i had built some meshtastic devices and solar-routers in different housings.
on vacation i used one very simple build, just a rak4630 in a plastic housing with a glued on solar-panel.
it functioned as a router in full sunshine on top of some roof, to get and send postion data of some gps equipped devices.
after 3 weeks the lipo battery, that lasted around 1 week in the beginning, only lasted abour 24hours…
so i opened the device to find the battery damaged…
i took some thermal images of the deive after being placed in the sunshine for some time … images below…
the temperature readings are not calibrated so its +/-5° …
if you have a device with the solar panel integrated / or directly mounted on the housing, the temperature can easily go to high for the lipo…specially if its for some longer time in full sunshine…
if you construct Solar-powered devices, better use the Solar panel to shade the part, that is housing the battery… leave some air between the panel and the shell…
nothing special, just central europe…
but that was on a very hot and sunny day… around 35°C outside and strong sun…
and the node was placed on a tin-part of the roof …
as i wrote, thermal imager was not calibrated, +/- 5°C
enclosure black plastik , also black solar panel.
pictures were taken on very hot day after some hours in full sunshine…
but as i wrote above, thermal imaging device was not calibrated…
still it was hot enough to get a lipo-battery to get stinky
yes, my fixed outside device is in an aluminium-case, and shadowed by the solar module. this one should not heat up from sunlight…
its a construction problem of the very simple designs… where the solar panel can dissipate heat into the enclosure…
i just read, that solar modules heat up to ambient+35° which is 70, sometimes 80°C when in full sun. so the measured temperatures can be right…
Lower elevations receive less solar radiation with atmospheric distortion. The difference between sea level and 5000ft are pretty noticable amounts in my testing. Black box and high elevation would surely be a heat issue. I consistently when it’s sunny hit 45c in my enclosures and that’s at 3200ft. Father in laws house has a node and that hits 55c on some days with full sun at 5400ft. No difference in weather, case design, just elevation. I’ve debated using the White 2.0 paint to help with this.
my permantly installed node is in some unpainted aluminium housing , reflecting and dissipating heat very well… 80% shadowed and the solar panel is installed a few cm above… this one does not have a problem.
the problem comes in the very simple designs, (like my simple design on the pictures above) where the solar panel is -part of /directly installed on- the housing, the heat from solar panel is dissipated into the housing. the solar panel is usually black and can get up to 70°C, the panel cannot be painted white… there should at least be some insulation between panel and housing of battery…
if not, the first part to die from the heat after some weeks is usually the battery…
As a side note, once I started introducing a pinhole on the bottom of my weatherproof enclosures, temps dropped noticeably. Prior, they never reached 70c, but they could sometimes reach more than 10c higher than the outside temps.
