I’m looking at using a Boron for a new project, where the device will be in deep sleep mode until an interrupt is triggered and publishes an event/alarm to the cloud. It will also use a timer to wake once a day at midnight and publishes its health status.
The Boron needs to achieve a battery life of 5+ years (depending on interrupt triggers) because of this I was planning on using a Saft LSH20 3.6V 13Ah battery connected to the Li+ Pin.
However, this approach doesn’t allow me to use the Fuel Gauge.
My question is, can I use the Saft LSH20 for long-term longevity and use a LiPo as a battery backup once the LSH20 is dead?
Will I see 100% Battery Charge in the Particle Console until the LSH20 has depleted and then the LiPo will start to get used and I can then generate power failure alarms in X Days…
Right now, the Sleep Current is between 0.7 to 1.0 mA for the Boron LTE (at least the last firmware I tested).
So, 0.001 Amps * 24 hours/day * 365 Days/year = 8.76Ah per year, just for Sleep.
As you said, your battery is rated at 13 Ah, so 5 years wont happen with 1-cell.
If you use external circuitry for the Boron’s EN Pin and to catch your Interrupts, you will reduce that by a factor of 10. That’s likely your best chance to reach your 5-year Target.
Even though the Fuel Gauge wont be correct for a Li-SOCl2, the Boron can still accurately report the Cell Voltage. A simple equation based on your Battery’s datasheet would be used to calculate the remaining “life” of the primary cell.
Thank you @Rftop, I’ve been experimenting with an old Electron I had lying around and wasn’t aware of the EN Pin.
This has now got me thinking, rather than using an interrupt, can I not just use a normally closed switch to connect the pin to ground and when triggered it powers up the Boron, connects to the cloud and publishes an event/alarm.
However, I’ll still need an external timer to trigger EN for it to connect and send a daily “I’m alive” message. Any ideas of the best way to achieve this?
Here’s an example project that I played around with one day:
The idea is the TPL5111 would wake the Boron every 2 hours, or during an interrupt event (PIR).
In a perfect world, this “2-hour” could be increased to 24 hours…
But the Boron would simply ignore the 2-hour scheduled Wake-Up and go back to Shutdown via EN pin unless the Interrupt caused the Wake Event.
We now have Manual System Mode, so the Boron can do this quickly without starting up the Cellular Modem, etc. You probably wouldn’t even notice that the Boron cycled during the 2-hour scheduled Wake-Up.
The easiest way would be to publish the Event for each interrupt that triggers the TPL5111. Then you don’t have to worry with keeping a counter on a separate IC for a Once-A-Day Publish when using the EN Pin Shutdown.
Your power budget might even allow for a Publish for Every Wake Event (2-hour schedule and Interrupts)
Example, This SAFT LSH20 is rated at 68 Wh (19 Ah @ 3.6V Nominal)
From this post, I calculated 7,100 mWh (7.1 Wh) per Year, publishing every 2 hours with a Boron LTE & EN Pin Shutdown.
68 Wh / 7.1 Wh per year = 9 years of life on a 2-hour publish schedule
Of course, your mileage may vary from my testing/location/environment/etc.
Rather than connecting it to the Li+ pin, I used a battery holder with a JST-PH2 + wires on my custom PCB to power it. But the main reason for this is that I’m using the Electron which doesn’t have a header for its Li+ pin (I didn’t want that manual work added to my design). On a Boron I’d just connect it to Li+.
I never tried connecting both a battery and LiPo at once, but others on the forum I’m sure are knowledgeable about that.
I’ve gone ahead and ordered an Argon and TPL5111 for playing around with for now, as it’s a pain in the backside to get hold of an NB-IoT SIM Card at the moment in the UK. I’ve also ordered a TPL5110 to use with my Electron on any other future projects.
My latest estimation puts it at approx. 2 years but I have it wake up once per hour. At once per day it’d probably go up by a couple of years.
One thing with these batteries is that under heavy current draw and/or low temperature the voltage will dip a lot - I haven’t really tested this extensively myself yet, but the datasheet here claims that even at room temperature it can go as low 3.2V under heavy-load. Since my design also needs to operate at down to -40C, I combined the battery with the TPS610995DRVR.
