Solar Node Build

[Chad Walter]

Thanks to Austinmesh.org for the following:

For this version we stopped using the RAK’s solar and battery connectors entirely. Instead we connected a large 12 watt solar panel to a Voltaic Systems battery via USB and then connected the battery to the RAK board via USB. The Voltaic Systems battery acts as the solar charge controller and also acts as the overdischarge protection circuit; the battery will charge at a range of voltages from the solar panel (if it gets shaded) and the battery will shut off if the voltages drops too low and will reboot itself once it has recharged sufficiently.

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.

[Chad Walter]

We have the following to build our first solar relay:

10 watt 5 volt solar panel

Wisblock 4631 or Heltec v4

10k USB power bank with charging pass thru