High & Low voltage cut-off with delay& alarm

Description.

This straight forward circuit will protect electrical appliances from over voltage as well as under voltage. The circuit also produces an alarm when the power supply comes back. An ideal circuit for home to protect your valuable equipments from voltage fluctuations. The same circuit with some modifications can be used  to make a automatic voltage stabilizer.

When the mains voltage is in the normal level, the voltage at the negative terminal of zener diode D4 will be less than 5.6 Volts. At this condition transistor T1 will not conduct. The same time voltage at the negative terminal of zener diode D5 will be greater than 5.6 and so the transistor T2 will be conducting. The relay will be activated and the green LED will be glowing.

When the mains voltage is higher than the set limit the transistor T1 becomes conducting since the voltage at the negative terminal of  D4 is greater than 5.6 V. At the same time transistor T2 will be non conducting which results in the deactivation of relay to cut the mains supply from load. When the mains voltage is less than the set limit transistors T1 & T2 becomes non conducting  making the relay to de-activate and cut the load from mains.

The timer NE555 is wired as a monostable multivibrator with a pulse width of 10ms.When the power comes back after a cut off a negative voltage is obtained at the trigger pin which triggers the IC NE555. The transistor T3 gets forward biased and it drives the buzzer to produce a beep as an indication of power resumption. Also the transistor T1 is made on which in turn makes T2 off. As a result the relay will remain de- activate for 10ms and this provides the sufficient delay and the equipment  is protected from surge voltages.

Circuit diagram with Parts list.Click to enlarge.

high-and-low-voltage-cut-of-circuit

Notes.

  • To calibrate the circuit a autotransformer is needed. Connect the output of autotransformer to the transformer primary.
  • Set the voltage to 260V and adjust  VR1 to make the relay deactivated.
  • Now set the autotransformer to 160V and adjust VR2  so that the relay is de-energized.
  • VR3 can be used to vary the volume of buzzer.
Show Comments

99 thoughts on “High & Low voltage cut-off with delay& alarm

    • seetharaman

      It should be connected to input supply circuit. Connect this unit to incoming supply and out put to equipment which requires protection

      Reply
  1. Adamu Abubakar Muhammad

    I picked High and Low Voltage Cut-Off with Delay And Alarm as my mini project and found this project very interesting because, I succeeded in Implementing the Project without any difficulties. I used a 12-0-12V transformer and BC547 transistors instead of S100. Thanks a lot for your post. Wish to get an explanation on that Car Parking Guard Using Infrared Sensor because I tried it but haven’t get it right due to absence of LM567 IC here. Is there any subtitude to that. What about S567? Thanks a lot.

    Reply
  2. Tneb kathirasan

    no need to use auto transformer as the component to be assembled in. it is to be tested after finishing this project.Hence one Auto trans needed.You all gets confused without reading the text completely

    Reply
  3. ajaykumar

    Sir can u plz tell me the functioning ic ne555 timer in the circuit how its getting triggered snd how vwe are using it to make the buzzer on in detail………

    Reply
  4. Keerthi reddy

    Sir,iam ece 2nd year student.i tried this as my mini project.iam working on this since one month.actually the indications leds and buzzer are not responding at crct time.any body had succeeded by doing this project.give me reply

    Reply
    • Seetharaman

      The auto variable transformer is adustable from 0 to 270 volt for an input of 230 volts. It is required to set the circuit accurately, which is also quite expensive to buy, without which adjustment is difficult by trial and error method. the circuit will work with 230 volt ac to the 12-0-12volt transformer primary. the relay NO contact can be used for switching on / off the load.

      Reply
      • Ajaykumar

        Thanku for ur earlier reply..i am tryng dis project…but d led’s(red nd green) are going at a time when d suppy provided to circuit..plz tell me..a.s.a.p

        Reply
      • Ajaykumar

        The led’s red and green are glowing at a time when the circuit is given the supply..plz give me d suggestion to make it run..nd plz tell me how to connect load(bulb 60watts) to the relay in which coil terminals we are connecting in d circuit and wat about other 3 terminals..does the load(bulb 60 watts) get d supply from circuit? Are any plz mention…reply a.s.a.p

        Reply
  5. ajay kumar

    hai i have tried this circuit but i hav not used autotransformer which u have said .i have used 12-0-12v center tapped transformer..but this only provides 12v to the circuit.. how could i supply 230 v supply to make the circuit work… plz reply a.s.a.p

    Reply
  6. ajaykumar

    Hai….can u plz tel wat is auto transformer since I could not get this in electronics shop. is there any the s name for this

