Energy Buffering for cr2032 battery

[Letho]

Hello,

I’m designing a custom nrf52832 device and i came across an issue with energy buffering. I am using inside of the device the battery CR2032, SoC nrf52832 and two proximity sensors VCNL3040 ( https://www.vishay.com/docs/84917/vcnl3040.pdf ). Those sensors have pulse current up to 200mA for a few mili seconds (as you can see on attached image), but the battery is rated only for 0.2 mA load. The problem is, those hight current pulses cause capacity drop and voltage drop of the battery, and on the end also cause hard restart of the device.

I was wondering, if you have some example design for energy buffering that would be suitable for my use case.

One more important thing is, the device is designed for long battery life, and most of the time is in sleep mode, therefore has the average power consumption of around 5 uA.

Thank you.

Best Regards,
Tomas

[Jared]

Hi,

I think the main problem is as you say that coin cell batteries are not made to deliver high current due to their low discharge rate. Is there any possibility of using other types of batteries such as Alkaline, Li-ion etc? You write energy buffering, does this mean that you are going to implement some kind of harvesting of energy such as solar panel etc?

A bit outdated but still interesting design is our nrf51 based beacon starter kit. 

regards

Jared 

[Letho]

Hi Jared,

Yes, you described my problem nicely.

The device I'm developing is smart home sensor, which should function for a few years without battery replacement.

It is important to have the device as small as possible, that is why I decided to use the battery CR2032, which has a decent capacity of 240 mAh. The battery CR2032 is small and easily replaceable. As the device can function up to 4-5 years (based on our  average power consumption), there is no need to use rechargeable batteries or energy harvesting at this point. 

The only issue is that the chemistry of the battery cannot keep up with the power requirements of the sensors pulse. But I think no battery of this size can keep up. 

I've checked the design of the beacon you linked, but it seems that the design doesn't take in consideration such problem. The pulse current of the SoC nrf51 is approx 5-7 mA when the beacon is transmitting (based on the online profiler https://devzone.nordicsemi.com/power/w/opp/2/online-power-profiler-for-bluetooth-le ). The pulse current will decrease battery's capacity, as it's mentioned in the study linked in this thread ( https://devzone.nordicsemi.com/f/nordic-q-a/62487/high-pulse-drain-impact-on-cr2032-coin-cell---graph-csv-data )

I was wondering if you don't have any idea (or, ideally, more example designs) of how to buffer energy. The only thing I found so far is using buck convertor in combination with super capacitor (as described here: https://www.ti.com/tool/PMP9753) . 

Thank you so much for your help, 

Best regards,

Tomas

[Jared]

Hi,

Letho said:

I was wondering if you don't have any idea (or, ideally, more example designs) of how to buffer energy. The only thing I found so far is using buck convertor in combination with super capacitor (as described here: https://www.ti.com/tool/PMP9753) . 

But would the super capacitor be able to store as much as the coin cell? Or were you thinking of doing a hybrid solution?

I'm sorry, but I'm not that very experienced in exactly this. Maybe you should try posting in some alternative electronic forum?

regards

Jared 

[Letho]

Hi Jared, 

As you say, I was thinking of doing a hybrid solution, where I would gradually charge the capacitor with a low current (max 0.2 mA) so the battery would not be stressed as much.

I don't have much experience in this field either. Can you recommend me any alternative electronic forum where someone might have more insight in this type of issues? 

Best regards,
Tomas

[Jared]

If this case doesn't contain any sensitive information, maybe I could convert this case to public? So you could get help from the community?