Need Advise to build an UPS for a DIY alarm systems

Thread Starter


Joined Feb 15, 2016
I am building my own alarm system based on Arduino UNO and some reed switches , and some PIR Sensors.
The main power will be 12VDC, for Arduino Uno 5VDC

I am thinking of an DIY UPS for this alarm
I plan to plug a 220V AC => 14VDC adapter connected to that module


The module will be connected to the adapter, connected to a battery, and connected to my alarm system
So my alarm system should be secure for a short period of time if the main power is cut.

What do you think of my solution ?
What kind of battery can i use ? (in term of battery technology and power)

Finally, i would like to plug a relay of something on the output of the adapter (220VAC to 14VDC) and plug it to my arduino and thus be able to receive an alert if the main power fail !

Please advise me ? how can i do that kind of relay or device ?

thanks a lot


Joined Aug 7, 2020
14V is about the right voltage to float-charge a lead-acid battery. Add a Schottky diode and it will be almost perfect. You also need a current limiter so that the power supply isn't overloaded when the battery starts to recharge, then a couple more diodes to stop current flowing the wrong way into the power supply.
A simple resistor-transistor circuit (R4,R5,Q3) will alert the Arduino if the main power supply fails.
Of you could just use R4/R5 and connect it to an A/D input.
You should probably also include a battery monitor to shut it down completely if the battery voltage falls below 10.8V because otherwise it will ruin the battery.Untitled 1.png