I am working on a design that needs to operate outside on two AA batteries for at least a year.
I have optimized the design to reduce power and using a spreadsheet analysis I now have an average current consumption. I should be able to verify that is right by monitoring a prototype for a while.
I have the following pieces of information:
- Average current consumption in mA \$Cave\$
- Supply of Duracell AA batteries in mAh \$Bsupply\$
- Starting battery voltage \$Bmax\$
- Minimum battery voltage for DC-DC converter \$Bmin\$
- Non-linear discharge profile from Duracell website https://d2ei442zrkqy2u.cloudfront.net/wp-content/uploads/2016/03/MN1500_US_CT1.pdf
- Climate data
How can I take this to create a realistic estimate?
I think it is perhaps reasonable to use the average environmental temperature \$Tave\$.
Note – I chose Duracell simply as an exemplar of a quality battery. I wouldn't need/want to consider poorer-quality batteries.
Many thanks!
Update – average power consumption is 1.11mW.
Best Answer
First, you need to make a realistic ballpark estimate before going to intergraion of discharge curves and buck boost converter inefficiencies.
The estimate would be: at 3 V input supply and 1.11 mW, the device will take about 0.45mA average (assuming 80% efficiency of converter, if any). The Duracell discharge curve says about 650 service hours at 5 mA discharge rate. At 0.45 mA it will take about 11 times longer, or about 7200 hours. This is about 300 days of operation. Which is about 20% short of one year.
Conclusion: you can't guarantee this device to work for a year from 2xAA batteries. No amount of more accurate mathematical massaging of discharge curves would change this conclusion.