Power issues

Hi,
I had made a system for switching of some solenoids in a certain time interval for some time. I used 5V relays and a LCD with i2c module. Both relay and LCD powered from arduino board. During installation it was working fine. But after three months a problem came with power so I separated the relay power from arduino then it worked.

What was the reason of problem?

You were lucky not to burn something out.
Relays and some displays displays can be power hungry and it is always recommended to use a seperate power supply with just a common GROUND back to the Arduino.

But, How it worked for three months?
At beginning the problem was not there after 90 days the problem came.

Why?

The short answer is "you were lucky"

The probable technical answer is there may be a chance that you have weakened a component either on the board or in your power supply where it will start to fail a bit easier.

Look at it as a lesson learned in that you need to work out what item needs how much voltage and current and what your supplies can provide and how much voltage current can the Arduino supply and sustain without putting stress on any of the above.

Luckily a lot of what you need to know for the Arduino itself is available HERE

Your power supply would normally have it marked somewhere on it.

External components may have to be researched on the internet.

Thanks
I'll work on it.