The article describes how an accurate transformerless 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.
Overview
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.
The following circuit utilizes a transformer for powering the circuit
Circuit Schematic
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:
How the opamps Operate as Comparators
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.
How the optocouplers function
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.
Why the opamps Comparators Arranged in Series
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.
Using Triac instead of Relays for the cut off
After some analysis, I realized that the above high, low mains voltage cut off protector circuit could be simplified into a much easier version using a single triac. 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.
Modifying the Design into a Transformerless Version
The transformerless mains high low voltage cut off circuit version of the above explained design can be visualized in the following diagram:
If a single relay is intended to be used instead of a triac, the design could be modified as shown in the following figure:
Please use a 22uF/25V capacitor across the transistor base and ground, just to make sure the relay does not stutter during the changeover periods...
Shiyanbola Segun says
R1, R2, R3, R4, R5, R6, R7, R8 = 4K7, What is 4K7
Swag says
4k7 is 4.7 k resistor
Resonance Resonance says
Hello yonder,
I found all your circuit and projects interesting but please I need a special assistance. I want to build a Low and high battery full cutoff that can handle about 360VDC (30 Batteries in series) such that when battery is full at 405VDC charging Voltage will cutoff and when battery drop to like 325VDC it also cutoff battery low.
Please, do share this experience with me.
Swagatam says
Hello yonder, I'll try to design it and post it soon…it might take sometime, please bear with me until then
vamsi krishna says
Thank you sir….:)
vamsi krishna says
Hi Sir,
In the above first circuit (Highly accurate over/under voltage CKT.)
can u pls tell me connections of OPTO coupler,
Pin 1 = anode (connected in CKT)
pin 2 = cathode (connected in CKT)
pin 3 = NC
pin 4 = Emitter (connected in CKT)
Pin 5 = collector (connected in CKT)
then where to connect pin 6 = Base of OPTO…..?
and Bc547 given in the components list, are not needed in the circuit. Right….?
Thanks in Advance…..:)
Swagatam says
That's correct Vamsi,
the base of the opto transistor is unused, so it can kept open.
BC547 are not used since the opto transistor itself are used as relay drivers.
vamsi krishna says
Hi SWAGATAM…
Here OPTO's output is too low to energise the 12v relays. can u pls explain the solution… Thanks
Swagatam says
Hi Vamsi, you can refer to the following article for solving the issue:
https://homemade-circuits.com/2013/02/how-to-drive-relay-through-opto-coupler.html
jeelani says
hi,i think rectifier is missing
Swagatam says
govind, you can try the second last circuit above with the following modifications:
remove the triac and R5, and replace R4 with a relay…
Unknown says
Sir I want a circuit for under voltage & high voltage mait cut for ac motor using for water pump.show me the direction please..govind
jeelani says
thanks for u r prompt response
jeelani says
hi once again,how r u hope fine
i want to use reliable transformerless power supply with auto cut off circuit as u published
https://homemade-circuits.com/2011/12/highly-accurate-mains-high-and-low.html
any modifications?and in this page there is also a second ckt which should b used and i am asking for transformerless power supply because the transformers i get are getting hot they will fail after some time and also in high voltages there is maximum chance of burning of transformer and if transformer fails the relay denergize and the connected appliance would burn then the cut off ckt will b safe but the main target the appliance will burn off
so please give me a ckt with a reliable reliable psupply which can bear high voltages, fluctuations ,no zenner shorted and no heating of components which should run continiously for example : i am using to led street lights with day night ckt ,the supply should b always connected if any small problem comes the main lights will surely b in trouble and u know how expensive are these
please dont mind for so long detailed approch thanks and i admire for ur great hobby
which is not only helping the persons like us and also ur providing good knowledge for the society
hats off for u .god bless u
Swagatam says
thanks jeelani, I have updated the required diagram in the above article…..
Anioko James says
DEAR SIR, PLEASE CAN I USE THE FIRST CIRCUIT FOR A PROJECT WORK. IF YES IS THERE ANY MORE CORRECTIONS THAT ARE TO BE ADDED TO THE CIRCUIT?
Swagatam says
Dear Anioko,
The first diagram is correct in all respects, you can use it for your project but it's unnecessarily complex, the lower one will give the same results and is more compact, a relay can also be used instead of triac in the second design.
Nisha says
dear sir recently Ibuilt the above circuit but it does not function the mct 2e even using a transister. please help me at dumbara27@gmail.com
thanks
Swagatam says
Dear Nisha, build the second circuit it's much easier, the circuit is a simple comparator based design and there's no way it won't function if you did everything correctly.
Connect an LED in series with R3 in the second diagram and check the response by moving the presets
Anioko James says
sir i want to use this circuit https://homemade-circuits.com/2011/12/simple-mains-high-and-low-voltage.html as a final year project. i submited the project as electronic wacthdog control system to the supervisor and he is requesting for the abstract, please sir can U assist me with the written materials for the project and what is the difference between this circuit and that of the stabilizer. thanks as i awaite your quick response. my email is canioko@yahoo.com
Swagatam says
Anioko, all the data are provided in the article explanation, you can rephrase the details appropriately as per your requirement.
