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.