Power consumption in Ampere Hour for nRF52840-DK

RE: Power consumption in Ampere Hour for nRF52840-DK

Kazi Afroza Sultana — Fri, 08 Apr 2022 10:10:34 GMT

Have you checked with the battery specification to know the details of battery along with life time?

RE: Power consumption in Ampere Hour for nRF52840-DK

JasonGeo — Thu, 07 Apr 2022 01:38:10 GMT

Not sure if I've got that spec. for my battery. Have to hunt it down!

RE: Power consumption in Ampere Hour for nRF52840-DK

JasonGeo — Thu, 07 Apr 2022 01:36:29 GMT

Thanks Kazi, thanks for the formula. The formula is perfectly fine.

Will investigate more into battery chemistry and self-discharge rate as well.

Thanks once again for the comprehensive write-up.

RE: Power consumption in Ampere Hour for nRF52840-DK

JasonGeo — Thu, 07 Apr 2022 01:34:14 GMT

I just double checked and it's indeed a 120Ah battery.

RE: Power consumption in Ampere Hour for nRF52840-DK

Stian Røed Hafskjold — Wed, 06 Apr 2022 12:32:38 GMT

Hi, are you sure it's a 120 Ah battery, not 120 mA battery? 120 Ah is like the size of the 12V batteries you have in your car.

RE: Power consumption in Ampere Hour for nRF52840-DK

Kazi Afroza Sultana — Wed, 06 Apr 2022 12:03:30 GMT

Hello Jason,

You were asking for formula, so that I mentioned in my reply.

The original life time is not easy to presume. Because the life cycle of battery depends not only on its charge levels, but also the materials (chemical), environmental factors (for example: temperature, ageing), the way of using ( charging after 90% or fully drained out). So, there are several issues that could fail the battery. You may check the datasheet of the battery manufacturer to know the practical life cycle. If you can manage to charge and discharge the battery according to the limit at a specific temperature you could probably get the life cycle close to the specification.

There is a lot of academic papers which describe the estimation of the life cycle of a battery as a statistical approach and calculated on historical data. A battery of a specific chemistry ( lithium, alkaline, carbon etc) will fail on average according to particular statistical distribution. Therefore, mean term between failure (MTBF) parameter is used to measure the life time of battery by battery manufactures.

Thanks.

Best Regards,

Kazi Afroza Sultana

RE: Power consumption in Ampere Hour for nRF52840-DK

PaKa — Wed, 06 Apr 2022 09:43:35 GMT

What is the battery self discharge rate? This is very often the limiting factor for battery applications. Remember that this is also temperature dependent.

RE: Power consumption in Ampere Hour for nRF52840-DK

JasonGeo — Wed, 06 Apr 2022 01:52:44 GMT

Thanks all for the quick response.

Using the suggested formula:

capacity (120000 mAh) / Average current (1 mA) gives 120000 hrs which equates to 13.7 years!

My team finds it hard to accept that figure. In the field, we are seeing an operational life of 10-12 months.

Where is the missing puzzle?

RE: Power consumption in Ampere Hour for nRF52840-DK

Kazi Afroza Sultana — Tue, 05 Apr 2022 12:43:49 GMT

Hello JasonGeo,

You can run the experiment for a bit longer time (for example: around one hour or less) to get a bit more accurate value of average current and maximum current. It is not uncommon when these two have difference. For example: there is different in current consumption for idle period and advertising period.

''I want to calculate how long I can run the DK board on this battery. Can you provide a formula for calculation?''

battery life calculation formula is -

Battery Life (hours) = capacity (mAh) / Average current (mA)

There is a few online calculator Battery Life Calculator | DigiKey Electronics to do this. You can calculate on there as well.

Thanks.

Best Regards,

Kazi Afroza Sultana

RE: Power consumption in Ampere Hour for nRF52840-DK

Ivan Herrera — Tue, 05 Apr 2022 10:34:52 GMT

Hi Jason!

It might be worth skimming through a basic physics course as this will clear up a lot. 1 Ampere Hour is the equivalent of the amount of charge that 1 Amp of constant current would have drawn for 1 hour straight. The formula is: current x time = ampere hours. So if you want to solve for time, you divide ampere hours by your current.

It's normal for the average and peak current to differ a lot. Use the average current you expect your application to use.