In this post I have explained an upgraded version of my previous mains 220V/120V high-low voltage cut off protection circuit which now includes a delayed restoration of power for the load with 3 LED power status indicators.
The idea was requested by one of the dedicated members of this website.
Circuit Objectives and Requirements
- I just followed you're explanation and is it possible that you can help us with the following:
- To design a safety circuit that should provide for household appliances for over-and under-voltage protection.
- The protective circuit must immediately switch off upon detection of low-and high-voltage household appliance and upon detection of normal voltage switch on again after 3 minutes.
Main Specifications
The protective circuit must comply with the following: If the line voltage is within the normal range (100 to 130V ac), it will wait for the protective circuit 3 minutes before the output will be energized. During these 3 minutes there is an amber
LED light. If the line voltage is outside the normal voltage, the output of the protective circuit will never be under tension. If the line voltage is less than 100VAC, the protection circuit "low voltage" must indicate by a red LED that lights up.
If the line voltage is present, the protection circuit must pass a voltage greater than 105 Vac "normal tension" it will indicate by a green LED that lights up.
Similarly, the line voltage protective circuit has to be higher than 130V ac "high voltage" will be indicated by a red LED that lights up. Only when a voltage is less than 125VAC, it must indicate the protection circuit "normal tension" by a green LED that lights up.
Upon detection of over-and under voltage protection, the circuit should give a beep of 5 seconds.
This should be constructed with an opamp oscillator circuit in this functionality.
Circuit Diagram
The Circuit Design
The above shown mains high/low voltage cut off protection circuit is an enhanced version of my previously explained design which had similar high low cut off protection feature except the delay timer stage which has been added in the present design as per the request.
The timer stage ensures a delayed power switch ON for the load each time the mains is cut off due to an abnormal fluctuating voltage so that the load is never subjected to an abrupt or random voltage switching situation .
The circuit also includes 4 distinct LEDs which indicate the corresponding mains voltage levels or status through their individual colors. The two red colors indicate high and low voltage situations respectively, the amber color LED indicates the intermediate delay counting status of the circuit, while the green LED informs the user regarding a healthy mains output condition.
The P3 preset or pot is used for setting up the delay time switch ON for the IC 4060 stage
How it Works:
We already know from our previous post that whenever the input voltage crosses the higher threshold, a logic high is created at the output of the upper opamp and when the voltage drops below the lower threshold the lower opamp generates a high logic at its output.
This implies that during both the conditions a high logic is generated at the cathode junction of the diodes connected with the opamp outputs.
We know that the timer IC 4060 is forced to reset in the presence of a positive trigger at its pin#12, and the IC stays disabled (output open) as long as a high is sustained at this pinout of the IC.
Therefore for so long the output from the opamps is held positive, pin#12 is kept high and subsequently the IC 4060 output pin#3 is held deactivated, which in turn keeps the relay switched OFF along with the mains load disconnected through the N/C contacts.
Now as soon as the mains voltage returns to its normal level, the high logic at pin#12 of IC 4060 is removed, so that the IC is allowed to commence its counting process.
The IC now begins counting as per the values set by C3/P3. Supposing the mains remains stable during the whole counting process, the IC counting finally elapses enabling a logic high at its pin#3, which triggers the relay and the load into action.
However suppose while the counting was in progress, the mains kept fluctuating, the IC would be forced to reset repeatedly and this would keep the output completely switched OFF making sure that the load was never allowed to face the unpredictable and fluctuating mains condition.
How to Set Up the Circuit.
Initially keep the power supply disconnected with the circuit.
Apply mains input to the power supply transformer and measure the DC output across the filter capacitor, and also measure the existing input mains level at the input of the transformer.
Let's say the mains voltage is found to be around 230V, which results in the production of a DC output of around 14V.
Using the above data now it may be possible to calculate the corresponding upper and lower cut off thresholds, which may be used for setting up the respective presets .
Suppose we want 260V to be the upper cut off level, and 190V as the lower cut off, the corresponding DC levels could be calculated with the help of the following cross multiplication:
230/260 = 14/x
230/190 = 14/y
where x represents the corresponding upper cut-off DC level and y the lower cut-off DC level.
