with a solar panel for getting an automatic charging facility from both the sources that is from the panel during day time and from mains after the sun sets.


Parts List


R1,R2,R3, R4, R5 = 1K
P1 = 470K
P2 = 1K
C1 = 1000uF/25V
D1---D5 = 1N4007
T1 = BC547
T2 = 8050
T3 = TIP127
ALL LED RESISTORS = 330 OHMS
LEDS = WHITE, 5MM
LDR = ANY STANDARD TYPE
TRANSFORMER = 0-12/1AMP

Need Help? Please send your queries through Comments for quick replies!




Comments

Abhishek Das said…
for lower voltages how LDR's can be configured
ie which transistor should i use???


waiting for ur reply............
Swagatam said…
Hello Tanmoy,

Using single resistor will make the LED brightness weaker and nonuniform.
Swagatam said…
the resistors distribute current equal among the LEDs creating uniform brightness and optimal response.
Swagatam said…
please check out this article

https://homemade-circuits.com/2011/12/how-to-wire-led-lights-easy-clues.html
Gopal Malviya said…
hello abhishek sir
i gopal malviya from m.p. and i have just started by cfl repair and making
business but i dont have any good reasonable electronics parts supplier so please suggest me parts supplier vendor contact detail with your reference

Thanks for kind support
Gopal Malviya
Gopal Malviya said…
hello sir
i gopal malviya from m.p. and i have just started my cfl repairing and making business but i don't have any good electronic parts supplier
so sir please suggest me any parts supplier with your reference
i'll thankfull for your

Thanks for Your Kind Support
Gopal Malviya
achilles hector said…
Good day sir!

I have some questions.

1.Can I replace the 12-0-12v 1A transformer with 15-0-15v 1A transformer then just use voltage regulator like LM7812 to regulate to 12v? Doesn't it affect the current?
Swagatam said…
7812 will not produce or allow more than 1amp at its output, irrespective of input current or voltage
mujahid bhutta said…
sir can I use same circuit for using 12v 7w led and battery of 12v 2.5Ah and how much time transformer needs to charge battery of 2.5 ah fully
mujahid bhutta said…
sir can I use same circuit for using 12v 7w led and battery of 12v 2.5Ah and how much time transformer needs to charge battery of 2.5 ah fully
Swagatam said…
12V/2.5 ah will not support the led for very long, may be only for 30 minutes.

lead acid battery needs 10 hours to get charged correctly.
aquarius said…
Sir, I want to build the second circuit (without 555), but want to additionally incorporate a small solar panel for charging battery (first priority solar charging, second priority mains). Will be obliged if you please suggest a modification in circuit. safdar
Swagatam said…
aquaris, it can be done by a simple modification, i'll try to update it as soon as i get some free time.
aquarius said…
I'm very delighted and thankful for your prompt response. I will look forward that u have time to advise a good circuit. To elaborate requirement further, the battery should normally be charged by solar panel, and if not sufficient, like cloudy days, it should auto switch to charging from mains till battery is fully charged (of course with overcharge protection). Thanks once again.
Swagatam said…
Thanks, I have updated the diagram please check it out.
aquarius said…
Many thanks for the goodness. You are genius. I will build this circuit for my home and give u feedback soon.
dhanish said…
hi
my battery is 12v and 7amp,so is there any problem. And i have Osram Dulux S/E 7W 4 Pin CFL - 827 so is it possible to connect that in this circuit.
dhanish said…
also i have a 10w solar panel is it sufficient to use with this circuit
Swagatam said…
hi how does the lamp work, please provide it's voltage and current specs for correct analysis.
Swagatam said…
please provide its V and I ratings
dhanish said…
when i measure the voltage and current of solar panel with multimeter i got 19.2 approx 20v and
current within .5A.

