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LED Emergency Light With Battery Over Charge Protection

Last Updated on by 255 Comments

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

 






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Comments

  4. 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.

    Reply

    • 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

      Reply

    • 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

      Reply

    • 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

      Reply

  5. 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.

    Reply

    • 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.

      Reply

  11. 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

    Reply

    • 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.

      Reply

  12. 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

    Reply

    • 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

      Reply

  13. 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

    Reply

  14. 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

    Reply

  16. 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.,.,

    Reply

    • 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

      Reply

  17. 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

    Reply

  18. 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//

    Reply

  19. 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

    Reply

  22. 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?

    Reply

    • 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

      Reply

  23. 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.

    Reply

    • 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

      Reply

  24. 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

    Reply

    • 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

      Reply

  26. 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

    Reply

  29. 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

    Reply

  30. 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

    Reply

    • 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

      Reply

    • 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 3×2 = 6 leds
      this would approximately run for 7 to 8 hours.

      Reply

    • 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.

      Reply

  32. 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

    Reply

    • 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

      Reply

  33. 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

    Reply

    • 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.

      Reply

  35. 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.

    Reply

  36. 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

    Reply

  39. 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?

    Reply

  41. what is the use of connecting so many resistor in series with the leds, cant we connect a single resistor in series with high watt and how to calculate the led resistor.

    Reply

  42. Hello Dada,
    Cant We Connect A single Resistance in Series instead of So many resistors in parallel and in Series with leds.
    And I have Send You a circuit Diagram in facebook Messages please reply.

    Tanmoy Singha Mahapatra

    Reply

  43. what about using a photo-transistor for the circuit ??
    i found one circuit on net but the problem is that i cant find the photo-transistor in market
    is their any other option for a "dark detecting circuit" which can operate in 4v dc batt.

    Reply

    • you can add a diode with the positive line ssuch that current only passes from the adapter to the battery and not in the reverse direction.

      Reply

  45. i made the circuit it works
    But the fully charged 9v battery gets discharged
    is it because of the transformer
    what is the solution for that?

    for charging a 9v battery which zener diode do i need 9v or 12v zener

    Reply

  46. give me u email id
    i need help in some circuits which i want to send so that u can help me

    secondly i need some modification in the circuit in which the charging stops automatically when the battery is fully charged
    all for 9v battery

    Reply

  47. instead of leds if i use two 1 watt leds do i need to attach resistors (5 ohms 1/4 watt)
    im using 9v battary
    is their any changes in the circuit (resistors)
    im using multi voltage adaptor instead of transformer ( 0-9v)

    Reply

    • your 9V battery should be rated at at least 4AH….

      make two parallel strings having 1 watt leds and connect 20 ohm 1 watt resistors with each led string.

      also replace T2 with TIP122

      Reply

    • 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

      Reply

    • disconnect the 7812 ground link and connect through 4nos 1n4007 diodes, do the connections as shown in the following article, connect the 2.2k resistor also as shown, ignore the rest of the components.

      https://homemade-circuits.com/2012/11/high-current-transistor-tip36-datasheet.html

      Reply

  55. Dear Sir,
    I make the second circuit ,it work well.Thank you.

    One point noticed that charging is very slow .At the time when i connected the circuits to battery ,battery voltage is 10.81v .After 3 hours it slightly increase but not exceed 11.I check overall connection again and again ,it found correct .Is charging need more time ??

    Reply

    • You can use the preset to adjust the charging rate, tweak the adjustment as per preference, but do not make it too fast otherwise the battery may get damaged.

      Reply

  58. Dear Sir,
    i wish to make one of this above circuit. Presently a 15-0-15v/1Amp transformer and 12V 7.5 AH battery in my hand .In your specification the value of transformer is 12-0-12 V.Can i use 15-0-15V transformer instead of 12V in this circuit??Waiting for your immediate reply .Thank you Sir

    Reply

    • Dear രജീഷ് പാലവിള

      You may use your transformer, use one 0-15V tap.

      But you will have to reduce the voltage to 12V with the help of IC 7812 if you are using the IC 555

      Reply

  59. Hi Swagatam,

    I was wondering if I am able to connect the output from a boost converter @24V/0.4A to replace the transformer? Could you advice me how to go about changing the config?

    Reply

  61. Hi, Swagatam,
    could u plz modified this circuit for me i need the 12v 7ah battery charger with over charge protection using 12v 1A transformer

    Reply

  63. Hi,

    Thanks for your help,
    I have done as you told. But now white LEDs are not illuminating in any situation, the T3 led is glowing both in battery and main power on condition.

    need help for troubleshooting.