For improving life time - my main method involved keeping my Electron in deep sleep as much as possible, as current draw is almost negligible in this mode compared to other actions. For instance, while at first I would transmit data hourly, I now send it once per 4 hours and use Ubidots timestamps to still get an hourly display.
There isn’t anything else in particular I did to my battery setup, other than adding the voltage booster. My project has been running fine so far for the last couple of months.
Sorry, I think my question was unclear. I was asking what voltage to directly power a Boron. The datasheet says that Li+ needs to be 3.6-4.2V. I was thinking of setting the TPS part output to 4V to allow for drop off during high current demand. I want to use 2 Alkaline batteries in series to power the Boron but alkaline batts output voltage drops linearly as they weaken, so the output current will tend to drop as well. I’ll add a large (3300uF) Cap on the TPS output to help deal with peak current loads.
@wineisgud4u, when you select your Primary battery chemistry and pack design, we typically look at the final “discharged” battery voltage that can still provide the required operating current. You want that final voltage to be close to the Input V(minimum) for the Device, in a perfect world. We determine the # of Parallel Cells as required to meet the Peak Current when ~discharged, and hit the design goal for run-time/pack-life. We determine the # of Series Cells to land in the Device’s Input range of V(max) to V(min) based on battery chemistry, considering both the V(initial) and V(final) battery conditions.
You might be better served by using a 3-Series Alkaline pack verses a 2-Series pack & boosting to 4V with TPS & then the Boron cutting back down to 3.3V.
I personally prefer the Energizer L91 battery in a 3-series format for the Boron (3xAA) over Alkaline. That may be all that you need?
Also, there is a substantial difference in the Peak Currents from @Vitesze’s Electron Project and your Boron. The TPS was beneficial for his Battery Chemistry/Operating Temperature and an Electron, but it might actually hurt your project. This is just a thought to consider, as we don’t know your project details
3xAA L91’s to the Boron LTE’s Li+ have shown great performance for me. But as with any primary pack using the Li+ pin, you obviously need to take measures to prevent the Boron from attempting to “recharge” the Primary Pack if it’s ever also connected to an external power source by the end user.
Thanks for sharing your experience. The L91 discharge voltage curve is much better than a classic alkaline battery. This would allow you to directly connect 3xAA cells in series to the Li+ pin on the Boron, as you describe. Per the BQ24195 datasheet it can accept up 6V, so 3 cells would fall well below that voltage. This would also eliminate the TPS regulator!! Always nice to reduce the BOM count.
Based on your experience, at what battery pack voltage do you typically see Boron failure/instability? And, have you seen any temperature effects on your battery pack voltage? In my case, low temps won’t be a concern, but high temps (45C+) could occur.
Thanks for the great input. Direct experience with power solutions is the best!
The graph below is a detailed graph for the 3xAA’s End-Of-Life Only, not the full test.
4.20 Volts (or maybe even as high as 4.4V) could be the Alarm Threshold, this depends on your duty-cycle and additional loads.
When discharged to ~3.4 Volts, the battery pack could not meet the Peak Current Demands of the Boron LTE during Startup, and the test was terminated.
Thank you again to everyone that has contributed to this thread, I’ve found it very useful indeed!
@Rftop I’ve not come across the L91’s before, they look like they could be a good replacement for the LSH20 instead. Looking at the datasheet I cant see where it says the rated Ah but there is a graph, which it looks like 3.5Ah…
Am I right in thinking, if I was to make up 2 packs of 3 L91’s in series and then connect them in parallel, I’d have an overall rating of 4.5V @ 7Ah ?
Yes, that would be correct. However, you would need to add a blocking diode to prevent one battery pack from recharging the other battery pack. Some recommend using one diode in series with each battery pack. This would prevent recharging but it will also lower the output voltage of the packs due to the loss going through the diode. Another option is to use 1 diode: connect the anode to the (-) ends of both battery packs, and the cathode to the (+) ends. This will prevent recharging and it will not lower the output voltage of the battery packs. Hope I’m explaining that correctly