Options and Recommendations

I recently created a new tool, RF Index, which compares the various node options. This includes DIY, "Off the shelf", solar, etc. Let me know if you have any feedback!

Building a Solar-Powered Repeater for Meshtastic

A brief history

History of versions

We have tried 5 permutations of solar powering nodes:

Lessons learned:

1. Don't trust the RAK board to handle varying solar voltage or varying battery voltage. It is very unhappy if either voltage goes outside of a narrow range. In fact there is a known issue where the Nordic nRF52840 module inside of the RAK 4631 chip causes it to enter a "Super Deep Sleep" fault state when it is supplied with 3.3V. This means when the battery voltage falls too low the RAK chip shuts down and can only be rebooted manually.
2. Solar panels: bigger is better. 10 watts or more is ideal.
3. Battery: bigger is better. 5,000 mAh or more is ideal.
4. Antenna: fiberglass antennas are the most robust and can handle wind, rain, and UV light better than rubber ducky antennas.
5. Heat can kill the battery – it is best to shade the box containing the battery.
6. Don't add any modules. The GPS module increases battery usage significantly and is unnecessary if the repeater is in a fixed position.
7. Seal everything properly and make sure water has a way to get out of the case. Use o-rings for the antenna mount and wrap connectors in proxicast. Add a drain plug to the case so any condensation has a way to escape. For high humidity environments, spray the electronics with conformal coating.

These are lessons learned from Austin Texas, where the main environmental stressors are heat and thunderstorms. In the summer of 2023 we 80 days over 100° F (38°C) and we had a stretch of 11 days over 105° F (40.5°C), during which two radios died. We also can have both high humidity and high temperature at the same time in Austin; in the summer the weather would swing from 80° F (27°C) with 85% humidity in the morning to 105° F (38°C) with 25% humidity in the afternoon. Weather history here. Our learnings are probably applicable to other southern and desert climates.

Considerations for other climates

1. Northern Climates and extreme cold
   • This isn't from our experience, but we felt it was so valuable that we shoud link to it here. YYC Mesh, a group in southern Alberta as well as the Greater Vancouver/Victoria recently published their findings on batteries in cold temperatures.
   • LiPo and Li-ion are fine(0 failures)
   • Capacity IS reduced. 3000mAh minimum kept nodes up and charge rates low(good thing)
   • Charging creates heat, enclosures trap heat
   • nRF52 > ESP32
   • Solar panel angle matters
2. Coastal Climates: salt spray and condensation from fog can kill electronics quickly. In coastal climates it is best to spray the electronics with conformal coating.