    Reply

    • OK, it's probably due to the battery voltage that's passing through the emitter of T3 to the base of T1…..add a blocking diode after C1, so that the positive from transformer passes through this diode to the charging section consisting of P2, T3 etc….but the battery voltage gets blocked by this diode.

      Reply

  64. Hi,

    I have prepared the 2nd circuit, and there is some issue kindly help..

    All white LEDs are glowing in the situation when the main on and the T3 LED is glowing but T1 LED is not glowing. And even no changes found when I switched off the main AC power, with battery power.

    Reply

  65. I'm going to build the 2nd circuit using 6v 4.5Ah lead acid battery. What should I modify in the circuit? should I change the LED resistors with another value?

    Reply

    • Yes the second circuit also has a over charge protection using the TIP127 transistor.

      For 6V battery you can make the LED resistor to 10 Ohms 1/4 watt.

      Reply

  70. Hi Swagatham,
    It would be very helpful if you please elaborate bit more on the procedure on adjusting the value of preset P2. and what are changes i have to make in the circuit if LDR is replaced with a switch so that light dependency is removed in it's working.

    Biju

    Reply

    • Hi Biju,

      T3 and the associated parts form a very crude type of automatic charger circuit, you just have to adjust P2 such that the LED becomes very dim at about 14.5 to 15V which is the full charge level of a 12V battery.

      You will have to remove LDR, R1, P1 for making the circuit not respond to light. An an/off switch may be connected in between LED positive and the battery positive.

      Reply

    • 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?

      Reply

    • 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

      Reply

    • 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.

      Reply

    • 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?

      Reply

    • 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.

      Reply

    • 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.

      Reply

    • 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?

      Reply

    • 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

      Reply

  71. Hi Swagatam,

    I am really honored for your timely help. Thanks a lot. Surely I will start assembling this circuit and send you the photos of it.

    Regards
    Nagaraj

    Reply

  72. Hi Swagatam,
    The circuit, https://homemade-circuits.com/2012/10/automatic-40-watt-led-solar-street.html is exactly to my needs. But can you modify to fit in the above circuit and without relay ( in case if you can do it sooner than designing a new one).

    Regards
    Nagaraj

    Reply

  73. Hi Swagatam,

    What i meant was to have both the protection in a single circuit. Since there were two to three circuits, i wanted your help in integrating them into a single circuit.

    Regards
    Nagaraj

    Reply

  74. Hi Swagatam,

    Thanks for your prompt reply. But again i am confused after going through your above comment to incorporate another circuit in the above link. Actually after going through the comment section there, i found that you have replied to one Mr. Ajay's query and have suggested another circuit (https://homemade-circuits.com/2011/12/high-current-10-to-20-amp-automatic.html)for more efficient working of the auto cutoff from low battery voltage. Actually I wanted this one only to be incorporated. Can I incorporate the above circuit for my requirement and how do i integrate it in the above circuit so that i can have my battery safe by protecting from over draining and from over charging.

    Regards

    Nagaraj

    Reply

  75. Hi Swagatam,

    Sorry to disturb you often. For the above circuit, I also need the battery to be protected from draining too much. can you help me in this aspect.

    Regards
    Nagaraj

    Reply

    • You may incorporate the circuit given in the following link, use the second circuit:

      https://homemade-circuits.com/2011/12/how-to-make-simple-low-battery-voltage.html

      Reply

  76. Hi Swagatam,

    One more help from your end for me to start building the above circuit. In one of your article "How to Make an Efficient LED Emergency Light Circuit", you have mentioned as "If we could maintain a voltage around an LED near to its rated forward voltage, we could use it more efficiently. That’s exactly what I have tried to fix in the circuit." Can you help me in achieving the same principle in the above circuit.

    Regards
    Nagaraj

    Reply

    • Hi Nagaraj,

      It won't be required actually, the resistors will take care of the voltage for the LEDs.

      In the other emergency light circuit, the voltage input was 6V so it was easy creating the required ideal voltage, but here it will be slightly difficult, so the above circuit is quite OK.

      Reply

  77. Hi Swagatam,
    I build the second circuit. But not working properly. Led's are illuminating in Battery. But When i give supply to charge the battery through transformer. The Illuminating Led's are not switching off. Where i gone wrong i dont know. I tried this circuit with 14 Led's. If this make any difference in circuit. Also 8050 Transistor getting heated. Please guide sir.

    Reply

    • Hi Pugazhenthrian,

      Have you connected D5,R2? If you have connected them correctly there's no way the LEDs can illuminate with power supply ON.

      With 14 LEDs (two in series with 330 Ohms) the current would be just 140mA, 8050 should not become hot…

      However you can replace the 8050 with TIP122 if you wish. With TIP122 you would be able to handle even 100 leds.

