Guru
Joined: 07/09/2016
Location: United KingdomPosts: 2171
| Posted: 02:59pm 29 May 2025 |
hey Phil - thanks for that.
the battery is 4x 2450mAh Ikea "Ladda" so actually quite nice cells (I think you can also get them in 1900mAh too) - 5% of that is just about the measured s/c current of the panel so I might just get away with no ballast resistor.
That is a really nice idea re a beefier diode - it had not occurred to me to go that way at all. I don't have any such devices but they are only a search away.
I have some tiny boards coming to build the ideal diode on so I can try both solutions really easily.
The unit is on soak test just now. It is approaching a week "in the wild" and not a hiccup so far... lots of improvements in the software have come out of it and it is already generating interesting data. It seems to charge itself and run nicely, which was a big worry - never seen the battery dip below 5.2V yet and 5.4V (which is the highest I see) is 1.35V per cell so just about optimum anyway... which is nice for early summer but I expect when we hit the dreary days of autumn and winter that panel really will need to squeeze every joule it can out of a weak, low sun.
As an aside, I used LoRa for the comms and had to play about with sensitivity and antenna design a bit, but so far it has sent over 280KB with only a single dropped packet (99.986% reliability) - well impressed as the radio path is a bit fraught and reciever is on the back side of a building away from the box. It is currently sending 76 characters in two packets every 72 seconds, which is much faster than necessary or intended (I was going to do once an hour) but I had it that fast so I got regular updates on the battery and granularity enough to see the panel performance as the light levels change (that alone suggested some useful tweaks for the software). Seeing that the electrical system can sustain that, I have decided to go for 10 times an hour which will be kinder on the power reqs but still reasonably fine-grained.
thanks very much for your input!
h
Edited 2025-05-30 01:18 by CaptainBoing