Once these values are calculated, using a variable DC power supply, feed the upper DC level to the circuit and adjust the upper preset such that the upper opamp LED just lights up.
Next, in a similar fashion apply the lower DC level and adjust the lower preset until the lower opamp LED just lights up.
That's it! The adjustments for the upper high, and lower under voltage cut-off setting up procedures are complete, and the system can be now be plugged-in with the mains for the actual test.
Parts List
- R1, R2, R3, R4, R7 = 4K7
- R6 = 4K7
- R5 = 1M
- P3 = 100K POT
- C2 = 0.33uF
- C3 = 1uF
- C1 = 1000uF/25V
- P1,P2 = 10K PRESET
- Z1, Z2 = 4.7V/ 1/2 WATT
- D1---D4, D8 = 1N4007
- D5----D7 = 1N4148
- IC1 = LM358
- IC2 = IC 4060
- T1 = BC547
- RELAY = 12V/250 OHMS, 10 AMPS
- L1----L4 = LEDS 20mA, 5mm
- transformer = 0-12V/1 AMP or 500 mA
UPDATE
For a transistorized version of the above high/low mains protection with delay timer, you can try the following design:
Questions & Answers
The circuit will short mains through relay contact
check it now
Hello, just seen your circuit of the over/under voltage protector. this is a very good circuit. My only concern is the mains transformer. If there is going to be a high voltage greater than 260v from the line this will definitly blow the transformer's primary winding. Any ideas, can one include a vdr to protect the transformer?
Thanks.
Bontech
Hi, thanks,
yes, above a certain level the transformer itself might become vulnerable of getting burnt, a simpler and effective approach could be to go for a triac based crowbar circuit across the primary of the transformer.
the crowbar could be set to trigger at around 260V using a 260V zener diode which would finally blow off the series connected fuse and cut the supply.
This is very valid question and a much more useful advice.
sir.
I have a doubt. No need connection in pin no 4 and 8 on LM358 ??
Raghu, obviously it will be required, I might have not shown it by mistake, but it’s an understood fact, without powering the IC pinouts the IC cannot work….
Pls mention that which one is -ve pin and which one is +ve pin.
And what’s the value of C3 ?
1mf ? Or 0.1mf ?
whenever in doubt always check the datasheet of the IC for LM358 pin#8 is (+), and pin#4 is (-)
You not mention the polarity of C3
C3 should be non-polar.
sir it’s a good work l always believe your circuits they don’t fail thanks my great teacher and a good master
thanks emapi, if you build them by understanding the concepts well, the circuits will never fail…appreciate your thoughts.
pls my teacher am trying to work on a meter that can read the resistance of the ground pls help me out.
You mean the degree or the level of “earthing” ground??
please sir, can you kindly help me with only 12v battery low voltage cut off circuit diagram
kabiru, you can try the concepts explained in the below article
https://www.homemade-circuits.com/how-to-make-simple-low-battery-voltage/
thank
Helo sir I love your circuit but my major concern is the labeling or naming of those components used in the circuit.
Please help me by naming the components pls…
Hi Akinbi, the schematic includes all standard symbols which can be easily recognized, you will have to get well versed with the basics of electronics in order to identify them correctly.
I have built the circuit but when T2 is in the circuit the relay operates regardless of any thing ,second the circuit operates for only 2s regardless of time delay seted. waiting for your help…thanks.
Thanks for informing regarding this isue, it could be due to the positive from the BC557 emitter interfering with pin#11 of the IC.
Please remove the entire T2 stage, and connect the yellow LED and its series resistor across collector/emitter of the T1.
Dear sir, thank you for your quick reply ,I will try your suggestions ,moreover in your article about cd4060 a capacitor is connected from pin 11 to ground which is not present in the circuit is it important. Lastly can you explain how to check cd4060 working or not …my great regards to you.
