Hi There,
I'm doing a school project and I don't have enough knowledge in electric calculations. I'm going to have two nodes one node will consist of :
Arduino Uno
PIR sensor 1.6mA@3.3V (constantly reading values)
nRF24L01 module 11.9mA @3.3V (constantly active)
4 lux sensors, each 5µA current @3.3 V (constantly reading values)
and another node, which consists of:
Arduino Uno
nRF24L01 module 11.9mA @3.3V
4 linear actuators 3A@12 V (estimated to work for about 40 minutes/day)
My question is how do I calculate the power needed for each node? and what battery size I should use? and what the battery life is? I need to have a battery that can live for years (if that's even possible: smiley-confuse: ). I'm going to test the model for few days but I would like to demonstrate to my professor that batteries won't need to be changed frequently.
Let's say an average car battery in good condition will last about a week, calculated from the top of my head.
Sincerely yours,
Mike
Hi,
raniat123:
My question is how do I calculate the power needed for each node? and what battery size I should use? and what the battery life is?
First one is quite easy, everything is running on 3.3v so just add up the current required:
PIR sensor (1.6mA) + nRF24L01 module (11.9mA) + 4 lux sensors (5uA ea.) = 13.5mA
So, roughly, to run this for 1 hour you would need a 13.5 mAh battery. For a day = 24*13.5 = a 324 mAh battery.
If you had a 1000mAh battery it would run for 1000/13.5 = 74 hours.
The another node, is a bit more complicated.
We'll say our nRF24L01 module runs from a 12V to 3.3V converter which takes 10mA
To run for an hour = 10 mAh, to run for a day = 24*10 = 240mAh
The 4 linear actuators take 3A, to run for an hour that would be 3Ah
To run for 40 minutes (3/4 of an hour) = 3 * 3/4 = 2.25Ah. running for a day is the same (it only runs 40mins/day)
So adding these we get 2.25Ah + 0.24Ah = 2.49Ah per day.
An average 12V car battery has a capacity of around 70Ah, so you would expect it to run for 70/2.49 = 28 days.
NOTE these are only very rough calculations which do not include the dropping voltage of the battery.
In reality, I think Mikeb1970 is spot-on with his estimate of 'about a week'.
Yours,
TonyWilk
TonyWilK Thank you so much for the detailed explanation. This is a great forum, I learn something new everyday here.
I wonder how automated systems in buildings run on batteries
I run my Arduino on a 12v 2200ah battery. A week is optimistic esp if your driving other stuff. I charge my system with a 100W solar panel.
From that.. I can run a mega, 8 relays, some 12v lights, bunch of sensors etc. run them 24h over 24h nonstop.
I could do all the math, but as I add more stuff, I know I can add another 12v batt in parallel for more stored power reserves. If I can’t fill those during the day, then I know I need to buy another 100w charging panel.
raniat123:
TonyWilK Thank you so much for the detailed explanation. This is a great forum, I learn something new everyday here.
I wonder how automated systems in buildings run on batteries
Automated systems in buildings run on Mains (A.C.) voltage with A.C. - D.C. power supplies where appropriate, they then have battery back up systems that carry the load for mains failures and recharge when the mains is restored.
I can help design your battery system if you like, but you need to think about a couple of things, how do you intend recharging the batteries? How OFTEN do you want to recharge batteries?
If you want a battery for years then it needs to be a Solar or Deep Cycle battery NOT a car battery, it needs to be oversized to prevent deep discharge and it needs a well controlled charge regime.
We used to supply Solar systems with 5, 10 or 15 year design life but the batteries were huge for the load supplied (not unusual to supply up to 3,000 Amp Hour 2 volt Gel Cells).
If you need a hand just let me know and I will dig out the calc sheets