I had repeat problems with the SunnyBuddy solar charge controller not wanting to resume charge. As the winter light levels dropped it seemed not to like lower charge input levels and never resume charge even on a sunny day. I grew tired of walking up the hill to reset it, so today collected it and vowed to get rid of the SunnyBuddy issue. It had been a sunny week. The solar panel was outputting about 20V, the LiPo cell was sat at 3.8v but wasn't receiving charge. The teensy was in standby mode as the voltage was low.
The kit has been left on an exposed Scottish mountainside for 6 months of winter. It survived reasonably well, except for a few problems
What didn't go well:
1) AIS receive antenna support failure
this was an old GRP telescopic fishing rod. The sections were epoxied together but the top section worked loose and collapsed inside. I will back this up with cable ties or drill and screw sections together next time.
2) LoRa tx antenna support failure
The LoRa transmit antenna was a Moxon loop built on 12mm marine ply, and a small radial arm of marine ply lashed to a treestump to make the angle adjustable in the field. Despite being marine ply, the support arm had delaminated and dropped out of alignment. I'll use some blocks of solid treated timber or plastic next time that won't delaminate
3) rodent damage!
Something had nibbled my LoRa coax cable! The copper braid was exposed and the dielectric removed where exposed at the antenna. I'll better protect with hot glue and heatshrink next time!
4) water / condensation ingress
I used a pretty cheap tupperware box with cable glands to house the electronics. I thought it was well sealed but there was 1cm water pooled in it at the end of the time on the hill. My power cable is not circular in cross section so probably wasn't very well sealed, but it was pointing down. Next time I'll use a better box and round section cable so the glands seal. I'll throw in some silica gel packets next time too. I might even drill a hole in the bottom, shield it from driving rain and just let it drain.
What went well:
The electronics survived the water ingress - mainly because of the following actions:
1) mount the electronics on small standoffs on 12mm marine ply. The water never rose above the level of the marine ply and the standoffs meant the underside of the PCB didn't get wet. The marine ply doesn't rot when wet.
2) spray everything with ACF-50 corrosion spray. Despite being in a condensing environment and visible moisture, everything I sprayed was fresh as a daisy. I missed one junction block and this was quite corroded.
3) solar panel was a semi-flexible type. This took a battering as it was just tied to a treestump to get a proper angle to it. It was a thin-ish aluminium sheet with individual cells on it. The ali plate took a whack from something - presumably a flying branch in a gale, but just bent slightly without cracking any solar units.
Design changes for V2:
1) simple charging
I'm thinking of ditching the SunnyBuddy and LiPo cell.
I want to try just a simple 12v 2Ah gel cell, and a high-efficiency Dc-DC converter. 5v 250mW are under £5 and >90% efficient. The 12V solar panel could go via a solar charger but I think is an OK size just to connect directly to the battery (via reverse blocking diode) and not have any complex battery chemistry worries.
2) watchdog circuit.
I could keep the SunnyBuddy from locking up with a watchdog circuit. I've seen some ICs dedicated to this idea with super low current draw, that the Teensy could just trigger every now and then.