Help with Battery Powered Circuit

[Dicko]

Hello folks,

I have an Arduino which has a jst connector for a 3.7 V LiPo battery, 3700 mAh, which I am using. The project will be placed outside and left alone to collect data and I would like this to run for over 2/3 years without having to change the battery.

I have done some calculations: The discharge rate for LiPo's is about 2.5% per month which is approximately a discharge loss of 3.083 mAH or 128.47uA self-discharge per day.

Now, I think my maximum current draw is about 30mA when on and 3uA when off. I have been playing with the on and off times to see what would work to give me 2 years usage, and my device would have to be on for about 10 seconds (enough time to collect sensor info and transmit data), but then it needs to be off for an hour, this would give me 1.97 years. Not really good enough, I would have like to take a reading every 5 minutes, not every hour.

I have read that alkaline batteries are the way to go, they would have a discharge of about 3% per year or just 0.25% per month.

I have circuit boards already made, ready to take an input to the battery jst terminal of the microcontroller. The Jst port can take up to a max of 4.4 V. Is there a way I could use rechargeable alkalines of series and parallel combinations , to do this? Or a better method ? Or if anyone knows a cheap enough but high capacity battery that would work, that would be amazing.

If there is no solution, there may be an alternate way to power the board, although I have not tried it yet, and time is against me. There are inputs to take a regulated voltage anywhere between 5 and 7V,  I guess I would need a regulator if I was to go down this route. I need whatever method to be as low power consumption as possible.

I guess I am looking for a solution to make my product last outside for 3 years untouched, I have the circuit boards already made  but I could make minor adjustments if necessary.

Thank you all in advance.

[Dicko]

Extra Info: This is the Microcontroller - https://docs.arduino.cc/hardware/mkr-wan-1310

[Picuino]

The arduino board draws too much current. You should use another Atmega or PIC microcontroller with low quiescent current consumption (XLP).
You can search here:
https://www.microchip.com/maps/Microcontroller.aspx
https://www.microchip.com/content/mchp/en-us/parametric-search.html/627

The problem is that you should make your own development board with the other microcontroller.

[tszaboo]

Go with a LiSOCl2 battery. With a C size cell, you get something like 8 Ah and 1% discharge per year.
If it gets cold outside, you might need to buffer the battery with a supercapacitor. Though the load current is quite small.

[Dicko]

Thanks for your reply, but I am unable to change the controller.

[Dicko]

Thanks for the information, could you please point me in the direction of where it says 1% per year ?

I was under the impression that Lithium-ion batteries discharge about 1-2% per month.

[tszaboo]

Thanks for the information, could you please point me in the direction of where it says 1% per year ?

I was under the impression that Lithium-ion batteries discharge about 1-2% per month.

That's not a lithium ion battery, it's a lithium primary battery. Meaning: it cannot be recharged. Different chemistry, which is better suited for what you do. Example:
https://tadiranbat.com/products/long-life-xol-series-batteries/

You can find cheaper ones from other suppliers, with similar characteristics.

[shapirus]

Thanks for your reply, but I am unable to change the controller.

is adding a small solar panel possible? just connect it (via a dc/dc converter) to the battery terminals, and it'll charge it whenever it can. however low its charging current might be, it will still be significant considering the low power consumption of the circuit, and it should definitely compensate for the self-discharge.
no modification of the circuit is required.

[Dicko]

SO I have found this one from a local supplier but it says its discharge current is 100mA, that seems quite a lot compared to the one I already have:

TADIRAN SL-760S 3.6 V Non-Rechargeable Lithium Inorganic Battery https://amzn.eu/d/0IViCxt

[Dicko]

That also sounds like an interesting idea.
Do you get low power dc/dc converters ?

[shapirus]

That also sounds like an interesting idea.
Do you get low power dc/dc converters ?

