Smart under and over voltage protection system for home is designed to insure protection of home devices like fan, light lamps, television, refrigerator and all other things you need to protect in case of under and over voltage in main supply. Although there are circuit breakers available in market to provide protection against under and over voltage. But once circuit breaker detect problem in main power supply voltage it turn off main power AC power supply to home devices permanently. Until someone manually press the button on circuit breaker again. The main disadvantage of circuit breaker is that you have to control it manually.The main objective of this project is to add automatic functionality to turn off and turn on main power supply to home devices in case of over voltage and under voltage of main power supply.
All electrical devices can bear voltage up to certain limits. For example your home fan normal operating voltage is 220 volt AC. If voltage input to fan become greater than or less than about 20% of normal operating voltage of fan it many burn your fan and in case of less voltage fan excessive current may flow which in turn cause short circuit in your home wiring. To avoid all these issues this project is designed which automatically turn on and turn off main power supply in case of issue in AC main power supply and on one need to control it manually. Microcontroller is embedded into this system to make it smart enough to handle all the issues intelligently and to provide control signals to turn on and off AC main power supply.
Circuit diagram description :
Followings are the main components of this project. I have explained function of each component used in this project. But you can modify each component rating according to your requirement.
Voltage sensor is used to measure voltage of AC main power supply. Voltage sensor is used difference amplifier to to step down voltage level from 220 volt AC to 2.8 volt AC or 311 volt peak of AC voltage to 3.96 volt of peak voltage of sine wave. Difference amplifier is used as a signal conditioning circuit to convert high voltage of AC main supply into low voltage which microcontroller can easily read. Because microcotroller analog to digital converter can not read voltage more than 5 volt and voltage more than 5 volt damage microcontroller. So difference amplifier as a signal conditioning circuit is used to step down voltage by adjusting the gain of difference amplifier. If you want to know more about voltage sensor read following article :
High speed relay :
Relay is used to to turn on and turn off main power supply. Relay get control signal from microcontroller through a transistor. Diode is use in parallel with coil pin of relay to avoid sparking in case of back emf. Because coil is made of inductive material. Selection of relay depends on load of your home. For example maximum load of your home devices is 10 ampere. So should use 10 ampere relay. Another important thing while selecting relay for this circuit is switching speed of relay. Your relay speed should be as fast as possible. Because more the switching speed of relay, more protection it will provide to your devices by turning them on or off in minimum possible time.
Liquid crystal Display :
LCD is used to display value of voltage and status of your power supply. If AC voltage of main power supply is greater than 20% of normal operating voltage, LCD display ” fault occur”. Otherwise LCD display ” No fault”. LCD also displays value of AC main voltage supply.
Voltage regulators :
7805 and 7812 is used to get regulated 5 and 12 volt which is supply voltage for microcontroller and relay respectively. 220 to 12 volt step down transformer and rectifier full bridge is used to produce DC voltage which is input of voltage regulators.
PIC16F877A microcontroller :
PIC16F877A microcontroller is use to make this project intelligent and smart. ADC of Pic microcontroller is used to measure analog AC voltage. Control signals from pic microcontroller is used to turn on or off transistor which control the relay. Microcontroller read the analog value of voltage and display it on LCD. Actually embedding this microcontroller make this project intelligent and smart enough so that it can take control actions automatically in case of under and over voltage.It can also automatically turn on or off power supply without having need of any person.
Circuit Diagram :
Circuit diagram of under and over voltage protection system is shown below. I have used just a lamp for simulation in this circuit. But you should connect this circuit at main panel of your home from where AC main power supply connections have taken for your home devices. Circuit diagram below shows when voltage is 220 volt AC or less than of normal operating voltage lamp is on and relay is working. Because relay is used as normally closed mode. But when voltage become greater than or less than normal operating voltage it will turn off relay in minimum possible time and relay in return turn off main AC power to ensure safety of devices.
circuit diagram of Smart under and over voltage protection system for home when no fault occur:
circuit diagram of Smart under and over voltage protection system for home when fault occur :
I have not used step down transformer along with full bridge rectifier in above circuit just for simulation purpose and I have connect 12 volt AC power supply directly with full bridge rectifier. While using this circuit practically you should use 220-12 step down transformer. Complete circuit diagram is shown in schematic below.
Schematic and PCB
Circuit diagram below shows schematic and PCB diagram of this project.
Smart under and over voltage protection system for home :
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you can also add more functionality in this project by adding GSM to send value and status of AC main power supply to your home cell number. If you have any issue after reading this article, your comments are welcome. I recommend you to write your own code for this project. But if you want to purcahse circuit diagram, PCB and code of this project, comment on this post with your email address.