      Reply

    • Is the red LED at T1s emitter glowing under the situations??

      It must glow, if it doesn't means T1 is not OK or connected wrongly.

      And if it's glowing means T2 is faulty or wrongly connected.

      Reply

    • Short circuit T1s emitter/collector points with a wire, this should illuminate the red LED and switch OFF the white LEDs. If this does not happen then either the red led is faulty or wrongly connected………….or just remove the red LED and connect T1s emitter directly to ground.

      Reply

    • Hi Pugazhenthrian,

      It's my humble request to you to get my circuits verified from any expert electronic engineer, because I cannot discuss the details with you or anybody who may be new in the field.

      Unless you understand the circuit functioning by yourself you won't be able to make it correctly, no matter how much help you get online.

      Also please read the disclaimer at the left hand side section of the page.

      Regards

      Reply

  79. Hi Swagatam,

    Thanks for your reply. Here I need to have some more refinement before starting to build this circuit.
    Firstly, I intend to have 100 LEDs in the above mentioned circuit. So do i have to modify the circuit in any way.
    Secondly, should the transformer be 2A.

    Regards
    Nagaraj

    Reply

    • Hi Nagaraj,

      You will have to dimension the transistor T2 so that it is able to handle the 100 leds safely…. probably a TIP122 would do nicely.

      Also the battery has to be rated at 7.5ah minimum.

      For charging the above battery a 1 amp transformer would be enough, no need of using a 2 amp transformer.

      Regards.

      Reply

    • Hi Srinu,

      For that to happen, you will have to remove the entire 555 IC circuit along with T1, T2, D3, R9 and connect the resistor common point of the LEDs directly to the negative of the battery.

      Reply

  84. hi swagatam,iam mohamed from egypt ,very nice circuit,and nice explanation ,but kindly can tell me what is the jop of the 2 zener diodes , and how the circiut feel that the battery became 14v thanks

    Reply

    • Hi Mohamed,

      Thanks! actually the zeners have no role and they can be removed. The preset at the base of T3 is set such that it conducts at 14v(battery fully charged), when T3 conducts, T4 switches off, which cuts of power to the battery, and the charging stops.

      Reply

  86. sir… we are currently using your guide for our project in logic that needs logic gates therefore we need to change the TTL parts to an IC… we also would like to make it a standard emergency light which means were gonna need an HD light shud i say… thank you for ur suggestions and help sir deeply appreciated it

    Reply

  88. Sir!
    I want to design a circuit for charging 4v SLA .7AH battery using 555 timer IC for over n under charge protection.As around 70mA charging current suffice i want to use capacitive power supply.Pls could u design this type of charging circuit.I am looking forword 4 ur urgent respose.thanks alot

    Reply

    • Sir!
      I didn't understand. How will be required 700mA for this circuit.COuld u pls explain little bit. I have no more electronics khowledge.THankx 4 ur attention

      Reply

    • if you want to trickle charge the battery for many days or even for months then a 70 ma will do, but for charging a 7.5 ah in one day you will require 700ma current.
      capacitive power supply will produce dangerous current in the circuit, that's another bad thing about it.

      anyway you can check out this circuit:

      https://homemade-circuits.com/2011/12/automatic-white-led-emergency-light.html

      Reply

    • Sir!

      I have mini sla battery 700mA capacity with 4.5V terminal voltage.I want circuit as per mentioned in post dated 7th Sep'12. Thankx.

      Reply

    • 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

      Reply

  93. …Sir,

    What are those type of LEDs which are called 1Wtt, 2Wtt and so on..???
    If these types of LEDs can be used in this particular circuit, how many of it will require…for more Bright and compactness.
    Please share the information..

    Regards,

    Reply

    • Higher wattage LEDs can be used here, however they will consume power and discharge the battery faster, you can involve as many leds as you like, but they must be connected in the shown format only….more leds would mean more powerful battery to be incorporated.

      So, LEds will depend on your personal choice, you may find the right numbers and type through some practical trial and error……

      Reply

  94. Sir..it's really Surprising greatly!!!
    You reply so fast…actually I thought it might take a weeks time to develop the circuit…which I requested.
    R5 Value is NOT mention and If I am Not wrong C2 should be of 1000mfd 25v and C1 of 1mfd 25V.
    Does IC555 needs a Heatsink.
    Would you like to suggest any good quality LDR.
    Can I use the Flat, which I guess 8mm, LEDs which comes fitted with Recharable Hand Torches.
    In my JunkBox I've some Zener Diode, How do I check the Value.
    …will it work in one go??? He..He..He..

    Regards,

    Reply

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