Need clarity on Battery Life calculations

[beemavishnu]

Hello,

 

I am trying to estimate Battery life. I am using CR2032 with 230 mAH capacity. I am confused with the calculations.

 

As per excels sheet in below link, for 500 ms Connection Interval, average Current consumed is 30.1 µA.

https://devzone.nordicsemi.com/f/nordic-q-a/6746/excel-sheet-for-power-consumption

 

The Connection will be there for 1 day. So my assumptions are,

 

For

500 ms                -->            30.1 µA

1 Second             -->           60.2 µA (30.1 µA * 2)

1 Minute              -->           3.612 mA (60.2 µA * 60 sec) of current is consumed

1 Hour                 -->           216.72 mA (3.612 mA * 60 minutes) of current is consumed

1 Day                   -->           5 A (216.72 mA * 24) of current is consumed

 

With Connection interval of 500ms and if device is in connection state continues for 1Day, whether current consumption is 5A. I am suspecting some basics are mission in my calculation.

 

In few examples its mentioned as (mAH / mA = Hours) to get number of hours. But this is not matching to my assumption.

It may be silly mathematical calculations, but I am trying to get a clear picture with better understanding. Please help me in getting clear picture.

 

Thanks & Regards

Vishnu Beema

[William E.]

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.

[beemavishnu]

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.

 

[William E.]

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.