I dnt know the rating of that bulb
Swagatam said…
the solar panel can be used with the above circuit but after stepping down through a LM317 voltage regulator.

the OSRAM bulb tat you have mentioned is a fluorescent tube so it cannot be used directly with the above circuit.
dhanish said…
Can you give me the circuit to connect LM317.

can i connect 12v 7ah battery?

can i use the given led bulb( 1w or 3w) in the link below in this circuit?
https://docs.google.com/file/d/0Bwgu3V_6cEZsdlZSRDM4QVJEcms/edit?pli=1
dhanish said…
I dont want to use ldr can i used a switch instead of that.
dhanish said…
can i use the circuit in the link below with the above mentioned solar panel, battery and bulb

https://drive.google.com/file/d/0Bwgu3V_6cEZsaUp1ZUEtdmpMR2s/edit?usp=sharing
dhanish said…
please also tell me that can i use circuit in the link below with 12v, 7ah battery to connect the led bulb shown in the above link with rating(Power: 1W, Voltage: DC 3.0V~3.2V,Current: 300~350mA).If yes then how long it will give light with that battery else please suggest an efficient circuit.


This is the link
https://docs.google.com/file/d/0Bwgu3V_6cEZsUjZhM2k3dXlhUGs/edit



Swagatam said…
if it's a 1watt led you can connect it directly with the 12V battery through a 40 ohm 1 watt series resistor
Swagatam said…
yes surely, remove the T1/T2 stage entirely.
dhanish said…
how many 1w led bulb can be connected to 12v, 7ah battery (pls give the resistor value also) which give max brightness and backup hrs.
dhanish said…
Can i use the above mentioned 1w (8Nos) led in this circuit.Will it give max light.
Swagatam said…
yes can be used.
Swagatam said…
yes can be used but the 317 will become very hot, use heatsink for it..

it may last for about 2 hours.
dhanish said…
Is it possible to show a charging led in this circuit.If yes pls tell me how to?
Swagatam said…
it's already there at the base of the transistor.
dhanish said…
Friend i am little bit confused thats why im asking to many questions dont feel irritated.please tell me that if i want to connect the 1w led direclty to 12 7ah battery then how many can be connected to the battery so that i will get a back up of 6-8hrs
Swagatam said…
friend, make strings of 3 leds in series with a 6 ohm 1 watt resistor.
make 2 such strings and connect them in parallel (join their positive/negative ends together)
and connect the network to the battery.

2 strings in parallel having 3 leds in each string gives 3x2 = 6 leds
this would approximately run for 7 to 8 hours.
dhanish said…
https://drive.google.com/file/d/0Bwgu3V_6cEZsZGZ6Y3R2WVRmSFk/edit?usp=sharing

i am using this circuit to charge 12v 7ah battery with the above mentioned solar panel.but its not charging is there any prblm in this circuit.if you have any better circuit to charge with solar panel pls give me.
Swagatam said…
check the output voltage without connecting the battery, it should be set to 14V, and the solar panel must be able to produce 1amp current minimum.
dhanish said…
my panel is only producing a max of 430 mA is there any circuit to charge the 12v 7ah sla battery with this panel.
Swagatam said…
430mA will not charge 7AH batt...change the panel with a 1 or a 2amp variant
dhanish said…
sir pls reply,
in the above comment you said to remove t1 t2 stage,then should i have to remove r1,r2,r3,p1 with that.
if yes then where i have to connect the led +ve and -ve.

I want to charge my 12v 7ah battery with this circuit pls tell me how.
dhanish said…
Sir I finally decided to make your circuit, i need your help during my assembling if any error arises. sir please answer each question.
Please reply as early as possible.
some doubts are

1) In the 2nd circuit does it have overcharge protection?If yes can you just elaborate please?

2) Sir please specify the rating of solar panel (max current and max voltage) in 3rd circuit?And how to show a charging indication for solar panel?

3) Sir i know you said that my solar panel(17.5-19v and 500mA) not capable of charging this battery eventhough if i am connecting that solar panel, can i connect it as shown in your circuit?
Swagatam said…
....please repeat your exact requirement pointwise.
Swagatam said…
1) it will stop overcharging if the preset is correctly adjusted, but it's a crude circuit.

2) solar panel should be 15V/2amp for 7ah batery, the base led will indicate charging state of he batt.