    Reply
  7. baqir raza

    Admin…i m.having difficulty in this circuit ,i hv tried to make it as it is shown here.bt in schematic the red led is running while the green is off even after changing the voltages..i hv put a double tapped transformer …where to put the auto transformer u r saying..please send me its schematic design which works …i ll be grateful to u

    Reply
    • Seetharaman

      If red is glowing the power is available for the circuit. Now to adjust the pots for correct operation you have to use an auto transformer (variable voltage transformer to input of the above circuit where it is shown as 230VAC. Adjust variable auto transformer and adjust the pots as shown in the procedure

      Reply
  8. Bharat

    Hello sir there is show only two terminal connection in figure. But in real there have minimum 4 terminal on relay. So how we can connect remaining terminal on circuit. Please give me location to connect to terminal in figure. Thanks

    Reply
    • Seetharaman

      Hi Sarat pa Please use the NO contact of the relay for switching on / off the load. As such no power will be available at relay contacts

      Reply
  9. Gerwin Dsouza

    if I want to avoid using 555,timer n buzzer i.e. only upto relay1 and t2, then where should input to t1 base from pin 3 of 555 go
    2)can I use 12-0 transformer without center tap and bridge rectifier
    3)is there a pcb designed or using which simple free software can I make a pcb
    very useful circuit thanks a lot,my water pump and tv was burnt due to 440v some time backplease reply to my queries by mail or on this site soon thanks a lot Gerwin Dsouza ,Malvan

    Reply
  10. CJK

    I’ve selectd dis as my project… Bt I’m not much familiar wid relay… I found 5 pins on d relay..bt only 2 terminals of d relay r cnctd in d circuit diagrm… Plz giv me details about d cnctn of relay….

    Reply
  11. daniel

    Hi im very interested of your circuit i wish i could build one but my problem is the ic SL-100 it very difficult to it in my country so can you please tell me different thank you looking forward to hear from you.

    Reply
    • Seetharaman

      HI Electronic buzzer volume cannot be controlled. You can try to paste a thin paper sheet on the sounder hole, this should solve your problem.

      Reply
  12. VIKTOR

    please, what will i use to set the cut-off voltage since i cant get the autotransformer. And also please what is the power capacity of the circuit? can it be used to power an air conditioner or refrigerator? please i need your reply, thanks and God bless

    Reply
    • Seetharaman

      Hi Madhuri when the input voltage is just above minimum value (say 160volts set by VR3) T2 picks up and relay RL1 switches on to give supply to load. If the load increases more than the safe limit (say 260 volts set by VR1)T1 picks up and removes the bias to T2 such that they RL1 switches off cutting off supply to load. once input voltage falls within 190 to 250 volts range the relay RL1 picks up and the supply to load is restored. The timer is to produce beep once the supply is resumed as well to delay the supply to load such that the inlet surge at the time of power resuming is also not sent to the load.

      Reply
      • Dhanush

        If it supplies load even under under-voltage conditions….. Why is it called High/low votage cut-off??… instead we can call it only High voltage cut-off… pls reply fast as we hav chosen this as our project topic….

        Reply
    • syama

      sir,
      we select this topic as our project.I Want to know more about the outputs of this.so pleae send me the details of the project as soon as possible
      Thanking you.

      Reply
    • Seetharaman

      Hi Madhuri there was an error in my earlier reply on voltage level this is correct one. when the input voltage is just above minimum value (say 160volts set by VR3) T2 picks up and relay RL1 switches on to give supply to load. If the load increases more than the safe limit (say 260 volts set by VR1)T1 picks up and removes the bias to T2 such that they RL1 switches off cutting off supply to load. once input voltage falls within 160 to 260 volts range the relay RL1 picks up and the supply to load is restored. The timer is to produce beep once the supply is resumed as well to delay the supply to load such that the inlet surge at the time of power resuming is also not sent to the load.

      Reply
  13. jyothi singh

    plzz tell me the high-low voltage cutoff with delay and alarm with some modification and advancement in circuit diagram.

    Reply
  14. JULIET

    plzzzzz tell me the size of the auto transformer to be used, and i didnt get what is no n where exactly the appliance to be checked should be kept ,kind request to you to send me all the details of working of the ckt by tonite

    Reply
  15. farhad

    Very nice post my brother but where will the load be connected,and what is the function of auto transformer here….

    Reply
  16. CALEB AMBOLE

    From the circuit where do i connect the appliance to be protected for both over/undervoltage conditions.And apart from the auto transformer what else can we use to vary the voltage to the circuit.Also after cutoff how can the appliance be automatically connected to the mains when the fault has been cleared.

