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Primary powering in cold settings

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    • #17286

        Following from the post @dysumner https://www.envirodiy.org/topic/mayfly-v1-1-technical-questions-forum-thread/#post-17284
        I thought I would share some data that I’ve got from running a Mayfly on non-rechargeable Primary Battery outside.
        Batteries are electro-chemical reactions and temperature does affect them. I chose 3.6V ‘D’ LiSOCL2 ~ 12Ahr@0C, 19Ahr@20C,as its specified to -30C https://www.evebatteryusa.com/lisocl2-specifications

        So far I think I have a test station that has been running 18months – basic details here
        It is of course the simplest of sensors ~ a simple ElectricalConductivity measurement.
        I’ve made Mayfly 0.5 measurements – Assuming all switches set to the lowest settings for Mayfly1.1 should be as good.
        Sleep/Quiescent – target 0.5mA ~ though I also have measurements 1.2mA to 2.0mA while sleeping
        Running ~ 16mA ~ 20mA

        As well as collecting all power usage ratings, I would suggest you look at what powering subsystem can work at a toasty adiabatic (for the artic) 1C.
        One side effect of the LiSocl2 is it has a high internal impedance – so need to consider what current demand happens when turning on sensors – and that becomes more of a problem as it gets to the end of its life – so adding some smoothing might be extend its life – http://www.gebc-energy.com/en-US/Product-99.html The Mayfly has minimal powerline capacitance.
        As an extension of the EC sensor, I mentored some Elec Eng students with final year project by adding an LTE transmitter. The purpose of it was for them to consider the power demand. They created a simple spread sheet, I can share if its of interest.

        IMHO the Mayfly doesn’t do specifications – there is a lot of description, but I have had to dig into the schematic and device specifications to get a better understanding of the powering subsystem. The benefit of open source. The Mayfly1.1 has much better defined devices LDO overheads, and 3.6V is at the edge of working, but is probably ok as the battery discharges to about 3.4V. The processor mega1284 works down to 2.7V. Using the Mayfly battery voltage measurement is challenging and I’ve blogged extensively elsewhere about that.
        How the atlas sensors take current could be challenging – and require a good super capacitor buffer, possibly 10F which are lo-cost – https://www.whiteboxes.ch/docs/tentacle/t1-mkII/#/power?id=power-consumption

        So for powering you may want to share what your thoughts are for working at 1C.

      • #17463

          I’ve been testing with Mayfly 1.1 and LiSOCl2 D batteries. Our package is using a Mayfly 1.1, and SD card, and a sensor on the switch power that pulls ~350 mA in pulses when its on.

          I initially tried using 1S4P configuration with 95sq015 protection diodes with the intent of preventing heating from cell imbalances. That puts the Vin at about 3.4 V. At temperatures down to about -10C it works fine, but below that the voltage would drop to the point that the 1284p will brownout. The internal battery measurement shows less than 3.1 V, but as the powersupply is not a buck/boost, I doubt this is accurate and I think the voltage is sagging to 2.7V and triggering the BOD (herm, note to self: try measuring battery voltage using internal 2.7 V VREF). After reading some papers and datasheets about LiSOCL2,  I wrote the company that makes the LiSOCL2 (Xeno) I’m using, they said for the use case where the cells are the primary power source and replaced as a group, the diodes aren’t needed.  I removed them, and, at least in the short term these are able to operate at -20C.

          Something else I noticed was that the LiSOCL2 cells have an activation period: they couldn’t power the Mayfly for a few moments after I first connected them (reboot loop) after a few minutes it started working. Several datasheets mention that the lithium electrode gets deactivated when the cells are not used and that some current draw is required to reactivate it.

        • #17466

            @khaase  interesting getting the LiSOCL2  activated.

            My 2Cents is it would be good to characterize the 350mA  pulse – and isolate it from the mega1284’s  high impedance LiSOCL2.   That could mean that for the “high impedance” (for a battery)  LiSOCL2,   the current draw has to be kept below a threshold, treated as a constant current source.

            Then the issue is also how to detect when the LiSOCL2 is running out of energy, and can’t take more high current pulses, can it gracefully manage the power situation.  Unfortunately its not a trivial problem.


          • #17509

              So far, your super-capacitor idea is holding up pretty well for me. A 100 uF capacitor buffered voltage sag to a degree, but the 10,000 uF supercap (1/10 the voltage rating and 1/2 the physical size) gets our setup able to use any given battery voltage measurement without having to consider if the sensors are on or not. (I want to write “Battery voltage measurement fairly close to the aliasing limit of the ADC” but I average a few hundred measurements, so one would expect the optimum result to be nearly invariant. Now we are aliasing across five 0.019V levels instead of ten.). I am curious how the capacitor buffers our pulses when the LiSOCL2 cells are nearing depletion, we’ll tune our deep-sleep cutoff voltage based on that.

            • #17511

                @khaase great to hear  – do you have a pn for the cap – be interested see what the internal ESR is.

                Seems to me a way to monitor the battery for maximum life is to read the voltage unloaded, and then again when it is loaded.  The capacitor moderates the voltage reading, but still droops. So it would be how much droop (lack of charging from high impedance   battery) can tell you something, and how much accuracy do you need from the ADC to be able to effectively detect a significant droop.

                BTW here are some observation on the battery voltage measurement.

                https://github.com/EnviroDIY/EnviroDIY_Mayfly_Logger/issues/36 ~ I implemented an algorithm to reduce the noise.

                https://github.com/EnviroDIY/EnviroDIY_Mayfly_Logger/issues/32 ~ discussion across different Mayfly versions

                and if you have anything to add to this https://github.com/EnviroDIY/EnviroDIY_Mayfly_Logger/issues/29

                Some real world, with two monitoring sources,  one a resistor divider to 12bit ADC, and the other the internal method, https://monitormywatershed.org/sites/TUCA-Na13/

                https://monitormywatershed.org/tsv/TUCA_PO03/ – battery V with inter Vbat and external  STC3100 to read battery V & Est battery capacity – however turns out to be hard problem to calculate

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