Off-Grid Meshtastic Repeater on Sodium-Ion 18650s
Sam in Michigan runs an off-grid repeater site for the local LoRa mesh. It relays both Meshtastic and MeshCore traffic, and it lives where there's no power to plug into. So Sam built a small solar battery for it, using our sodium-ion 18650 cells.
Why sodium-ion for a repeater
A repeater sits outside all year with nobody watching it. Sodium-ion suits that job:
- Cold weather: our layered oxide cells are rated to discharge down to -40 C, which matters on a Michigan winter night.
- Safety: sodium-ion runs calmer than lithium-ion NMC, a good thing for a box nobody checks on.
- Small and cheap: standard 18650 cells, easy to build into a pack sized for a low-power radio.
Battery
- Chemistry: Sodium-ion, layered oxide
- Cells: 18650 sodium-ion – Buy here
- Configuration: 3S3P (3 series × 3 parallel), 9 cells
- Nominal voltage: about 9 V
- BMS: Heltec 3S (HTNA-310S03A20)
Solar and charging
- Panel: 18 V, 20 W
- Charge controller: Victron SmartSolar MPPT, set up with custom charge voltages for sodium-ion
- Role: the Victron handles charging only; the radio runs from the battery
The radio
- Firmware: Meshtastic and MeshCore repeater
- Load: a low-power LoRa node running around the clock
Building one yourself?
A few tips if you're planning a solar node like this:
- 4S makes a 12 V pack. Four sodium cells in series run about 10 to 16 V, which matches 12 V gear and the 12 V mode on most charge controllers. Three in series gives you about 9 V.
- Pick a BMS you can set for sodium. Sodium cells use a different voltage window than lithium-ion or LFP. Our 12V sodium-ion BMS ships pre-programmed for these cells.
- Use the controller's load output. A low-voltage cutoff on the charge controller turns the radio off before the battery gets too low, so the BMS is only a backup.
- Plan for winter. Size the pack to carry the radio through several cloudy days in a row.
For voltage windows and BMS settings, see Sodium-Ion Pack Math.
Working on a build of your own? Reply to any of our emails and tell us about it. Each month we feature a few customer builds here.