Hi Mohammad,
Can you please show me where I have mentioned this? Pin#11 of IC 4060 does not require any capacitor
Tanks alot please,can you check the circuit in your article under ic4060stage ,calculating RC components for timing and see c2 is connected to pin#11.The high low voltage section is working very nice .thank you again.
Thank you Mohammad, I am glad it is working…. but I still couldn’t find pin#11 related issue, is it in the above article or some other article??
Hello sir, pls can i use 555 timer instead of cd4060 for the timing? How can i do
IC 555 can be difficult to customize as per the given objective, but transistorized circuit may be possible instead.
Thank you for a very useful circuitry and a detailed description about the working and setup of the same.
Wanted to clarify if all capacitors are polarized ?
Thank you! Only C1 is polarized rest are non-polar
Hello,
Your circuit is very good.
My question is that how it is alter if I donot want to use transformer and relay also in this circuit to achieve the same result?
The transformerless/triac version is also given in the above article. Connect the delay timer in place of the LOAD, and connect the motor at the output of the delay timer
I have not seen transformerless/triac version in the above article. Can you please tell me if it is on another link?
“Connect the delay timer in place of the LOAD, and connect the motor at the output of the delay timer”
in above so ask for “delay timer”.you mean delay timer circuit or delay timer sold in market?
I think I had referred you this article in your previous comment on some other post:
https://www.homemade-circuits.com/highly-accurate-mains-high-and-low/
so I thought that you were in this linked article.
For the circuit on this page you can add a transformerless power supply in the same way as done for the 3rd circuit in the above link.
I have checked you link “https://www.homemade-circuits.com/highly-accurate-mains-high-and-low/”, but the problem is that this lacks delay timer. And you have said that “Connect the delay timer in place of the LOAD and then connect the motor on output of delay timer”, it confuses me that first I have to built the circuit mentioned above and then make another circuit mentioned on “https://www.homemade-circuits.com/highly-accurate-mains-high-and-low/” and connect as you said.
My Question is that is it not possible to add some alteration in circuit mentioned at link “https://www.homemade-circuits.com/highly-accurate-mains-high-and-low/” to achieve delay result? I think it is more practical as easy for me and starter hobbiest. I do not want to use relay which is mentioned in this article and I like delay option mentioned in this article. And on other hand your article “https://www.homemade-circuits.com/highly-accurate-mains-high-and-low/” have the option which I like is Triac base option but it lacks delay option.
I want to build 1 circuit with blend of your both articles to acheive the following results:
1: Triac based with out relay
2: Delay time
Regards,
I had provided you two links in your earlier comment, so the connection details was referenced to those two links.
You can add a 1000uF capacitor across base/emitter of T1 in the following circuit to get the required delay:
https://www.homemade-circuits.com/highly-accurate-mains-high-and-low/
Dear Swagatham
I am planning to build your above circuit.
My transformer is 220VAC primary to 12VAC-0-12VAC, 1amp secondary transformer. As I know the RMS secondary DC (after rectification and filteration) voltage is 12VAC *1.414=16.968vdc. Is it correct….?
So what will be corresponding secondary DC voltages for:-
Primary voltage=210VAC (lower limit)
Primary voltage=250VAC (upper limit)
Thanks in advance.
Dear Anil Kumar,
Your calculation is correct, but here we only need the RMS, the peak voltage may not be necessary.
First you will have to find the practical transformer secondary voltage that corresponds to the input AC volatge.
Let’s say it is 220V (must be verified practically) primary that produces 12V at the secondary, then the calculations can be done using simple cross multiplications, as shown below:
220/210 = 12/L——-This is for low voltage.
220/250 = 12/H——-This is for high voltage.
Dear Swagatham,
The second paragraph in your reply cleared my whole doubts. Till this day it was a burden for me and many others like me to set the Hi-Lo cut off point without a variac or some other devices.
What is the purpose of Z3….?Can we simply avoid it….?
Thank you verymuch.
Glad it helped you Anil,
Yes you can remove Z3, it is not important.
Hi thanks for detailed circuit. But I did like to know the amps of the circuit.
And I will be glad if you would help me with similar circuit but 30amps
Hi, the current handling capacity will depend on the relay contact specs, for 30 amps please use a 30 amp relay.
