Making an automatic ‘ON’ Switch using only relay and a charger!!!

Materials needed:

AC/DC 3.7V 1.78A Power Adaptor 

Any AC/DC converter or charger with an output of 5V or (Preferably)3.7V and an old and unused charger within the given voltage can be used but not a battery(read further to know why).

Hi everyone I will be showing you how to make a switch that automatically switches on when there is a power outage if you have a Backup battery power supply in your home(Should read if you have frequent power outages).


I have been having many power outages in my place and it is frustrating when there is a power outage and the AC goes off and I need to manually switch on the fan, that is connected to my backup battery power supply, every time that happens so I decided to make a switch that automatically turns on the fan without the work of any microcontrollers in middle so read on:

Circuit Diagram:

Here the AC/DC converter charger can be taken out of any old phone or any device charger till it is in the range of voltage. I prefer 3.7V as the relay is kept on for long periods of time. Here we have connected the +ive terminal to the VCC port of the relay and the -ive terminal to the GND and IN port of the relay because of which the relay will always be ON until the power supply to the charger is cut off by a switch or there is a power outage.

When the relay is ON then COM i.e. Fan Input doesn’t have any power input as it is connected to “NO” port. But when the relay is OFF then COM connects to the “NC” Port and there is a connection between the backup power supply and the Fan and it turns ON.

In case you want to turn the fan on while there is no power outage then you just have to switch OFF the “Fan Switch” but, if you want to turn OFF the fan while there is a power outage then you just have to turn the regulator to “0” or no power mode. If you know that there are going to be no power outages in a while and want the relay to rest you can switch OFF the power and turn the regulator to “0”.

If you are going to place the modules in your switchboard, as I did, then I suggest you place the “Fan Switch” upside-down to avoid confusion as breaking the circuit switches ON the fan.

This is how my modules looked after installing:

This Project can also be integrated into other scenarios such as when there is a power outage and you want to automatically switch to less power-consuming appliances like Low power led lights and when the power is back you want to return to the high power high output lights like tube lights etc. you need to just replace COM with Power input and NC with the low power appliances while NO with the high power appliances.

Though the circuit may be a little complex due to a lack of a regulator type primary switch but, I may just upload a blog sometime in the future so keep checking in.

Happy Moduling ╰(*°▽°*)╯ !!!

(P.S. The Relay lights give a cyber look to my switchboard when the lights are turned off)

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