Wednesday, December 21, 2011

Highly Accurate, Mains High and Low Voltage Cut OFF Circuit, Using IC 324 Explained

The article describes how an accurate over and under voltage cut out circuit can be made at home for protecting the domestic appliances from sudden dangerous high and low voltage influxes.The AC mains high and low voltage cut off circuit explained in this article is very easy to build and yet very reliable and accurate. The circuit utilizes a single IC LM 324 for the necessary detections and instantly switches the relevant relays so that the connected loads are isolated from the dangerous inputs. The circuit also provides visual indications of the respective voltage levels during any instant.




Parts List for the proposed high, low mains voltage protector circuit.

R1, R2, R3, R4, R5, R6, R7, R8 = 4K7,
P1, P2, P3, P4 = 10 K Presets
C1 = 1000 uF/ 25 V,
OP1, OP2 = MCT 2E,opto coupler
Z1, Z2, Z3, Z4 = 6 Volts, 400 mW,
D1, D2, D3, D4 = 1N4007,
D5, D6 = 1N4148,
T1, T2 = BC547B,
LED = RED, GREEN as preferred,
Transformer = 0 – 12 V, 500 mA
Relay = SPDT, 12 Volt, 400 Ohm

Circuit Description

In one of my previous posts, we saw a very simple yet effective design of a mains over voltage and low voltage cut off circuit, which is able to switch and cut off the mains power from reaching the connected appliances once the input voltage crossed over or below the dangerous thresholds. However due to the over simplicity of the design, involving just a couple of transistors, the circuit has its own limitations, the major limitation being less accuracy and considerable hysteresis, resulting high threshold gap of more than 60 volts between the high and the low limits.
The present design of a high voltage and low voltage cut off circuit is not only highly accurate but also provides visual indications regarding the relevant voltages insteps. The accuracy is so high that virtually the thresholds can be separated and sensed within 5 volts range.
The incorporation of op amps in the circuit equips it with the above feature and therefore the whole idea become very much reliable.
Let’s understand the circuit in details:
The op amps, A1, A2, A3, A4 are obtained from a single IC 324, which is a quad op amp IC, means consists of four op amp blocks in one package. The IC is outstandingly reliable and easy to configure and hardly poses a problem with its functioning, in short it has robust specs and is too flexible with most of the configurations.

The four op amps are rigged as voltage comparators. The inverting inputs of all the op amps are clamped to a fixed reference value of 6 volts which is done through a resistance/zener network for ech of the op amps discretely.

The non-inverting input of A1 to A4 are connected to the power supply of the circuit through a voltage divider network formed by the presets P1, P2, P3 and P4 respectively.

The presets can be adjusted as desired to flip the outputs of the respective op amps when the relevant input level crosses the reference level set over the inverting inputs of the respective op amps.

The outputs of A1 to A4 are integrated to LED indicators in a rather special way. Here instead of following th conventional method of connecting the LED cathodes to the ground, it is connected to the output of the preceding io amp’s output.

This special arrangement ensures that only one relevant LED is switched ON in response to the rising or falling voltage levels from the op amps.

Two opt couplers are introduces in series with the uppermost and the bottom LEDs so that the optos also conduct with the relevant LEDs during high and low voltage levels, specified as dangerous thresholds.

The conduction of the opto couplers instantly switches the internal transistor which in turn toggles the respective relay.
The poles of the two relays and the poles of the relays are connected in series before supplying the output through them to the load. The series connection of the contacts ensures that if any one of the relay conducts, cuts of the mains supply to the load or the connected appliance.

At normal levels opamp A1, A2 or even A3 may be conducting because all these are arranged in an incremental order and go on switching in sequence in response to gradually rising voltages and vice versa.
Suppose at certain normal levels A1, A2 and A3 are all conducting (outputs high), and A4 not conducting, at this point only the LED connected to R7 would illuminate, because its cathode receives the required negative from the output of A4, whereas the cathodes of the lower LEDs are all high because of the high potentials from the above op amps. The LED connected to R8 also remains shut off because A4’s output is low.
The above results appropriately influence the respective opt couplers and the relays such that the relays conduct only during dangerous low or dangerous high voltage levels detected by only A1 and A4 respectively.

