nRF52 'online power profiler' battery life calculation check

[Roger]

Good day everyone,

I would like to utilise the nRF52832 BLE chip in an application that requires radio communication between a master and slave. The slave needs to be powered by a coin size battery and ultimately I would like to explore an energy harvesting circuit that might replace the battery.

To test the initial phase of the concept, I made use of the 'power online profiler' on devzone.nordicsemi.com/power to determine the energy consumption during a broadcast event by the slave. Once a connection is established by the master to slave, I then would like to exchange data only once a minute.

My calculations are as follows (please see image):

nRF52 Current Consumption Example.png

Power = (161uA * 3V) * 1/60s = 8.05uW

Using a 300mAh @ 3V coin size battery with 70% efficiency:

Battery life = ( (300mAh * 3V) / 8.05uW ) * 0.7 = 78261 hrs

Does my calculation bare any fruit? It seems to be a bit unrealistic to me.

Looking forward to someone's response.

Regards,

Roger

[Roger]

Hi Jørgen,

Thank for the quick response.

For advertising I set the BLE interval to 10.24 seconds which equaled 3.5uA. Please see the following image: nRF52 Advertising - Current Consumption Example.png

For a peripheral connection I set the BLE interval to 2 seconds which equaled 5.4uA. Please see the following image: nRF52 Peripheral connection - Current Consumption Example.png

The power consumption is now significantly less. You're saying once the slave advertises and pairs/bonds with the master, devices must communicate between a minimum and maximum interval of 7.5ms to 4s in order to keep the connection alive.

The way I understand then the power consumption is as follows: (neglecting the advertising current consumption, this I assume will only happen once till a connection is established with the master)

Radio power consumption = (5.4uA * 3V) * 1/2s = 8.1uW

System power consumption = (2uA * 3V) = 6uW (Assuming RTC running and I have RAM retention)

Total power consumption = 14.1uW

Battery life = ( (300mAh * 3V) / 14.1uW ) * 0.7 = 44681 hrs = 1860 days

I hope I'm on the right track?

Kind regards,

Roger

[Jørgen Holmefjord]

To clarify, the online power profiler reports the average current consumption of the device from the given settings. If you input a connection interval of 2s, the 5.4 µA returned includes the sleep current between events (System On IDLE in the table). If this is the connection interval you will have, the device will on average consume 5.4 µA, or 16.2 µW with a 3 V battery. This will give a battery life estimate of 4.44 years (not so far from your last calculation).

[Roger]

That is absolutely awesome! Thanks for the great answer.