Budget Solar Repeater Build (~$80)
Budget Solar Repeater Build (~$80)
This guide walks through assembling a low-cost, outdoor solar-powered LoRa repeater using the RAK4631 WisBlock platform. The build is weatherproof, low-power, and deployable on a single weekend afternoon.
Parts List
| Part | Approx. Cost |
|---|---|
| RAK4631 WisBlock Core (nRF52840 + SX1262) | ~$25 |
| RAK19007 WisBlock Base Board | ~$15 |
| 5W 6V solar panel | ~$10 |
| CN3791 MPPT solar charger board (5V/6V in, 3.7V LiPo out) | ~$8 |
| 3.7V 3000 mAh LiPo battery (flat pack) | ~$10 |
| Hammond 1554B enclosure (IP67 polycarbonate, 120×65×40mm) | ~$15 |
| M12 cable glands (×2) | ~$3 |
| SMA female bulkhead connector | ~$2 |
| 5 dBi 915 MHz fiberglass antenna + SMA pigtail cable | ~$15 |
| Misc: wire, shrink tubing, desiccant packet | ~$5 |
| Total | ~$108 (under $80 bare-bones, omitting fiberglass antenna) |
Assembly Steps
- Flash firmware. Connect RAK4631 to your computer via USB. It presents as a USB mass-storage device. Drag the MeshCore repeater
.uf2firmware file onto the drive; the board reboots automatically when flashing completes. - Wire the CN3791 charger board. Connect the solar panel leads to the
IN+/IN-pads. Connect the LiPo battery toBAT+/BAT-. Run the charger output (labeledOUT+/OUT-or VCC/GND) to the RAK19007 5V and GND supply pads. Double-check polarity before applying power. - Prepare the enclosure. Mark and drill two M12 knockouts in the enclosure: one in a side wall for the antenna SMA pigtail, one for the solar cable entry. Deburr holes cleanly.
- Install cable glands. Thread M12 glands into both holes, finger-tight plus a quarter turn. Route the SMA pigtail through one gland and the solar cable through the other. Apply thread-sealant compound on the gland threads before tightening fully.
- Mount the RAK19007. Attach M2.5 brass standoffs to the enclosure floor using self-tapping screws or nuts. Secure the RAK19007 to the standoffs. Affix the LiPo battery to the enclosure wall with double-sided foam tape, away from the standoff hardware.
- Route the SMA pigtail. Connect the SMA pigtail's u.FL end to the RAK4631 antenna port. Route the cable through the gland to the external SMA bulkhead connector and tighten the bulkhead nut.
- Seal and protect. Apply silicone RTV around all cable-gland entry points and the bulkhead fitting flange. Drop a desiccant packet into the enclosure before sealing.
- Test charging. Connect the solar panel externally and expose it to light. The CN3791 has two indicator LEDs: one for charging, one for charge-complete. Verify both states cycle correctly.
- Configure the node. Power on the board. Using a phone or laptop, open the MeshCore app and connect via Bluetooth. Set the device role to Repeater, enter your callsign or node name, and input the GPS coordinates of the deployment site (or enable GPS fix if a GPS module is attached).
- Deploy and mount. Close the enclosure lid and engage the IP67 latches. Mount the enclosure at the chosen site using UV-stable zip ties or a small bracket. Attach the external antenna to the SMA bulkhead and angle the solar panel toward the equator at a 20–45° tilt.
Expected Performance
- Average current draw: ~10 mA (RAK4631 in repeater mode with periodic transmit)
- Battery runtime without sun: 3000 mAh ÷ 10 mA = 300 hours ≈ 12+ days
- Solar recharge time: A 5W panel fully recharges a 3000 mAh pack in 1–2 sunny days under direct sun
- RF range: 5 dBi antenna typically adds 2–3 km over a stock stubby in clear line-of-sight terrain
Tips & Troubleshooting
- If the CN3791 does not charge, verify the solar panel open-circuit voltage is within the 4.5–6.5V input range of the board.
- Use self-amalgamating tape over the SMA bulkhead nut as an extra moisture barrier.
- If Bluetooth pairing fails, confirm the firmware was flashed correctly — a solid blue LED on the RAK4631 indicates the BLE stack is running.
- For areas with heavy frost, consider replacing the LiPo with a LiFePO4 cell; LiPos lose significant capacity below 0°C.
No comments to display
No comments to display