A Simpler Approach

After some analysis, I realized that the above high, low mains voltage cut off protector circuit could be simplified into a much easier version. Please refer to the diagram given below; it's self-explanatory and very simple to understand.

However if you have problems understanding it, shoot me a comment.


92 comments:

  1. Just having problems with the load..Is it AC or DC??

    ReplyDelete
  2. You may connect any load with the relay contacts, whether its AC or DC it won't matter, it will be controlled appropriately.
    However what is the DC load you want to control? How much is the voltage?

    ReplyDelete
  3. The second circuit will only control AC loads, though.

    ReplyDelete
    Replies
    1. hi
      i am trying to construct your second circuit. May i know where do u connect the round? it seems it connect to AC main?

      Delete
    2. Hi, yes the ground connects with one of the mains inputs, the entire circuit then floats with dangerous mains AC, so be cautioned while testing it.

      Delete
  4. like the motor of a ceiling fan...

    ReplyDelete
    Replies
    1. Motor of a ceiling fan is an AC load, not DC, it can be connected to the above circuit for the protections.

      Delete
  5. hey thanks...can u kindly enlighten me about the MCT 2E opto coupler??

    ReplyDelete
    Replies
    1. It's a component which contains an internal LED and a photo-transistor laid down side by side.
      When the LED outputs are connected to a voltage source, it lights up internally and this light comes in contact with the photo-transistor which instantly conducts, switching ON the connected load at its output pins.

      Delete
  6. hey i got this video on youtube...just want to find out if this your circuit works just like that
    http://www.youtube.com/watch?v=NlK2-qfpDcc

    ReplyDelete
    Replies
    1. Yes, the above circuit will perform in the same way as shown in the video.

      Delete
  7. hey could you pls explain the part relating to the AC main input(Phase and Neutral) connected to the output..and the output should also represent the load hun??

    ReplyDelete
  8. Those are relay contacts..I've explained relays in one of my articles, you can find it from the search box.
    Yes, the output refers to the load terminals.

    ReplyDelete
  9. HI SWAGATAM,

    Can I have the part list of the new version?

    TRANSFORMER:
    D1 -D4:
    D5:
    D6:
    D7:
    P1:
    P2:
    Z1:
    Z2:
    R1:
    R2:
    R3:
    R4:
    R5:
    T1:
    TRIAC:

    Thank before hand.

    ReplyDelete
    Replies
    1. Hi Joomunm,

      Here goes:

      TRANSFORMER:0-12V, 500mA
      D1 -D4:1N4007
      D5:1N4007
      D6:1N4007
      D7:1N4007
      P1:10K preset,
      P2:10K preset,
      Z1:4.7V 0.5 watt
      Z2:4.7V 0.5 watt,
      R1:1K
      R2:1K
      R3:1K
      R4:1K
      R5:1K
      T1:BC557
      TRIAC:BT136

      Regards.

      Delete
    2. Will you please explain the pin configurations also? I am a beginner.

      Delete
  10. I want to power ur circuit using transformerless power supply.can u please post the circuit.thanks

    ReplyDelete
    Replies
    1. type "transformerless power supply" in the search box, you will find a few of them.

      Delete
  11. Dear Swagatam,
    I am Maksud. you have provided fine circuit of overvoltage protection ckt.can u provide me with power factor correction. but output is 230V. Actually i am unable to convert 24V dc into 230V,5A

    ReplyDelete
    Replies
    1. Dear Maksud,

      I'll try to figure it out, if I succeed I'll provide you with the data.

      Regards.

      Delete
  12. hello swagatam.. I'm doing this project as my final year project.. but i'm not sure how to set the limitations to prove that the circuit is currently functions.. Can you help me??

    ReplyDelete
    Replies
    1. Hello Mohd Rafi,

      You may try the second circuit.
      Please make the circuit first then I'll explain how to set it.

