High & Low voltage cut-off with delay& alarm
Description.
This straight forward circuit will protect electrical appliances from over voltage as well as under voltage.The circuit also produces an alarm when the power supply comes back.An ideal circuit for home to protect your valuable equipments from voltage fluctuations.The same circuit with some modifications can be used to make a automatic voltage stabilizer.
When the mains voltage is in the normal level ,the voltage at the negative terminal of zener diode D4 will be less than 5.6 Volts.At this condition transistor T1 will not conduct.The same time voltage at the negative terminal of zener diode D5 will be greater than 5.6 and so the transistor T2 will be conducting.The relay will be activated and the green LED wil be glowing.
When the mains voltage is higher than the set limit the transistor T1 becomes conducting since the voltage at the negative terminal of D4 is greater than 5.6 V.At the same time transistor T2 will be non conducting which results in the deactivation of relay to cut the mains supply from load.When the mains voltage is less than the set limit transistors T1 & T2 becomes non conducting making the relay to de- activate and cut the load from mains.Ω
The timer NE555 is wired as a monostable multivibrator with a pulse width of 10ms.When the power comes back after a cut off a negative voltage is obtained at the trigger pin which triggers the IC NE555.The transistor T3 gets forward biased and it drives the buzzer to produce a beep as an indication of power resumption.Also the transistor T1 is made on which in turn makes T2 off.As a result the relay will remain de- activate for 10ms and this provides the sufficient delay and the equipment is protected from surge voltages.
Circuit diagram with Parts list.Click to enlarge.
Notes.
- To calibrate the circuit a autotransformer is needed.Connect the output of autotransformer to the transformer primary.
- Set the voltage to 260V and adjust VR1 to make the relay deactivated.
- Now set the autotransformer to 160V and adjust VR2 so that the relay is de-energized.
- VR3 can be used to vary the volume of buzzer.
Hello,
I found your circuit simple and interesting.
could you suggest the necessary change I need to do if I want to protect a 6V, 4.5 AH Lead Acid battery from overcharging and over discharging.
To get a steady charging voltage of 7.3V for charging the battery, I will be using a 12V, 500 milliAmp Adapter, Send it through IC 7808 followed by diode 1N7004 in series. That will give me 7.3V.
Thereafter I need a overcharge protection circuit.
Similarly I need to protect the battery from over discharging.
only 30% discharging will be good for me. it will give me a good life.
will you be able to guide me.
thanks
kind regards
shubhro
Hello,
First it is a good circuit, but i want to ask about a replacement for the (SL100) transistor, because i have searched alot for that transistor but i didn’t find it. Please if you have an answer for this send me an email.
Thanks
best regards
Mohamed
you can try BD 139, BC 107 or simply any medium power npn transistor
Hello,
Well thank you alot for your response, and i have another question, can i use a lower power diod than the (400w 5.6v D4 & D5 & D10)?, if you have an answer please post it or send me an email, again thank you for your fast response.
best regards
Mohamed
Mohamed Anany
I am pretty confident that D4 and D5 should be 400 milli Watts and not 400 Watts. 400mW is suggested as it is a commonly manufactured value and therefore normally cheaper.
that was an error in the circuit diagram
D4 and D5 are 400 milli watts. I have corrected the circuit diagram.
Have a look.
thanks to Mohammed and twits4twats for pointing out.
can u please tell me or mail me the circuit diagram of the stabilizer at saqi240@hotmail.com
Thanks for this good cct.
it’s good for our inst. that work in bad local Elec. Voltage
Am working on one of your circuit(street light) as a project.I need your help on written area(materials).Thanks
Plz i want to build this project, with tyhe circuit diagram of automatic voltage stabilizer and the works pls send me the details to my email address.which is snowboy3k0@yahoo.co.uk. thanks.
Plz i want to build this project, with tyhe circuit diagram of automatic voltage stabilizer and the works pls send me the details to my email address.which is snowboy3k@yahoo.co.uk. thanks.
i need someone who has experimented with substitute for sl100 transistor to give me his/her sub.thanks
SL100 can be substituted with 2N2218, 2N2219 or 2N1711 switching transistors reliably. If you are in India then you can use BEL100N, CL100 also. The above circuit is very reliable one. I have used it in auto phase change over circuit in house. i will be sending the circuit to “Circuits today” soon.