3) yes can be done
dhanish said…
sir i made the circuit but i have problem with the preset.pls help me to how to adjust it.
when i started adjusting a spark is coming from the 1k preset. so i stopped adjusting is that due to any wiring mistake .

please reply fast sir.
Swagatam said…
i am answering this for the second time, pls don't repeat your questions.

connect 3 leds in series with 6 ohm 1 watt resistor

make two such strings and connect their common ends with the battery

backup will be upto 3 to 4 hours
dhanish said…
sir now its ok.
sir how long it take to charge the battery current charge is 12.68v?

sir how can i check my circuit that everything is working well?when i checked the output given to battery terminal without connecting battery it shows 13.00v and 400mA and the t3 base led lights up is it correct?
dhanish said…
sir now ok your 2nd circuit is working but 3rd circuit i have problem.i want to use switch instead of ldr so i didnt use ldr,r1,p1.

and i didnt connected the white leds and the remaining circuit is completed without giving solar panel input.And when i give transformer input it gives only 400mA output without connecting battery terminals.
Swagatam said…
dhanish, adjust it to get 14.5V and the LED should glow dimly at this voltage.
after this setting this done, you can connect the discharged battery which should force the voltage to drop to the level of the battery and render a higher brightness on the LED, as the battery charges the LED brightness will reduce and at full charge of 14.4V the LED will glow very dimly.

another point is, your panel voltage must be first regulated to 15V and then applied to the circuit.
use an LM317 circuit for this.
dhanish said…
sir some doubts again
1)for connecting p2 preset there are 3pins two pins give fixed resistance,two pins give variable resistance, i connected the variable pin to r4 resistance, is it correct?

2)As you said i adjusted the voltage level to 14.5 without connecting battery but the t3 base led is not that dim.And when i connected the battery which have a voltage level of 12.6v the base led again becomes dim.Is that any problem in my wiring ,but i made the circuit 2nd time pls help me sir?

3)but with all these i connected battery it charges to13.06v and stops further charging.the base led is glowing still the battery voltage not increasing.why?
Swagatam said…
dhanish, the center lead or the slider lead of the preset must go to R4.

The LED will become dim only if the supply voltage is 15V or equal to the battery full charge level.

Are you supplying 14 to 15V to the circuit? If not pls do it.

A single transistor charger is always very crude so you canot get accurate resuts from it....if you want better results make the first circuit using two transistors, it will be more responsive.

and if you are looking for even better and satisfactory results you can try the following design which is by far the most reliable of the designs.

https://homemade-circuits.com/2013/02/make-this-automatic-10-watt-to-1000.html
Arka Roy said…
what is the value of r9
Arka Roy said…
thank you sir...
but the 1st circuit is not working
Batharakala said…
hello there sir, thanks for your hard working. its really useful here.
may i request an led indicator for battery level like low, med and full when charging and using battery power :)
thanks for your answer sir
Swagatam said…
Thanks Batharakala, you can try the following circuit:

https://homemade-circuits.com/2013/06/3-step-dc-voltage-level-monitor.html
arun kumar said…
how to tansformerless in used first circuit modifying circuit digrams. how to remove LDR in modifying circuit
azeez fatai said…
which simulation software do you use sir, am using proteus and i have problem editing its transformer to give a desire voltage. so i'd appreciate if u can share me the one you think will help me the best or suggesting me the link to downloading it. moreso am new to designing but love to design
Swagatam said…
replace the following circuit with the transformer:

https://homemade-circuits.com/2011/12/cheap-yet-useful-transformerless-power.html
Swagatam said…
simulators are like blind persons with a stick, do you want to depend on a blind man's judgement??

Therefore i never depend on simulators and have never used any, rather I design the circuits by simulating them in my mind...I know it may be difficult for a new hobbyist to follow this but it also may not be a wise idea to depend on something which itself is so unreliable.

the best way (although hard) is to develop knowledge and understanding regarding the various concepts and begin simulating them with the help of the acquired knowledge
Kishore Cp said…
Hi Swagatam, GN,

Your circuit is awesome and Good. Could u plz clarify some doubt! Thanks in advance.