      Delete
  13. Hi Swagatam

    I am brice, just want to know which of the circuit is better the one with the relay or with the triac. CAn i test the circuit using a variable PSU, where i make the voltage greater than 12 V.

    ReplyDelete
    Replies
    1. Hi Bruce,

      The lower circuit is better, select the triac specs as per the load current...yes you can test it with a variable PSU

      Delete
  14. hello swagatam nice work. I want to use this low/over voltage protect circuit for high power transformer approximately of 2000watts. I will employ this circuit at the primary of the transformer.I want the transformer input voltage to be strictly 215-235v. I want to use the first circuit with relays. so I want to know what are the high and low voltage cutoff's of the existing circuit above. do i need to make changes? also can you add a push to on/off switch circuit for the whole circuit? Thank you.

    ReplyDelete
    Replies
    1. Thank you!

      The cut offs ranges will be as per your preferences, you can set the presets as per your wish, at voltages where you would want the circuit to trip.

      Possibly I'll try to update the circuit with a push-button soon...

      Thanks!

      Delete
  15. hi swagatam,
    in this circuit mct2e output is too low not switching 12v 400 ohm
    s relay, what to do

    ReplyDelete
    Replies
    1. Hi Shiva,

      You can add another transistor and form a Darlington configuration with the opto transistor externally. Use a BC547 transistor.

      This will enable the relay operations.

      Delete
  16. could you plz emplaned this "http://www.brighthubengineering.com/consumer-appliances-electronics/68396-over-voltage-and-low-voltage-protection-circuits-easy-home-projects/#" components for low and heigh voltage circuit i hope this is your circuit and put these in your blog also

    ReplyDelete
    Replies
    1. I have the circuit already posted in this blog, please check this out:

      http://homemadecircuitsandschematics.blogspot.in/2011/12/simple-mains-ac-over-voltage-and-under.html

      Delete
  17. please add a delay circuit so we can use it with Refrigerators.

    ReplyDelete
    Replies
    1. Yes a delay feature is crucial,,,,possibly I'll try to include it here soon....

      Delete
  18. HI, Very interesting. I would like to build a circuit to detect the precise voltage from a storage 12VDC deep Cycle battery which range from 11.8V to 13.2VDC ( charge/discharge cycle). If the voltage across the battery falls below 11.9V, the circuit will trigger a relay ( 12VDC or 24VDC coil)and remain OFF and if the voltage across the battery goes above 12V or higher, relay will remain ON. I think a time delay to remain ON or OFF is needed so the relay won't fluctuate in case the voltage across the battery fluctuates between 11.9 and 12V. Thanks for your help.

    ReplyDelete
    Replies
    1. Thanks!

      I have a better circuit for you, you may try the LAST circuit in the following link, here the relay won't fluctuate due to the inclusion of some hysteresis in the design, the feedback resistor value decides the gap between the over voltage, and the under voltage cut off thresholds, here the value of the resistor is chosen arbitrarily as 47K

      http://homemadecircuitsandschematics.blogspot.in/2011/12/how-to-make-simple-low-battery-voltage.html

      Delete
    2. I am sorry, actually you should try the second circuit in the following link, ignore and remove the other relay which is outside the circuit..

      http://homemadecircuitsandschematics.blogspot.in/2012/11/making-40-watt-led-emergency-tubelight.html

      Delete
  19. Michael C.

    Hi Swagatam,

    Would this Circuit works if the load is a Vacuum pump 5Amax?

    ReplyDelete
  20. ello sir,
    can I connected it in three phase source?

    ReplyDelete
    Replies
    1. no this circuit is not suitable for the 3P operation

      Delete
  21. hello sir,
    can i get more details about this project ?

    ReplyDelete
  22. hi,swagatam
    i have made another ckt for this but that is not accurate.is the 2nd ckt can operate accurately within a range of 20v variation.

    ReplyDelete
  23. hi,swagatam
    i have made another ckt for this but that is not accurate.is the 2nd ckt can operate accurately within a range of 20v variation.

    ReplyDelete
    Replies
    1. Hi Rashmi,

      Both the circuits are very accurate but the second one is much easier to build.