That would be a separate interesting topic. What you would need is a high-efficiency boost converter with a regulated 4.2 V output (no need for constant current limiter in this case, I guess) that doesn't have to provide high current, considering the output capability of a small solar panel, thus optimized for its highest efficiency at low current. There's a lot of options on AliExpress, for example, however they are mostly oriented at providing USB output and are to be used with larger (think camping) panels.

A custom-made step-up circuit might be a better choice, and I know that there's a lot of suitable ICs, but unfortunately I can't readily recommend anything specific. I'm sure someone else can, though :).

[tszaboo]

SO I have found this one from a local supplier but it says its discharge current is 100mA, that seems quite a lot compared to the one I already have:

TADIRAN SL-760S 3.6 V Non-Rechargeable Lithium Inorganic Battery https://amzn.eu/d/0IViCxt

That means 100mA is the maximum current you can pull from it. Since you use 30mA it's OK.

[shapirus]

That means 100mA is the maximum current you can pull from it. Since you use 30mA it's OK.

It's however rated at a nominal 2mA discharge current. At lower temperatures capacity drops significantly as current increases, see the performance curves in the datasheet: https://www.batterystation.co.uk/content/datasheets_MSDS/Tadiran/Tadiran%20SL760%20Data%20Sheet.pdf

[Dicko]

Oh, thats not good then.

[Dicko]

Would this be a good enough panel?

https://cpc.farnell.com/seeed-studio/313070004/solar-panel-55x70-0-5w/dp/MK00380?mckv=s_dm%7Cpcrid%7C224646539664%7Ckword%7C%7Cmatch%7C%7Cplid%7C%7Cslid%7C%7Cproduct%7CMK00380%7Cpgrid%7C49734053271%7Cptaid%7Cpla-1212017578951%7C&CMP=KNC-GUK-CPC-SHOPPING-945765023-49734053271-MK00380&s_kwcid=AL!5616!3!224646539664!!!network%7D!1212017578951!&gclid=CjwKCAiAuOieBhAIEiwAgjCvcqJiOXxSJGhAlo1UY4-MR3G8UcDlMZAzP-dM2aMXGJ2bOGe7YSHDoBoC2ygQAvD_BwE

[shapirus]

Would this be a good enough panel?

https://cpc.farnell.com/seeed-studio/313070004/solar-panel-55x70-0-5w/dp/MK00380?mckv=s_dm%7Cpcrid%7C224646539664%7Ckword%7C%7Cmatch%7C%7Cplid%7C%7Cslid%7C%7Cproduct%7CMK00380%7Cpgrid%7C49734053271%7Cptaid%7Cpla-1212017578951%7C&CMP=KNC-GUK-CPC-SHOPPING-945765023-49734053271-MK00380&s_kwcid=AL!5616!3!224646539664!!!network%7D!1212017578951!&gclid=CjwKCAiAuOieBhAIEiwAgjCvcqJiOXxSJGhAlo1UY4-MR3G8UcDlMZAzP-dM2aMXGJ2bOGe7YSHDoBoC2ygQAvD_BwE

specs look very good (and you'll need a buck or a buck-boost converter, it seems, if the voltage is true) on the screen, 0.5W will allow to keep your battery near full charge most of the time. The question is how it performs in reality.

I'm pretty sure you should be able to find people on this forum who have experience with things like this (is there a dedicated forum section, maybe?). Solar energy is popular.

[Dicko]

Thanks very much for your reply 😀, I found one of these I could use with it. https://uk.farnell.com/dfrobot/dfr0264/solar-lipo-charger-3-7v/dp/3769969?st=Dfrobot%20Solar

[shapirus]

Thanks very much for your reply 😀, I found one of these I could use with it. https://uk.farnell.com/dfrobot/dfr0264/solar-lipo-charger-3-7v/dp/3769969?st=Dfrobot%20Solar

yeah, looks about right. Again, no idea how it performs in practice. Let us know what you get in the end :).

[Dicko]

Thanks