Thanks @Rftop and @no1089. I hadn’t appreciated the additional current draw from the BQ24195L when powered by VUSB. I’ve taken a look at the datasheet and have a clearer understanding of this now. Interestingly, the Boron datasheet states an absolute maximum input on the Li+ pin of 6.5V vs the BQ24195L datasheet maximum of 6V (unless I’m missing something). Either way, there’s a bit of headroom for an initial cell voltage above 1.5V when using 3 cells. I wonder whether I might get away with using 4 cells…?
I’ve been using alkaline D cells (Duracell Procell Intense, nominal capacity 15k mAh), partly for their high capacity and partly because some systems will be deployed in Africa where access to replacement lithium cells may not be possible. The plan was to use a 4S2P configuration to maximise capacity. One reason I’ve been using VUSB is the greater flexibility it gives with input voltages, and the ability to use the full discharge curve of the batteries. If I supply power with 3 cells on Li+ it will only allow the cells to drain to 1.1V (as the minimum voltage on Li+ is 3.3V). That’s not an issue with the lithium Energiser L91 cells, but is with the discharge curve of alkaline cells. Again, I wonder if I could get away with using 4 cells?
@Rftop I note that you had planned to test a 4S and 3S2P cell setup (Low-Power Boron LTE, using the EN Pin - #2 by Rftop). I can’t find any reference to the results of these tests (sorry if I’ve missed it). Are you able to give any feedback on these?
Note 1: Another reason for using VUSB is that I need to provide a regulated 5V to a sensor (Sensirion SPS30), and this is simplest when my battery voltage is well above 5V (so I can use an efficient buck converter MPM3610 5V Buck Converter Breakout - 21V In 5V Out at 1.2A : ID 4739 : $5.95 : Adafruit Industries, Unique & fun DIY electronics and kits). If I provided power via Li+ I would need a boost or buck-boost converter. That’s not necessarily a big deal.
Note 2: I’m using the 2G/3G version of the Boron, so power consumption is somewhat higher than for the N American version.
I’d very much welcome any/all observations on the above.
D