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

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.
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




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 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.



 The transformerless mains high low voltage cut off circuit version of the above explained design can be visualized in the following diagram:







If a relay is intended tyo 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...

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111 comments

comments
January 27, 2012 at 7:01 PM delete

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

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January 28, 2012 at 9:08 AM delete

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?

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January 28, 2012 at 9:14 AM delete

The second circuit will only control AC loads, though.

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January 28, 2012 at 6:37 PM delete

like the motor of a ceiling fan...

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January 28, 2012 at 6:43 PM delete

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

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February 1, 2012 at 12:16 AM delete

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

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February 1, 2012 at 12:50 AM delete

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

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Anonymous
February 1, 2012 at 12:55 AM delete

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??

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February 1, 2012 at 8:46 AM delete

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.

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February 1, 2012 at 8:51 AM delete

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

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February 1, 2012 at 8:57 AM delete

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.

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February 15, 2012 at 8:27 PM delete

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.

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February 16, 2012 at 8:51 AM delete

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.

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Anonymous
July 16, 2012 at 8:00 AM delete

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

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July 17, 2012 at 3:20 PM delete

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

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July 23, 2012 at 4:42 PM delete

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

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July 23, 2012 at 6:21 PM delete

Dear Maksud,

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

Regards.

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October 2, 2012 at 8:52 PM delete

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??

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October 2, 2012 at 10:30 PM delete

Hello Mohd Rafi,

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

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November 27, 2012 at 12:20 PM delete

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.

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November 27, 2012 at 3:42 PM delete

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

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Anonymous
November 30, 2012 at 8:44 PM delete

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.

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December 1, 2012 at 5:33 PM delete

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!

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January 3, 2013 at 11:04 PM delete

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

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January 4, 2013 at 10:00 AM delete

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.

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January 18, 2013 at 4:15 PM delete

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

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January 19, 2013 at 10:07 AM delete

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

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Anonymous
February 3, 2013 at 7:52 AM delete

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

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February 3, 2013 at 10:00 PM delete

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

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March 24, 2013 at 6:27 AM delete

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.

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March 24, 2013 at 10:18 AM delete

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

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March 24, 2013 at 10:24 AM delete

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

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Anonymous
May 14, 2013 at 8:13 PM delete

Michael C.

Hi Swagatam,

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

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Anonymous
May 21, 2013 at 10:47 AM delete

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

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May 21, 2013 at 7:52 PM delete

no this circuit is not suitable for the 3P operation

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June 15, 2013 at 8:51 PM delete

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

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August 6, 2013 at 6:07 PM delete

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.

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August 6, 2013 at 6:09 PM delete

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.

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August 6, 2013 at 8:20 PM delete

Hi Rashmi,

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

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September 27, 2013 at 3:59 PM delete

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?

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September 27, 2013 at 7:25 PM delete

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.

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October 2, 2013 at 6:42 AM delete

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

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October 3, 2013 at 3:49 AM delete

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

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October 3, 2013 at 10:08 AM delete

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

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Anonymous
October 30, 2013 at 4:08 PM delete

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

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October 30, 2013 at 8:15 PM delete

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

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Anonymous
November 7, 2013 at 12:13 PM delete

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.

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Anonymous
November 8, 2013 at 6:42 AM delete

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

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Anonymous
November 8, 2013 at 11:00 AM delete

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

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November 8, 2013 at 2:28 PM delete

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.

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Anonymous
November 9, 2013 at 3:26 AM delete

Do the capacitors have to be 250Vac ?

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November 9, 2013 at 10:09 AM delete

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

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Anonymous
November 13, 2013 at 6:30 AM delete

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?

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November 13, 2013 at 12:22 PM delete

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.

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Anonymous
November 13, 2013 at 3:30 PM delete

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

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Anonymous
November 14, 2013 at 2:27 AM delete

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.

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November 14, 2013 at 1:19 PM delete

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.

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Anonymous
November 14, 2013 at 4:52 PM delete

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.

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November 15, 2013 at 9:54 AM delete

yes it may be done in that way also.

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January 27, 2014 at 2:06 PM delete

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 .

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January 28, 2014 at 9:44 AM delete

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

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January 29, 2014 at 11:22 PM delete

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 :)

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January 30, 2014 at 12:07 PM delete

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.

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January 30, 2014 at 12:55 PM delete

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?

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January 31, 2014 at 11:31 AM delete

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.

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January 31, 2014 at 2:05 PM delete

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 :)

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February 3, 2014 at 5:36 AM delete

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

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February 5, 2014 at 1:43 AM delete

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

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February 5, 2014 at 1:25 PM delete

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.

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February 6, 2014 at 2:43 AM delete

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?

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February 6, 2014 at 1:23 PM delete

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.

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February 7, 2014 at 3:01 AM delete

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.

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February 7, 2014 at 5:54 PM delete

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.

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February 25, 2014 at 3:16 AM delete

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

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February 25, 2014 at 11:18 AM delete

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

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February 25, 2014 at 8:56 PM delete

if it reach 250v AC and low110v

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February 26, 2014 at 12:02 PM delete

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

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May 10, 2014 at 6:14 PM delete

can it as a surge protector?

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May 21, 2014 at 12:07 AM delete

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

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May 22, 2014 at 12:18 AM delete

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

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May 22, 2014 at 5:58 PM delete

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

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May 23, 2014 at 11:56 PM delete

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

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May 24, 2014 at 6:21 PM delete

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

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June 28, 2014 at 9:42 AM delete

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,

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June 29, 2014 at 9:08 AM delete

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

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September 22, 2014 at 8:56 AM delete

sir i want to use this circuit http://homemadecircuitsandschematics.blogspot.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

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September 22, 2014 at 2:19 PM delete

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

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September 26, 2014 at 1:48 PM delete

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?

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September 26, 2014 at 9:59 PM delete

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.

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October 14, 2014 at 8:40 AM delete

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

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October 14, 2014 at 2:03 PM delete

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

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September 4, 2015 at 2:30 AM delete

hi once again,how r u hope fine
i want to use reliable transformerless power supply with auto cut off circuit as u published
http://www.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

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September 5, 2015 at 12:33 PM delete

thanks jeelani, I have updated the required diagram in the above article.....

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September 6, 2015 at 11:47 PM delete

thanks for u r prompt response

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November 19, 2015 at 8:12 AM delete

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

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November 19, 2015 at 6:11 PM delete

govind, you can try the second last circuit above with the following modifications:

remove the triac and R5, and replace R4 with a relay...

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November 29, 2015 at 11:21 AM delete

hi,i think rectifier is missing

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December 13, 2015 at 8:22 PM delete

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.....:)

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December 14, 2015 at 11:19 AM delete

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.

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December 16, 2015 at 7:43 AM delete

Hi SWAGATAM...
Here OPTO's output is too low to energise the 12v relays. can u pls explain the solution... Thanks

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December 16, 2015 at 11:38 AM delete

Hi Vamsi, you can refer to the following article for solving the issue:

http://www.homemade-circuits.com/2013/02/how-to-drive-relay-through-opto-coupler.html

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January 22, 2016 at 12:33 PM delete

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.

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January 22, 2016 at 6:59 PM delete

Hello yonder, I'll try to design it and post it soon...it might take sometime, please bear with me until then

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