      Delete
  24. I am a beginner, please specify the full IC details, PIN configurations and connections. Thanking u!

    ReplyDelete
    Replies
    1. Please check out the datasheet of the IC LM324 online, you'll be able to compare the pinouts with the above diagram.

      Delete
  25. Dear sir,
    i am working in over voltage and under voltage protection ckt for Micro Hydro Power in NEPAL. i would be grateful if you would provide reliable ckt for my project.
    thank you

    ReplyDelete
    Replies
    1. Please provide complete and elaborate technical information about your requirement, I'll try to design it for you.

      Delete
    2. thanks for your response......sorry i was out of network since last week ....may i know your email address so that i would send my design regard my project for convenient.

      Delete
  26. I have a lighting circuit that has a motion sensor/dusk till dawn switch on it. The sensor comes on at half light (40v) and ramps up to full light (104v) when it detects motion. I also have it wired to a 120v relay that turns on several other lights at full voltage. My problem is that my relay just buzzes at the lower voltage. I would like to a have a cut out below 90v. How could I adjust this circuit for that?
    Thank You

    ReplyDelete
    Replies
    1. Put 3 or 4 10uF/250V capacitors in parallel right across the coil of the relay, this will restrict the buzzing of the relay and will simply not allow the relay to activate below a certain minimum level.

      Delete
    2. Do the capacitors have to be 250Vac ?

      Delete
    3. what is your relay coil operating voltage?....use capacitors with voltage rating twice of that.

      Delete
    4. Would these have to be the larger motor start capacitors. I put 3 of the smaller caps(like what's on a circuit board) on and they blew up and fried one of my motion sensors. The caps I used just say 250v they do not specify AC or DC.The motor start caps say 250VAC is this what I need to use?

      Delete
    5. a relay coil will always respond to DC and not AC, yet I will suggest that you first measure the voltage across the relay coil using a good quality multimeter, and then procure the matching capacitor as specified earlier by me.

      Delete
    6. I already used a meter and the coil gets between 40 and 104 VAC. The relay is a 120vac ice cube relay. Are you saying that the voltage inside the relay in changed to dc? The relay is a sealed unit and I can only check the voltage going into the relay base and it is ac

      Delete
    7. I've already checked the voltage going to the coil and it ranges between 40 and 104 VAC. The relay is a 120 VAC ice cube style relay.

      Delete
    8. according to me to activate an electromagnet so that it pulls an iron shaft we would need a DC. so I assume the AC being converted to DC inside the relay

      You can connect a bridge rectifier externally and supply the relay coil through this bridge rectifier and then use many 10uF/250V caps across the relay coil, this would make sense.

      Delete
    9. The relay coil is ac but I can get it in 12 and 24 vdc. I'll get transformer 0-12v and rectify the output and see what my voltages are first.

      Delete
    10. yes it may be done in that way also.

      Delete
  27. I had send mine document in your mail id ..thank you

    ReplyDelete
  28. sir the first circuit
    Highly Accurate, Mains High and Low Voltage Cut OFF Circuit, Using IC 324 Explained can i replace 4n35 optp in place of MCT 2E,opto coupler,so this circuit also need to be sets by variable power supply? sir i have a 12 transformer 2000mA can i use it to power the circuit? thank you .

    ReplyDelete
    Replies
    1. bianzz, you can use MCT2E, however the last circuit is much simpler and sensible so you could try the last one.
      a variable PS is a must for setting up the circuits.

      if your relay is 12v, then you can use a 12v trafo for powering the circuit

      Delete
  29. Sir, can you please explain this more clearly = http://i.imgur.com/ejlMplj.jpg
    Moreover in your new diagram, where I have to wire relay to get DC power?

    Thanks in advance :)

    ReplyDelete
    Replies
    1. Unknown, your questions suggest that you are very new in the field and in that case the above circuits are not recommended for you, anyway here are the answers:

      (+) of the IC will go to the positive of the bridge rectifier.

      the load is supposed to be a 220V load that's why it's connected across the mains via the triac.

      the left side TR1 stands for trafo, while the right side TR1 indicates the triac, these are accidentally taken identically

      R5 is connected to the gate of the triac TR1.