    Reply
  17. Seetharaman

    Hi Balu VR2 is wrongly shown as VR3 in the schematic. For appliance connection please refer to my 6th Feb comment.

    Reply
  18. Balu prasad

    please help me to find where vr2 is.Also where should we connect the appliance to be protected in case of over voltage?

    Reply
    • rohit

      how can we connect appliance operating on 230v to a transformer operating at 12-0-12v secondary? & where to connect the load? please reply….

      Reply
  19. Seetharaman

    Hi John use the normaly open contact(when the relay is in off condition)of the relay RL1 to switch on off the load.
    Hi ipoy20 this is a working model and a proven design for step voltage regulators.

    Reply
  20. john n

    hey ,thanx for the contribution to technology,i have tried making this project but the sl100 transister is rare so i tried the D313 as an option its still not workin ,pliz suggest another option,thanx in advance.

    John.

    Reply
  21. حسامالورد

    Great and simple circuit, but I searched for circuit that protects the drive three phase 380V AC interruption of one of the stages, but I did not find it, or the opposite one of them.

    Reply
  22. Bernard

    Hello, since i’m working on a circuit for shutting off my diving light when my battery’s get too low, i’d like to integrate this circuit into it. However is it possible to leave everything right of Transistor T2 out of it? And could you please tell me if i could directly use this transistor in series with the base of a BUZ11 MOS-FET, wich I am now using to switch my load. Thanks in advance.

    Reply
  23. seetharaman

    Hi Hiren Use standard straight or dotted PCB and wireup yourself. For testing you require a variable auto transformer of 0 to 270volt.
    Use the supply to the load to be protected through RLA1 contact

    Reply
  24. Rilwan

    Hi, pls i need details of how the transistors and the Zener diodes work. Pls kindly see me through in my email. Thanks

    Reply
  25. seetharaman

    Hi Adamu The load should be connected through the potential free contacts of the Relay RLA1 (NO contact- Normally open contact). The relay will switch off/on the load.

    Reply
  26. rilwan

    i am still awaiting your response in my email, i need you to see me through this. i need details on how the circuit works since i have found this project very interesting and finally approved my supervisor. thanks very much

    Reply
  27. seetharaman

    Hi Rilwan the NO contact of the ralay RL1 is used for controlling the load. I will be in touch with you soon through your email id

    Reply
  28. seetharaman

    SL100 can be substituted with 2N2218, 2N2219 or 2N1711 switching transistors reliably. If you are in India then you can use BEL100N, CL100 also. The above circuit is very reliable one. I have used it in auto phase change over circuit in house. i will be sending the circuit to “Circuits today” soon.

    Reply
  29. Ita E Bassey

    Am working on one of your circuit(street light) as a project.I need your help on written area(materials).Thanks

    Reply
  30. priyanka

    hai sir iam a final year EEE student.i want to do a project on high voltage and low voltage cutoff with time delay(a model based on the circuit).you please give me the information regarding to the operation,you please send the information to my mail.

    Reply
  31. twits4twats

    Mohamed Anany
    I am pretty confident that D4 and D5 should be 400 milli Watts and not 400 Watts. 400mW is suggested as it is a commonly manufactured value and therefore normally cheaper.

    Reply
    • admin

      that was an error in the circuit diagram
      D4 and D5 are 400 milli watts. I have corrected the circuit diagram.
      Have a look.

      thanks to Mohammed and twits4twats for pointing out.

      Reply
  32. Mohamed Anany

    Hello,
    Well thank you alot for your response, and i have another question, can i use a lower power diod than the (400w 5.6v D4 & D5 & D10)?, if you have an answer please post it or send me an email, again thank you for your fast response.
    best regards
    Mohamed

    Reply
  33. Mohamed Anany

    Hello,
    First it is a good circuit, but i want to ask about a replacement for the (SL100) transistor, because i have searched alot for that transistor but i didn’t find it. Please if you have an answer for this send me an email.
    Thanks
    best regards
    Mohamed

    Reply
  34. shubhrodutta

    Hello,
    I found your circuit simple and interesting.
    could you suggest the necessary change I need to do if I want to protect a 6V, 4.5 AH Lead Acid battery from overcharging and over discharging.
    To get a steady charging voltage of 7.3V for charging the battery, I will be using a 12V, 500 milliAmp Adapter, Send it through IC 7808 followed by diode 1N7004 in series. That will give me 7.3V.
    Thereafter I need a overcharge protection circuit.
    Similarly I need to protect the battery from over discharging.

    only 30% discharging will be good for me. it will give me a good life.
    will you be able to guide me.
    thanks
    kind regards
    shubhro

    Reply

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