power requirements for a motion sensing system

Submitted by goddey on Sun, 11/10/2019 - 12:38

Hello all

i'm working on a security system that involves up to twenty (20) PIR sensors (HC-SR501) with a microcontroller, a buzzer and a few LEDs.  what will be the power requirements if i want this system to run on a single rechargeable power source?

can a 12v  made up of three (3) 3.7v batteries connected in series work effectively?

pls  I need your help to make this device as economical as possible

Thank you

I'm thinking of the 12v because of the distance the sensors will be spread across (50ft x 100ft fence )

  Joined October 12, 2019      6
Saturday at 11:01 PM

Thank you

I'm thinking of the 12v because of the distance the sensors will be spread across (50ft x 100ft fence )

  Joined October 12, 2019      6
Saturday at 11:01 PM

Hi goddey,

Your project sounds too big to be powered by a battery. I would suggest using an SMPS to convert your AC mains to 12V DC with a current rating of 3-5A. If you want inspiration you can look at how CCTV cameras are installed, you just have to replace the cameras with sensors and DVR with MCU, you can even use the same type of wires to power your sensors and get you output back to the MCU

  Joined August 16, 2016      997
Tuesday at 12:29 AM

Thanks a lot Aswinth Raj

What if I get a 12v battery and make a charger for it so that I can use but AC then there power and then switch to battery when power is out?

  Joined October 12, 2019      6
Saturday at 11:01 PM

Hi goddey, yes a 12V battery will work. As Brayden pointed out your system will consume around 2A so with a 12V 2Ah battery you can expect your system to work for around 60 mins with battery power.

A good way to proceed from here would be to first set-up thins to work directly from AC mains, then introduce a 12V battery with a charging and protection circuits as required. 

  Joined August 16, 2016      997
Tuesday at 12:29 AM