Need clarity on Battery Life calculations

RE: Need clarity on Battery Life calculations

Stian Røed Hafskjold — Fri, 15 Mar 2019 14:34:59 GMT

Please check out the online power profiler to get the average current for the 52 series: https://devzone.nordicsemi.com/power/ . The excel sheet you linked to is for nRF51, which has a different consumption than the 52 series.

Once you find the average current using the online power profiler, the calculation for battery life is pretty basic, as William E says:

battery_capacity / average_current = battery_life_time
or:
mAh / mA = hours

Ampere is not a measure on "amount of current consumed", it's charge per unit time. You can't say that "my device consumed 1 A".
The solution to your calculation in the original post should have a unit of Ah not A, something like this:

30.1uA * 1 Day = 30.1uA * 24 hours = 722 uAh.

RE: Need clarity on Battery Life calculations

William E. — Fri, 15 Mar 2019 09:29:23 GMT

1) 30.1 uA is the average of a number of instantaneous measurements. There is no concept of time here except for the duration of which the average current was calculated. As long as the power conditions stay constant, the average current consumption for 500 ms is the same for 1s or 9 billion years (30.1 uA).

2) No, the current flowing through the circuit is the same after 1 second (30.1 uA).

3) The calculations in the Excel sheet might consider battery characteristics since you can choose battery type.

You should read up on some basic electrical formulas and concepts. Your question probably belongs to some electrical forum instead since it is not directly related to any of Nordic's products.

RE: Need clarity on Battery Life calculations

beemavishnu — Fri, 15 Mar 2019 08:51:25 GMT

Hello William,

Thank you for your reply.

1) I am not getting about your statement "The current measured in A is an instantaneous measure". Actually 30.1uA is average current but not instantaneous value. The same is mentioned even in excels sheet.

2) If 30.1 µA is the average current consumed for 500ms, whether can I assume for next 500ms current consumption is another 30.1 µA. So for 1 second, average current consumption will be 60.2 µA.

Assume the same Connection event is present for 1 minute, then in that case whether I can do (30.1 µA * 2 in sec * 60 sec in a Minute) = 3.612 mA average current.

3) Even the calculation you mentioned is not matching with excels sheet. In your calculations it is 318 days. So can I assume Connection even will be there in entire 318 days. But in excels sheet, for 90 minutes per day, Batter life is 0.8 years for 230mAH.

Sorry for this. I feel, I am missing some basic understanding in my calculations. Please help me.

RE: Need clarity on Battery Life calculations

William E. — Fri, 15 Mar 2019 07:37:49 GMT

The current measured in A is an instantaneous measure.

If the average current consumption is 30.1 µA at a certain voltage then the energy consumption for one hour is 30.1 µAh. A very simplified battery life time calculation can then be performed with the formula that you mentioned:

230 mAh / 30.1 µA = 7641 hours = 318 days.

This neglects any battery characteristics and battery imperfections and other conditions that might affect the battery lifetime.