Okay, thanks Sir. I will do that right away
Dear Mr. Swagatam, Thanks for your circuit ideas.
I am a Sr. Citizen hobbist and engaged in my electronic hobbies with simple circuits useful for home appliances. Recently my fridge Stabiliser went off and I wanted to repair the circuit.
First my background. We stayed in Delhi for last 40 years where in there is peculiar problem of very low voltage mains supply which is mostly around 160-170 V AC. So my Fridge stabiliser was designed with step down transformer of supplying boost up secondary voltage accordingly.
Now we have moved to Pune and the AC supply is 250 V AC. My stabiliser is giving problem of stabilised supply ( for aforesaid boost up volatge) at 300 V AC. The mains Transformer of the stabliser has 5 taps ( secondary) of these 2 are giving 250 V AC while remaining 3 are giving 300 V AC output.
The Transformer tapping supply to the control circuit is 17 V AC step down with circuitry of 4 nos BC 547 and wired RC networks.
In summer , due to overloading, sometimes the AC mains goes temporary to 160 V AC and my fridge shakes violantly.
Now I want to use your valuable Low/Over Voltage circuit with built in PCB supply of 17 V AC inlieu of 12 V AC.
I shall wire out your components in this circuit but now Pl. let me know the variations in resistor/zener/capacitor values to adopt to 17 V AC supply from secondary of same transformer.
Also pl. let me know if you sell PCB readymade for the purpose.
This circuit shall certainly help me to protect under and high volatge supply to fridge with using same stepdown transformer and metal box assembly.
Thanking you in advance.
Wishing for a reply.
Dear Mohan ji, Thank you for your interest and for visiting my site!
For 17V supply no changes would be required in the circuit except the supply pin connections of the IC1, IC2 and the relay. The 17V will need to dropped to 12V through a 7812 IC for feeding the pin16 of IC2, and pin8 of IC1, and the relay positive line.
I wish you all the best with the construction, let me know if you have further problems.
Mains High Low Voltage Protection Circuit with Delay Monitor
Refer your Reply :
Dear Mohan ji, Thank you for your interest and for visiting my site! For 17V supply no changes would be required in the circuit except the supply pin connections of the IC1, IC2 and the relay. The 17V will need to dropped to 12V through a 7812 IC for feeding the pin16 of IC2, and pin8 of IC1, and the relay positive line. I wish you all the best with the construction, let me know if you have further problems.
Dear Sir,
Thanks for your reply to my querry. Further, I would request to please denote/show the IC1 Pin connections which are apparently not shown in the circuit diagram published.
Another querry is the Relays in my Fridge stabiliser unit are 18 V DC rated where as the above circuit is designed for 12 V DC operation. I am afraid the relays may chatter due to under volatge of operation ( 12 V DC as against 18 V DC) and may not function properly. So, is any change/modification is required for the Relay operation voltage? or alternatively if I operate the circuit at 17 VDC , will it affect functioning of ICs ?
Thank you, I have updated the IC pin diagram in the above article, you just have to replace the pin numbers accordingly, in the main diagram.
If you have 18V relays, then the relay positive can be directly connected with your 17C DC, only pin#8 and the pin#16 of the two ICs will need to be fed through a 7812 IC regulator.
Sir: You specified a 1 amp Transformer for this circuit but a 500MA transformer for the previous design which looked to be more power hungry than your updated design. Question: I am having difficulty sourcing a 12va 230 volt transformer for this new upgraded circuit. Can I use a 6VA transformer? Where do you source your parts? Also, you have stipulated a BC557 Transistor for T2 but I do not see a T2 transistor on the schematic. Thank you for your patience and help.
Charles, 1 amp transformer is more easily available than 500 mA, therefore I mentioned a standard 1 amp transformer, you can use a 500 mA if you wish to.
BC557 was earlier used at the output of IC1, but later on removed…I have removed it from the list now. You can use a 6 V transformer if the relay is also a 6V relay.
Nice Circuit, Can I replace Z1 and Z2 with 7805?