0

Power Consumption for battery backup sizing
Moderators: adafruit_support_bill, adafruit

Please be positive and constructive with your questions and comments.

Power Consumption for battery backup sizing

by wsquared58 on Thu Aug 22, 2019 7:24 am

Is there any way to estimate normal power consumption of a project to provide an appropriate battery backup to run project for several hours on lack of AC power and internet. Have realtime clock and sd writer to record data locally on utility power loss but not sure how to tally up raspi power use along with breakout board power and provide ample buffer

wsquared58
 
Posts: 119
Joined: Sun Jun 09, 2019 9:13 pm

Re: Power Consumption for battery backup sizing

by millercommamatt on Thu Aug 22, 2019 11:59 am

The best way would be to directly measure your power consumption over time. However, that assumes you have the tools to do so.

The cheapest way is to look at the datasheets for all your components and look for the stated power draws. Assume worst case, and then add up your total watts used. Use that power draw number combined with your desired battery run time to arrive at a battery.

e.g.
These are fake numbers and may not be realistic
Microcontroller - 300 mA @ 5V
RTC - 10 mA @ 5V
Sensor - 100 mA @ 5V

Total - 410 mA @ 5V = 2.05 W

Desired battery run time = 8 hours

2.05 W x 8 hr. = 16.4 W Hr

For a 3.7 V LIon battery
16.4W hr / 3.7 v = 4.43 A Hr

So, you would need a 3.7 V lithium ion battery with greater that 4,430 mA hr capacity to get an 8 hour run time assuming no power loss from any other source. Realistically, you'd want closer to 5,000 mA hr.

millercommamatt
 
Posts: 410
Joined: Tue Jul 31, 2018 4:57 pm

Re: Power Consumption for battery backup sizing

by adafruit_support_mike on Fri Aug 23, 2019 2:11 am

We have a tutorial in the Learning System that explains the math necessary to calculate things like battery life:

https://learn.adafruit.com/energy-budgets

adafruit_support_mike
 
Posts: 58799
Joined: Thu Feb 11, 2010 2:51 pm

Please be positive and constructive with your questions and comments.