I am using 12v 7.5AH rechargable battery, i am planning to connect 6 1 Watt LED to the battery. Can this circuit be used or do i need to modify or add any resistance to the circuit.
Swagatam said…
Thanks kishore, you can try the above circuits, but T2 will need to be changed to TIP122 for driving 6 watt LEDs safely. Use large heatsink for T2
Rahul Ravishob said…
Hello Sir,
Firstly I would like to appreciate your effort !!! G
Now my question is ...can I use a 6V battery instead of 12 V...I would like to avoid LDR....Is there any modification neeeded?
Swagatam said…
Thanks Rahul!

Just remove P1, R1 and the LDR if don't want the dark activation section.

yes 6V can also be used, the LED series resistors will not be required with a 6V supply
Tony Thomas said…
Sir,

Please mention diode D1 connect which pin of ic 555
Tony Thomas said…
Sir,

i set first circuit.i want remove LDR and insert switch. how to change this ciruit pls help me.
Swagatam said…
Tony, insert the switch in place of the LDR...
Tony Thomas said…
thank u sir...

Sir i need a circuit for a good amplifier pls help me
Swagatam said…
please provide complete specifications of your requirement, only then i would be able to suggest
Tony Thomas said…
Sir i want 200-200 watts power amplifier including sub system pls give me the circuit. please provide power section also
Swagatam said…
Tony, you can make two of the following circuits:

https://homemade-circuits.com/2012/04/how-to-make-simplest-100-watt-mosfet.html

the circuit can handle well over 200 watts if the input voltage is around 50V.

presently i do not have a subwoofer circuit in this blog, will try to include it soon.
Tony Thomas said…
thank u sir

sir i want one emergency light circuit for using 500leds.please give a circuit
Swagatam said…
i'll look for it and inform you soon...
Adnaan February said…
Hi Sir
i am really interested in this circuit, please advise if you have a sketch of the circuit on a breadboard
Adnaan February said…
Hi Please advise if you have this circuit on breadboard, if so, a pic will be much appreciated.
Hans said…
Sir i have an emergency lamp at home which is not working, LEDs and battery are intact. I would like you to suggest me a circuit so that I can charge it from mains, Thanking you
Hans John D'cruz
hansdcruz@gmail.com
Swagatam said…
Hans, please provide the battery current/voltage specs so that I can calculate the parameters...
Hans said…
I guess the battery is 6V 2A there are no details reg the battery on it
Swagatam said…
you can use a mobile charger for charging it with a 470 ohm 1 watt resistor in series with the positive line. The battery may need more than 2 days to get charged fully.
Hans said…
Thank u swagatam
hello Sir,

i build your second cct ,its working fine ,except the charging part........ you are right single transistor cct is crude.........could you please integrate the charging cutoff section in first cct in second one..............I tried some thing ............kindly make necessary ammendments...........

i have sent u this modified cct at homemadecircuits@gmai.com ,please check and reply accordingly.

Thanks in advance for your kind response//
Swagatam said…
Thanks Muhammad, I'll check it soon and update the diagram here..........
gogutu said…
domnule;sunteti o comoara.as dori sa stiu cum pot modifica incarcatorul pentru o baterie de 12v/75A.pot folosi un triac in locul tranzistorului?multumesc.astept raspuns pe lacustagelu_68@yahoo.com sau gogutu68@gmail.com
Swagatam said…
thanks gogutu, you mean want to adjust the voltage of the charger using transistor circuit instead of triac??
hello sir swagatam.
sir i want to create your wonderful circuit above but the problem is., i never have bc547 if i substitute this by 2n5551 what is the difference and what transistor that can be substitute in bd139 if i never have tip122.,., i wait for your answer sir.,., thanks.,.,
Swagatam said…
hello eroll

although not very much suitable, 2N5551 can be used in place of BC547, for BD139 you can use any other equivalent rated to handle at least 2 amp at 30V
Pritam Bhowmik said…
it seems in the 1st ckt, no need of z1,z2.. whats the function?
mani said…
Sri. Majumdar,
You say that the IC555 in your first emergency light ckt. can be dropped and have given the modified ckt. without the use of IC555. Does the second ckt.retain all functions of the first ckt?
svs
Swagatam said…
it delays the response...but it's not important.
lokesh lokesh said…

