Current Draw & Power Budgets
Current Draw & Power Budgets
Understanding how much power your node consumes is the starting point for sizing batteries and solar panels. LoRa mesh nodes have variable current draw depending on what they are doing at any given moment.
Typical Current Draw by State
| State | Current Draw | Notes |
|---|---|---|
| Deep sleep (nRF52) | 2–20 µA | Heltec Wireless Paper: ~20 µA; T-Echo: ~2–5 µA |
| Deep sleep (ESP32) | 10–100 µA | ESP32 deep sleep varies widely by implementation |
| Idle / listening | 15–30 mA | Radio on, waiting for packets; display off |
| Active with display | 30–60 mA | OLED adds ~10–20 mA; e-ink adds ~0 mA between refreshes |
| Transmitting | 50–120 mA | Depends on TX power setting; 22 dBm ≈ 80 mA typical |
| Transmitting (Station G2, 36.5 dBm) | 800–1200 mA | Requires 15V PD supply capable of delivering this current |
Average Current for a Repeater Node
A repeater node running MeshCore is mostly in idle/listening mode, with brief transmit bursts when relaying traffic. Typical average:
- Idle listening: ~25 mA most of the time
- Transmit duty cycle: Low (a few percent in typical mesh traffic)
- Average current: ~20–40 mA total, typically ~25 mA for a lightly-loaded repeater
Calculating Daily Energy Use
Daily energy (Wh/day) = Average current (A) × Voltage (V) × 24 hours
Example for a Heltec V3 repeater:
- Average current: 25 mA = 0.025 A
- Battery voltage: 3.7V (nominal LiPo/Li-ion)
- Daily energy: 0.025 × 3.7 × 24 = 2.22 Wh/day
This is the baseline figure used in solar sizing calculations. A Room Server running with active connections may draw more — budget 3–4 Wh/day for a heavily used Room Server node.
Power Budget Worksheet
| Parameter | Your Value | Notes |
|---|---|---|
| Average current draw (mA) | ___ | Measure with a USB power meter or estimate from table above |
| Supply voltage (V) | 3.7 | Standard LiPo/Li-ion nominal voltage |
| Daily energy (Wh/day) | ___ | = current(A) × 3.7 × 24 |
| Days of battery reserve needed | ___ | 3–7 days recommended for outdoor solar nodes |
| Battery capacity needed (Wh) | ___ | = daily energy × reserve days ÷ 0.8 (usable fraction) |
| Worst-case peak sun hours | ___ | Look up your location; use December value for year-round reliability |
| Solar panel needed (W) | ___ | = daily energy ÷ (peak sun hours × 0.70) |
Measuring Real Current Draw
For accurate power budgeting, measure actual current with a USB power meter (for 5V USB-powered nodes) or a multimeter in series with the battery lead. A USB meter like the UM25C gives real-time current and accumulates energy over time. Log over a 24-hour period under typical traffic conditions for the most accurate average.
Reducing Power Consumption
- Disable unused peripherals (OLED display off when not needed)
- Use nRF52-based boards (T-Echo, T114, RAK4631, Wio series) instead of ESP32 for lower idle current
- Reduce TX power if the node is within range with lower power — every 3 dB reduction halves transmit current
- Enable deep sleep between transmit windows for infrequent sensor nodes
No comments to display
No comments to display