Power Supply
🔋 Power Supply for PuffiMail¶
PuffiMail is designed to operate on a single 18650 lithium-ion battery, making it ideal for long-term outdoor or mailbox installation. The circuit is optimized for ultra-low power consumption and intelligent wake-up to maximize battery life.
🔧 Battery Type¶
- Recommended Battery: 18650 Lithium-Ion
- Capacity: 2600–3400mAh (high capacity preferred)
- Voltage: 3.7V nominal (charged at 4.2V, cutoff at ~3.0V)
📊 Battery Life Estimation (3400mAh)¶
PuffiMail wakes up automatically every hour to check for new mail, even if the magnetic sensor is not triggered. This ensures constant reporting and reliable behavior.
| Wake-up Frequency | Power Use per Day | Estimated Runtime |
|---|---|---|
| 24×/day (hourly) | ~3.6mAh | ~755 days (~2 years) |
Assumptions:
- Each wake-up consumes ~0.1mAh (Wi-Fi + MQTT + measurement + upload)
- Deep Sleep current: ~0.05mA → 1.2mAh/day
- Effective usable battery: ~2720mAh (80% of 3400mAh after conversion loss & aging)
🔄 Replacing or Charging the Battery¶
There are two easy ways to recharge:
-
Replace the battery
Open the back cover and swap in a fully charged 18650 cell. This is fast and requires no waiting. -
Charge via USB
PuffiMail includes an onboard charging circuit, so you can simply plug in a USB cable to charge the battery directly.
⚠️ Be sure not to charge unprotected cells without a proper protection circuit.
📝 Battery Recommendations¶
- Choose reputable brands: Panasonic, etc.
- Avoid low-cost no-brand cells marked with unrealistic capacities (e.g., 9800mAh)
- Choose cells with flat top for holder compatibility
🔌 Optional Enhancements¶
- Add low-voltage warning to Home Assistant (already built-in via MQTT)
By optimizing firmware and hardware together, PuffiMail can operate for up to 2 years on a single charge — all while checking for new mail hourly.