Hi sir
I am so glad to see ur interest towards electronic circuitry ..
So eagerly waiting for circuit which will be having following (few or all) features
-Low Battery Cut-off
- Overloading protection
- Short Circuit protection
- Reverse current protection
- Reverse polarity protection
- Thunder protection
- Over discharge protection
- Auto battery shut-off at Low voltage detection
- Overcharge protection
- Auto charge stop/ High Volt Detection
- Battery capacity level display(SOC)

Making this circuit for underprivileged location as donation for poor via charity
So hope I can have one ckt diagram with some or all features mentioned above or lts link..
Looking for ur reply ..
With full excitement

Thank you
Regards
Lokesh

If successful I am in plan to put ur & website name on my device :-)
As part of tribute to you sir

Email: Lokeshelectronic@gmail.com
Plz WhatsApp me sir if possible to
9986829004

Swagatam said…
Thanks Lokesh,

I'll try to publish it soon.....please keep in touch.
FARHAN NASEEM said…
dear sir i implemented your fiirst circiut with ic lm 555 i am having an issue emergency leds are not glowing becasue in every case current is flowing from leg 3 of ic if we opened leg 3 of ic the emergency light works fine plz help me and make circiut operational with LDR
image url is
2.bp.blogspot.com/-eT2gHZxSr_A/UcEtp0coNDI/AAAAAAAAEhU/_9SJyCbGqWQ/s320/emergency+light+with+overcharge+cut+off.png
FARHAN NASEEM said…
DEAR SIR
i implemented your circiut with ic lm555 ,the current with leg 3 of ic is fllowing in every condition of LDR if we opened the leg 3 of ic the emergency light works fine plz help me to make LDR operational in this circiut
2.bp.blogspot.com/-eT2gHZxSr_A/UcEtp0coNDI/AAAAAAAAEhU/_9SJyCbGqWQ/s320/emergency+light+with+overcharge+cut+off.png
Swagatam said…
Dear Farhan,

in the absence of light on the LDR, pin3 will stop producing a voltage.....so make sure the LDR is held in sufficient darkness for this to happen.....or reduce the value of R2 until pin3 becomes zero volts at the desired darkness level
Kanta said…
Hi Swagatam..
I just constructed the second circuit using 6 volt battery, with 24 Led, single series with R combined 3 diodes. For the emergency light, it is functioning well. However, for the charging and cut off section, i set up the LED with the fully charged battery (6.9volt) by triming the pre set of TIP 127, to get very dim LED. When the battery discharged to 4.4 volt, the LED is still dim, then i detached the Battery and measure the collector voltage of TIP 127, the output is zero. I trimed the VR in such away to get the output of the collector to 8.5 volt, the LED became very brigth. I put on the battery and let it get charge. After the whole day, i still saw the LED bright. Then i detached the battery and measured the voltage of battery, it was 6.9 volt. i put on the battery again and trimmed down the LED until dim. After that, i detached the battery and measure the output of TIP 127, it was zero volt. Could you please advise me, what is my fault. I use 7.5 volt transformer of 1 amp and 6 volt 4.5AH batery.
Many thanks
Regards
Kanta
Swagatam said…
Hi Kanta,

using a single transistor as a sensor can be very crude and produce less accurate results...still you can try attaching a 3V zener diode in series with the base of the transistor (cathode towards base) and check the results, or you can opt for the next design using two transistors.
Sir can i ask where is the positive and negative in solar panel . the positive side is connected in the diode right ?
Swagatam said…
yes that's correct
Sandeep v menon said…
what changes should be made to the circuit if a large number of LEDs (say White coloured,75 or more in number) should be included??
Swagatam said…
battery, T2 and the transformer rating will need to be increased accordingly
SPARROW'Z TECH said…
Hi am Akhil

