Battery life calculation for NRF52 and NRF51(Beacon kit)

[Usman Rashid]

Hi,

Is there any battery life calculations for NRF52 and NRF51 (Beacon)?

For example: if TX power of NRF52 is 0 dBm and it broadcast every 5 seconds ? Or with any other random settings.

[Sigurd]

Hi,

You can estimate the current consumed by the nRF52 using the nRF52 Online Power Profiler. Based on this and the capacity of your battery you can calculate the battery life as:

Battery Life [hours] = Battery Capacity [mAh] / Device Consumption [mA] * 0.70

where the factor of 0.7 makes allowances for external factors which can affect battery life.

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Using 0 dBm, TX payload 15 bytes, voltage 3 and BLE interval 5000 ms you will get a total average current at 4.2 uA. If you use a CR2032 coin cell battery with a 220 mAh capacity we can calculate the battery life as:

220 mAh / 0.0042 mA * 0.7 = 36666.66 hours =  4.18 years

[Nakul Nair]

I want to broadcast every 1 min so how to calculate battery life for that..the max value in the online power profiler is 10240 ms

[Sigurd]

Hi Nakul93,

The BLE specification does not allow the advertising interval to be larger than 10.24 s.

From the BLUETOOTH SPECIFICATION Version 4.2 [Vol 6, Part B]:

The advInterval shall be an integer multiple of 0.625 ms in the range of 20 ms
to 10.24 s. If the advertising event type is either a scannable undirected event
type or a non-connectable undirected event type, the advInterval shall not be
less than 100 ms. If the advertising event type is a connectable undirected
event type or connectable directed event type used in a low duty cycle mode,
the advInterval can be 20 ms or greater.

[Nakul Nair]

Hi Sigurd,

My advertising interval is set for 150 msecs and advertise for 3 secs using a timer and when the timer expires I stop advertising using sd_ble_gap_adv_stop function, I then go in idle state for 1 min using another timer and the above cycle repeats. 

I have successfully achieved this, my only query here is what will be my battery life, I am using CR2032 coin cell.

[Sigurd]

Hi Nakul Nair,

Let's say you are using around 1.9 µA in sleep(RTC timer running). And with the online profiler, we get around 77µA average during the 3 second advertising with 15 byte payload and intveral set to 150ms. This gives us around 5.5 µA average for the 63 second cycle. Using the forumula in the originally answer in this post, this gives us around 3.2 years battery life, that is including the 0.7 factor accounting for external factors which can affect battery life.