      Delete
    2. Sir, yes I'm quite new to this field and will be more careful to apply this diagram.

      1) Can you please tell me why should I add preset instead of 10k resistor?
      2) Where should I wire 12v DC relay?
      3) If I want to add 2 second delay timer by 555 IC how can I do that?

      Delete
    3. 1) presets are used for setting the cut-off thresholds by adjusting them appropriately.
      2) triac and R5 can be removed and R4 replaced with a relay (with bocking diode)
      3) for switching delays add a 220uF/25V capacitor across transistor base and positive.

      Delete
    4. Sir, please let me know if this OK = http://i.imgur.com/oWIZzrK.jpg

      a) I have removed 220v AC line across PCB.
      b) Wired (+) of the IC to the positive of the bridge rectifier.
      c) Added 12v DC relay as per your instruction.

      If anything goes wrong it will be helpful if you correct this diagram for me :)

      Delete
  30. sir i have finish build the lats circuit tell me how to set it sir can this lats circuit be use for refrigerator?

    ReplyDelete
  31. sir can you please help me set the last circuit how do i set to?

    ReplyDelete
    Replies
    1. feed the lower threshold AC to the trafo and adjust P1 to just switch OFF the triac.
      Next feed the higher threshold voltage to the trafo and adjust P2 to just again switch OFF the triac.
      the triac will remain switched ON only in between the above high/low thresholds,

      your circuit is set now.

      you will need a variac for doing this.

      Delete
  32. ok sir please can i use this circuit
    How to Make a Simple 220V Transformerless Power Supply Circuit Using a Single MJE13005 Transistor to set this last circuit?

    ReplyDelete
    Replies
    1. yes, can be used, but be careful as the circuit is not isolated from mains and could give lethal shocks if touched with naked hands.

      Delete
  33. ok sir thank you for the respond,sir there's something confused me a bit how will i know if the triac is off? sir how can one voltage supply circuit be use at the same time to feed low and high voltage to the transf? or should i connect the supply out put to the rectified and adjust the supply variable to high and low ?can you please provide me what current the triac need before it can switch off? thank you.

    ReplyDelete
    Replies
    1. you can put a LED in series with the triac gate for the indications.
      yes you can use a variable power supply for quickly varying the supply high to low and oppositely for confirming the results.
      the opamps will take care of the triac switching as per the settings.

      Delete
  34. sir im asking can i use 12v batt to set high out put and extra 6v batt for low out put?

    ReplyDelete
    Replies
    1. tell me the mains AC threshold cut-off levels that you desire, i'll give you the equivalent DC values for setting

      Delete
  35. if it reach 250v AC and low110v

    ReplyDelete
    Replies
    1. please also measure and provide the DC voltage supplied to the circuit at normal 220v....this will be required for the calcualtions

      Delete
  36. hey budy i wana make Transformerless Stabilizers plz hlep me how can i make it.

    ReplyDelete
  37. why thats not possible plz tell me any kind of salutation thats importatn plz im try to understand the complication of the circut tell me any diagram any data

    ReplyDelete
    Replies
    1. the voltage step-up transformers will need to be built using ferrite transformers involving complex switching circuits, just as we have in compact inverters.

      Delete
  38. tell me about compact inverters sir i will try for switching circuits and i wana use (pic16f72) with lm 324 guide me about that.

    ReplyDelete
    Replies
    1. presently i don't have enough info regarding it, once i get them will provide it you.

      Delete
  39. Hi Swagtam,
    Can you send me circuit diagrams of both the above circuits on my email add. as my browser not loadingthe circuit diagrams. my email add. is instructions555@gmail.com

    Thanks & Regards,

    ReplyDelete
    Replies
    1. Hi SW, refresh or restart your browser or try some other browser it will surely load, or there may be some problem with your internet connection

      Delete

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Readers are advised to proceed with the construction of the presented circuits only after understanding the concepts from the core. Not adhering to this can lead to failures and frustrations.