In the first circuit circuit using IC555,where should the earth sign indicated point be connected?
to the battery -ve or bridge circuit's -ve?
Swagatam said…
Hi, it's already connected with the negative of the bridge rectifier....no need to connect it anywhere else.
varun gopal said…
Sir
I have 12v 12AH led acid battery. For this how much Amp transformer need for making charging circuit
Thank you
varun gopal said…
Sir
Please reply me
I have 12v 12AH led acid battery. I need to charge it. Please tell me the spec of 12v transformer
Swagatam said…
Varun, you can use a 0-12V 2amp transformer for it, connect a bridge-rectifier with a 6800uF/25V to getting the required 14V 1 amp charging output for the battery.
mayu takuma said…
Hi Sir. We want to make a request. Is it possible to add a feature on this circuit? We would like to add a fan in this circuit so we can use it when there is power failure. Thank you.
Swagatam said…
Hi Mayu, you can connect the fan exactly where the LEDs/resistor network is connected that is across the positive of battery and the collector of T2
Alihan Güllü said…
Hello Swagatam,

I built the 2nd circuit you gave and checked a couple of times to make sure everything is connected to each other well. I got some issues though. First of all, I would like to use a led strip (rated 12V - 4,8W per meter), but I don't know how much length I need yet. I also discarded the LDR section with the LDR, P1 and R1. A couple of times I tried, it worked as expected. Later on, it didn't work. Here are the issues:

1- While it was working fine, when A/C mains was cut off, it took some 7-8 seconds for the leds to light up :)

2- As you mentioned in the description and in some of the answers you gave, I adjusted P2 to get 14V from battery terminals and I got a dim red light, but when it went down to 12V the light got dimmer, almost not visible.

3- With the use of strip leds, I guess I fried T2 (S8550), because after a few tries turning A/C power on and off, the leds starting lighting up with the A/C power on turning off when the power goes off :) Also, the transistor was pretty hot.
Swagatam said…
Hello Alihan,

the issues which you have mentioned can never take place because there's no possibility of those happening.

there's no capacitor associated with the T1/T2 so the delay effect cannot happen.

I hope you have only removed the LDR, R1 and P1 in your circuit and kept rest as shown in the diagram with R2 connection intact with the base of T1?

T2 can only become hot if the LEDs current is much higher than its tolerance level.

The charging LED will become dim as the battery voltage reaches 14V and vice versa so that's fine.

when mains is present T1 will be triggered ON through R2, which will keep T2 switched OFF, keeping the LED bank switched OFF, so the LEDs can never light up when mains is present unless one of the transistors has gone faulty.

by the way this a very basic and crude design so you cannot expect high precision from it.

for a high precision you can probably refer to the following design.

https://homemade-circuits.com/2015/10/smart-emergency-lamp-circuit-with.html
Alihan Güllü said…
Thanks for your reply, you've been pretty helpful..

The only direct connection between T1/T2 and the capacitor is the negative pole, which I guess not very important.

As I presumed, I had fried T2 and when I replaced it, it worked fine again. Then it got fried again as I forgotten to remove some part of led strip before plugging it back :))

I realize that it is a crude design, still it is important for me to start building something small and make it useful at home..I have seen the other project you have mentioned and I will surely have some questions for that one too :)

If I change T2 to a more powerful transistor, would I be able to use it with a load of 2-2,5A? Or I need to upgrade the whole circuit for that? For T2, I found BDX53C, which seems to be pretty powerful, still not sure if I can use it for the same purpose, or do you have another suggestion?

Thanks in advance..have a great week
Swagatam said…
yes obviously T2 must be dimensioned as per the LED current otherwise it will keep blowing of.

Only T2 and R3 will need to be upgraded as per the load current rest will as is unless any other parameter such as battery is upgraded too.

R3 = Batt supply - LED operating voltage / LED operating current

e-tutor said…
Hi
How to adjust the over charge cut off circuit for a 4v 1ah battery?plz help..
Krishan Chauhan said…
sir which software your using for designing the circuit???
salman said…
is it possible to cuf off load (led panel) when battery get discharged at 10.5v
Swag said…
if you add 3 LEDs in series instead of two, then this can be implemented automatically

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