The abstract material can be found at the beginning of the article.
a stabilizer will automatically correct the voltage fluctuations by supplying extra voltage to the appliance or by deducting it as per the mains situation.
The above circuit will not do this rather cut off the mains supply to the appliance if it tends to shoot above or below a certain predetermined danger level
Solar Waves says
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,
Swagatam says
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
Mohammad Azhar says
thanx sir
Mohammad Azhar says
tell me about compact inverters sir i will try for switching circuits and i wana use (pic16f72) with lm 324 guide me about that.
Swagatam says
presently i don't have enough info regarding it, once i get them will provide it you.
Mohammad Azhar says
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
Swagatam says
the voltage step-up transformers will need to be built using ferrite transformers involving complex switching circuits, just as we have in compact inverters.
Mohammad Azhar says
hey budy i wana make Transformerless Stabilizers plz hlep me how can i make it.
Swagatam says
sorry, that's not possible.
Swagatam says
will be very complicated.
Joseph Jub says
can it as a surge protector?
Swagatam says
no
biannz says
if it reach 250v AC and low110v
Swagatam says
please also measure and provide the DC voltage supplied to the circuit at normal 220v….this will be required for the calcualtions
biannz says
sir im asking can i use 12v batt to set high out put and extra 6v batt for low out put?
Swagatam says
tell me the mains AC threshold cut-off levels that you desire, i'll give you the equivalent DC values for setting
biannz says
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.
Swagatam says
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.
biannz says
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?
Swagatam says
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.
biannz says
sir can you please help me set the last circuit how do i set to?
Swagatam says
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.
biannz says
sir i have finish build the lats circuit tell me how to set it sir can this lats circuit be use for refrigerator?
Unknown says
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 🙂
Swagatam says
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.
Unknown says
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?
Swagatam says
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.
Unknown says
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 🙂
Swagatam says
yes everything's correct.
biannz says
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 .
Swagatam says
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
Anonymous says
I had send mine document in your mail id ..thank you
Anonymous says
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
Swagatam says
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.
Anonymous says
Do the capacitors have to be 250Vac ?
Swagatam says
what is your relay coil operating voltage?….use capacitors with voltage rating twice of that.
Anonymous says
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?
Swagatam says
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.
Anonymous says
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
Anonymous says
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.
Swagatam says
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.
Anonymous says
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.
Swagatam says
yes it may be done in that way also.
Anonymous says
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
Swagatam says
Please provide complete and elaborate technical information about your requirement, I'll try to design it for you.
Anonymous says
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.
Swagatam says
hitman2008@live.in
reghuthalikuzhy says
I am a beginner, please specify the full IC details, PIN configurations and connections. Thanking u!
Swagatam says
Please check out the datasheet of the IC LM324 online, you'll be able to compare the pinouts with the above diagram.
Swagatam says
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.
Eleanor Ong says
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?
rashmi sahoo. says
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.
Swagatam says
Hi Rashmi,
Both the circuits are very accurate but the second one is much easier to build.
rashmi sahoo. says
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.
NOKIA says
hello sir,
can i get more details about this project ?
Anonymous says
ello sir,
can I connected it in three phase source?
Swagatam says
no this circuit is not suitable for the 3P operation
Anonymous says
Michael C.
Hi Swagatam,
Would this Circuit works if the load is a Vacuum pump 5Amax?
Swagatam says
Hi Michael,
yes it will work
Technosavy says
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.
Swagatam says
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
https://homemade-circuits.com/2011/12/how-to-make-simple-low-battery-voltage.html
Swagatam says
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..
https://homemade-circuits.com/2012/11/making-40-watt-led-emergency-tubelight.html
Anonymous says
please add a delay circuit so we can use it with Refrigerators.
Swagatam says
Yes a delay feature is crucial,,,,possibly I'll try to include it here soon….
Jose says
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
Swagatam says
I have the circuit already posted in this blog, please check this out:
https://homemade-circuits.com/2011/12/simple-mains-ac-over-voltage-and-under.html
Shiva Kumaren says
hi swagatam,
in this circuit mct2e output is too low not switching 12v 400 ohm
s relay, what to do
Swagatam says
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.
Anonymous says
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.
Swagatam says
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!
Kadima Mpata says
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.
Swagatam says
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
Mohd Rafi Bin Hamid 51210209220 says
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??
Swagatam says
Hello Mohd Rafi,
You may try the second circuit.
Please make the circuit first then I'll explain how to set it.
Maksud Khan says
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
Swagatam says
Dear Maksud,
I'll try to figure it out, if I succeed I'll provide you with the data.
Regards.
Anonymous says
I want to power ur circuit using transformerless power supply.can u please post the circuit.thanks
joomunm says
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.
reghuthalikuzhy says
Will you please explain the pin configurations also? I am a beginner.
Anonymous says
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??
gbengoose says
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
gbengoose says
hey thanks…can u kindly enlighten me about the MCT 2E opto coupler??
gbengoose says
like the motor of a ceiling fan…
gbengoose says
Just having problems with the load..Is it AC or DC??