nRF9151 Feather long duration Primary Cells

sageduggal

Hi there,

I’d like to use the Circuit Dojo nRF9151 for a project of mine in order to avoid making my own board.

My goal is an 8-10 year device lifetime with a primary cell, however I see that the nRF9151 Feather uses a Nordic PMIC designed primarily for secondary batteries that are not quite in line with my use case.

If I designed my own board, I would likely choose an LiSOCl2 battery along with a TI TPS63900.

I understand the nRF9151 feather has a 2W power requirement which my LiSOCl2 battery of choice (Jauch 18505) cannot support out of the box.

Are there any recommended primary batteries or power strategies to take advantage of the Circuit Dojo nRF9151 Feather in a years-long use case?

Thank you!
Sage

jaredwolff

Hi @sageduggal

Good news — primary cells are supported on the nRF9151 Feather. You’ll want to
disable charging on the nPM1300 PMIC (see the battery requirements
(https://docs.circuitdojo.com/nrf9151-feather/specs.html#battery-requirements)
section), and after that the board runs happily off a primary cell as long as the
voltage stays in the 2.8–5.5V range.

A couple of strategies to deal with the 2W transient that LiSOCl2 cells like the
Jauch 18505 can’t sustain on their own:

Supercap in parallel. LiSOCl2 cells have high impedance and will brown out during
RF transmit if you draw directly from them. Sticking a supercap across the cell
lets it absorb the TX current spike while the primary cell does the slow recharge
between transmissions. This is the standard trick for LTE/NB-IoT on LiSOCl2 and it
works well.
Solar / energy harvesting. Worth considering for an 8–10 year deployment
regardless — primary cells alone are a tight budget at that timeframe. Voltaic
Systems makes a Solar System with a Lithium-Ion Capacitor
(https://voltaicsystems.com/Solar-System-Lithium-Ion-Capacitor) that drops right
onto the Feather since they already use JST connectors. I have a few here that I
haven’t fully characterized yet, but the topology is exactly what you want for this
use case — the LIC handles the TX spikes and the panel keeps the system
trickle-charged. @AchimKraus has had good results with the Adafruit BQ25185 solar
charger on his nRF9160 Feather beehive scales as well, so there are a few viable
paths here.

sageduggal

jaredwolff

Thanks for the reply!!

Strategy 1 would work best for me. I will take a look into Supercaps that could work with the Feather.

I’d love a solar solution however this application will be indoors without solar power.

jaredwolff

I would recommend cells that come with a supercap integrated rather than trying to do it yourself.

I’ve used ER14505+HPC1520 combination from PKCell but they don’t sell it “off the shelf”

I’ve also used the larger Lithium Thionyl Chloride batteries which usually do support larger amounts of current for cellular:
https://www.batteryjunction.com/collections/lithium-thionyl-chloride-batteries/products/titus-er34615?variant=47771015839976

There’s tons of options here:

https://www.batteryjunction.com/collections/lithium-thionyl-chloride-batteries?productListFilters=battery_size%3AC%2CD&productListPgNo=1

Of course try before you buy. 😃

AchimKraus

Just to mention, before you fall into “dies in 15–93 days vs expected ₁ year”:

Outside in the field, the signal strength may vary much more than in your lab. That causes not only higher energy consumption on transmissions, it also causes higher energy consumption in network searches. So be careful and do realistic field tests, before you assume it lasts for 10 years.